L16 & 17 Infection PART 2 Flashcards
(36 cards)
how much normal microbial flora is there in saliva and in faeces?
saliva - 10^8 - 10^9 bacteria per ml
faeces - 10^11 - 10^12 bacteria per gram
where is normal flora found?
skin
gut
upper airways
genital tract
what is cystitis?
Infection of lower urinary tract: Lower abdominal pain Urgency Dysuria Frequency
Most commonly bacteria from gut flora
E.g. Escherichia coli
E.coli: Gram-negative bacillus
what is the difference between an endogenous and an exogenous infection?
endogenous - comes from ourselves
exogenous/communicable - person to person, non-human species eg animals/birds/insects, environment eg soil/water
what are the routes of transmission for endogenous infections?
migration
perforation
blood
what are the routes of transmission for exogenous infections?
direct/indirect contact injuries - trauma/bites airbourne oral (food/water) sex mother to baby (vertical)
give an example of an endogenous infection caused by migration
Bowel flora e.g. E.coli contaminates perineum Gains access to urethra Causes local infection Spreads to bladder (cystitis) and beyond UTI = Urinary Tract Infection
give an example of an endogenous infection caused by perforation
Diseases of bowel especially colon e.g.
Cancer
Diverticular disease
Perforation of bowel wall leads to contamination of abdominal cavity with faecal flora
Severe life-threatening infection results
Faecal peritonitis
give an example of an endogenous infection caused by blood spread
Endocarditis:
dental work may allow mouth flora eg streptococci to enter blood stream
Circulation of organisms allows them to reach distant sites e.g. heart valve
Invasion can occur especially if valve tissue is abnormal e.g. congenital defect
Causes inflammation ‘vegetation’ and structural damage
give an example of an exogenous reaction caused by direct contact
Impetigo:
superficial skin infection due to staphylococci and/or streptococci
spreads rapidly from person to person
give an example of an exogenous reaction caused by indirect contact
Micro-organisms can be transmitted indirectly via hands, equipment, furniture etc
Major route of health-care associated infections
Examples:
methicillin-resistant staphylococcus aureus (MRSA)
Clostridium difficile
Norovirus gastroenteritis
what is tetanus?
(lockjaw) Clostridium tetani - Bacterium present in soil Contaminates wounds Releases toxin causing muscle spasm Prevented by vaccination
what is malaria?
Parasite infection
Present in large areas of tropics
Causes severe febrile illness affecting all body systems
caused by bite
what is the influenza virus?
airbourne infection
Coughing & sneezing
Droplets formed containing infectious viruses
Inhaled by others
how are infections spready by oral route - foodbourne?
Food prepared with poor hygiene E.g. not washing hands after going to toilet Contaminate food with harmful bacteria Result: food poisoning! Vomiting, diarrhoea
what is hepatitis B?
hepatitis B virus Liver infection Some viruses spill into blood (and other body fluids) blood-borne infection: Transfusion Sharing of needles etc Tattoos & body piercing
how is chlamydia spread?
unprotected sex
new partners
multiple partners
partners with high risk e.g. prostitutes
how is vertical transmission mother to baby spread?
During pregnancy e.g. rubella
At time of birth e.g. herpes
Breast milk e.g. HIV
what are the 2 steps involved in staphylococcus aureus soft tissue infection?
Step 1: colonisation of skin – joins skin flora
Step 2: penetration of skin – spreads & damages
which pathogen factors influence infection?
Infectious dose
Minimum number of organisms required to produce disease
E.g. 18 for norovirus, 108 for cholera
Direct infection of cells/tissues
Virulence factors & toxins
Invasion
Disease
Resistance to antibiotics
what is ebola and what are it’s effects on the body?
direct infection and damage or destruction of cells
ebola and marburg virus to macrophage and dendritic cells.
causes tissue damage (liver, spleen, adrenal), systematic inflammatory response, coagulation factors, and impairment of adaptive immunity (no antibodies produced)
what are virulence factors?
Allow invasion of host tissues eg streptolysin O
Lyses cells - ‘cytolysin’
Produced by certain streptococci (Group A)
what does cholera do to the body?
Severe watery diarrhoea – ‘rice water’ Bacteria produce toxin Binds to gut lining cells (mucosa) Massive loss of fluid and electrolytes Causes severe dehydration, kidney failure & death
what is the cholera toxin mechanism?
Cholera toxin enters cells of gut lumen
Activates adenyl cyclase increasing cAMP
Reduces Na+ absorption
Increases Cl- secretion
Water and other electrolytes drawn into bowel lumen = diarrhoea
