MICROBIOLOGY AND PARASITOLOGY IN NUTRITION

DIPLOMA IN NUTRITION HEALTH MICROBIOLOGY

1WALTER WAKHUNGU WASWA

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Food microbiology

• Food microbiology is the study of the microorganisms that inhabit, create, or contaminate food and the study of microorganisms causing food spoilage.

• What is the importance of food microbiology?• To study microorganism causing food

spoilage,fermentation,and yeast production essention in food production


http://en.wikipedia.org/wiki/Microorganism

http://en.wikipedia.org/wiki/Microorganism

• What is Microbiology?• Microbiology is the study of microorganisms, that

exist as single cells or cell clusters; it also includes viruses, which are microscopic but not cellular.

• Parasite• Living organism that live in or on a host that

provide physical protection and nourishment.term usually applied to protozoans and helminths

• What is Parasitology?WALTER WAKHUNGU WASWA 10

Roles of microorganisms found in food

Spoilage, fermentation, food production. Microorganisms are used in brewing,

winemaking, baking, pickling and other food-making processes.

They are also used to control the fermentation process in the production of cultured dairy products such as yogurt and cheese. The cultures also provide flavour and aroma, and inhibit undesirable organisms.

Do you think bacteria can be consumed as prophylactic measures?


https://en.wikipedia.org/wiki/Brewing

https://en.wikipedia.org/wiki/Winemaking

https://en.wikipedia.org/wiki/Baking

https://en.wikipedia.org/wiki/Pickling

https://en.wikipedia.org/wiki/Food

https://en.wikipedia.org/wiki/Fermentation_%28food%29

https://en.wikipedia.org/wiki/Dairy_product

https://en.wikipedia.org/wiki/Yogurt

https://en.wikipedia.org/wiki/Cheese

Primary sources of microorganisms

1. Soil and water2. Plant and plant products3. Food utensils4. Git of animals and humans5. Food handlers6. Animal hides7. Air and dust8. Animal feeds


Primary source of food poisoning bacteria

WALTER WAKHUNGU WASWA 13

• A synopsis is provided to give you a glimpse of what we are going to encounter in the course of our study.


Synopsis of common food borne bacteria


Synopses of Genera of Moulds common to food

• assignment1


Synopsis of Genera of Yeasts common to foods

• Assignment2


Synopsis of mould• Molds are filamentous fungi that grow in the form of a tangled

mass that spreads rapidly and may cover several inches of area in 2 to 3 days.

• The total of the mass or any large portion of it is referred to as mycelium. Mycelium is composed of branches or filaments referred to as hyphae.

• Those of greatest importance in foods multiply by ascospores, zygospores, or conidia.


cont

• Aspergillus• Aureobasidium (Pullularid).• Botrytis.• Byssochlamys.• Cladosporium• Colletotrichum.• Fusarium.• Penicillium• Rhizopus.


SYNOPSIS OF COMMON GENERA OFFOODBORNE YEASTSYeasts may be viewed as being unicellularfungi in contrast to the molds, which are multicellular;Some yeast produce mycelia to varying degrees.Yeasts can be differentiated from bacteria bytheir larger cell size and their oval, elongate, elliptical,or spherical cell shapes.


Genus: BrettanomycesCandidaCryptococcusRhodotorulaTrichosporon


The Causes of Food Spoilage• INTRINSIC PARAMETERS• This are parameters of plant and animal tissues

that are an inherent part of the tissues .• These parameters are as follows:• pH• Moisture content• Oxidation-reduction potential (Eh)• Nutrient content• Antimicrobial constituents• Biological structures


Conditions for Spoilage

•Water•pH •Physical structure•Oxygen•temperature


Microorganism Growth in Foods


Composition and pH

• putrefaction– proteolysis and anaerobic breakdown of proteins,

yielding foul-smelling amine compounds

• pH impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food


Water availability• in general, lower water activity inhibits microbial

growth• water activity lowered by:– drying– addition of salt or sugar

• osmophilic microorganisms– prefer high osmotic pressure

• xerophilic microorganisms– prefer low water activity


Physical structure

• grinding and mixing increase surface area and distribute microbes– promotes microbial growth

• outer skin of vegetables and fruits slows microbial growth


Antimicrobial substances

• coumarins – fruits and vegetables• lysozyme – cow’s milk and eggs• aldehydic and phenolic compounds – herbs

and spices• allicin – garlic• polyphenols – green and black teas


Extrinsic parameters• These are those properties of storage environment

that affect both the foods and their microorganisms.1.temperature

I. lower temperatures retard microbial growth

2.relative humidityI. higher levels promote microbial growth

3.atmosphereI. oxygen promotes growthII. modified atmosphere packaging (MAP)III. use of shrink wrap and vacuum technologies to

package food in controlled atmospheres29WALTER WAKHUNGU WASWA

Incidence and types of microorganisms in food

Fresh meat and poultry• Primary sources and routes of microorganisms• 1.stick knife• 2.animal hide• 3.git• 4.hands of handlers• 5.containers• 6.handling and storage environment• 7.Lymph nodes WALTER WAKHUNGU WASWA 30

Extended ground meat


• EXTENDED by addition of soy flour and frozen • Ie chicken soy blend• However bacteria grow faster in meat soy

blend meat than non extended


• Ground meat or comminuted meat• Higher level of contamination.– Higher surface area– Meat grinders, cutting knives, storage utensils– One heavily contaminated meat portion ie lymph

node• Bacteria– Bacilli and – Clostridium botulinum,perfringens,JEJUNII– E.coli– S.aureus– Klebsella pneumoniae,Enterobacter cloacae


• Mechanically deboned meat


• By machines• Less contact by man• Which bacterial group is minimized?• Coliforms


Hot boned meat• Processing meat 1-2 hrs after slaughter while

carcass is still hot(pre rigor)• COLD BONED MEAT?• Mesophiles elevated


• Organ and variety meat


• Liver kidney hearts tongues• Higher ph and glycogen levels


• Vaccuum packaged meat


• Anaerobic bacteria will survive


• Storage of various meat products• Bacon• Sausage• bologna


• poultry


• Sea food


• vegetables


• Delicatessen


• Frozen meat pie


• Dehydrated foods


Microbial Growth and Food Spoilage

• food spoilage– results from growth of microbes in food• alters food visibly and in other ways, rendering it

unsuitable for consumption– involves predictable succession of microbes– different foods undergo different types of spoilage

processes– toxins are sometimes produced• algal toxins may contaminate shellfish and finfish



Food Spoilage•Approximately 1/3rd of all food manufactured in world is lost to spoilage•Microbial content of foods (microbial load): qualitative (which bugs) and quantitative (how many bugs)•Shelf life

•Non-perishable foods (pasta)•Semiperishable foods (bread)•Perishable foods (eggs)


Minimize contamination by:

1. Good management processes2. Acceptable sanitary practices3. Rapid movement of food through processing

plant4. Well-tested preservation procedures


Source Common Food Spoilage•Meat

•Cutting board contamination•Conveyor belts•Temperature•Failure to distribute quickly•Fecal bacteria from intestines

•Fish•Polluted waters•Transportation boxes


Cont……•Poultry and Eggs

•Human contact•Penetration by bacteria

•Milk and Dairy Products•Lactobacillus and Streptococcus species that survive pasturization (sour milk)

•Breads •Spores and fungi that survive baking

•Grains•Fungi produce toxins


>>>>Food Microbiology• Foodborne Illnesses– Due to consumption of spoiled foods or foods

containg harmful microbes or their products– Two categories of food poisoning• Food infections

– Consumption of living microorganisms• Food intoxications

– Consumption of microbial toxins rather than the microbe

– Symptoms include nausea, vomiting, diarrhea, fever, fatigue, and muscle cramps


Preventing Foodborne Disease

•Food infections (microbes are transferred to consumer)•Food poisoning (results from the toxin consumption)



FOOD POISONING1. Food intoxication: Illness is caused by ingestion

of food with• preformed toxin. Examples of food intoxication• Bacillus cereus 1-6 hours Vomiting, cramp Rice,

Pasta dishes• Staphylococcus aureus 2-4 hours Vomiting Meat,

Salads• Clostridium botulinum 12-72 hours Flaccid

paralysis Meat, Vegetables57WALTER WAKHUNGU WASWA

2. Food infection: Illness is caused by ingestion of food with microorganism.

• Incubation period and severity of disease in food infection is determined by inoculum of micro-organism ingested.


LABORATORY DIAGNOSIS OF FOOD POISONING• Specimen: Left over food, vomits, stool• Culture the specimen for microbial isolation.• Serological technique for toxin isolation.• Treatment: Depends on the causative agent.


MYCOTOXINS• Ergotism– toxic condition caused by growth of a fungus in

grains• Aflatoxins– carcinogens produced in fungus-infected grains

and nut products• Fumonisins– Carcinogens produced in fungus-infected corn

• ACRATOXINS60WALTER WAKHUNGU WASWA


Controlling Food Spoilage

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Canned food spoilage organisms may be characterized as follows:• Mesophilic organisms-Putrefactive anaerobes-Butyric anaerobes-Aciduric flat sours-Lactobacilli-Yeasts-Molds• Thermophilic organisms-Thermophilic anaerobes producing sulfide-Flat-four spores-Thermophilic anaerobes not producing



Radiation1.ultraviolet (UV) radiation– used for surfaces of food-handling equipment– does not penetrate foods

2.Gamma radiation– use of ionizing radiation (gamma radiation) to

extend shelf life or sterilize meat, seafoods, fruits, and vegetables

3.Beta rays-may be defined as a stream of electrons emitted from radioactive substances.

4.Microwaves5.X -rays 65WALTER WAKHUNGU WASWA

NATURE RADIATION RESISTANCE OF MICROORGANISMS

• The most sensitive bacteria to ionizing radiation are gram-negative rods such as the pseudomonas

• the coccobacillary-shaped gramnegative cells of moraxellae and acinetobacters are among the most resistant of gram negatives.

• Gram-positive cocci are the most resistant of nonsporing bacteria, including micrococci,staphylococci, and enterococci.


IRRADIATION

• Types of Organisms• Gram-positive bacteria are more resistant toirradiation than gram negatives. • Spore formers are more resistant than non-

spore formers.


Characteristics of radiation resistant microorganisms

1).can survive 15 kGy eg D. radiophilus2).contain red water-insoluble pigments

(carotenoid) plasma membrane is red,3).contain L-ornithine as the basic aminoacid in their murein4).Posses an outer membrane5).High content of fatty acid in their envelope6).Abudant DNA-Actively dividing cells may

contain 4 to 10 copies68WALTER WAKHUNGU WASWA

1.Numbers of Organisms The larger the number of cells, the less effective is a given dose.

2.Composition of Suspending Menstrum(Food)• Microorganisms in general are more sensitiveto radiation when suspended in buffer solutions3.Presence or Absence of Oxygen• The radiation resistance of microorganisms is• greater in the absence of oxygen than in its

presence

EFFECTIVENESS OF RADIATION TECHNOLOGY IS DETERMINED BY:


4.Physical State of Food• The radiation resistance of dried cells is, in• general, considerably higher than that for

moist• cells.5.Age of Organisms• Bacteria tend to be most resistant to

radiationin the lag phase just prior to active cell division.


How do we effectively Detect Food-Borne Pathogens?

First the method must be rapid and sensitive• methods include:– culture techniques – may be too slow– immunological techniques - very sensitive– molecular techniques• probes used to detect specific DNA or RNA• sensitive and specific


Surveillance for food-bornedisease• PulseNet– established by Centers for Disease Control– uses pulsed-field gel electrophoresis under

carefully controlled and duplicated conditions to determine distinctive DNA pattern of each bacterial pathogen

– enables public health officials to link pathogens associated with disease outbreaks in different parts of the world to a specific food source


Surveillance…

• FoodNet– active surveillance network used to follow nine

major food-borne diseases– enables public health officials to rapidly trace the

course and cause of infection in days rather than weeks


Helpful Suggestions

•Refrigerate quickly•Wash hands•Clean cutting boards•Leftovers•Avoid home-canned foods


Microbiology of Fermented Foods

• Major fermentations used are lactic, propionic, and ethanolic fermentations

• Fermentation=Any partial breakdown of carbohydrates taking place in the absence of oxygen.




Meat and Fish Fermented Products

• Sausages• Hams• Bologna• Salami• Izushi – Fish, Rice And Vegetables• Katsuobushi – Tuna


Wine

White vs. Red: juice or juice and skin

Yeasts: Ferment when no oxygen around.Saccharomyces species

DrySweetSparklingFortified


Production of Breads

• involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions– maximizes CO2 production, which leavens bread

• other microbes used to make special breads (e.g., sourdough bread)

• can be spoiled by Bacillus species that produce ropiness


Other Fermented Foods

• silages– fermented grass, corn, and other fresh animal feeds


Microorganisms as Foods and Food Amendments

• variety of bacteria, yeasts, and other fungi are used as animal and human food sources

• probiotics– microbial dietary adjuvants– microbes added to diet in order to provide health

benefits beyond basic nutritive value


PSYCHROPHILICMICROORGANISMS• This term is applied to organisms that grow

over the range of subzero to 20C.Are those organisms capable of growing relatively rapidly at commercial refrigeration temperatures with out reference to optimum temperature for growth. Species of Pseudomans, Achromobacter, flavobacterium and Alcahigenes are examples of Psychrophilic bacteria.

• Large no=change in flavors as well as defects in foods.


Thermophilic microorganism Thermophilic microorganisms are those

organisms which will survive so significant measure of heat treatment . The thermophilic organisms not only survive the heat treatment but also grow at the elevated temperature

. Thermoduric bacteria are important with regard to milk and milk products as they may survive pastourisation temperature.

Those of greatest importance in foods belong to the genera Bacillus, Clostridium, and Thermoanaerobacterium.


XTERISTICS OF THERMOPHYLIC MICROORGANISMS

• On the basis of growth temperatures, thermophiles may be characterized as organisms with a minimum of around 45C, an optimum between 50C and 60C, and a maximum of 70C or above.


EXAMPLES

• Genera Lactobacillus, Bacillus and Clostridium are recognized as containing some species which will qualify as thermoduric.


STAPHYLOCOCCUS

• The three main species of clinical importance• Staphylococcus aureus• Staphylococcus epidermidis• Staphylococcus saprophyticus


cont

• Can readily grow in ordinary media under aerobic and microaerophilicconditions

• grow most rapidly at 37 0c but form pigment best at room

• temperature of 20-25 oc


cont

• Some of them are normal flora of the skin and mucus membrane of human, otrhhers cause suppuration abscess

• Formation and fatal septicemia• Produce catalase, which differentiate them

from the streptococci.• Converts H202 into H20 and 02


toxins Exotoxins(α, β, γ, δ) . Enterotoxin-Produced by S.aureus when

grown in carbohydrate and protein foods. Multiple (A-E, G-I, K-M) soluble heat-stable,

gut enzyme resistant toxins which act on neural receptors in the gut to stimulate vomiting center in the central nervous system.

It is superantigen causing staphylococcal food poisoning

.90WALTER WAKHUNGU WASWA

cont

• Toxic shock syndrome toxin- Superantigen desquamative toxin Produced by S.aureus and Causes fever, shock,multiple-organ failure and skin rash.

• . Exfoliative toxin-Epidermolytic superantigen produced by


Incidence in Delicatessen and related foods

• Delicatessen foods, such as salads and sandwiches, are sometimes involved in food-poisoning outbreaks. These foods are often prepared by hand, and this direct contact may lead to an increased incidence of food poisoning agents such as Staphylococcus. Once organisms such as these enter meat salads or sandwiches, they may grow well because of the reduction in numbers of the normal food biota by the prior cooking of salad ingredients. 92WALTER WAKHUNGU WASWA

incidences

• Most microorgansm are enteric bacteria and some environmental fungi

• Staphylococcus• S.aureus• C.perfringens• E.coli• Yeast and moulds• Corliforms


Determining microorganisms and their products in food

• The examination of foods for the presence,types, and numbers of microorganisms and/ortheir products is basic to food microbiology.• Culture• Microscopic examination• Sampling


Direct microscopyIn its simplest form, the DMC consists ofmaking smears of food specimens or culturesonto a microscope slide, staining with an appropriatedye, and viewing and counting cells withthe aid of a microscope (oil immersion objective).


sterilization

: Destruction of all forms of microbial life includingspores.


How would you determine efficiency of a sterilizer

1. Recording of temperature and time of each sterilizing cycle.2. Heat-sensitive autoclave tape fixed to the outside of each pack... Color change of autoclave tape from blue to brown-black indicates completesterilization.4. Biological indicator : Use of paper strips impregnated with spores of Bacillus stereothermophilus


Quality of water quality of water is odorless, colorless, tasteless and free fromfecal pollution and harmful chemicals.Human illness is caused by water supplies becoming contaminated from feces being passed or washed into rivers, streams, or being allowed to seep into wells.Feces contain microorganisms like Escherichia coli, Streptococcusfaecalis and Clostridium perfringenes, which contaminate safewater.


lab

Determining whether a water supply is fecally polluted is to test for the presence of normal fecal organism.Testing for normal fecal organisms as indicators of fecal pollution is a reliable way of determining whether water is bacteriologically safe to drink.


coliforms

Organisms used as indicators of fecal pollution are the coliformgroup particularly E. coli.


Food contamination

Food may acquire their micro-organism from various sources and the following are the important sources.


1. Animals- Animals could be a source of contaminationof food.- The surface of animals, the respiratorytract, the gastrointestinal tract, hides,Loofs and waste products of animals areimportant sources of contamination.


2. Plants- Food may get their microbial contamination from green plants.- The natural flora of growing plants includes pseudomonas, alcaligenes,bacissus, Micrococcus, coliform etc.


3. Sewage- Gastrointestinal pathogens, coliforms,Enterococci of untreated domesticsewage could be source of contaminationof raw plant foods.- Sewage can also contaminate naturalwaters and contribute micro-organisms toshellfish, fish and other sea foods.


4. Soil- Soil is a very rich environment in microbesand is a major source of contamination offood.- Bacillus, clostridium, enterobacter,Escherichia, Micrococcus, Alkaligens,Flavobacterium, Pseudomonas, proteus,Aerobacter, molds and yeast are kinds oforganisms that contaminate food fromsoil.

5. Air and water:- are also important source of foodcontamination.-


1.Indicator microoganisms

Indicator organisms are bacterial groups (orspecies) whose presence in foods, above a certainnumerical limits, is considered to indicate exposureof food to conditions that might introduce hazardousorganisms and/or allow proliferation of pathogenic ortoxinogenic species.

MICROORGANISM IMPORTANT IN FOOD


Indicator organismsInclude coliforms and faecalstreptococci.Coliform group is defined to include all aerobic andfaculitative anaerobic, gram negative, non-sporforming, rod shaped species which ferment lactosewith the production of acid and gas within 48 hoursat 35C• Coliform are either part of the normal flora ofintestinal tract of man and animals or found inenvironments such as soil and plants. 107WALTER WAKHUNGU WASWA

Coliform that are commonly found in the intestinaltracts of man and animals (faeces) are called faecalcoliform and those coliforms that are normalinhabitants of soil and plants are called non faecalcoliform.


2.INDEX MICROORGANISMS

=is one whose presence implies thepossible occurance of a similar but pathogenicorganism.E. coliis used an index organism and its presence indicates possible presence of pathogenic enteriobacteriacea eg.salmonellae species.


3.FOOD POISONING MICROORGANISMS

• those which cause the disease by infection• those which produce toxin in food


Those which cause infection must grow infood in large numbers and cause infectionwhen consumed together with food. The most most common microorganismsincludes salmonella tyhimurrium, entropathogenicE.coli,Vibrio parahaemolyticus etc.


Those which cause intoxication must growin food large numbers and produceenough toxin and when consumedtogether with food cause intoxication.Themost common microorganism in thisgroup are clostridiumbotulinium,staphylococcus and toxigenicfungi eg. Aspergillus flavus.


5.INFECTIOUS MICROORGANISMS

Organisms whose presence in small numbers in food and when consumed can cause infection. In this case the food acts as avector but not necessarly as a growth medium.organisms in this group are, Vibrio choleraeO1, salmonella typhi, shigella sonnei,Bacillus anthracis, HepatitisB virus etc.


6.Spoilage microorganisms

The spoilage microorganisms include bacteria, yeasts andmoulds that cause undesirable changes of the appearance,odour, texture or taste of the food. They are commonly groupedaccording to their type of activity or according to theiri growthreguirements.a) Psychrophilic microorganismsb) Lipolytic Microorganismsc) Proteolytic microorganismsd) Halophilic microorganismse) Halotolerant organisms 114WALTER WAKHUNGU WASWA

f)Acid producing microorganismsg)Yeasts and mouldsh)Mesophillic spore forming aerobesi)Thermophillic anaerobes


Microbiological examination of food

• Sampling• It is important to not

that samples of foods collected for microbiological analysis should reflect the microbiological condition at the time of collection. This implies that

• Sampling should be carried out aseptically

• Samples should be protected against extraneous contamination

• Moreover, samples must be held under conditions thatpermit neither die off nor multiplication of the original

• microflora present in the food. 116WALTER WAKHUNGU WASWA

Terms used

• A LOT:Is a quantity of food produced and handled under uniform

• condition. This means that food produced within a batch or

• in a continuous process a food produced within a limited

• period of time

• FILED SAMPLE:The amount of material actually used in the analysis of food for

microorganisms. The sample unit is recommended to be 25 g for

all types of food


Microbiological criteria

• is a microbiological value (eg. Number of

microorganism per g of food) or a range established by use of

defined procedures and includes the following information.

• ENDELEA


STAPHYLOCOCCUS

• Characteristics:• Gram positive non spore-forming non-motile,

spherical cells, usually arranged in grape-like clusters

• The three main species of clinical importance• Staphylococcus aureus• Staphylococcus epidermidis• Staphylococcus saprophyticus


HABITAT

• Some of them are normal flora of the skin and mucus membrane of human, others cause suppuration abscess formation and fatal septicemia

• relatively resistant to drying , heat, and 9% NacI, but readily inhibited by 3 % hexachlorophene


. Exotoxins(α, β, γ, δ)

. Enterotoxin-Produced by S.aureus when grown incarbohydrate and protein foods.Multiple (A-E, G-I, K-M) soluble heat-stable, gut enzymeresistant toxins which act on neural receptorsin the gut to stimulate vomiting center in the central nervoussystem. It is superantigen causing staphylococcal foodpoisoning. Toxic shock syndrome toxin- Superantigen desquamativetoxin Produced by S.aureus and Causes fever, shock,multiple-organ failure and skin rash.. Exfoliative toxin-Epidermolytic superantigen produced byS.aureus and uses generalized desquamation of the skin.

TOXINS PRODUCED BY STAPHYLOCOCCUS


. Food poisoning: Caused by enterotoxin produced by S.aureus

PREVENTION AND CONTROL?

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STREPTOCOCCUS• They are non-motile, non- sporulating, gram-

positive facultative anaerobes• Spherical or oval cells characteristically

forming pairs or chains during growth.• They are widely distributed in nature and are

found.• in upper respiratory tract, gastrointestinal

tract and genitourinary tract as normal microbial flora.


BACILLUS

• Characteristics:• • Aerobic, non-motile,spore-forming, gram-

positive chain• forming rods.• • Bacillus species are ubiquitous saprophytes• Important human pathogen• B. anthracis• B. cereus


B.CEREUS

• General characteristics:• Exhibit motility by swarming in semisolid

media• Produce β lactamase, so not sensitive to

penicillin


CLINICAL FEATURES• 1. Food poisoningPathogenicity determinant: Exotoxina.Emetic type food poisoning IP is 1-5 hrs after

ingestion of preformed toxin contaminating rice and pasta dishes Characterized by nausea, vomiting, abdominal cramps, and self-limited with in 24 hrs

b. Diarrheal type food poisoning IP is 1-24 hrs after ingestion of contaminated meat dishes with sporulating or preformed toxin Characterized by profuse diarrheaand abdominal cramps. Fever and vomiting is uncommon 126WALTER WAKHUNGU WASWA

CONTROL AND PREVENTION

• YOU KNOW?


CLOSTRIDIUM PERFRINGEN

• Characteristics:• Clostridia are anaerobic, spore-forming motile,

gram-positive rods.• Most species are soil saprophytes but a few

are pathogens to human.• They inhabit human and animal intestine, soil,

water, decaying animal and plant matter


PATHOGENICITY

• 1. Enzymes: Digest collagen of subcutaneous tissue andmuscle.. Collagenase. Proteinase. Hyaluronidase. Dnase

• 2. Toxins. PhospholipaseC (α toxin)• It has lethal, necrotizing and hemolytic effect on tissue.

It causes cell lysis due to lecithinase action on the lecithin which is found in mammalian cell membrane.

• . Theta toxin It has hemolytic and necrotic effect on tissue.


Clinical manifestation:• 1. Clostridial myonecrosis: Gas gangrene• . IP(Incubation period) =1-3 daysColonization of devitalized tramatized wound byC.perfringens spores, and organism germiation

and release of toxinsPresentation: Muscle and subcutaneous tissue

necrosiss andcrepitationFoul smelling wound discharge

• Fever, toxaemia, hemolytic anemia, Shock


CLOSTRIDIUM BOTULINUM

• • Spores of C. botulinum are widely distributed in soil, they often contaminate vegetables, fruits and other materials.

• Produce a neurotoxin which is the most active• known poison, and considered to be the

major agent of bioterrorism and biologic warfare


PATHOGENESIS• 1. Food botulism. INCUBATION PERIOD = 18-24 hrs. Route of entry is under cooked consumption of

C.botulinum toxin contaminated spiced, smoked, vaccumpacked or canned food

.The toxin is absorbed from the gut and acts by blocking the release of acetylcholine at synapses and neuromuscular junction and manifests with flaccid paralysis and visual disturbance, inability to swallow, and speech difficulty.Death is secondary to respiratory failure or cardiac arrest132WALTER WAKHUNGU WASWA

CONT…• 2. Infantile botulism C.botulinum implicated

and affects infants when mixed feeding starts (after fourth month of life).

• Ingestion and colonisation of the gut with C.botulinum, and production of toxin and adsorption of toxin leads to poor feeding, paralysis (floppy baby), and cranial nerve palsy.

• Diagnosed by demonstration of the organism or toxin from the stool.


BRUCELLOSIS• Brucellosis/ Undulant fever• 2 stages of illness1. Acute stage: Fever, malaise, sweating,

hepatosplenomegally, lymphadenopathy• Associated with 80% spontaneous recovery• Prevention and control:Pasteurization of milk and milk productsSlaughter of all infected animals in dairy herdsVaccination of cattle.


ESCHERICHIA COLI• Characteristics:• . Normal flora in human and animal

gastrointestinal tract.• . Found in soil, water and vegetation.• . Most are motile; some are capsulated.• . E.coli-associated diarrheal disease


DIARRHOEA

• 1. Enteropathogenic E.coli(EPEC) . causes outbreaks ofself-limiting infantile diarrhea

. they also cause severe diarrhea in adults• 2. Enteroinvasive E.coli(EIEC) invadethe mucosa of the ileum and colon, and causesshigellosis-like dysentery


3. Enterotoxigenic E.coli(ETEC) adherence to epithelial cells of small intestine followed by release of enterotoxin which causes toxin-mediated watery diarrhea in infants and young adults.. It is an important cause of traveller’s diarrhea

4. Entero haemorrhagic E.coli( EHEC) causes haemorrhagic colitis (severe form of diarrhea)

5. Enteroaggressive E.coli( EAEC) .Adhere to human intestinal mucosal cells and produce ST-like toxin and hemolysin, and causes acute and chronic diarrhea


SALMONELLA• Species of medical importance are:S. typhi S.

paratyphi S. enteritidis


CLINICAL PATHOGENESIS

• 1. Enteric fever:It is caused by S.typhi and S.paratyphi, and transmitted by fecal-oral route via contaminated food and drinks

Incubation period: 10-14 daysPredisposing factors:.Reduced gastric acidity.Disrupted intestinal microbial flora.Compromised local intestinal immmunity


CONT..

• Both manifest with persistent fever, headache,malaise, chills, enlargement of liver and spleen,

and skin rashes.• Paratyphoid fever is milder than typhoid feverComplications:Intestinal perforationLower gastrointestinal bleedingDissenmination to different body organs including

meninges and brain.140WALTER WAKHUNGU WASWA

2. Gastroenteritis• It is caused by S. enteritidis• S. typhimurium• IP= 8-48 hrs• It manifests with initial watery diarrhea, and

later• bloody mucoid diarrhea associated with crampy• abdominal pain and tenesmus.• Bacteremia is rare (2-3 % of cases)• It usually resolves in 2-3 days


SHIGELLOSIS

• S. dysenteriae • S. flexneri • S. boydii • S. sonnei • In developing countries, shigellosis (bacillary

dysentery) is caused by S. flexneri and S. dysenteriae.


• Pathogenesis and Clinical features:• Route of infection is fecal-oral route Inoculum dose:

103 organismsPathogenicity determinant:Toxins:• Endotoxin: irritate the bowel wall• Exotoxin: Enterotoxin and neurotoxin• S.dysenritiae type 1(shiga bacillus) produce heat

labile exotoxinmediated diarrhea• IP: 1-2 days


• It causes shigellosis (bacillary dysentery) characterized by sudden

• onset of bloody mucoid diarrhea, abdominal cramp, tenesmus, fever,

• generalized muscle ache and weakness.• Complication: Dehydration• Electrolyte and acid-base disturbance• High prevalence: Poor sanitation• Poor personal hygiene• Polluted water supply• Young children are frequently affected.


YERSINIA

• Animals are natural hosts of yersinia, and humans are accidental hosts of yersinia infection

• Important human pathogens• Y. pestis• Y. pseudotuberculosis• Y. enterocolitica


• Yersinia pestis• . Plague bacillus with gram negative, non-

motile, facutatively• anaerobe possessing bipolar granules


• Pathogenesis and clinical features:• Rat flea (Xenopsylla cheopis) gets infected by

biting an infected rodent → infected rat flea bites human (accidental host) → organism migrate to regional lymphnodes from the

site of bite (bubonic plaque) and gets into the blood via lymphatics (septicemic plaque), or Primary pneumonic plaque results from inhalation of infective droplets, usually from an infected coughing person

• IP=2-6 days• Human Plaque: 3 types


• 1. Bubonic plague: Fever, vomiting, painful• lymphadenitis(buboes) in the groin or axillae• 2. Pneumonic plague: Ip is 1-3 days• Profuse mucoid or bloody expectoration with• signs of pneumonia• 3. Septicemic plague• Fever, vomiting, diarrhea, hypotension, altered• mentation, renal and heart failure, intra

vascular• coagulopathy


• HUMAN INFECTION• Human infection results from ingestion of food

and drinks contaminated by animal feces• Antigenic structure• . Inv (invasion) locus• . AIL (attachement invasion locus)• Pathogenesis and clinical feature:• Route of transmission: Contaminated food and

drinks• Inoculum dose: 108-109 org• IP=5-10 days• Yersinosis: Enterocolitis


Cont…

• . Fever, abdominal pain, toxin and invasion-mediated diarrhea

• Usually self-limited disease• Post-diarrheal diseases• Arthritis• skin rash/nodules• Complication: Sepsis/ Meningiti


VIBRIO. Actively motile, gram-negative curved rods.. Species of medical importance: Vibrio cholerae• Characteristics:1.Found in fresh water, shellfish and other sea

food..Man is the major reservoir of V. cholerae-01, which causes epidemic cholera.

2. Readily killed by heat and drying; dies in polluted water but may survive in clean stagnant water, esp. if alkaline, or sea water for 1-2 weeks.


• CLINICAL FEATURES:• Route of infection is fecal-oral route.• After ingestion of the V.cholerae-01, the

bacteria adheres to the intestinal wall with out invasion then produces an exotoxin causingexcessive fluid secretion and diminished fluid absorption resulting in

diarrhea (rice water stool) which is characterized by passage of voluminous watery diarrhea containing vibrios, epithelial cells and mucus; and result in severe dehydration.


CAMPYLOBACTER

• Characteristics:• Small, delicate, spirally curved gram-negative

bacteria.• Motile bacteria with single polar flagellum.• . Stricly microaerophilic bactria requiring 5-

10% o2 and 10% co2 enriched environment.


Clinical features:• Inoculum dose: 104 organisms• Source of infection is contaminated food,

drinks,and unpasteurized milk• The organism multiply in small intestine, invade

the epithellium and produce inflammation Campylobacter enteritis manifests with fever, headache, malaise, crampy abdominal pain and bloody mucoid diarrhea, and usually self-limited enteritis in a week period

• Laboratory diagnosis:• Specimen: Stool


LISTERIOSIS

• General characteristics:• . Widely present in plants, soil and surface

water• . Zoonotic pathogen of domestic animals• . Non-sporulating, facultative anaerobe,

intracellular. Gram positive rods


Pathogenesis and clinical features:

• Transmitted to humans through ingestion of poorly coooked

• meat and unpasteurized milk and milk products

• 1. Perinatal human listeriosis: Granulomatous• infantisepticum• . Early onset syndrome: Intrauterine sepsis• . Late onset syndrome: Neonatal meningitis


Cont……

• In Adults • . Meningoencephalitis• . BacteremiaPrevention and control:• Proper cooking of animal souce foods• Pasteurization of milk and milk products/


parasites

• The animal parasites that can be contractedby eating certain foods belong to three distinctgroups: protozoa, flatworms, and roundworms.• Animal parasites do not proliferate in foods.


PROTOZOA• Giardiasis Giardia lamblia is a flagellate

protozoan that exists in environmental waters.

• The protozoal cells (trophozoites) produce cysts, which are the primary forms in water and foods.

• Upon ingestion, Giardia cysts excyst in the• gastrointestinal tract with the aid of stomach

acidity and proteases and give rise to clinical giardiasis in some individuals.


• Excystation of the trophozoites occurs somewhere in the upper small intestine, and this step is regarded as being equivalent to a virulence factor.

• The trophozoites are not actively phagocytic, and they obtain their nutrients by absorption. Occasionally, bile ducts are invaded, leading to cholecystitis.

• ENVIRONMENTAL DISTRIBUTION• Water=waterborne


giardiasis• The incubation period for clinical giardiasisis 7-13 days, and cysts appear in stools after3-4 weeks. Asymptomatic cyst passage is themost benign manifestation of G. lamblia

infectionin humans, but when clinical giardiasis occurs, symptoms may last from several months to a year or more. Up to 9.0 x 108 cysts are shed each day by patients, and they may survive as long as 3 months in sewage sludge.


Clinical symptoms

• Abdominal cramps• Abdominal distention• Weigh loss• Diarrhoea• Fatigue• Vomiting• Nausea


• Giardiasis is a highly contagious disease. Ithas been documented in daycare centers whereunsanitary conditions prevailed. The human

infection rate ranges from 2.4% to 67.5%.18 The minimum infectious dose of G. lamblia cysts for humans is 10 or less.


Giardiasis is diagnosed by the demonstration• of trophozoites in stool specimen by

microscopic examinations using either wet mounts or stained specimens. G. lamblia can be grown in axenic culture, but this does not lend itself to rapid diagnosis.

• Effective enzyme-linked immunosorbentassay (ELISA) tests have been developed.


The drug of choice for the treatment of giardiasis

• is quinacrine, an acridine derivative. Also effective are metronidazole and tinidazole.


Incidence in Foods and Foodborne Cases

• Giardia has been shown to occur in some vegetables, and it may be presumed that the organism occurs on foods that are washed with contaminated water or contaminated by unsanitary asymptomatic carriers.


Amebiasis

• Amebiasis (amoebic dysentery), caused byEntamoeba histolytica, is often transmitted bythe fecal-oral route, although transmission isknown to occur by water, food handlers, andFoods.• In warm stools from a case of active dysentery, E.

histolytica is actively motile and usually contains red blood cells that the protozoan ingests by pseudopodia.


• Although generally outnumbered in stools by Entamoeba coli, the latter never ingests red blood cells.

• Although the trophozoites do not persist under environmental conditions, the encysted forms can survive as long as 3 months in sewage sludge.

• The possible transmission of cysts to foodsbecomes a real possibility when poor personalrestroom hygiene is practiced.


• In its trophozoite stage, the organism induces• infection in the form of abscesses in intestinal• mucosal cells and ulcers in the colon.• It reproduces by binary• fission in the large intestine. It encysts in the

ileum,• and cysts may occur free in the lumen. The• organism produces an enterotoxic


• Syndrome, Diagnosis, and TreatmentThe incubation period for amebiasis is 2-4weeks, and symptoms may persist for several• months. Its onset is often insidious, with loose• stools and generally no fever. Mucus and blood• are characteristic of stools from patients. Later• symptoms consist of pronounced abdominal• pain, fever, severe diarrhea, vomiting, and

lumbago,• and somewhat resemble those of shigellosis.


• Amebiasis is diagnosed by demonstrating trophozoites

• and cysts in stools or mucosal• scrapings. Immunological methods such as

indirect• hemagglutination, indirect immunofluorescence,• latex agglutination, and ELISA are• useful.


• This syndrome can be treated with theamebicidal drugs metronidazole and

chloroquine.


• Toxoplasmosis• This disease is caused by Toxoplasma gondii,• a coccidian protozoan that is an obligate

intracellular• parasite.


• Domestic and wild cats are the only definitive hosts for the intestinal or sexual phase of this organism, making them the primary sources of human toxoplasmosis. Normally, the disease is transmitted from cat to cat, but virtually all vertebrate animals are susceptible to the oocysts shed by cats. As few as 100 oocysts can produce clinical toxoplasmosis in humans, and the oocysts can survive over a year in warm, moist environments.


• Symptoms, Diagnosis, and Treatment• In most individuals, toxoplasmosis is

symptomless,but when symptoms occur, they consist of fever with rash, headache, muscle aches and

• pain, and swelling of the lymph nodes. The• muscle pain, which is rather severe, may last

up• to a month or more.


cycle

• The disease is initiated upon the ingestion of• oocysts (if from cat feces), which pass to the

intestine• where digestive enzymes effect the release• of the eight motile sporozoites.


• Fresh meats may contain toxoplasma oocysts.• Undercooked meat was suspected to be the

source of human toxoplasmosis.


• Control• Toxoplasmosis in humans can be prevented by

avoiding environmental contamination withcat feces and by avoiding the consumption of

meat and meat products that contain viable tissue cysts. The cysts of 7. gondii can be destroyed by heating meats above 600C or by irradiating at a level of 30 krad (0.3 kGy) or higher. The organism may be destroyed by freezing.


• Sarcocystosis• Of the more than 13 known species of the

genus Sarcocystis, two are known to cause anextraintestinal disease in humans. One of these is

obtained from cattle (S. hominis) and the other from pigs (S. suihominis). Humans are the definitive hosts for both species; the intermediate host for S. hominis is bovines, and pigs for S. suihominis.When humans ingest a sarcocyst, bradyzoites are released and penetrate the lamina propria of the small intestine, where sexual reproduction occurs that leads to sporocysts. 179WALTER WAKHUNGU WASWA

• Since most of the above cases have been traced to meats, the consumption of raw or undercooked meats carries the risk of this infection.


Cryptosporidiosis• The protozoan Cryptosporidiunparvum was

first described in asymptomatic mice, and for decades now it has been known to be a pathogen of at least 40 mammals and varying numbers of reptiles and birds. Although the first documented human case was not recorded until 1976, this disease has a worldwide prevalence of 1-4% among patients with diarrhea,96 and it appears to be increasing.


• The prevalence of C. parvum in diarrheal stools is similar to that of Giardia lamblia. In humans, the disease is self-limiting in immunocompetent individuals, but it is a serious infection in the immunocompromised, such as AIDS patients. The protozoan is known to be present in at least some bodies of water and thus exists the potential for food transmission.The fecal-oral route of transmission is the most important, but indirect transmission by food and milk is known to occur.


• C. parvum carries out its life cycle in onehost. Following ingestion of the thick-walledoocysts, they excyst in the small intestine andfree sporozoites that penetrate the microvillousregion of host enterocytes, where sexual

reproduction leads to the development of zygotes.

They invade host cells by disrupting their ownmembrane as well as that of the host.


• Symptoms, Diagnosis, and Treatment• The clinical course of cryptosporidiosis in• humans depends on the immune state, with the• most severe cases occurring in the

immunocompromised.• In immunocompetent individuals,• the organism primarily parasitizes the intestinal

epithelium and causes diarrhea.


• FLATWORMS• AU flatworms belong to the animal phylum• Platyhelminthes,


• Fascioliasis• This syndrome (also known as parasitic biliary• cirrhosis and liver rot) is caused by the digenetic• txQmdXo&t Fasciola hepatica. The disease• among humans is cosmopolitan in distribution,• and the organism exists where sheep and cattle• are raised;


• in humans results• from eating raw Fflsczo/fl-ladedbovine liver• where young flukes become attached to the

buccal• or pharyngeal membranes, resulting in pain,• hoarseness, and coughing.18


• Symptoms, Diagnosis, and Treatment• Symptoms develop in humans about 30 days• after the infection; they consist of fever,

general• malaise, fatigue, loss of appetite and weight,

and• pain in the liver region of the body.


• Fasciolopsiasis• Fasciolopsiasis is caused by Fasciolopsis buski,

and the habitat of this organism is similar to that of E hepatica.

• Humans serve as definitive host, • Snails serve as first intermediate hosts, and

water plants (watercress nuts) as second intermediate hosts.


• no symptoms• occurring when only a few parasites exist In

the body. When symptoms occur, they develop within 1-2 months after the initial infection and consist of violent diarrhea, abdominal pain, loss of weight, and generalized weakness.


• Paragonimiasis• This parasitic disease (also known as parasitic• hemoptysis) is caused by Paragonimus spp.,

especially P. westermani.


Diphyllobothriasis

• Contracted from the consumption of raw or undercooked fish,

• Causative organism, Diphyllobothrium latum, fish tapeworm.

• Definitive hosts are humans andother fish-eating mammals;

• Intermediate hosts are various freshwater fish and salmon, where plerocercoid (or metacestode) larvae are formed.


• Symptoms, Diagnosis, and Treatment• Although most cases of diphyllobothriasis are• asymptomatic, victims may complain of

epigastric• pain, abdominal cramps, vomiting, loss of• appetite, dizziness, and weight loss. Intestinal• obstruction is not unknown.


• Prevention• Diphyllobothriasis can be prevented in

humans• by avoiding the consumption of raw or• undercooked fish.


• Cysticercosis/Taeniasis• This syndrome in humans is caused by two• species offlatworms: Taeniasaginata (also

Taeniarhynchus• saginatus; beef tape) and Taenia• solium (pork tape).


• The adult worm consists• of a scolex (head) that is about 1 mm in size• and lacks hooks but has four sucking discs.

Behind• the scolex is the generative neck, which• segments to form the strobila composed of

proglottids.


• fully developed embryos, and may survive for• months. When the eggs are ingested by

herbivores,• such as cattle, the embryos are released,• penetrate the intestinal wall, and are carried

to• striated muscles where they are transformed• into larval forms designated cysticerci.


• Symptoms, Diagnosis, and Treatment• Most cases of taeniasis are asymptomatic

regardless• ofthe Taenia species involved, but symptoms• differ when humans serve as intermediate• host.


• ROUNDWORMS• The disease-causing roundworms of primary• importance in foods belong to two orders

ofthe• phylum Nematoda.


• Phylum Nematoda• Class Adenophorea (= Aphasmidia)• Order Trichinellida• Genus Trichinella• Class Secernentea (= Phasmidia)• Order Rhabditida


• Trichinosis• Trichinella spiralis is the etiological agent of• trichinosis (trichinellosis), the roundworm

disease• of greatest concern from the standpoint of• food transmission.


• the trichinae are transmitted from host• to host; no free-living stages exist. In other

words,• both larval and adult stages of T. spiralis are• passed in the same host. It is contracted most• often from raw or improperly cooked pork• products.


• Although they• may remain in the intestines for about a

month,• no symptoms are produced.


• As the larvae burrow into musclesseveral weeks later, severe pain, fever, and

othersymptoms occur, which sometimes lead to

deathfrom heart failure (see below).


Symptoms and Treatment

One to 2 days after the ingestion of heavilyencysted meat, trichinae penetrate the

intestinal mucosa, producing nausea, abdominal pain, diarrhea,and sometimes vomiting.


Diagnosis

• Because the trichinae exist as coiled larvae in• ovoid capsular cysts in skeletal muscles,

biopsies• are sometimes performed on the deltoid,

biceps,• or gastrocnemius muscles.


Prevention and Control

• Trichinosis can be controlled by avoiding the• feeding of infected meat scraps or wild game• meats to swine and by preventing the

consumption• of infested tissues by other animals.


Health & Medicine

MICROBIOLOGY AND PARASITOLOGY IN NUTRITION