PA2 - Enterobacteriaceae. Vibrio cholerae. 2

Characteristics of Enterobacteriaceae

  • Classification: Gram-negative, enteric rods; non-fastidious, aerobic or facultative anaerobic.

  • Metabolism: Glucose fermenters, catalase positive, oxidase negative.

  • Major Pathogens: Salmonella spp., Shigella spp., Yersinia spp.

  • Normal Flora: Some species part of intestinal flora, acting as opportunistic pathogens.

Specimen Collection

  • Intestinal Infections (E. coli): Stool, bile

  • Extraintestinal Infections: Urine, pus, cerebrospinal fluid, blood

  • Klebsiella: Urine, sputum, pus, cerebrospinal fluid, blood

  • Proteus: Urine, sputum, pus, cerebrospinal fluid, blood

  • Shigella: Stool, food (source detection)

  • Salmonella: Blood, intestinal secretions, stool, urine

  • Yersinia enterocolitica: Stool, lymph node tissue, blood

  • Vibrio cholerae: Watery stool with mucus, food and water samples.

Direct Examination and Microscopy Techniques

  • E. coli: Gram-negative rods with rounded ends.

  • Klebsiella: Gram-negative cocobacilli with capsules in negative stain.

  • Proteus: Gram-negative rods, swarming on non-selective media.

  • Shigella: Gram-negative rods with distinct colony morphology.

  • Salmonella: Gram-negative rods in microscopy.

  • Vibrio cholerae: Gram-negative, curved rods with one polar flagellum.

Cultivation Techniques

  • E. coli: Blood agar, MacConkey agar (lactose fermenter), lactose agar, Levine medium.

  • Klebsiella: Blood agar, lactose agar, MacConkey agar.

  • Proteus: Blood agar, lactose agar, MacConkey agar.

  • Shigella: MacConkey agar, SS agar.

  • Salmonella: Enrichment media, lactose agar, MacConkey agar, SS agar.

  • Yersinia enterocolitica: MacConkey agar, lactose agar, CIN agar.

  • Vibrio cholerae: Alkaline peptone water, blood agar, TCBS agar.

Identification Techniques

  • Biochemical Patterns:

    • E. coli: H2S negative, motility positive, indole positive, TSI reactions for glucose/lactose/sucrose.

    • Klebsiella: H2S negative, motility negative, indole variable, urease positive.

    • Shigella: Indole variable, H2S negative, TSI reactions negative for lactose/sucrose.

    • Salmonella: H2S positive, motility positive, specific serogroup identification via antibody reactions.

    • Yersinia: H2S negative, motility variable at 30°C, identification of O serogroups.

    • Vibrio cholerae: Oxidase positive, glucose sucrose fermenters; serogroup identification via antigen-antibody reactions.

Antibiotic Susceptibility Testing

  • General Phenotypes:

    • Klebsiella spp.: ESBL and KPC resistance mechanisms.

    • Shigella: Resistant to aminoglycosides, 1st and 2nd generation cephalosporins.

    • Salmonella: Resistant to aminoglycosides; caution in therapeutic selection.

Additional Considerations

  • Serological Testing: For typhoid fever detection (Widal reaction).

  • Vibrio cholerae: Requires rapid detection techniques like ELISA for bacterial antigens from stool samples.

  • Molecular Typing: Used in reference laboratories for confirming suspected strains.