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• General characteristics of enterics or coliforms

  • 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
  • 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
  • Catalase positive except Shigella dysenteriae type 1
  • Motile at body temperatures [peritrichous flagella] except for Klebsiella, Shigella, and Yersinia
  • Possess a complex antigenic structure
  • Produce a variety of toxins and other virulence factors
  • On the surface of BAP or SBA, usually, the Enterobacteriaceae family will appear large, moist, and gray color [even on CAP]

  
• 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 biocharacteristics
  • 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]
  • Among the tribes, SPACE [Salmonella, Proteus, Arizona, Citrobacter, Edwardsiella] produces H2S on TSI
  • Among the tribes, SACE [Salmonella, Arizona, Citrobacter, Edwardsiella] can produce H2S on LIA

  
• 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
  • However, outside their normal body sites, these organisms are able to produce serious extraintestinal opportunistic infections
• Opportunistic pathogens


  • E. coli
  • Citrobacter, Enterobacter, Klebsiella, Proteus, Serratia species
• 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
  • Urinary tract infections, bacteremia, neonatal meningitis, and nosocomial infections of other various body sites
  • Most common cause of gram-negative nosocomial infections

  
• 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

  
• 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


  • 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
  • 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: Verotoxin I – identical to the Shiga toxin [produced by Shigella dysenteriae] – produces damage to Vero cells [African green monkey kidney cells], 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
  • Associated with different opportunistic and hospital infections (pneumonia, 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
• Friedlander's Bacillus


  • Isolated species
  • Large polysaccharide capsule

  
• Capsule


  • Provides protection against phagocytosis
  • Responsible for the moist and mucoid colonies that tend to "string"
• Friedlander's Bacillus is able to cause pneumonia, which is very necrotic and hemorrhagic, resulting in "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, an infection in the nasal cavity that causes 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)


  Causes granuloma inguinale, a chronic, genital, ulcerative disease that is sexually transmitted
• Characteristics of ENTEROBACTER, CRONOBACTER, AND PANTOEA

  • Motile
  • Resemble Klebsiella spp. when growing on MAC agar
  • Grow on Simmons citrate medium and in potassium cyanide broth
  • 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