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Gram Negative Cocci  


  • Strict aerobe, oxidase +, diplococci, NM
  • N meningitidis, N gonorrhoeae 
  1. N meningitidis:
    1. Adjacent sides are flat
    2. In lesions, generally Intracellular
    3. Fresh isolates: Capsulated
    4. Growth: blood, serum, ascitic fluid
    5. 5-10% CO2; BA, CA, MHA ( MHA was 1st formulated for isolation of neisseria, now widely used for antimicrobial susceptibility testing)
    6. catalase +, oxidase +, glucose +, maltose+
      1. ​​​​Antigens:
        Capsular: 13
        A, B, C, W135, Y are important cause of epidemics and outbreaks
        A: epidemics; C: local outbreaks; B: both;  29E, W 135 & Y: outbreaks
      2. ​​Pathogenicity:
        Meningitis & septicemia (WF syndrome)
        trict human pathogen; carrier state in nasopharynx
        WF syndrome: shock, DIC, multisystem failure
        Pathogenesis of septicaemia: Lipo-oligosaccharide LOS mediated damage of vascular v. endothelium
      3. ​​T/T: i. Penicillin G, Chloramphenicol, III generation cephalosporin; Rifampicin (to prevent carrier state) 
  2. N. gonorrhoeae:
  • Adjacent sides concave; kidney shaped
  • Predominantly I/ C
  • Virulence by PILI; attachment, inhibition of phagocytosis
  • Growth: may grow aerobically; 5-10 % carbon dioxide
  • CA, Modified Thayer Martin, New York City medium
  • Morphological types-T1toT4: T1 & T2 are pilated, small, brown colonies, autoagglutinable; T3 & T4 are nonpilated, large nonpigmented colonies,  smooth
  • Catalase +, oxidase +, glucose +, maltose- 

a. Antigenic properties:

  1. Heterogenous; capable of changing their surface structures
  2. PILI: antigenic & phase variation
  3. Protein I: antigenic diversity, typing gonococcal strains
  4. Protein I & III: attachment to host cells, porin
  5. Protein II: opacity of gonococcal colonies (OPA)
  6. LPS: endotoxicity
  7. IgA1 protease 

b. Pathogenicity:

  1. I/P: 2-8 days
  2. Urethral discharge, acute urethritis, prostatitis, epididymitis
  3. “Water-can perineum”
  4. Cervix; no vaginal involvement (vulvovaginitis in prepubertal girls)
  5. Bartholin gland, endometritis, salpingitis
  6. Fitz-Hugh Curtis syndrome
  7. Less severe in women
  8. Proctitis, arthritis, endocardits, ophthalmia neonatorum
  9. Natural infection in humans
  10. Source: human carrier, women 

B. Non Gonococcal Urethritis:

  • Chlamydia trachomatis (most common cause)
  • U urealyticum
  • M hominis 

C. Moraxella catarrhalis

  • Gram negative diplococcus with adjacent sides flattened
  • Normal commensal in respiratory tract
  • Aerobic, oxidase positive
  • Grows on BA and CA-non-hemolytic
  • Identifying biochemical’s for differentiating from Neisseria- non fermenter, reduces nitrates, DNase and tributyrin hydrolysis +
  • Causes otitis media and sinusitis in healthy
  • Causes bronchitis and pneumonia in patients with chronic lung disease
  • Can cause bacteremia and meningitis in immunocompromised
  • More than 95% produce beta lactamases

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