Gram Negative Cocci

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Medstudents thanks Dr. Martin Nachbar, M.D. from New York University, because this section can only be here with permission of the Hippocrates Project of the New York University School of Medicine

The organisms to be considered in this group are the Neisseria, Moraxella (Branhamella), and the Acinetobacter. The genus Neisseria includes two important human pathogens,

• Neisseria gonorrhoeae (urethritis, cervicitis, salpingitis, proctitis, pharyngitis, conjuntivitis, pharyngitis, PID - pelvic inflammatory disease, arthritis, disseminated disease)
• Neisseria meningitidis.(meningitis, septicemia, pneumonia, arthritis, urethritis)

   

Previously considered harmless,

• Moraxella catarrhalis (bronchitis and bronchopneumonia in patients with chronic pulmonary disease, sinusitis, otitis media) has recently been shown to be an common cause of human infections.

   

While most Neisseria, Moraxella and Acinetobacter can grow on simple media, and under varying temperatures, Neisseria meningitidis. and Neisseria gonorrhoeae(especially fresh isolates) are sensitive to fatty acids and trace metals present in these media and require an enriched medium containing blood or blood products. In addition, a carbon dioxide atmosphere and incubation at 37 degrees Celsius are requirements for growth.

Identification Scheme for Gram negative aerobic cocci

Properties useful in distinquishing among the Gram negative cocci

• oxidase test - detects the presence of the enzyme cytochrome oxidase using a dye, tetramethyl-p-phenylenediamine dihydrochoride. The dye is colorless in the reduced state but purple in the oxidized state.

  A positive oxidase test is commonly used for presumptive identification of Neisseria species because these organisms contain large amounts of the enzyme, cytochrome oxidase, but Moraxella (Branhamella) catarrhalis and some gram negative bacilli (e,g. of the genus Pseudomonas or Flavobacterium) also give a positive test.

  A typical positive oxidase test of a pathogenic Neisseria is shown below.

  

  A Moraxella (Branhamella) positive test result

  

• Ability to grow on NYC media - this is an enriched media containing antibiotics ( vancomycin, colistin, nystatin, and trimethoprim) which permits the growth of pathogenic Neisseria but supresses the growth of nonpathogenic Neisseria, Moraxella and other gram negative organisms

  Neisseria meningitidis on NYC agar

  

  Moraxella (Branhamella) catarrhalis on NYC agar

  

• carbohydrate degradation - oxidative breakdown of the sugars glucose, maltose and sucrose can help to distinquish among Neisseria meningitidis, Neisseria gonorrhoeae, and Moraxella (Branhamella) catarrhalis.

  Neisseria meningitidis sugar utilization

  

  Neisseria gonorrhoeae sugar utilization

  

  Moraxella (Branhamella) catarrhalis.

  

  Uninoculated sugar media

  

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