The genus Neisseria belongs to the family Neisseriaceae. It contains 25 species. About 12 species and biovars of these can be isolated from humans. They can be naturally isolated from the mucous membranes of the respiratory and urogenital tracts. N. meningitidis and N. gonorrhoeae require iron for growth. They have to compete with their human host in order to attain iron by binding human transferrin to specific surface receptors. This ability of these certain genera to bind transferrin may be a primary reason that they are considered as strict human pathogens. N. weaver is a commensal in the upper respiratory tract of dogs which is the reason why it may be isolated from dog bites in humans. All other Neisseria spp. are considered opportunistic pathogens which means they take advantage of the hosts’ weakened immune system which may be due to a prior or another infection. These opportunists must be identified and differentiated from N. gonorrhoeae and N. meningitidis in isolates from clinical specimens.
General Characteristics
The most well-known general characteristic of Neisseria spp. is that they are gram-negative diplococci that demonstrate the shape of a kidney or a coffee bean with a flattened adjacent sides, with an exception of Neisseria elongata, Neisseria weaveri, and Neisseria bacilliformis which are rod-shaped. Most Neisseria spp. are aerobic, nonmotile, non–spore-forming, gram-negative diplococci.
Listed below are other characteristics of Neisseria:
- Cytochrome oxidase positive
- Catalase positive (except for except for N. elongata and N. Bacilliformis)
- Most are capnophilic (requires an increase of 3-10% carbon dioxide tension for growth)
- Can grow anaerobically if alternative electron acceptors are available
Cultural Characteristics
Neisseria spp. are fastidious organisms requiring complex nutritional requirements for growth. They are highly sensitive or susceptible to chilling, drying and exposure to unfavorable environmental state. They also exhibit or appear as translucent, grayish, convex, shiny colonies with entire magins that are non-hemolytic and non-pigmented.
Culture Media Used
- Thayer-Martin medium
- Modified Thayer-Martin (TM)
- Transgrow medium
- Martin-Lewis medium
- New York City medium (NYC)
- GC-LECT
- John E. Martin Biological Environmental Chamber (JEMBEC) plates
Virulence Factors
Pathogenic Neisseria spp. have several characteristics that contribute to their virulence, which are the following:
- Receptors for human transferring
- Capsule (N. meningitidis)
- Pili (fimbriae) for attachment
- Cell membrane proteins
- Lipooligosaccharide (LOS) or endotoxin; lipid A moiety and core LOS that differentiates it from the lipopolysaccharide found in most gram-negative bacilli and is loosely attached to the underlying peptidoglycan
- Immunoglobulin A (IgA) protease that cleaves IgA on mucosal surfaces
Infections Caused by Neisseria Species
- Meningitis lactamica
- sicca
- subflava
- mucosa
- flavescens
- Endocarditis sicca
- subflava
- mucosa
- elongate
- flavescens
- bacilliformis
- Prosthetic valve infection sicca
- Bacteremia lactamica
- flavescens
- cinerea
- Pneumonia Sicca
- Empyema mucosa
- Bacteriuria subflava
- Osteomyelitis sicca
- Ocular infection cinerea
- mucosa
- Dog bite weaveri
Laboratory Diagnosis
Since there are only two species of Neisseria that are considered as human pathogens, the focus of this section is to list the common laboratory diagnoses and tests needed to identify N. gonorrhoea and N. meningitides.
- Stained smear
- Culture
- Oxidase test (presumptive identification test)
- Confirmatory identification test
- CTA
- Gonobio test
- Gonochek II
- Direct fluorescent antibody technique
- Anitbody-based particle agglutination
- GonoGen
- Phadebact
- Maritec-GC
- ELISA
- Limulus test (rapid screening test for N. Gonorrheae)
- Superoxol test
Treatment
Treatment for infections caused by Neisseria spp. varies depending on the origin of the infection. Focusing on the two important Neisseria spp, listed below are the treatment for N. gonorrhoeae and N. meningitides:
- Neisseria meningitides
- Penicillin- drug of choice
- Third-generation cephalosporins- best used to treat meningococcemia
- Chemoprophylaxis with rifampin or ciprofloxacin- recommended for contacts.
- Azithromycin- alternative
- Chemoprophylaxis-not recommended for asymptomatic carriers
- Neisseria gonorrhoeae
- Cephalosporins- currently recommended
- Amoxicillin, ampicillin and aqueous procaine penicillin G
- Spectinomycin, trimethoprim-sulfamethoxazole, ciproflaxin and cefuroxime- alternatives