Enterobacteriaceae

• Enterobacteriaceae

  Predominant facultative flora of the bowel

  
• Enterobacteriaceae

  • Facultative anaerobes, non-sporeforming
  • All motile species have peritrichous flagella except Tatumella ptyseos which is monotrichous
  • All are catalase (+) except for Shigella dysenteriae
  • Some strains possess fimbriae or pili
  • Grow on most media at 35°C within 24 hours
  • Some may grow at 1 - 5°C (psychrophiles) especially Yersinia enterocolitica and some strains of Serratia

  
• Opportunistic pathogens

  Part of the usual intestinal microbiota, may produce infection outside their normal body sites (extraintestinal), produces significant virulent factors
• Primary pathogens

  Not present as commensal biota in the GI tract of humans, produce infections resulting from ingestion of contaminated food and drink
• Primary pathogens

  • Salmonella spp.
  • Yersinia spp.
  • Shigella spp.
  • Plesiomonas shigellosis
• Enterobacteriaceae divided into two broad categories

  • Coliforms in normal flora
  • Non-coliforms in normal flora

  
• Coliforms in normal flora

  • Escherichia coli
  • Proteus
  • Klebsiella
  • Enterobacter
  • Providencia
  • Serratia
  • Morganella

  
• Non-coliforms in normal flora

  • Salmonella
  • Yersinia pestis
  • Shigella
  • Yersinia enterocolitica
  • Edwardsiella
  • Hafnia
  • Citrobacter

  
• Lactose fermentation classification

  • Rapid lactose fermenters (Permease and ONPG positive): Escherichia, Salmonella arizonae, Klebsiella, Shigella sonnei
  • Late lactose fermenters (ONPG positive): Salmonella, Shigella, Enterobacter, Serratia, Proteus, Hafnia, Providencia
  • Non lactose fermenters (Permease and ONPG negative): Yersinia, Morganella, Edwardsiella
• Colony Morphology

  Klebsiella and Enterobacter have large and very mucoid colonies

  
• Presumptive identification methods

  • EMB
  • MAC
  • HE or HEA (Hektoin enteric)
  • XLD (Xylose Lysine Deoxycholate)
  • Sodium thiosulfate and ferric ammonium citrate
• Definitive identification depends on

  • Biochemical reactions
  • Serologic antigenic structures
• Enterics reaction to TSI

  • A/A + gas (Escherichia)
  • K/A + gas + H2S (Klebsiella, Enterobacter, Salmonella, Proteus, Arizona, Citrobacter, Edwardsiella)
  • K/A (Shigella)
  • K/K (Pseudomonas)
• O antigen

  The most external component of the lipopolysaccharide (LPS) of gram negative bacteria, heat stable, somatic antigen, antibodies are predominantly IgM, used for E. coli & Shigella spp. serotyping
• H antigen

  Flagellar antigen, only bacteria that are motile will possess this antigen, heat-labile, protein in nature, used for Salmonella spp. serotyping
• K antigen

  Capsular antigen or envelope antigen, heat-labile polysaccharide found only in encapsulated species like Klebsiella spp., K1 antigen in Escherichia coli, Vi antigen of Salmonella enterica subsp. enterica serotype Typhi
• Escherichia coli

  Major facultative inhabitant of the large intestine, indicator organism for fecal contamination of water and foods, normally resides in the colon without causing disease, may acquire virulence factors and cause disease
• Escherichia coli

  • Ferments glucose, lactose, trehalose, xylose
  • IMViC ++-
  • Does not produce H2S, Dnase, urease, phenylalanine deaminase
• Uropathogenic Escherichia coli

  Production of pili for adherence, cytolysins to kill immune cells, chemotaxis of certain WBC, aerobactin to chelate iron
• Strains of Escherichia coli that cause diarrhea

  • Enteropathogenic Escherichia coli (EPEC)
  • Enterotoxigenic Escherichia coli (ETEC)
  • Enteroinvasive Escherichia coli (EIEC)
  • Enteroadherent Escherichia coli (EAEC and DAEC)
  • Enterohemorrhagic Escherichia coli (EHEC) serotype 0157:H7
• Enteropathogenic Escherichia coli (EPEC)

  Does not produce enterotoxin, associated with infantile diarrhea, causes nursery outbreak diarrhea, watery diarrhea with mucus but no blood
• Enterotoxigenic Escherichia coli (ETEC)

  Produce enterotoxins, major causes of traveller's diarrhea, heat-labile toxin (LT) similar to cholera exotoxin, heat-stable toxin (ST), infective dose 106 - 1010
• Enteroinvasive Escherichia coli (EIEC)

  Bacillary dysentery in all age groups similar to shigellosis, main virulence factor is encoded in a plasmid shared by Shigella spp., watery diarrhea is bloody with WBC, RBC and mucus
• Types of enteroadherent Escherichia coli

  • DAEC - diffusely adherent Escherichia coli
  • EAEC - enteroaggregative Escherichia coli
• Enterohemorrhagic Escherichia coli (EHEC) serotype 0157:H7

  Causes hemolytic uremic syndrome (HUS) and hemorrhagic colitis, bloody diarrhea without WBC, appears colorless in MacConkey agar
• Verotoxin I

  Identical to the Shiga toxin (Stx) of Shigella dysenteriae, damages Vero cells, neutralized by antibody against Stx
• Verotoxin II

  Not neutralized by antibody against Stx
• Uropathogenic Escherichia coli

  Most common cause of UTI in humans
• Other Escherichia species

  • Escherichia hermannii - CSF, wounds, blood
  • Escherichia vulneris - infected wounds
  • Escherichia albertii - diarrheal disease in children
• Tribe Klebsielleae

  • IMViC -+-+
  • Growth in potassium cyanide broth
  • Do not produce H2S
  • Lactose fermenting, mucoid
  • Motility is variable
  • Few hydrolyze urea slowly
• Genus Klebsielleae

  • Klebsiella pneumoniae subsp. pneumoniae
  • Klebsiella oxytoca
  • Klebsiella pneumoniae subsp. ozaenae
  • Klebsiella pneumoniae subsp. rhinoscleromatis
  • Raoutella ornitholytica
  • Raoutella planticola
  • Klebsiella terrigena
• Klebsiella pneumoniae subsp. pneumoniae

  Antibiotic associated hemorrhagic colitis
• Klebsiella oxytoca

  Identical to K. pneumoniae except for indole (+), ornithine decarboxylase (+), associated with plasmid-mediated ESBL
• Klebsiella pneumoniae subsp. ozaenae

  Ozaena - a chronic atrophic rhinitis characterized by a fetid odor
• Klebsiella pneumoniae subsp. rhinoscleromatis

  Rhinoscleroma - infection of the nasal cavity, swelling and malformation of the entire face
• s

  infected wounds
• Escherichia albertii

  diarrheal disease in children
• Tribe Klebsielleae

  • Genus Klebsiella
  • Genus Enterobacter
  • Genus Serratia
  • Genus Pantoea
  • Genus Cronobacter
  • Genus Hafnia

  
• Tribe Klebsielleae

  • IMViC - - + +
  • Growth in potassium cyanide broth
  • Do not produce H2S
  • LF, mucoid
  • Motility is variable
  • Few hydrolyze urea slowly
• Genus Klebsiella

  • Klebsiella pneumoniae subsp. pneumoniae
  • Klebsiella oxytoca
  • Klebsiella pneumoniae subsp. ozaenae
  • Klebsiella pneumoniae subsp. rhinoscleromatis