Enteropathogenic Bacterial Infections

Question 1

Escherichia coli

Answer 1

• antigenically diverse, aerobic (facultatively anaerobic), gram(-) rod, most commensal and opportunistic
• synthesize vitamin K2, virulence after plasmid transfer
• 90% of all urinary tract infections -bladder mucosa infection–dysuria, pyuria (leukocytes in urine)
• Immunocompromised: Pneumonai, sepsis
• neonatal meningitis: colonizes vaginal canal
• Four strains:
  
  • ENTEROTOXIGENIC: traveler’s diarrhea from contaminated water and food, self-limited (Africa, Latin America)–produce 3 enterotoxins–secretory dysfunction of small bowel (one similar to cholera-adenylyl cyclase, other acts on guanylyl cyclase)
  • ENTEROPATHOGENIC: diarrheal illness in tropical regions among infants and children, spread from contaminated food and water, deforms microvilli of intestinal epithelial cells, fever + malaise
  • ENTEROHEMORRHAGIC: bloody diarrhea, fever, cramping abdominal pain, hemolytic-uremic syndrome (anemia, acute kidney failure, thrombocytopenia), contaminated meat/milk, enterotoxin similar to Shigatoxin
  • ENTEROINVASIVE: food-borne DYSENTERY, indistinguishable from shigella (similar toxin to shiga toxin)-self-limited, invades and destroys mucosal cells of ileum and colon. abdominal pain, fever, tenesmus (feeling of incomplete defecation), bloody diarrhea. week long illness

Question 2

Salmonella Enterocolitis

Answer 2

• gram(-) rod, facultatively anaerobic
• SELF-LIMITED -spread by fecal-oral route, contaminated foodstuff
• proliferate and invade enterocytes in ileum and colon-acute inflamation and some superficial ulceration
• diarrhea (self-limited), nausea, vomiting, abdominal cramping, fever–food poisoning: takes 12-48 hours to manifest (no exotoxin production like S. aureus)
• antibiotics rarely improve clinical course
• major cause of childhood mortality in 3rd world countries (lack of oral rehydration therapy)

Question 3

Salmonella typhi

Answer 3

• P2P spread (chronic carriers commonly old women with gallstones or biliary scarring), and contaminated water/food–dairy and shellfish, oral-fecal route rarer
• granulomatous infection: proliferation inside infected macrophages
• Typhoid fever (SEVERE): degeneration of intestinal epithelium brush border (Peyer patch hypertrophy as well)–capillary thrombosis with ulcerated bowel tissue leading to infectious peritonitis; Systemic dissemination: focal granulomas in liver, spleen (typhoid nodules-macrophages with ingested bacteria,erythrocytes, dead lymphocytes)
• 10-14 day incubation period
• Signs: Bacteremia/invasion: daily increase in temperature (IL-1 + TNF), malaise, arthralgias, abdominal pain–Fastigium: fever/malaise increase–septicemia from release of endotoxin from dead bacteria and hepatomegaly and splenomegaly. Fever abates over weeks to months -10-20% mortality in untreated patients (complications including pneumonia)
• Typhoid antitoxin curative if given within 3 days of fever onset.

Question 4

Shigellosis (Shigella dysenteriae)

Answer 4

• aerobic, gram(-) rods
• SELF-LIMITED necrotizing infection -spread oral-fecal route (fecally contaminated food/water or surfaces)–areas of poor sanitation
• self-limiting disease (3-8 days) with watery diarrhea
• 300,000 annual cases in US diarrhea/dysenteric stools, abdominal pain, tenesmus, fecal urgency
• Produces Shiga exotoxin: inhibits protein synthesis and inhibits fluid absorption in colon)–affects distal colon and sometimes distal ileum–dysentery
• infected mucosa is edematous, inflamed, eroded with presence of pseudomembrane composed of neutrophils, fibrin, and necrotic epithelium (healing complete in 10-14 days)

Question 5

Cholera (Vibrio cholerae)

Answer 5

• aerobic, curved, gram(-) rod
• spread from ingesting contaminated food/water; shellfish are natural reservoir–sporadic outbreaks
• epidemics in areas where human feces pollute water supply -cholera exotoxin: binds GM1 ganglioside in enterocyte cell membrane to enter cell and activated adenylyl cylase- increase cAMP and increase Na+/H20 secretion into intestinal lumen. -severe watery diarrhea with flecked mucus (rice water stools)–leads to fluid and electrolyte loss that leads to shock
• 50% mortality rate in untreated patients (lacking electrolyte and oral rehydration therapy +antibiotis)
• vaccine available (50% effectiveness)

Question 6

Campylobacter jejuni

Answer 6

• microaerophilic, curved, gram(-) rod (similar to vibrios) self-limited
• spread through contaminated food/water + fecal-oral route
• most common cause of bacterial diarrhea in developed world–2 million annual cases in US -affects farm animals–huge economic losses
• causes superficial enterocolitis–terminal ileum and colon with focal necrosis of interstitial epithelium and acute inflammation -severe cases: ulcers and patchy inflammatory exudates (necrotic cells, fibrin, neutrophils)
• cytolethal distending toxin (DNA damaging-necrosis)
• watery stools, gross blood containing stools
• associated with Guillain-Barre syndrome (autoimmune peripheral neuropathy)

Question 7

Yersinia enterocolitica + pseudotuberculosis

Answer 7

• gram(-) coccobacillus, facultative anaerobes
• fecal-oral route and contaminated water + milk.
• painful diarrhea
• enerocolitica: contaminated meat; proliferates in ileum and invades mucosa–necrosis and ulceration of Peyer patches–fever, diarrhea (bloody), and abdominal pain (can be confused with appendicitis); rare septicemia
• 50% mortality rate in those persons
• pseudotuberculosis (Far East scarlet-like fever): contact with infected animals, penetrates ileal mucosa, localizes in ileal-cecal lymph nodes and causes abscesses and granulomas in lymph nodes, spleen, and liver–fever, diarrhea, and abdominal pain (appenicitis mimic)