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GI pathogens

Microbiology

QuestionAnswer
Stomach normal flora include: Lactobacilli, Streptococci
Small bowel/colon contain ____ bac/gram; mostly ____ 10(11); anaerobes
Small bowel/colon normal flora include: Peptostreptococci, Bacteroides, Enterobacteriaceae
Normal GI flora: Viruses/Fungi Adenovirus, Enterovirus; Candida
Normal GI flora: Parasites Mostly amoebae; Blastocystis hominis; Entamoeba coli; Endolimax nana; Trichomonas hominis
Etiologic agent of gastroenteritis is related to: Age
Most important agent of gastroenteritis in infants Rotavirus A
Other agents of gastroenteritis in infants Adenovirus (serotypes #40/41); Coxsackie Virus
Most important viral agent of gastroenteritis in children/adults Calicivirus
Other viral agents of gastroenteritis in children/adults Norwalk virus; Astrovirus; Reovirus
What age group more affected by viral GI syndromes? Infants
Viral GI syndromes are usually ____ and require _____ mild; only symptomatic tx
Bac agents of cholecystitis/biliary disease: Enterobacteriaceae, Enterococcus, Bacteroides Clostridium spp.
Bacterial agents of gastritis/PUD: Helicobacter pylori
Bile stimulates growth of ___ Bacteroides
traveler’s diarrhea Escherichia coli (ETEC)
food intoxication S. aureus, C. botulinum, B. cereus
food infection: “Big Three” Campylobacter jejuni; Salmonella spp.; Shigella spp.
Other poss bacterial agents of gastroenteritis C. difficile, C. perfringens, C. botulinum, Vibrio cholerae, Listeria monocytogenes, Yersinia species
Causes of primary (spontaneous) peritonitis Enterobacteriaceae (70%), S. pneumoniae, Enterococcus, anaerobes
Causes of secondary peritonitis (Secondary: poss from trauma); Enterobacteriaceae, Bacteroides, P. aeruginosa
Agents of peritonitis from continuous ambulatory peritoneal dialysis (CAPD) S. aureus (mostly), S. epidermidis, sterile (20%)
Diverticulitis Enterobacteriaceae; Enterococcus; Bacteroides
AIDS-associated diarrhea Mycobacterium avium-intracellulare (MAI)
When to suspect bacterial gastroenteritis Severe abd pain; large #’s of stools; bloody stools; fever (≥ 101°F); fecal leukocytes; tenesmus
Often considered the hallmark of bacterial gastroenteritis Bloody stools
Bloody diarrhea+ fever+ tenesmus = ? dysentery
GI syndromes: exceptions to 3-day rule travelers diarrhea; dysentery s/s
5 major groups of E. coli Enterotoxigenic; enteropathogenic; enteroaggregative; enterohemorrhagic; enteroinvasive
E. coli groups = small bowel processes Enterotoxigenic; enteropathogenic; enteroaggregative
E. coli groups = colon processes (bloody diarrhea) enterohemorrhagic; enteroinvasive
E coli group = in developed countries Enterohemorrhagic
E coli group = more common in pediatric populations (usu developing countries) Enteropath & enteroaggregative
E coli group = most common in developing countries Enteroinvasive
E coli group = travelers diarrhea Enterotoxigenic E coli
ETEC Enterotoxigenic E coli: profuse, watery diarrhea; mild: supportive tx only
Severe cases of ETEC can be treated with: SMZ/TMP or quinolone; prophylaxis not recommended
Enteropathogenic E. coli (EPEC) AKA enteroadherent E. coli; can be part of normal human flora; childhood diarrhea associated with daycare outbreaks (infection rarely seen in older children or adults); mild self limiting disease; non invasive
Enteraggregative E. coli (EAggEC) Similar to EPEC in dz; self limiting diarrhea in children (rarely seen in older children and adults except travelers to endemic areas); difference is vigorous adherence to mucosal cells (facilitated by fimbriae); may be part of normal human flora
E coli group characterized by vigorous adherence to mucosal cells (facilitated by fimbriae) Enteraggregative E. coli (EAggEC)
Like EHEC, disease can be mild to severe hemorrhagic colitis Enteroinvasive E. coli (EIEC)
Most common strain of E coli seen in developed countries Enterohemorrhagic E. coli (EHEC)[mediated by Shiga toxins (STEC)]
E coli group: small inoculum size (<100 bacteria) can cause infection Enterohemorrhagic E. coli (EHEC)
>50 serotypes; 0157 most common in US Enterohemorrhagic E. coli (EHEC)
HUS (hemolytic uremic syndrome) dreaded complication (ARF, thrombocytopenia, hemolytic anemia) Enterohemorrhagic E. coli (EHEC)
E coli group that is mild & self limiting & noninvasive Enteropathic
E coli group that may be normal flora Enteraggregative E. coli (EAggEC)
most common cause of BACTERIAL gastroenteritis C. jejuni
Risk factors of C. jejuni gastroenteritis ages < 5yrs and 20-30 years; males; raw/ undercooked poultry etc; unpasteurized milk & dairy prods; consumption of untreated water; contact with pets and farm animals
Most common clinical presentation of non-typhoidal salmonella Gastroenteritis
transmission risk increased with foods of animal origin salmonella
Risk factors = consumption of contaminated water, exposure to infected reptiles, and person-person transmission salmonella
incidence of severe disease greater in infants, elderly, and those with immunosuppressive conditions salmonella
Fecal shedding serves as reservoir for new infections (children < 5 yrs made shed bacteria for months) Salmonella
Mostly a pediatric disease; transmission almost exclusively fecal-oral; travelers at risk Shigella
As few as 10 bacilli = infective dose Shigella
Prolonged fecal carriage in Shigella… …is rare
Tx for Shigella Antimicrobial therapy, even for mild disease, helps with complete eradication
Etiologic Agents of Food Intoxication S. aureus; Clostridium botulinum; Bacillus cereus; C. difficile
enterotoxin A is preformed in food S. aureus
ingestion disrupts intestinal mucosa S. aureus
Vomiting & diarrhea; onset within 2-4 hrs after digestion S. aureus
Organism can colonize colon in neonates; avoid honey Clostridium botulinum
neurotoxin; types A, B, and E Clostridium botulinum
spore formation enables survival in extreme conditions Clostridium botulinum
home canning is risky Clostridium botulinum
What type of C. botulinum infxn rare in USA? Wound botulism
Can cause upper or lower food infection; both self limiting Bacillus cereus
Upper food infection: emetic symptoms; spores in fried rice, onset of symptoms 2-6 hrs Bacillus cereus
S/S of B. cereus upper food infection Emetic symptoms; spores in fried rice, onset of symptoms 2-6 hrs
Lower food infxn: diarrheal symptoms; spores in reheated meats and vegetables (microwave); onset is 24 hours B. cereus
S/S of B. cereus lower food infection Diarrheal symptoms; spores in reheated meats and vegetables (microwave); onset is 24 hours
agent of antibiotic associated colitis (AAC) C. diff
enterotoxin mediated C. diff
antibiotic resistence C. diff
explosive bloody diarrhea C. diff
S/S include many stools (double digits) C. diff
20-30% may need retreatment due to relapse C. diff
Toxin A = enterotoxin; Toxin B = cytotoxin C. diff
Normal GI flora in some; disrupted by antibiotics; metronidazole, vancomycin C. diff
C. diff toxin types Toxin A = enterotoxin; Toxin B = cytotoxin (Both can cause S/S = high # bloody stools, explos. Diarrhea)
Parasitic GI Syndromes in AIDS patients/protracted diarrhea: MAI, Giardia lamblia, Cryptosporidium parvum, Isospora belli
Parasitic GI causes of diarrheal disease G. lamblia, C. parvum, B. hominis
Intestinal amoebiasis Entamoeba histolytica
Common cause of acute self-limiting diarrhea in immunocompetent hosts Cryptosporidium
Worldwide distribution; more common in summer; seroprevalence in US ~30% Cryptosporidium
Cryptosporidium sources Contaminated water (drinking & recreational), apple cider, raw produce; daycare settings
Most common cause of parasitic diarrhea in US Giardia
Giardia infxn most common when? Late summer, fall
~5% of patients with diarrhea >1 week Giardia
Low infective dose (10-20 cysts) Giardia
Antigenic variation important in pathogenesis Giardia
Giardia infection can result in: Asymptomatic carriage; acute self-limiting diarrhea; chronic diarrhea; chronic diarrhea + malabsorption
Cyst form swallowed, gets decysted; troph form seen in sm bowel Giardia
Has an on/off clinical presentation (s/s come & go; pt may have it for a long time before coming for tx) Giardia
Antigenic variation Important in pathogenesis; not unique to giardia; way to rearrange cell surface pro’s, hide from body’s immune system; all RNA-interference-based
GI parasites only affects brush border cells (aot isospora belli which it may resemble clinically) Cryptosporidium
GI parasite that tends to appear in “showers” Giardia
Created by: Abarnard