Enterobacteriaceae

• Enterobacteriaceae


  Family of Gram-negative, non-spore-forming, facultatively anaerobic bacilli
• Enterobacteriaceae


  • Microscopic and colony morphology: Gram-negative, nonspore-forming, facultatively anaerobic bacilli
  • SBA and CHOC: Large, moist, gray colonies
  • Klebsiella and Enterobacter: Large and very mucoid colonies
  • E. coli: β-hemolytic
  • Differential and selective media: MAC, HE, XLD
• Enterobacteriaceae classification


  • Edwards and Ewing's Identification of Enterobacteriaceae
  • Table 19-1
• Enterobacteriaceae virulence and antigenic factors


  • Plasmids that code for antimicrobial resistance (E. coli, K. pneumoniae, K. oxytoca, ESBLs)
  • O antigen / somatic – cell wall
  • H antigen / flagellar
  • K antigen / capsular
• Enterobacteriaceae clinical significance


  • Ubiquitous in nature
  • GIT
  • Normal flora except for SSY
  • Two categories based on infections caused: 1. Opportunistic pathogens, 2. Primary pathogens
• Opportunistic pathogens


  • E. coli
  • Klebsiella
  • Enterobacter, Cronobacter, and Pantoea
  • Serratia
  • Hafnia
  • Proteus
  • Morganella
  • Providencia
  • Edwardsiella
  • Erwinia and Pectobacterium
  • Citrobacter
• Escherichia coli


  • Most significant species
  • Primary marker of fecal contamination in water purification
  • Most strains are motile
  • Fimbriae
  • Sex pili
  • O, H, and K antigens
  • Cross-reactivity with O antigen (Shigella)

  
• Escherichia coli colony characteristics

  • MAC: Pink colony with surrounding area of precipitated bile salts (Lactose fermenter)
  • EMB: Greenish metallic sheen

  
• Escherichia coli biochemical tests (p. 431)

  
• Uropathogenic Escherichia coli


  • Most common cause of UTIs in humans
  • Produce factors that allow them to attach to the urinary epithelial mucosa (Pili)
  • Cytolysins
  • Aerobactins
• Gastrointestinal Escherichia coli


  • ETEC
  • EIEC
  • EPEC
  • EHEC
  • DAEC
  • EAEC
• ETEC (Enterotoxigenic E. coli)


  • Diarrhea of infants and adults in tropical and subtropical climates
  • Traveler's diarrhea
  • Consumption of contaminated food and water
  • High infective dose (10^6 to 10^10)
  • Colonization mediated by fimbriae
  • Heat-labile toxin (LT) - Increase in cAMP
  • Heat-stable toxin (ST)
• EIEC (Enteroinvasive E. coli)


  • Produce dysentery with direct penetration, invasion, and destruction of the intestinal mucosa
  • Affects adults and children
  • Resembles Shigella
  • Nonmotile
  • Do not ferment lactose
  • Sereny test
  • DNA probes
  • HEp-2 cells
• EPEC (Enteropathogenic E. coli)


  • Causes infantile diarrhea
  • Hospital nurseries and daycare centers
  • Stool contains large amounts of mucus
• EHEC (Enterohemorrhagic E. coli)

  • O157:H7 strain (hemorrhagic diarrhea, colitis, and HUS)
  • Watery diarrhea that progresses to bloody diarrhea
  • Stool contains no WBCs
  • Processed meats, unpasteurized dairy products and apple cider, bean sprouts, and spinach
  • Two cytotoxins: Verotoxin I and Verotoxin II
• Enteroadherent E. coli


  Two kinds of disease: 1. Diarrheal syndromes, 2. UTIs
• Other Escherichia species


  • E. hermannii (E. coli atypical or enteric group II)
  • E. vulneris
  • E. albertii
• Klebsielleae


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


  • Nonmotile
  • K. pneumoniae - Capsule, moist, mucoid colonies, LRT infections among hospitalized and immunocompromised hosts
  • K. oxytoca - Indole (+), infections similar to K. pneumoniae
  • K. pneumoniae subsp. rhinoscleromatis - Rhinoscleroma (Africa and South America)
• Enterobacter


  • Motile
  • Colonies resemble Klebsiella
  • Ornithine decarboxylase (+)
  • E. cloacae and E. aerogenes
• Pantoea agglomerans


  • Enterobacter agglomerans
  • Nationwide outbreak of septicemia from contaminated IV fluids
  • "triple decarboxylase negative"
• Cronobacter sakazakii


  • Enterobacter sakazakii
  • Yellow pigment
  • Neonatal meningitis and bacteremia
  • Powdered infant formula
• Serratia


  • Nosocomial outbreaks
  • Slow lactose-fermenters and ONPG (+) except for S. fonticola
  • Extracellular DNAse (+)
  • S. marcescens, S. rubidaea, S. plymuthica: Pink to red pigment (Prodigiosin)
• Hafnia


  • Hafnia alvei
  • Two biotypes: Biotype 1 - Beer wort of breweries
  • Delayed positive citrate reaction
• Proteeae


  • Proteus
  • Morganella
  • Providencia
• Proteus


  • Normal intestinal flora
  • Able to deaminate phenylalanine (phenylalanine deaminase)
  • Non-lactose-fermenters
  • P. mirabilis and P. vulgaris
  • Nosocomial infections (UTI)
  • "Swarming" colonies on SBA
• Morganella


  M. morganii - UTI
• Providencia


  • P. rettgeri - Urinary tract pathogen, diarrheal disease among travelers
  • P. stuartii - Nosocomial outbreaks in burn units, urine cultures
  • P. alcalifaciens - Feces of children with diarrhea
• Edwardsiella


  E. tarda - Urease (-), Lysine decarboxylase (+), H2S (+), Indole (+), Citrate (-)
• Erwinia and Pectobacterium


  • Plant pathogens
  • Grow poorly at 37°C
  • Fail to grow on EMB and MAC
• Citrobacter


  • Hydrolyze urea slowly
  • Ferment lactose
  • MAC: Resembles E. coli
  • Citrate (+)
  • Methyl red test (+)
  • C. freundii - Diarrheal stool cultures, endocarditis in IV drug abusers, colonies resemble Salmonella
• Primary intestinal pathogens


  • Salmonella
  • Shigella
  • Yersinia
• E. coli O157:H7 causes bloody diarrhea and hemolytic uremic syndrome.
• E. coli O157:H7 causes hemorrhagic colitis and hemolytic uremic syndrome.
• Escherichia coli (E. coli) is the most common species found in the human intestine and is considered part of the normal flora.
• Enterobacter cloacae is an opportunistic pathogen that can cause urinary tract, respiratory tract, wound, bloodstream, and surgical site infections.
• Klebsiella oxytoca produces gas from lactose but not sucrose.
• Enteroaggregative E. coli (EAEC) can cause watery diarrhea and dysentery.
• Shiga toxin-producing E. coli (STEC) strains produce Shiga toxins that damage blood vessels and lead to kidney failure.
• Klebsiella oxytoca is a member of the family Enterobacteriaceae and is commonly isolated from clinical specimens.