The Neisseria

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The Neisseria

• Recommended reading
• Sherris p309-320
• Mandell p1928-1930

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Biology of the Neisseria

• There have been 10 species described of which 2
  are strict human pathogens
• N. gonorrhoeae
• N. meningitidis
• Other species may be colonisers of the oropharynx
  and ano/genital areas

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Biology of the Neisseria contin...

• aerobic gram negative cocci-tend to be seen as
  diplococci
• non motile
• do not form endospores
• Do not ferment sugars
• All are oxidase positive and most are catalase
  positive
• Other species may be opportunistic in compromised
  hosts

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Type species N. gonorrhoeae

• General character
• Fastidious microbe requiring specialised media to
  enable culture
• Has typical gram negative cell wall
• Surface may be covered by pili
• ( associated with lack of protective immunity due
  to pili Ag variation)

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• Has 3 other major antigens in/on outer membrane
• Por (porin protein)
• Opa (Opacity protein important in binding to
  epithelial cells)
• Rmp (associated with the Por )

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• LOS (LPS component important in inflammatory
  response induced by the infection)
• Iron is an essential growth factor
• Has a range of virulence factors
• eg may produce proteases specific for cleaving IgA

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Pathogenesis N. gonorrhoeae

• The gonococci attach to mucosal cells, penetrate
  the cell and multiply
• The absence of pili deems a strains non virulent
• Opa protein ensures a tight attachment to the
  epithelial cell
• Por protein prevents phagocytosis by inhibiting
  the formation phagolysosomes
• LOS -gt inflammatory response-gt release of TNF
  (alpha) -gt most symptoms of disease)

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Infection N. gonorrhoeae

• Attack rates are highest in 20-24 yo age group
• Risk is increased directly with number of sexual
  contacts
• Can be transmitted by non sexual contact eg linen
  and towels but this tends to be rare

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Symptoms N. gonorrhoeae

• Incubation 7-10 days
• gt90 men are symptomatic
• Dysuria
• Discharge
• Frequency
• Course of infection females not as well
  understood and may include
• Abnormal menses
• Unusual discharge
• Erythema
• Cervical tenderness

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REF http//www.telemedicine.org/GON.HTM
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• Anorectal and pharangeal infections are also
  common
• Rectum may be the only infected site in
  homosexual men
• Gonococcal pharangytis may be present in up to
  20 infected heterosexual women and 25of
  infected homosexual men

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Diagnosis N. gonorrhoeae

• Presumptive diagnosis detection of gram negative
  diplococci in urethral exudate (gt90 accurate in
  men)
• Grams of cervical exudates less definitive
• Confirmation by culture
• FAT available
• PCR and DNA probes are becoming increasingly
  used.

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Complications N. gonorrhoeae

• PID in 10-20
• Epididymitis
• Prostatitis
• Disseminated infection -gt eg sepsis, bacteraemia,
  meningitis, endocarditis

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Treatment and control

• Uncomplicated infection 3rd generation
  cephalosporin such as
• ceftriaxone 125mg, im single dose
• or
• Ciprofloxacin 500mg oral single dose
• Coinfection with chlamydia should be considered
  and appropriate co-therapy doxycycline or
  erythromycin instituted if warranted
• Spectinomycin is generally used in penicillin
  allergy (less effective against pharangeal
  infection)

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• Partners exposed to infection within 30 days
  should have cultures taken and be given
  prophylactic treatment
• Hospitalisation is recommended in complicated
  infections including disseminated infection

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• Cultures also recommended in 1st trimester
  (should be repeated in 3rd trimester in high risk
  patients)
• Ceftriaxone is the treatment of choice in special
  cases such as pregnancy infants at risk eg
• neonatal ophthalmia
• infants of positive mothers

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• Immunity to N.gonorrhoeae is not well understood
• Reinfection can occur particularly where multiple
  partners are involved
• Poor immunity may be due to high levels of
  antigenic diversity- eg vaccines developed
  against pilin antigens protective for homologous,
  but not for heterologous strains
• Antimicrobial prophylaxis has not effective and
  may increase the risk of selecting resistant
  strains