MMI 301: Lecture 18: Enterobacteriaceae

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  1. Enterobacteriaceae morphology/species
    • Large gram - bacilli
    • E. coli, Klebsiella, Proteus, Salmonella, Shigella, and Yersinia
  2. Enterobacteriaceae are found where/how many
    • Ubiquitous in soil, water, GI flora
    • 40 genera
    • >150 species/subspecies
    • <20 species responsible for 95% of infections
  3. Enterobacteriaceae and catalase
  4. Enterobacteriaceae and spores
    No spores formed
  5. Enterobacteriaceae and oxygen
    Facultative anaerobes
  6. Enterobacteriaceae and capsules
    Some encapsulated
  7. Enterobacteriaceae and bile salts
  8. Enterobacteriaceae and MacConkey agar
    Used to differentiate lactose fermenting from non-lactose fermenting
  9. Enterobacteriaceae identification
    • Serotypical "fingerprint" based on antigenic features: O-antigen-polysaccharide (LPS), H-antigen flagella, K antigen capsules
    • Test by looking for agglutination in response to specific antisera
  10. E. coli serotypes for diseases
    • UTI: O1, O4, O6, O75
    • Hemorrhagic Colitis/Hemolytic Uremic Syndrome: O157:H7
    • Meningitis: K1
  11. Key Concept of Serotypes: Clones
    Strains of O:K:H antigens that are associated ubiquitously with certain pathogens imply they evolved away from other lineages to exchange with. These completely similar strains are clones.
  12. Virulence Factors for Enterobacteriaceae
    • •Endotoxin(LPS)- endotoxin leading to shock
    • •Capsule -poor immunogens & antiphagocytic
    • •Antigenic phase variation- K & H antigens
    • •Type III secretion- syringe-like injectors
    • •Sequestration of iron- different siderophores
    • •Serum resistance – OmpA binds C4BP
    • •Exotoxins - variety of enzymatic and lytic toxins
  13. Medical Terms for Diseases
    • •Diarrhea: frequent, liquid stools (stools that assume the shape of their container).
    • •Dysentery: a disease marked initially by frequent watery stools but followed by scant stool production characterized by excretion of mucus and blood.  There is usually abdominal pain, fever, and tenesmus.
    • •Enteritis:  inflammation of the intestine.
    • •Enteric fever:  an acute illness presenting as fever, headache, abdominal pain, and occasional skin rash.  There is bacteremia.
    • •Food poisoning:  the ingestion of a food containing a preformed toxin.  No growth of the
    • bacteria required in the host. 
    • •Emesis:  vomiting
  14. Scope of Gastrointestinal Disease
    • Number 2 killer of children after pneumonia
    • Bangladesh: 7 srs infections a year for first two years
    • US: average 2 cases a year
  15. E. Coli Morphology
    • Lactose Fermenter
    • Oxidase +
    • Motile (Flagella)
    • Most common facultative aerobic
    • Gram neg rod in GI tract
  16. Diarrheagenic E. coli
    • •Enterotoxigenic (ETEC)
    • •Enteroinvasive (EIEC)
    • •Enteropathogenic (EPEC)
    • •Enterohemorrhagic (EHEC)
    • •Enteroaggregative (EAEC)
    • •Diffuse aggregative E. coli (DAEC)
  17. Extraintestinal E. coli
    • Septic Shock/UTI (UPEC)
    • Neonatal meningitis
  18. Septicemia
    • Most usually from initial infection of GIT/UT
    • High mortality in immunocomp/ primary abdominal/CNS infection
    • E. coli is leading cause of endotoxic shock/death
  19. Septic Shock from E. coli
    • Too much inflammation from gram - septicemia (LPSs)
    • IL-1/6 produced by macrophages/lymphocytes/endothelial/keratinocytes and causes fever by release of prostaglandins in hypothalamus, contributes to hypotension/anorexia/increased PMNs/Increased transferrin
  20. Neonatal Meningitis
    • •E. coli (2nd) and group B streptococci (1st) cause majority of CNS infections in infants younger than 1 month
    • • 75% of E. coli possess K1 capsular antigen
    • •Commonly found in GI tract of mother and child
  21. Uropathogenic E. coli (UPEC)
    • Contamination of urethra from colon
    • Ascends urethra to bladder, can infect kidneys and prostrate
    • Type I pili under phase shift
    • Causes 70-90% of uncomplicated UTI
    • Cystitis Symptoms: dysuria, frequent and urgent need to urinate
  22. Enteropathogenic E. coli (EPEC)
    • Colonizes small intestines
    • Infant diarrhea in undeveloped countries
    • Symptoms: Watery diarrhea, vomiting, nonbloody stools, fever
    • Has Bundle-forming pili (BFP)
    • Characterisitic attachment/effacement (A/E) lesions
    • Recently recognized "atypical" EPEC are frequent cause of diarrhea
  23. Enterohemorrhagic E. coli (EHEC)
    • Colonizes human large intestines Cattle can carry, pass on through feces
    • Few as 10 bacteria can cause disease
    • Between diarrhea-hemorrhagic colitis
    •     -HC: diarrhea to bloody stool
    • A/E legions and Shiga toxin, EHEC toxin encoded by prophage
  24. Hemolytic Uremic Syndrome (HUS)
    • Happens in small number of EHEC infections
    • Presents with: Acute renal failure, Thrombocytopenia, Microangiopathic hemolytic anemia
    • Severe sequelae in 30%
    • Death in 3-5%
  25. Enterotoxigenic E. coli (ETEC)
    • Colonizes small intestine, illeum
    • -Infant diarrhea/traveler's diarrhea
    • -Symptoms: watery diarrhea, vomiting, cramps, nausea, low-grade fever, no inflammation of intestinal mucosa
    • -Heat-labile toxins (LT-I, LT-II) and heat-stabile toxins (STa, STb)
    • LT-1 and STa associated with human disease-mediate hyper secretion of fluids/electrolytes
  26. LT-1 and STa
    • Mediates attachment to GI epithelial with no invasion, leads to net fluid output by cells
    • LT-1 Toxin similar to cholera toxin (AB5 toxin)
    • STa is peptide that binds guanylate cyclase increasing cGMP levels and fluid loss
  27. Enteroinvasive E. coli (EIEC)
    • Colonizes large intestine
    • Disease in developing country children
    • Symptoms: fever, cramping, watery diarrhea, progress to dysentery
    • Closely related to Shigella
    • Bacteria invade and destroy colonic epthelial
  28. Enteroaggregative E. coli (EAEC)
    • Colonizes small intestine
    • Infant diarrhea/traveler's diarrhea
    • Symptoms: persistent watery diarrhea, vomiting, dehydration, low-grade fever
    • Autoaggregate in 'stacked brick' formation
    • Shorten microvilli and stimulate mucus production
  29. Diffuse Aggregative E. coli (DAEC)
    • Watery diarrhea in children
    • Vomiting common
    • Stimulates elongation of microvilli into finger-like projections which wrap around bacteria (embedding)
  30. Shigella Morphology
    • Does not ferment lactose
    • Non-motile
  31. Shigella species:
    dysenteriae, flexneri, boydii, sonnei
  32. Shigella virulence factors
    Invasion plasmid antigen (Ipa), Shiga toxin (S. dysenteriae only)
  33. Who first isolated Shigella
    Kiyoshi Shiga (1898)
  34. Who isolated S. flexneri
    Simon Flexner (1900)
  35. Shigella Pathogenesis
    • No animal reservoirs, all human
    • High communicable (100 bacteria will cause disease)
    • Fecal vector
  36. Shigella Pathogenesis Disease Pathway
    • 1. Induces endocytosis in M cells
    • 2. Transport to macrophage in lamina propria
    • 3. Escapes macrophages and uses invasins to enter enterocyte
    • 4. Escape phagosomes by lysis
    • 5. Forms actin filaments propelling bacteria through cytoplasm
    • 6. Invades adjacent cells
  37. Shigellosis Caused by
    • S. sonnei in developed countries
    • S. flexneri in undeveloped countries
  38. Shigellosis
    • Estimated 150 million cases
    • 70% of cases in children
    • Fecal-->oral
    • Infects colon
    • Symptoms: abdominal cramps, diarrhea, fever, bloody stools, can progress to HUS
    • Symptoms 1-3 days after ingestion
    • Can have asymptomatic carriers
    • Dysentery: severe shigellosis caused by S. dysenteriae
  39. Histopathology of Shigella
    • •Diffuse erythema and swelling of mucosa
    • •Focal hemorrhages and purulent exudate
    • •PMN infiltration into intestinal epithelium
    • •Formation of intestinal crypt abscesses
    • •Excessive inflammatory response
    • •Delayed apoptosis and cytokine response by 
    • mono-nuclear phagocytes (macrophages)
  40. Klebsiella pneumoniae capsulated?
  41. Klebsiella pneumoniae fermentation
    Lactose +
  42. Klebsiella pneumoniae found in/causes
    • Community-acquired primary lobar pneumonia
    • Necrotic destruction of aveolar spaces, cavity formation, blood tinged sputem
    • Alcoholics and people with compromised pulmonary function most at risk
  43. Proteus
    • Several common species
    • Chronic UTI
    • Associated with kidney stones
    •    -Produces urease, converts urine to ammonia/CO2
    •    -Leads to alkalinization of urine and precipitation of dissolved salts.
  44. Proteus motility
    • Highly motile, will not form colonies on plates, rather swarm
    • Swarming is diagnostic hallmark
  45. Reservoirs for Enterobacteriaceae
    • Most of the genera are considered members of normal flora of animals
    •     -Not Salmonella, Shigella and Yersinia
    •      -Shigella only in humans/apes
    •      -Salmonella typhi only in humans
    •      -Klebsiella and Proteus have enviromental reservoirs
  46. Lactose Fermentation
    • Negative/Cannot ferment: Shigella, Salmonella, Proteus, Yersinia
    • Positive/Can ferment: Escherichia, Klebsiella, Enterobacter
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MMI 301: Lecture 18: Enterobacteriaceae
MMI 301
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