Micro - GI infections Flashcards
(27 cards)
What are the types of clinical GI infection syndromes
Secretory diarrhoea: toxin production → Cl secretion into lumen → loss of water and electrolytes → D&V
- Watery diarrhoea with no fever
- Cholera, ETEC, EPEC, viruses
Inflammatory diarrhoea → inflammation and bacteraemia
- Bloody diarrhoea (dysentery), fever
- C. jejuni, shigella, non-typhoidal salmonella, EIEC
Enteric fever
- Fever, fewer GI symptoms
- Typhoidal salmonella, yerisinia, brucella
What are the features of clostridium botulinum and what is the treatment
Gram +ve anaerobe
Canned/vacuum packed foods: Honey (kids),
beans (students)
Ingestion of preformed toxin (inactivated by cooking)
Blocks Ach release from peripheral nerves →
Descending paralysis (differentiates from GBS)
Tx: antitoxin
What are the features of Clostridium perfringens infection
Gram +ve anaerobe
Normal flora of the colon, but not the small bowel where the enterotoxin acts
Reheated meats, 8-16hrs incubation
Watery diarrhoea + cramps, lasts 24hrs
Also causes gas-gangrene
What are the features of Clostridium difficile infection and what is the treatment
Gram +ve anaerobe
2 exotoxins (A,B)
- Toxin A = enterotoxin = inflammation
- Toxin B = cytotoxin = virulence factor (more dangerous)
Pseudomembranous colitis
Suspect if severe diarrhoea + recent Hx of Abx (usually cephalosporins/fluorquinolones)
Tx: metronidazole, 2nd line vancomycin
What are the features of bacillus cereus infection
Gram positive rods, spore-forming
Reheated rice (spore germinates)– suspect after re-heated takeout
Short incubation ~4hrs
Sudden vomiting and watery, non-bloody diarrhoea
Superantigen — short incubation (4hrs)
Increased cAMP— long incubation (18hrs)
Self-limiting
May cause cerebral asbcess
What are the features of staph aureus infection
Gram +ve clusters of cocci on gram stain, catalase, coagulase +ve, yellow colonies on blood agar
Spread by skin lesions on food handlers
Produces enterotoxin (acts as superantigen → IL1/2
release)
Short incubation ~2hrs
Prominent vomiting, watery non-bloody diarrhoea
Self-limiting
What are the features of E. Coli infection and how is it treated
Gram negative rod (Facultative anaerobes, glucose/lactose fermenters (LF), oxidase-negative)
Transmitted in faeces/contaminated water
ETEC: toxigenic, traveller’s diarrhoea
EIEC: invasive dysentery
EHEC: Haemorrhagic → HUS
HUS: Anaemia, thrombocytopenia, renal failure (0157:H7 toxin)
EPEC: Infantile diarrhoea (Paeds)
Tx: self-limiting, can treat with cipro
What are the features of typhoidal salmonella infection and how is it treated
Typhi + paratyphi
Multiplies in Peyer’s patches, spreads ERS
Enteric fever: Constipation, fever, rose spots,
splenomegaly
Tx: IV ceftriaxone → PO azithromycin
What are the features of non-typhoidal salmonella infection and how is it treated
Enteritides
Poultry, eggs, meat
Non-bloody diarrhoea, no fever
Tx: self-limiting, Ceftriaxone if required
What are the features of shigella infection and how is it treated
No animal reservoir (human → human transmission)
Affects the distal ileum + colon → mucosal inflammation, fever, pain, bloody diarrhoea (dysentery)
Tx: self-limiting, cipro if required
What are the features of vibrio infection
Curved, comma shaped, late lactose fermenters, oxidase positive
Cholera: Faeco-oral transmission (shellfish, oysters, shrimp). Rice water stool (massive diarrhoea without inflammation)
- Enterotoxin A and B subunit → persistent stimulation of adenylate cyclase
Parahaemolyticus: raw seafood (common in Japan)
Vulnificus: cellulitis in shellfish handlers
All self-limiting, treat dehydration, consider doxicyclin for para + vulni
What are the features of campylobacter jejuni infection and how is it treated
Curved, comma or S shaped; Microaerophilic
Undercooked poultry (chicken at a BBQ)
Prodrome of fever and headache, then abdo cramps and bloody diarrhoea
Lasts ~10d
Associated with GBS, reactive arthritis, Reiter’s
Tx: erythromycin or cipro in first 5 days
What are the features of listeria monocytogenes infection and how is it treated
Refrigerated food, unpasteurised dairy
Perinatal infection
Severe infection in immunocompromise
Water diarrhoea, cramps, headaches, fever
Tx: Ampicillin
What are the features of entaemoeba histolytica infection and how is it treated
Motile trophozoite in diarrhoea; Non-motile cyst in non-diarrhoeal illness
Flask-shaped ulcer on histology with 4 nuclei
Dysentery, flatulence, tenesmus
More common in MSM
Tx: metronidazole
What are the features of giardia lamblia infection and how is it treated
Pear-shaped trophozoite with 2 nuclei, 4 flagella and suction disc
Causes malabsorption of fat → foul-smelling non-bloody diarrhoea
Tx: metronidazole
What are the features of cryptosporidium parvum infection and how is it treated
Severe diarrhoea in immunocompromised
Infects jejunum
Oocysts seen in stool by modified Kinyoun acid fast stain
Tx: paromomycin
What are the features of viral causes of GI infection
Norovirus: secretory diarrhoea in adult outbreaks, no long-term immunity, low ID load with environmental resilience
Adenovirus: secretory diarrhoea <2yo
Rotavirus: secretory diarrhoea <6yo, dsRNA “wheel like”, exposure 2x → lifelong immunity
All self-limiting
Define gastroenteritis
rapid onset diarrhoeal illness, lasting <2 weeks with diarrhoea (loose or unformed stool) ≥3/day or ≥200g of stool which is either viral or bacterial in aetiology
Define diarrhoea
loose or watery stool, ≥3 times in 24 hours
What defines acute, persistent, and chronic diarrhoea
Acute <14 days (may be viral or bacterial)
Persistent 14-29 days
Chronic >30 days (may be due to parasites and non-infectious aetiology)
What are the differences between small and large bowel diarrhoea
Small bowel diarrhoea = watery, crampy abdominal pain, bloating and gas; inflammatory cells rare
Large bowel diarrhoea = small volume, painful, occur with blood/mucous; inflammatory cells common
How does cholera toxin work
Subunit production
cAMP opens Cl- channels at the apical membrane of the enterocytes causing an efflux of Cl- to lumen with loss of water and electrolytes → profoundly dehydrated
What are superantigens
Superantigens bind directly to TCRs and MHC molecules
Outside the peptide binding site there is massive cytokine production by CD4 cells (systemic toxicity and suppression of adaptive response) → secretory diarrhoea
What investigations should be done for GI infections
Stools testing – cultures or independent methods (i.e. multiplex molecular PCR)
Enteric fever – blood and stool tested by culturing and independent testing methods (BM, duodenal fluid and urine)
Parasites – stools for microscopy and culture (inc. ova cysts and parasites)
