Enterobacteriaceae

• Enterobacteriaceae


  • Often referred to as enterics or coliforms
  • Large heterogenous group of gram-negative rods in which their natural habitats are on the intestinal tract of humans and even on animals
• Enterobacteriaceae


  • Gram-negative bacilli and coccobacilli
  • Facultative anaerobes or aerobes
  • Do not produce cytochrome oxidase except for Plesiomonas spp.
  • Ferment a wide range of carbohydrates (all ferment glucose) [glucose-fermenters]
  • Reduce nitrate to nitrite except for Photorhabdus and Xenorhabdus
  • Motile [w/ presence of peritrichous flagella] at body temperatures except for Klebsiella, Shigella, and Yersinia
  • Catalase positive except Shigella dysenteriae type 1
  • Possess a complex antigenic structure
  • Produce a variety of toxins and other virulence factors
• Tribes


  • Used to classify the families or genus and species
  • Proposed by Ewing in 1963
  • Classifiying species into tribes, Ewing grouped the species with similar biochemical characteristics
  • Within these tribes, organisms are further classified to their genus and species
• H2S


  Blackening of the colony or blackening of the medium; can be observed on a Triple Sugar Iron Agar [TSI] or Lysine Iron Agar [LIA]
• Tribes that produce H2S

  • SPACE [Salmonella, Proteus, Arizona, Citrobacter, Edwardsiella]
  • SACE [Salmonella, Arizona, Citrobacter, Edwardsiella]
• Urease

  • Rapid Urease Producers – PPM [Proteus, Providencia, Morganella]
  • Slow Urease Producers – CKEYS [Citrobacter, Klebsiella, Enterobacter (except Enterobacter gergoviae), Yersinia, and Serratia]
• Deaminase producing

  PPM [Proteus, Providencia, Morganella]
• Lysine Decarboxylation (LDC +)

  KEESSH [Klebsiella, Escherichia, Edwardsiella, Serratia, Salmonella (except Salmonella paratyphi A), Hafnia]
• Lysine Decarboxylation (LDC -)

  PPMCYES [Proteus, Providencia, Morganella, Citrobacter, Yersinia, Enterobacter (except Enterobacter aerogenes and Enterobacter gergoviae), Shigella]
• Opportunistic pathogens


  • Part of the intestinal microbiota of humans and animals
  • Outside their normal body sites, these organisms are able to produce serious extraintestinal opportunistic infections
• Intestinal pathogens


  Referred to as the primary pathogens
• Intestinal pathogens

  • Salmonella typhi
  • Shigella
• O Antigen or Somatic Antigen


  Heat-stable antigen; located on the cell wall
• H Antigen or Flagellar Antigen


  Heat-labile antigen found on the surface of flagella, structures responsible for motility
• K Antigen or Capsular Antigen


  • Heat-labile polysaccharide found only on certain encapsulated species
  • Examples are the K1 antigen of E. coli and the Vi antigen [Vi stands for Virulence] of Salmonella enterica (subsp. enterica serotype Typhi)
• Escherichia coli


  • Indole (+) – Methyl Red (+) – Voges-Proskauer (-) – Citrate (-)
  • 1885 – Escherich
  • Colon bacillus or Golden Bacillus
  • Initially considered a harmless member of the colon resident biota
  • Facultative anaerobic, glucose fermenting, gram- negative, oxidase-negative rods capable of growth on MacConkey Agar
  • Used as primary marker of fecal contamination in water quality testing
  • Motile and generally possess adhesive fimbriae and sex pili and O, H, and K antigens [has flagella]
  • Lactose-positive (pink) colony with a surrounding area of precipitated bile salts on MAC agar
  • Lactose-fermenter; glucose-fermenter
  • EMB [Eosin Methylene Blue] Agar: it has a green metallic sheen
• Properties of Escherichia coli

  • Fermentation Of glucose, lactose, trehalose, and xylose
  • Production of indole from tryptophan
  • Glucose fermentation by the mixed acid pathway: methyl red positive and Voges-Porskauer negative
  • Does not produce H2S [no blackening on the colony or agar], deoxyribonuclease (DNase), urease, or phenylalanine deaminase
  • Cannot use citrate as a sole carbon source [citrate (-)]
• Uropathogenic Escherichia coli


  • Most common cause of UTIs in humans
  • Usually, these strains that causes UTI allows them to attach to the epithelial urinary mucosa
• Gastrointestinal pathogens


  • Causes diarrhea
  • Enterovirulent E. coli or diarrheogenic E. coli:
• Types of enterovirulent E. coli

  • Enterotoxigenic Escherichia coli (ETOC)
  • Enteroinvasive Escherichia coli (ENEC)
  • Enteropathogenic Escherichia coli (EPEC)
  • Enterohemorrhagic Escherichia coli (EHEC)
  • Enteroadherent
  • Diffusely adherent Escherichia coli (DAEC)
  • Enteroaggregative Escherichia coli (EAEC)
• Enterotoxigenic Escherichia coli


  • Diarrhea of adults and especially children
  • One of the major causes of infant bacterial diarrhea
  • Most common cause of a diarrheal disease sometimes referred to as traveler's diarrhea
  • MOT: consumption of contaminated water or food
  • Achlorhydria: high risk factor; deficiency of the Hydrochloric acid in the stomach
  • Produces heat-labile enterotoxin
  • Watery diarrhea, abdominal cramps, and sometimes nausea, usually with no vomiting or fever
• Enteropathogenic Escherichia coli


  • Known to cause infantile diarrhea
  • Characterized by low-grade fever, malaise, vomiting, and diarrhea
  • O serogroups – cause of diarrhea
  • H antigenic – intestinal infections
  • Appearance of Stool: watery with mucus but without blood
• Enteroinvasive Escherichia coli


  • Produce dysentery with direct penetration, invasion, and destruction of the intestinal mucosa
  • Similar to shigellosis [cause by shigella]
  • MOT: person-to-person via the fecal-oral route
  • Nonmotile and generally do not ferment lactose
  • Do not decarboxylate lysine
• Enterohemorrhagic Escherichia coli


  • Hemorrhagic diarrhea, colitis, and hemolytic uremic syndrome (HUS) – low platelet count, hemolytic anemia, kidney failure
  • Does not ferment sorbitol in 24 hours
  • Biochemical test: 4-methylumbelliferyl-B-d- glucuronide (MUG) assay – fluorescent product is formed
  • 2 Toxins:

  a. Verotoxin I – identical to the Shiga toxin [produced by Shigella dysenteriae] – produces damage to Vero cells (African green monkey kidney cells)

  b. Verotoxin II – reported as Shiga-like toxin, but most likely to be found in the literature as the Shiga toxin 1 and Shiga toxin 2; (Shiga-toxin producing E. coli) [STEC])

  • Watery diarrhea
  • Bloody diarrhea with abdominal cramps and low- grade fever or an absence of fever
• Neteroadherent Escherichia coli


  • Diarrheal syndromes and UTIs – DAEC [Diffusely Adherent E. coli]
  • EAEC [Enteroaggregative E. coli] – diarrhea by adhering to the surface of the intestinal mucosa
  • Extraintestinal infections
  • Most common causes of septicemia and meningitis among neonates
• Other Escherichia species

  Escherichia hermannii - Yellow-pigmented, Isolated from cerebrospinal fluid (CSF), wounds, and blood

  Escherichia vulneris - Yellow-pigmented, Isolated from humans with infected wounds

  Escherichia albertii - Associated with diarrheal disease in children
• Klebsiella and Raoultella


  • Most grow on Simmons citrate and in potassium cyanide broth
  • None produce H2S

  A few hydrolyze urea slowly

  All are methyl red test negative and Voges-Proskauer positive

  With a few exceptions, no indole is produced from tryptophan

  Motility is variable

  Usually, its members can be found in the intestinal tract of human and animals

  Associated with different opportunistic and hospital infections (pneumonia, wound infection, & UTI)
• Klebsiella pneumoniae


  Most commonly isolated species; large polysaccharide capsule

  Capsule: will provide protection against phagocytosis; responsible for the moist and mucoid colonies [tend to "string"]

  Friedlander's Bacillus - Able to cause pneumonia [very necrotic and hemorrhagic]

  "Currant jelly-like sputum"
• Klebsiella oxytoca


  The only indole positive among Klebsiella species

  Isolated in stool and blood cultures

  Ornithine-positive

  Linked to antibiotic-associated hemorrhagic colitis
• Klebsiella pneumoniae subsp. ozaenae


  Highly associated with the presence of plasmid- mediated ESBLs

  Isolated from nasal secretions and cerebral abscesses
• Klebsiella pneumoniae subsp. rhinoscleromatis

  Has been isolated from patients with rhinoscleroma [infection in the nasal cavity; intense swelling and malformation of the entire face and neck]
• Raoutella (Klebsiella) ornithinolytica


  Indole and ornithine decarboxylase-positive
• Raoutella (Klebsiella) planticola


  Have been isolated from the urine, respiratory tracts, and blood of humans
• Klebsiella variicola


  Has been isolated from primarily sterile sites
• Klebsiella granulomatis


  (formerly Calymmatobacterium granulomatis)

  Granuloma inguinale – chronic, genital, ulcerative disease

  A sexually transmitted disease
• "Currant jelly-like sputum"


  Description of sputum appearance
• Klebsiella granulomatis (formerly Calymmatobacterium granulomatis)


  • Granuloma inguinale – chronic, genital, ulcerative disease
  • A sexually transmitted disease
• ENTEROBACTER, CRONOBACTER, AND PANTOEA [IMVC --++]
• ENTEROBACTER, CRONOBACTER, AND PANTOEA


  • Motile
  • Resembles Klebsiella spp. when growing on MAC agar
  • Grow on Simmons citrate medium and in potassium cyanide broth
  • The methyl red test is negative, and the Voges- Proskauer test is positive
  • Usually produce ornithine decarboxylase
  • Lysine decarboxylase is produced by most species but not by Enterobacter gergoviae or Enterobacter cloacae
  • Considered as slow urease producer except for Enterobacter gergoviae
• Enterobacter taylorae


  • Lactose negative but ONPG positive