Neisseria

Neisseria meningitidis is one of the most common causes of meningitis; transmission is through inhalation of respiratory droplets and so outbreaks are common in areas of close contact eg schools. Neisseria gonorrhoeae is one of the most reported infections in the USA; transmission is usually through sexual contact, however can also occur between mother and baby at birth.

The gram-negative, aerobic diplococci N.meningitidis and N.gonorrhoeae cause infections characterised by the production of a pus-like material consisting mainly of white blood cells. N.gonorrhoeae colonises the epithelia of the urethra, cervix, rectum, conjunctiva and pharynx. N.meningitidis colonises the epithelia of the nasopharynx and the infection commonly remains asymptomatic. In some cases, however, N.meningitidis can cross into the blood and further disseminate around the body. Passage across the blood-brain barrier and subsequent infection of the meninges causes the symptoms characteristic of meningitis such as fever, severe headache, rash and a stiff neck. N.meningitidis can also go on to cause a rapidly developing (< 12 hours), life threatening septicaemia. Both N.meningitidis and N.gonorrhoeae manufacture an IgA protease which help them evade the host immune repsonse; nonpathogenic neisseriae do not manufacture this protease.

Treatment. Due to the risk of septicaemia, treatment for bacterial meningitis must be immediate and can cannot wait for bacterial diagnosis. Treatment is via intravenous administration of penicillin G or ampicillin, or more recently with cefotaxime or cetriaxone. Penicillin resistance is now fairly widespread amongst N.gonorrhoeae, however most are still sensitive to third generation cephalosporins

Vaccines. Vaccines are available that protect individuals against serogroup A and C N.meningitidis infections. However, no vaccines are available against the most common serogroup causing meningococcal infection in Europe (serogroup B) or against N.gonorrhoeae.