Gram-Negative Bacteria in GI Tract Flashcards
Differentiate dysentery and non-dysenteric diarrhea
Diarrhea:
o Frequent stool, increased from normal for individual
o Often profuse loose or liquid stool
o Often painless and without fever
Many different causes:
• Infectious (bacteria, viral, parasitic)
• Non-infectious (altered flora, allergy, drugs, osmotic supplements, irritable bowl disease)
o Variety of mechanisms that result in increased secretion and/or decreased absorption in small or large intestine
Dysentery
o Pus and blood in stool
o Often painful (cramps, tenesmus) and with fever
o Caused by microbial deep invasion and/or cytotoxins resulting in tissue destruction in large intestine
Define Gastroenteritis
o “Catch-all term”
o Describes numerous syndromes associated with GI tract
o Symptoms include: nausea, vomiting, diarrhea
o Caused by toxins or superficial inflammation from a variety of infectious microbes or by non-infectious etiologies
Define enteric fever
o Systemic infection (sepsis) starting in GI tract
o Fever and abdominal pain more prominent than diarrhea
o Ex: typhoid fever caused by Salmonella typhi
Identify which bacteria cause these common syndromes: watery diarrhea, dysentery, and enteric fever.
Watery diarrhea
o Enterotoxigenic E. coli (ETEC)
o Vibrio cholera (rice water stools)
Dysentery
o Enteroinvasive E. coli (EIEC)
o Shigella
o Campylobacter
Enteric fever
o S. typhi (main cause)
o Other Salmonella species (S. paratyphi, S. enteritidis)
o Yersina enterocolitica and other species
o Campylobacter jejuni (rare late manifestation)
o Non-cholera Vibrio species (V. parahemolyticus, V. vulnificus)
o Colonization of gall bladder reservoir → continuous fecal shedding by asymptomatic carrier
Distinguish enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC),
enterohemorrhagic E. coli (EHEC), and enteroinvasive E. coli (EIEC).
Overall: o Variable inoculum required Transmission: • Fecal/oral • Contaminated foods (meats, fruits, vegetables)
Enterotoxigenic E. coli (ETEC) o Traveler’s diarrhea o Secretory toxins = heat stable and heat labile • Similar to Vibrio cholera o Toxins are plasma-mediated o Virulence also associated with colonization factors o Toxins cause hypersecretion of fluid • Water diarrhea for 3-4 days
Enteropathogenic E. coli (EPEC) o Infantile diarrhea o Mucosal colonization and destruction o Similar to non-typhoid Salmonella o Gastroenteritis, fever, vomiting, non-bloody stools
Enterohemorrhagic E. coli (EHEC); includes 0157:H6 strain
o Food contaminant
o Only small inoculum needed
o Hemorrhagic colitis = severe abdominal pain and bloody diarrhea
o Zoonosis from cow intestines or from infected humans
o Cytotoxin = verotoxin (Shiga-like toxin)
• Similar to some Shigella
May cause Hemolytic uremia syndrome (HUS)
• Caused by verotoxin produced in intestinal lumen and enters blood circulation → systemic disease
• Associated with EHEC, some Shigella strains, some other enteropathogens
Features:
• Thrombotic microangiopathy
• Hemolytic anemia
• Thrombocytopenia with renal lesions
• Renal failure
• Overall = rare
• Increased risk = children and elderly
• Show higher morbidity and mortality
Avoid antibiotics with EHEC infection
Enteroinvasive E. coli (EIEC)
o Bloody, purulent dysentery
o Deep invasion = destroy colonic mucosa
o Similar to some Shigella
Salmonella
- Large inoculum required
- Most infections occur in children in warm months
Transmission:
o Fecal/oral
o Contaminated food (eggs, poultry)
o Animals (may have wide host range)
Gastroenteritis
o From mucosal colonization and destruction
o “Rotten egg” odor of stool from sulfhydryl compounds
o Relative resistance to bile salts = reservoir in gall bladder
o Mainly non-typhoid Salmonella (other than S. typhi)
• Disease has increased due to mass production and distribution of foods
Enteric fever
o From systemic dissemination:
• Ingestion → adhesion to small intestine mucosa → invasion and penetration to submucosa → phagocytosis, replication, and transport in macrophages → transport to lymphatics → access to blood → primary bacteremia → uptake by mononuclear phagocytic system/reticuloendothelial system (liver, spleen) → transport to gall bladder → reinvasion of small intestine → gut (in stool)
• Blood culture usually positive before stool culture
o Mainly S. typhi
• Obligate human pathogen (human-human transmission via oral/fecal route)
• Bloodstream invasion capability = typhoid fever
Disease has declined:
• Improved hygiene
• Improved water treatment
• Antibiotics for typhoid fever
o Positive blood culture likely before a positive stool culture
o Reservoir sites (gall bladder) → carrier state
Vaccination for high-risk travel or occupations
o Oral live-attenuated
o Parenteral (injection) capsular polysaccharide
o Neither useful for non-typhoid enteric fever
Shigella
- Obligate human pathogen
- Small inoculum required
Transmission:
o Fecal/oral (food or person-to-person)
Dysentery from deep invasion o Bacillary dysentery o Fever, headache, occasionally seizures o Does not invade bloodstream Some strains also make cytotoxin (Shiga toxin)
Campylobacter jejuni
• Most common bacterial enteric infection agent in U.S.
Transmission:
o Fecal/oral
o Contaminated food (milk, meat [poultry])
o Animals (may have wide host range)
- Early gastroenteritis from mucosal colonization and destruction
- Occasional late dysentery from deep invasion
- Rare enteric fever from systemic dissemination
May be able to diagnose microscopically in stool
o Characteristic darting motility
o Mediated by polar flagella
Yersinia
Y. enterocolitica, Y. pseudotuberculosis Transmission: • Fecal/oral • Animals o Most infections during cold weather months Causes: o Gastroenteritis o Diarrhea o Occasional “pseudoappendicitis” o Bacteremia rare
Y. pestis
o Completely different lineage
o Not associated with enteric infection
o Human-human transmission via fleas or respiratory droplets
o Causes plague: bubonic (infection in lymph nodes), pneumonic (in lungs), septicemic (in blood)
Vibrio cholera
• Very large inoculum needed
Transmission:
o Fecal/oral
Secretory toxin (cholera toxin)
o Constitutive enterocytes cAMP production
o Massive water and electrolyte secretion
o Results: voluminous (10-20 L/day) watery diarrhea (rice water stools)
Risks:
o Lack of effective sewage treatment
o Host gastric achlorhydria (from malnutrition or drugs)
Cholera:
o Mostly disease of developing world
o Occurs in epidemics
o Deadly for children, malnourished or debilitated
Treat:
o Hydration and electrolytes
o Antibiotics not used
Vibrio parahemolyticus
Transmission:
o Salt water
o Shellfish
o Sushi
- Gastroenteritis, rare enteric fever
- In U.S. = primarily seen in NW and NE
Vibrio vulnificus
Transmission: o Salt water o Shellfish o Skin abrasions • Especially in immunocompromised and alcoholics
- Wound infections (bullous lesion)
- Septicemia (50% mortality)
- NOT gastroenteritis
Explain the route of transmission, clinical syndromes, and mechanisms of pathogenesis of
Helicobacter pylori.
Transmission:
o Fecal/oral
o Long-term, even lifelong colonization of stomach
Survival Mechanisms o Colonized host mucosal slime layer (mucosal secretions provide microenvironment) o Expresses urease: • Hydrolyzes urea to CO2 and ammonia • Raises pH
Symptoms:
o Asymptomatic colonization
o Gastritis → epigastric pain, nausea, vomiting
o Gastric and duodenal ulcers (predominant cause)
o Gastric malignancies
Treatment:
2 antibiotics (amoxicillin and clarithromycin) and a proton pump inhibitor
• Antibacterial activity
• Reduces host acid secretion = decreases inflammation, damage, symptoms
Avoid infection/disease:
• Minimize agents that raise gastric pH (antacids, H2 antagonists, PPIs)
Treatment (overall) for enteric Gram-negative bacteria
Usually supportive only:
o Maintain hydration and electrolytes
o Syndromes are frequently self-limiting
Clinical status of patient is most important:
o How sick? Dehydrated?
o Able to ingest and retain fluids?
o At risk? (Infant, elderly, immunocompromised)
o Possibility of life-threatening infections
• EHEC leading to HUS
• Typhoid fever
o THEN use fluoroqunolones (ex: ciprofloxacin)
Avoid antibiotics with EHEC infection
• May increase duration of disease (bacterial lysis and cytotoxin release)
Medications for symptomatic relief of nausea, vomiting, diarrhea
o Bismuth subsalicylate = may have some antimicrobial activity
GI motility-reducing agents:
• Loperamide [Imodium]
• Diphenoxylate (in Lomotil)
• Do NOT use if blood or pus in stools (do not delay passage of invasive pathogens or cytotoxins; would allow more time for systemic absorption of cytotoxins from gut)
Consider probiotic therapy for antibiotic associated diarrhea (due to C. difficile)
