Gram-Negative Cocci Overview

Gram-Negative Cocci

• Genus: Neisseria

  • Species: N. gonorrhoeae
    • Characteristics: Gram-negative diplococci, oxidase-positive, catalase-positive, glucose-positive, fastidious, encapsulated, pili
    • Growth: No growth on MAC, grows on CHOC
    • Diseases: Gonorrhea (STI), can cause PID, Fitz-Hugh-Curtis syndrome
    • Key Points: Not normal flora, primarily infects the urogenital tract, carried in nasopharynx
  • Species: N. meningitidis
    • Characteristics: Gram-negative diplococci, oxidase-positive, maltose-positive, glucose-positive, fastidious, encapsulated
    • Growth: Growth on CHOC, BAP, SBA
    • Diseases: Meningitis, meningococcemia, Waterhouse-Friderichsen syndrome
    • Key Points: Carried in nasopharynx, can cause outbreaks in close communities, causes eye infection in children

• Genus: Moraxella

  • Species: M. catarrhalis
    • Characteristics: Gram-negative diplococci, oxidase-positive, catalase positive, beta-lactamase, asaccharolytic
    • Growth: Growth on CHOC, BAP, not on MAC
    • Diseases: Otitis media, sinusitis, bronchitis
    • Key Points: Common cause of respiratory infections, especially in children

Gram-Negative Coccobacilli

• Genus: Haemophilus

  • Species: H. influenzae
    • Characteristics: Small Gram-negative coccobacilli, fastidious, grows on CHOC, requires X & V factors
    • Diseases: Meningitis, pneumonia, otitis media, epiglottitis, (invasive and non-invasive)
    • Key Points: Most invasive diseases are type B, Hib vaccine has reduced infections. Uses virulence factors like capsule, IgA protease, etc
  • Species: H. ducreyi
    • Characteristics: Gram-negative coccobacilli, fastidious, growth around X and XV
    • Diseases: Chancroid
  • Species: H. parainfluenzae
    • Characteristics: Gram-negative coccobacilli, fastidious, growth around V and XV factor
    • Diseases: Rarely pathogenic, endocarditis

• Genus: HACEK Group

  • Species: Haemophilus aphrophilus, Aggregatibacter actinomycetemcomitans, Cardiobacterium hominis
  • Characteristics- Gram-negative coccobacillus, requires X factor for growth, CO2 increased, grows on chocolate and BAP.
  • Diseases: Endocarditis, respiratory infections, meningitis
  • Key Points- part of normal flora in upper respiratory system

• Genus: Pasteurella

  • Species: P. multocida
    • Characteristics: Gram-negative bacilli, non-fastidious - grow on BAP and CHOC. Gamma hemolytic, Nonmotile, Oxidase-posititve (in Most isolates), nitrate positive.
    • Diseases: Animal bite infections, cellulites.
    • Key Points: Can be easily mistaken for Haemophilus, often ovoid, filamentous, or bacilli-shaped, with bipolar staining, retaining more stain in the ends

• Genus: Kingella

  • Species: K. kingae
    • Characteristics: Gram-negative coccobacillus, non-motile, sugar fermentor that produces no gas, Oxidase positive, catalase negative
    • Diseases: Osteoarticular infections, bacteremia
  • Key Points: May be mistaken for Neisseria (gram stain identification).

• Genus: Enterobacter

  • Species: Enterobacter spp.
    • Characteristics: Gram-negative rods, pink/colorless colonies on MAC, facultative anaerobe, motile, large shiny colonies on BAP, H2S negative, oxidase negative, indole variable
    • Diseases: UTI, pneumonia, wound infection
    • Key Points: Known for multidrug resistance.

• Genus: Salmonella

• Species: S. enterica

  • Characteristics: Gram-negative rods, non-lactose fermenting, facultative anaerobe, motile
  • Diseases: Gastroenteritis, enteric fever (Typhoid),
  • Key Points: Produces H2S (except S. paratyphi A)

• Genus: Shigella

  • Species: Shigella spp.
    • Characteristics: Gram-negative rods, non-lactose fermenting, facultative anaerobe, non-motile, RED colonies on XLD, GREEN/clear on HE
    • Diseases: Dysentery, blood diarrhea, inflammatory disease
    • Key Points: Non-motile, can invade epithelial cells, no H antigen, no gas production, (except in some S.flexneri).

• Genus: Yersinia

  • Species: Y. enterocolitica
    • Characteristics: Gram-negative rods, non-lactose fermenting, facultative anaerobe, safety pin, colonies vary based on temperature
    • Diseases: Gastroenteritis, appendicitis-like syndrome. plague (Y. pestis)
      • Key Points: Motile at 25°C, but not at 37°C. Resists phagocytosis, invades intestinal mucosa

• Genus: Pseudomonas

  • Species: P. aeruginosa
  • Characteristics: Slender gram-negative rods, motile, polar flagella, oxdiase positive, BAP with metallic sheen
  • Diseases: Nosocomial UTI, pneumonia, wound infection
  • Key Points: Fruity/grape-like odor.

• Genus: Acinetobacter

  • Species: A. baumannii
    • Characteristics: Gram-negative coccobacilli, grows on MAC, nonmotile, oxidase-negative, no pigment.
    • Diseases: Nosocomial UTI, pneumonia
  • Key Points: Small coccobacilli, can falsely stain as gram-positive.

• Genus: Stenotrophomonas

  • Species: S. maltophilia
    • Characteristics: Gram-negative rods, grow on MAC, nonmotile, oxidase-negative.
    • Diseases: Nosocomial UTI, pneumonia
  • Key Points: Strong ammonia smell, DNase positive.