MICROBES AND DISEASE

MICROBES AND DISEASEF 6PATHOGEN- a micro-organism which causes a disease when it infects.VIRULENCE-ability of a pathogen to cause diseaseINFECTIOUS DISEASE- which can be passed from one sufferer to anotherAn infection does not always result in disease Mode of TransmissionDirect contactperson to person via the mucous membrane, which is thinner, softer and moister and thru blood Horizontal kissing, sexual intercourse, sneezing less than 1 meter, touchingVertical Placenta , breast milkIndirect contact Air /dustFungi spores ---influenza and SARS viruses Food, Water, Fomites Vector borne Insects , Protozoans, poor hygiene, Cholera and Typhoid bacteria-sewage- contaminated water Salmonella bacteria (raw meat)Prion as disease agent(CJD)-Creutzfeldt-Jacob diseaseHuman pathogenic diseases and their means of transmission

Mode of transmission Indirect contact vector borne Example: bacterial dysentery

* The bacterium Shigella causes a type bacterial dysentery .

* Flies can spread Shigella when they carry infected faecal matter on their feet to drinking water or food.

* Symptoms can vary from mild diarrhoea through to a more severe disease with watery or bloody diarrhoea, fever, stomach cramps and vomiting . Mode of transmission Indirect contact vehicle borne Example: athletes foot

* The fungus Trichophyton that causes athletes foot can be spread indirectly through towels, changing room floors etc.

* The fungus thrives in the damp warm environment found between the toes.

* The skin between the fourth and fifth toe is usually affected first. A flaky itchy red rash develops. The skin becomes cracked and sore and small blisters may appear.

* If the infection is left untreated it can spread to other parts of the body.

Fomite - a non-living object that can carry disease-causing organisms. Mode of transmission Indirect contact vehicle borne Example: tuberculosis (TB)

* Air/dust

* The bacterium Mycobacterium tuberculosis causes tuberculosis (TB).

* TB is spread from person to person through the air.

* When a person with active TB coughs or sneezes, droplets loaded with the infectious organism are propelled into the air.

* The moisture evaporates from these particles to leave droplet nuclei that can remain airborne for days and spread long distances.

* The Mycobacterium has a waxy coat, which protects it from drying out allowing it to survive for many months in the air and dust. Mode of transmission Direct contact person to person Example: German measles

* Rubella virus causes German measles. * When infection occurs during pregnancy the virus crosses the placenta in the blood leading to infection of the fetus . * The virus can affect all the organs of the developing fetus . * T he risk to the baby is highest in the first 3 months up to 85% of babies are affected if infected during this period.

Eight week old fetus attached to its placenta by the umbilical cord. Vertical across the placenta or via breast milk Mode of transmission Direct contact person to person Example: German measles

* Congenital rubella syndrome is the name given to a group of defects that occur in a child when infected as a fetus.

* Defects are

# deafness (most common)

# eye problems such as cataracts

# heart disease

# impaired mental development

# bone deformities

# liver damage

* The number of cases has dropped significantly due to the introduction of rubella vaccine which is offered to all children as part of the MMR jab. Mode of transmission Direct contact person to person Example: SARS

* Horizontal sneezing closer than 1 metre

* SARS - associated coronavirus causes severe acute respiratory syndrome (SARS).

* SARS is transmitted when an infected person coughs or sneezes infectious droplets onto a nearby person .

* T he droplets land on another person s face or hands, and become introduced to the nose or mouth.

Jets of droplets erupt from a mans nose as he sneezes. Mode of transmission Direct contact person to person Example: SARS

* The main symptoms of SARS are a high fever >38.0C, dry cough and breathing difficulties.

* Other symptoms may include headaches, loss of appetite and body aches.

* About 10 -20% of patients have diarrhoea.

* Most patients develop pneumonia. Mode of transmission Direct contact person to person Example: cold sore

* The virus particles invade the cells of the skin around the mouth and enter the nerve tissue where they lie dormant until something triggers their reactivation.

* Common reasons for the virus becoming reactivated are tiredness, illness, stress and sunlight. Bacterial infectionIntracellular---ChlamydiaExtracellular---StreptococcusExtra cellular bacteriaDamage tissues from outside cells.Host cells produce antibodies OPSONINSProduce acute diseaseLast for short timeStreptococcus--------Gram +ve bacteriaS.agalactiae- mother to infant during child birthS.pyogenes cause-strep throat, rheumatic fever and scarlet fever

An Opsonin is any molecule that acts as a binding enhancer for the process of phagocytosisAction of opsonins a phagocytic cell recognises the opsonin on the surface of an antigen

Capsule of Streptococcus pneumonia produces proteins that inhibits phagocytosis by human immune systemIntra cellular bacterial infectionAre able to grow and reproduce only within the cells of other organismsEg., Chlamydia, RickettsiaChlamydia trachomatis- blindness The Rickettsia survival depends on entry, growth, and replication within the cytoplasm of Eukaryotic host cells. Rickettsia species are carried as Parasites by many ticks, fleas and lice.TyphusAfrican tick bite feverChlamydia spc.are the most common bacterial sexually transmitted infections in humans Leading cause of infectious blindnessBacterial toxinExotoxinEndotoxin----- Lipopolyscaccharides in the wall of the Gram ve bacteria For eg., SalmonellaReleased when the bacteria die or cell wall is damagedCauses fever and achesOnly gram+ve Listeria monocytogenesExotoxinA protein secreted by the bacterium. may produce even in the absence of bacterium.majority of them can be destroyed by heatingBoth gram-ve and +ve produce exotoxinCan be destroyed by antibodies, but some are so toxic that they may be fatal before immune system can respond.Vibrio choleraThree main types of exotoxin

Acts on connective tissue-spread the bacteriaActs as enzymes-enter the cell and effect their metabolismMembrane damaging toxins-puncture the CM-killing cells.Clostridium tetani-gram +veTetanusExotoxin- neurotoxin-tetanospasminInfection thru wound contaminationMuscles spasmsin the jaw-lockjawdifficulty in swallowing, and muscle stiffness and spasms.Sustained contraction of skeletal muscle

ExotoxinClostridium botulinum inhibitor of neuromuscular junctionSmall doses of toxin is used in commercial preparation of botox

Methods of controlling microbial growthAntisepticsto prevent sepsisCarbolic acid (phenol) the first antiseptic Today-chlorohexidine mouthwash-and alcohols---ethanol and isopropanol

Disinfection

Destruction of infective organismsHypochlorite ---purify water in swimming poolsDisinfect feeding bottlesToiletsbleaching agents-pH 5Active ingredient is HOCl-hypochlorous acidKills bacteria by releasing oxygen, and act as oxidising agentEffective when used in warm solutionBacteriocidal- to kill the bacteriaBacteriostatic to prevent multiply

The action of bacteriocidal and bacteriostatic agents.

PastuerisationSterilise foodMilkBoiling upto72 celsius for 15 seconds

RadiationGamma radiation used to sterilise culture mediaMedical suppliesDrugsBacterial and fungal cells-need low doseSpores and viruses need higher dose Spices and condimentsIn lab 1.Culture media---all nutrientAgar-complex polysaccharide ---extracted from seaweed and can be warmed to 370 C.Agar is mixed with liquid medium to prepare a solid medium.2. Inoculation-introduction of bacteria3. IncubatorLiquid media/ broth-incubated in a waterbath.Condition for growthTemperature- bacterial growth increases with slight increase in temperature Wide range of temperatures. Most grow at neutral pH use buffersObligate aerobes require molecular oxygen so on solid agar they grow on surface and if growing in liquid medium it must be well aerated.

4. Culture-bacteria grows in a medium one bacterial strain or many strains growing together. Colony- visible growth of bacteria on an agar plate Streak Plate is a method of inoculating an agar plate with bacteria so that they are gradually diluted.

Lawn- is a layer of bacteria growing on the surface of agar plate. To test the effectiveness of antibiotics or antiseptics.

Viruses Obligate parasitesGrow in specific living host cells.Tissue culture techiquesGrowth of bacterial cellsCounting number of cellHemeocytometer- individual cells under microscope-used for large cells such as yeast

Turbidometry-less accurateLiquid culture in a cuvette in colorimeter or spectrophotometer and the absorbance of light is measured.

Mechanisms of action of antibioticsOriginally defined as susbstance produced by microorganism that kill or inhibit growth of microorganismsSir Alexander Fleming in 1928 first antibiotic discovered Penicillin from a fungus Penicillium notatum

Antibiotics

Treat infectious bacterial diseasesMicrobicidal kill the bacteriaMicrobistatic- slow down the growth of bacteriaGenerally gram+ve bacteria are more sensitive to antibiotics than gram-ve bacteria.

Chloramphenicol and Tetracyclines- are broad spectrum of antibiotics and acts on wide range of bacterias

Action of antibiotics

Effectiveness of antibiotics---resistanceNatural resistance mutation,conjugationEpidemiologyStudy of spread of diseaseTo find the source of an infectionTo establish mechanism of transmission Pathogens come from infected person or from other reservoir of infection. Three main reservoirs of human infection- a. Person who have had an infection but do not show symptom. Carriers.b. Some animals contain pathogens, which infect both animals and human called zoonosis.c. Many pathogens are found in soil and water Some pathogens

English doctor in 1799Edward Jenner Vaccine to prevent a human disease. Small pox.W H OEpidemic-occurs when a large number of people in several communities suffer from the infectionPandemic- occurs when a large number of people in several countries all suffer from the same infectionPandemic-emergence of a disease or new strain to the human population, infects human, causing serious illness and spreads among human.Influenza virusA, B, C, D.New strains of A commonly emergeC and D are stable Epidemics occur on regular seasonal basisPandemics- 1918, Spanish flu(A2 strain) killed more than 20 million people.-attack the epithelial lining of bronchioles infection ----Droplet

2004- avian influenza(H5N1) was detected in birds in S .E. Asia1300 Bubonic plague ---Yersina pestis spread by fleasHIV infectionSpongiform encephalopathy (SE)Affects the brain of Humans and animalstiny hole appears in cortex of the brain , look like a sponge.BRAIN FUNCTION IS IMPAIRED Memory lossPersonality changesProblem in movementCreutzfeldt Jacob disease (CJD) most common form of SE. RareAges 60-65.

Prions (proteinaceous particle)Misfolded, single type of proteinslack nucleic acid,Carry disease , cause deterioration of the brain leading to deathThey can be inherited, occurs spontaneously or spread via infectionTransmission occurs when healthy animals eat infected tissuesBritain in 1980s cows were infected by eating the processed remains of sheep nervous tissue.Bovine form of spongiform encephalopathy (BSE- mad cow disease) A new variant Creutzfeldt Jacob (nvCJD)Occurs early in their life -20sBelieved that nvCJD is transmitted by eating nervous tissue of cows infected with BSE.PrionsLack nucleic acidSingle type of proteinTo infect and propagate by refolding into abnormal shapeResistant to denaturation, radiation and heatPrion hypothesis 1960s

Infectious agent of SE was resistance to UV radiation ( break the nucleic acid)But responded to chemicals and treatments that disrupt proteinsStanley Prusiner 1982 purified and confirmed the presence of a protein.news.bbc.co.uk/2/hi/health/medical_notes/355601.stm