Upload
lily-griffith
View
216
Download
0
Tags:
Embed Size (px)
Citation preview
Infection and diseaseLecture 3
Bacterial toxinsPortals of exit
Common bacterial diseases
(7) Bacterial toxins• Toxins - Poisonous substances produced by microorganisms
– Toxigenicity - The ability to produce toxins.– Toxemia refers to the presence of toxins in the blood.
(a) exotoxins• Mostly produced by gram positive bacteria
• Soluble in body fluids
• Transported throughout blood / lymph
• Disease is often not due to the bacteria per se, but due to the exotoxins
• Most exotoxins are called AB toxins - 2 components: Active and Binding
Examples of exotoxins: Diptheria toxin
Diphtheria; nasopharyx is affected Toxin A inhibits protein synthesis in the host cell – leads to host cell death
Examples of exotoxins: Cholera toxin
• Vibrio cholera – diarrhoea
• Toxin A – increased cAMP – which controls the efflux of H2O ions from cells
• Increased secretion of water and ions into the intestine Diarrhoea
(b) Endotoxin
• Gram negative bacterial cellwall have lipid A (lipopolysaccharide -LPS) – endotoxin
• Important for pathogenesis
How are endotoxins released ?
• Complement-mediated lysis mediated of bacteria
• Phagocytic digestion of bacterial cells
• Antibiotics usage
What does an endotoxin do ?
ENDOTOXINInflammation
Secretion of Cytokines
Fever
BBB
Endotoxin are pyrogens
Killing of bacteria by some sterilization methods may to necessarily eliminate endotoxins
Endotoxins are heat stable
(8) Bacterial spores
• Formed by some bacteria under stress / nutrient depletion
• Most spore forming bacteria are Gram positive bacteria
• Can become a vegetative cell (what we normally refer to as bacteria) under favourable conditions
Bacterial spores
Unfavourable condition
Favourable condition
Bacterial spores
• Spores are highly resistant – to heat, cold, antibiotics
• Spores survive for centuries under harsh conditions
• Spores are dormant – no reproduction
• High levels of calcium dipicolinate – heat resistance / DNA protection
• High levels of sulphur
Portals of exit• Respiratory tract
– Coughing, sneezing
• Gastrointestinal tract– Feces, saliva
• Genitourinary tract– Urine, vaginal secretions
• Skin
• Blood– Biting arthropods, needles/syringes
Examples of bacterial diseases
Tetanus
• Exotoxin from Clostridium tetani
• Neurotoxin – causes muscle spasms
• Starts with pain in the jaw – inability to open jaw
• Spreads to all the muscles throughout the body
• 10% untreated – die due to the toxin
• Vaccine preventable (DPT /TT)
Disease causing organism
symptoms Reservoir Mode of transmission
Clostridium tetani Severe spasms, rigidity of muscles, lockjaw
Soil Puncture wounds contaminated by bacterial spores
Source: Royal College of Surgeons of Edinburgh, Scotland
Tetanus
Anthrax• Bacillus anthracis – spore forming
• Spores are present in soil
• Common disease of grazing animals
• Human infection: Pulmonary anthrax – inhalation of spores Gastrointestinal anthrax – eating of infected animal meat Cutaneous anthrax – hide porter’s disease (cuts in skin)
Disease is linked to exotoxin
Anthrax
Cutaneous anthrax
Anthrax – potential use in bioterrorism; Spores - inhalation
Plague• Yersinia pestis
• Major outbreak in the 14th
century – 200 million deaths
• Many minor outbreaks
• Transmitted through infected rat
fleas (rodents are reservoirs)
Plague: the disease
“Black death”
Plague: pathogenesis
• Resist digestion by macrophages
• Spread via lymphnodes /blood / shed from lungs
• Human-to-human transmission – cough /aerosol
• Acute inflammatory response
• Clogs capillaries
• Reduced blood supply – tissue death by necrosis
Cholera
• Vibrio cholera
• Transmitted by contaminated food /water
• Severe diarrhea (exotoxin)
• Dehydration / can be fatal in young children if untreated
Cholera
• Oral /IV rehydration / antibiotics
Typhoid fever
• Salmonella typhi
• Usually transmitted by contaminated food
• Can affect multiple organs – including brain, lungs, heart
• Small proportion (<5%) – asymptomatic carriers bacteria replicates Able to spread disease
Typhoid Mary
Asymptomatic carrier – cook; several families were infected, changed jobs. Quarantined for 3 decades
TB
• Mycobacterium tuberculosis
• Inhalation (long-term contact)
• ~90% - latent infection (No replication)
• ~10%- progression to pulmonary TB (immune system not able to control replication)
• Fever > 3 weeks, fatigue, cough, night sweat..
TB
• Extrapulmonary TB – brain, bone, joint
• Slow grower (~18 hours to double)
• Requires special antibiotics
• Requires long-term treatment
Food poisoning
Symptoms due to bacteria take > 2 days to manifest
Pre-formed exotoxins
Food poisoning
• Vomitting, abdominal pain
• Eg. Staphylococcus aureus
• Eg. Salmonella species
• Antibiotics may not prevent disease
Can normal flora cause disease ?
• Yes !
• Eg. E.coli (normally in the intestine) – can cause urinary tract infection