Neisseriae

 

 

Neisseriae are gram-negative cocci of which two species are pathogenic for man: meninigitidis and gonococcus. Several other nonpathogenic Neisseriae species colonise the upper respiratory tract and may be confused with meningococci.

 

Properties

 

Gram-negative coccci, nonmotile

Most often growing in pairs but occasionally in clusters

The individual cocci are small and their shape may be distorted

A capsule may be present in some isolates of meningitidis

Pili may be present

 

 

Neisseriae meningiditis

 

N. meningiditis often inhabits the upper respiratory tract without causing any symptoms. This carrier state may last a few days to a few months and provides the reservoir for the organism. In the general population, the carrier rate is appreciable at all times and in military populations, it may exceed 90%.

 

Pathogenesis

 

Meningococcal disease occurs with an endemic incidence of 2 in 100,000 pa. More than half of these cases occur in children less than 5 years of age, with the highest incidence in the first year. Mennigococcal disease is rare below the age of 3 months because of the presence of maternal antibodies. During epidemic periods, the incidence may rise 100-fold and the incidence over 2 years of age increases disproportionately. In the absence of treatment, the mortality rate is 85% but can be reduced to less than 10% provided vigorous treatment is given. The rate of neurological sequelae is low. Individuals with deficiencies of the complement components C5, C6, and C7 are susceptible to recurrent meninigococcal disease. Infrequently, menigococcoaemia does not progress to meningitis but causes thromboembolic lesions in the skin, joint, lungs, middle ear, or adrenal glands. Acute adrenal insufficiency occurs (Wterhouse-Friderichsen syndrome) occurs in fulminant cases.

 

Diagnosis and treatment

 

In cases of suspected meningococcal diseases, stained specimens of blood, CSF, and NPA should be examined for N. meningiditis. N. meningiditis may be cultured by routine methods. Neisseria colonies may be tentatively recognised by the oxidase test. The further identification of N. meningitidis requires biochemical and serological tests. It is imperative that treatment be started as soon as the provisional diagnosis of bacterial meningitis is made. A broad spectrum antibiotic such as ampicillin should be used to cover haemophillus influenzae. Once the diagnosis of meningococcal disease is established, penicillin should be used.

 

Prevention

 

Chemoprophylaxis and immunoprophylaxis may be used for the prevention of meningococcal disease. Rifampin is now routinely used for chemoprophylaxis. However, it has several disadvantages and should only be used for individuals in close contact with a case, such as those living in the same household. There is no evidence that classroom or the usual hospital personnel contact entails a significant risk. Vaccines consisting of purified group A and C polysaccharides are available. The group B polysachharide has poor antigenicity.

 

 

Nessierrae Gonnorhae

 

There are 2 million cases a year of gonorrhoea in the US. In heterosexual men, the most commonly infected site is the anterior urethra, producing symptoms in 90% of cases. In homosexual men, rectal and pharyngeal infections are common. The latter are usually asymptomatic. Asymptomatic infections, although they are in the minority, represent an important reservoir of the disease: because they are not usually treated and therefore the infection may last for months. In women, the most commonly infected site is the endocervix; the urethra, the rectum, the periurethral glands, and Bartholinís glands are also sites of infection. Perhaps as many as 50% of women have insufficient symptoms to seek treatment.

†††††† The most common complication is ascending infection of the fallopian tubes. Acute PID occurs in 15 to 20% of infected women, usually within a week of the onset of the first menses following infection. Acute gonococcal PID frequently necessitates hospitalisation and scarring of the oviducts, resulting in infertility and ectopic pregancies. The scarred fallopian tubes may become superinfected with a number of bacterial specieis leading to chronic PID, which often require surgical treatment.

†††††† In 1 to 3% of infected men or women, the gonococcus invade the blood stream, leading to disseminated gonococcal infection. Patients may present with either of two syndromes; polyarthralgias, tenosynovitis, and dermatitis or purulent arthritis. Very rarely, additional complications such as perihepatic abscess, endocarditis, or meningitis may occur. It is not unusual for an individual to acquire gonorrhoea repeatedly, even from the same consort.

 

Diagnosis and treatment

 

In acute gonoccocal disease, stained smears of fresh exudate will often reveal the presence of intracellular gram-negative diplococci. This finding, together with a convincing clinical history may permit the physician to make the provisional diagnosis of acute gonorrhoea and institute antibiotic therapy. Wherever possible, the exudate should be cultured for gonococci before treatment. †The diagnosis is established by the recovery of typical gram-negative oxidase-positive diplococci that ferment glucose but not maltose, sucrose or lactose. Rectal cultures are sometimes positive when urethral and cervical cultures are negative. Because gonococci are not hardy, specimens should be cultured immediately or placed in special transport media. Penicillin is the drug of choice but resistance is being increasingly encountered. Tetracycline may be used instead with the added bonus that it is effective against chlamydia.