Microbiology Flashcards
What bacteria have short incubation times (1-6 hours)?
Bacillus cereus, staph aureus.
What type of bacterium is bacillus cereus and describe how it gets into the body and what it does.
Gram positive bacillus.
Colonises starchy food and has heat resistant spores (consumed with reheated rice), causes profuse vomiting.
What foods does staph aureus colonise?
Foods left at room temperature. Milk, meat, fish.
What does GI staph aureus infection cause?
Vomiting and abdominal pain.
How do these pathogens have such short incubation times?
They have pre-formed toxin.
What was the original shigella described by Shiga?
Shigella dysenteriae.
How does Shiga-toxin work?
Binds to receptors found on renal cells, RBCs and others. Inhibits protein synthesis causing cell death.
What are the 2 names for E.coli that produce shiga-like toxin?
STEC (shiga-like toxin producing E.coli, more recent), VTEC (verotoxin producing E.coli).
What does shiga-like toxin produced by E.coli do when it enters the bloodstream via damaged epithelium?
Causes the death of vascular epithelium. Endothelial cell lysis, platelet activation and aggregation, cytokine secretion, vascular constriction contributing to fibrin deposition, clot formation within capillaries.
What does HUS stand for?
Haemolytic uraemic syndrome.
What causes haemolytic uraemic syndrome?
Microangiopathy as toxin carried to kidneys, causing clinical syndrome of haematuria and renal failure.
What feature of E.coli O175 gastroenteritis is uncommon in other gastroenteritis?
Bloody diarrhoea/blood PR.
How can E.coli O175 spread?
Food (beef, raw milk/water, wide range), person to person, animal contact.
What is the most virulent kind of shiga toxin?
Type 2.
What are the symptoms of HUS?
Abdominal pain, fever, pallor, petechiae (haemorrhagic spots), oliguria (diminished urine output), bloody diarrhoea.
What would you see in blood tests for HUS?
High white cells, low platelets, low HB, red cell fragments.
What investigations would you ask for if you suspect HUS?
Stool culture samples (all patients with blood in faeces), U&E, FBC, fil, LFT, clotting, urine, lactate dehydrogenase.
What people does HUS normally affect?
Under 16s.
What are the 3 parts of HUS?
Acute renal failure, thrombocytopenia (low platelets), haemolytic anaemia.
What are 4 other E.coli pathotypes?
Enterotoxigen (ETC), enteropathogenic (EPEC), enteroinvasive (EIEC), enteroaggregative (EAIC).
What foods does campylobacter live on?
Poultry and raw milk.
What antibiotic would you give for campylobacter infection and when?
Macrolide e.g. clarithromycin. If there are co-morbid factors but there is increasing resistance.
What food (and species) does salmonella colonise?
Food: poultry, meat, raw egg. Reptiles.
What are the risk factors for listeria monocytogenes infection becoming invasive?
Immunosuppressed (particularly T cell), age>50, pregnant.
What is the main complication of invasive listeria monocytogenes infection?
Meningitis/bacteraemia.
What foods does listeria monocytogenes colonise?
Unpasteurised milk products, deli counter.
How do you diagnose the causative organism for viral gastroenteritis?
PCR.
What are the 3 main normal flora in the large bowel?
Enterobacteriaeceae (coliforms), enterococci, anaerobic gm-ve bacilli (bacteroides). Also anaerobic gm-ve cocci.
What test can be used to differentiate between enterobacteriaceae?
The lactose fermenting test.
Give some examples of lactose fermenting enterobacteriaceae.
E.coli, citrobacter, klebsiella, enterobacter, serratia.
Give some examples of non-lactose fermenting enterobacteriaceae.
Morganella, proteus, providencia, salmonella, shigella, yersinia.
Describe the process of identifying enterobacteracaea.
Appropriate clinical sample -> select correct culture medium -> perform gram stain -> lab selects appopriate biochemical tests -> report results to clinician -> other tests.
Describe some types of agar in the identification of enterobacteriaceae.
MacConkey agar, CLED agar (cysteine lactose electrolytes deficiency), chromogenic.
Are enterobacteriaceae aerobes or anaerobes?
Faculative anaerobes.
Give an example of an enterotoxin.
Shiga-toxin.
What is the problem with MALDI-TOF?
It doesn’t tell you what caused the illness, just that it is there.
What are some other molecular methods of identifying pathogens?
16s RNA, whole genome sequencing, pulsed field gel electrophoresis, multilocus sequence typing (MLST), multiple locus variable number tandem repeat analysis (MVLA), SNP assays.
What is the normal flora of the mouth?
Strep viridans, neiserria, anaerobes, candida, staph.
What are the 3 types of strict anaerobes in the GI tract (mostly in large intestine)?
Clostridium sp, bacteroides sp, anaerobic cocci.
