Lec 32 Flashcards
What does it mean if diarrhea < 24 hours after source?
means there is a preformed toxin
What 2 bugs will cause a diarrhea within 6 hours?
- staph aureus
- B. cereus
What 2 bugs will cause a diarrhea within 6-24 hours?
- C. perfringens
- B. cereus
What 3 organisms will cause vomiting within 1-6 hours?
- staph aureus
- B cereus
- norwalk virus
What is the dominant symptom in things with a preformed toxin?
vomiting
What are our defenses against GI infections?
- gastric acid secretion
- gastric pH < 4
- intact small bowel motility
- intestinal microflora
- secretion IgA and serum IgG
What is enteroadherence?
attachment and effacing adherence
pili serve as antigen which allows colonization
What is mech of enterotoxin?
can be pre-formed or not
toxin-receptor interaction increases intracellular signaling [cAMP, cGMP, Ca, etc]
What is acute bacterial dysentery?
diarrhea that is mucopurulent, bloody and accompanied by ab pain, fever, and leukocytosis
= enteroinvasive mech
What are 5 causes of acute bacterial dysentery?
- salmonella
- shigella
- campylobacter
- yersinia
- clostridium perfringens
What is cytotoxic mech of bacterial infection?
- inhibits protein synthesis and triggers inflammatory cascade
- disrupts tight junctions and mitochondria
What is mucosal invasion mech of bacterial infection?
main mech for colon –> invade enterocyte and multiply intracellularly and get cell death
What are 2 mechs of shigella infection?
- adherence to mucosal surface w/ release of toxin
2. invasion of epithelial lining
What part of GI does shigella?
usulaly infects colon w/ some terminal ileum
What is classic presentation of shigella?
watery diarrhea then entero-invasion –> multiple small volume bloody mucoid stool
Can shigella cause bacteremia?
rarely
What is the action of vibrio cholera’s two enterotoxin subunits?
B unit = Binds enterocytes usually in proximal small bowel
A unit = Activates intracellular adenylate cyclase –> stimulate intestinal secretion
What is presentation of vibrio cholera?
severe watery diarrhea = rice water diarrhea; can present with shock
no inflammatory cells in stool
What part of GI does cholera infect?
upper small intestine; colon relatively unaffected
What are the 2 toxins of enterotoxigenic E coli?
heat labile toxin = similar to cholera toxin; activates adenylate cyclase
heat stable = activates guanylate cyclase
What is usually the source of enterotoxic e coli?
contaminated food and beverages
What is clinical presentation of enterotoxigenic e coli?
most common cause of travelers diarrhea
non-invasive, watery non-bloody non-purulent diarrhea; can have variable volume loss
What is mech of EColi 01:H157?
epidemic E coli; usual route of infection is infected meat
adheres to distal small bowel with shiga-like toxin that causes mucosal destruction and allows toxin to enter circulation
What part of GI does E Coli 01:H157 infect?
distal small bowel
What is the major illness that enterotoxigenic E coli 01:H157 causes?
hemolytic uremic syndrome = due to endothelial cell injury have localized prothrombic state in glomeruli; hemolysis of RBCs due to shearing in damaged vessels
What kind of food is usually the source of staph aureus?
food with egg products or cream that is not adequately refrigerated
What is typical presentation of staph aureus infection?
within 4-8 hours have upper GI symptoms; N/V followed by watery diarrhea and resolved in 24 hours
What is source of clostridium perfringens infection?
inadequately heated meat
What is typical presentation of clostridium perfringens?
diarrhea within 8-24 hours that resolves spontaneously
What is pathogenesis of C Diff?
- may colonize colon in normal flora; when normal colonic flora is disturbed ie following antibiotic use it becomes pathogenic
releases toxins A and B –> destroy epithelium –> get pseudomembrane of dead leukocytes and mucosal cells
What are the actions of CDiffs two toxins?
toxin A = initiates inflammatory process but is non-essential for infection
toxin B = cytotoxic and causes cellular damage and destruction
What are risk factors for c diff infection?
antibiotic use - particularly clindamycin
hospital stay
increased age
PPI use
What is clinical presentation of C Diff infection?
profuse watery non-bloody stools with crampy abdomen
leukocytes [WBC > 20k] in stool
What are two potential complications of C Diff?
toxic megacolon
toxic colitis
associated with NAP1 strain = more severe
How do you diagnose CDiff?
C Diff toxin in stool or sigmoidoscopy to show pseudomembranes
What are the 5 Fs of salmonella?
fingers, food, feces, flies, fomites
What part of GI is usually infected by salmonella?
terminal ileum
What is invasive non-typhoid salmenollosis?
usually in terminal ileum; maybe colon
salmonella penetrates lamina propria then lymphatics and bloodstream –> can lead to septic arthritis, meningitis, endocarditis, osteomyelitis
= salmonella bacteremia
What are some conditison predisposing to salmonella infection?
- sickle cell
- lymphoma/leukemia
- AIDS
- aschlorhydria –> PPI
- UC
- schitosomiasis
What is the presentation of salmonella gastroenteritis?
after 6-48 hrs have N/V then ab cramps and bloody diarrhea that may last days and be accompanied by fever
What happens in typhoid fever?
salmonella typhi invades small bowel mucosa, lamina propria, lymphatics, blood stream
have minimal intestinal symptoms early on –> diarrhea, bleeding, perforation
high fever, headache, toxemia, mental status change
Where do you get pain in typhoid?
RLQ b/c organisms localize in peyers patches of ileum
What is source of campylobacter?
farm animals; chickens; raw milk + eggs
What is clinical presentation of campylobacter?
invades mucosa; asymptomatic or watery diarrhea or dysentery 1-3 days after ingestion
stool has fecal leukocytes / obvious blood
How do you diagnose campylobacter?
stool culture
What can yersinia mimi?
appendicitis or crohns ileitis = RLQ pain of acute onset
What is source of yersinia?
food or pets
What is clinical presentation of yersinia?
mucosal invasion –> diarrhea, RLQ pain
What 6 bugs produce blood diarrhea?
- shigella
- salmonella
- entamobea
- e coli
- c diff
- yersinia
What 4 bugs produce watery diarrhea?
- viruses
- vibrio
- giardia
- enterotoxigenic E Coli
What is most comon cause of community acquire gastroenteritis?
rotavirus
What is transmission of rotavirus?
fecal-oral, respiratory secretions, or contaminated surfaces
What kind of virus is rotavirus?
double stranded RNA virus
What is mechanism of rotavirus
destruction of mature enterocytes in proximal small intestine –> secretory diarrhea; decreased brush border enzymes
What is clinical presentation of rotavirus?
watery diarrhea without inflammatory cells
lasts 3-7 days
What are our defences against rotavirus?
virus specific but short lived IgA –> Ab increases with subsequent infection
What type of virus is norovirus?
single stranded RNA
What is most common cause of community acquired infectious diarrhea in adults?
norovirus
What makes norovirus so infectious?
viral shedding can occur during asymptomatic and in post-symptomatic state
What is pathogenesis of norovirus infection?
non invasive
causes reversible lesions in upper jejunum –> blunting villi, lose brush border enzymes –> osmotic loose watery diarrhea
lasts 12-60 hours
Who classically gets giardia?
IgA deficient patients
Where does giardia infect?
mucosa of duodenum and jejunum –> upper GI symptoms more common than diarrhea
What is mech of giardia infection?
not enteroinvasive = adheres to small bowel and destroys tight junctions
watery diarrhea= non-bloody, no mucous
What is clinical presentation of entameoba histolytica?
varies from asymptomatic to severe dysentery with bloody stools; crampy abdominal pain; can cause ameobic liver abscess
What is pathogenesis of entameoba histolytica?
ingest cyst –> beomce trophozoites in bowel –> phagocytose RBCs and cause ulcers throughout large intestine
What do you see on endoscopy with entameoba histolytics?
punched out ulcers = mimic UC
dense inflammatory granulomas = ameoboma
How do you diagnose entameoba?
microscopic examination of fresh stool specimen for trohpozoites
What is pathogenesis of cryptosporidium infection?
sprozoites attach to enterocytes along their microvilli –> watery/profuse diarrhea
diagnose by stool assya
