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Other Neisseria Species
Neisseria gonorrhoeae and N. meningitidis are the 2 most pathogenic Neisseria species. Other Neisseria species are common commensal inhabitants of the upper respiratory tract and oral cavity of humans and other animals, but they have been implicated in clinical disease in occasional cases, particularly in immunocompromised patients. The focus of this chapter is on these other Neisseria species, with mention of species that previously have been misidentified as either of the more pathogenic Neisseria species , N. gonorrhoeae , and N. meningitidis .
Microbiology and Laboratory Diagnosis
Neisseria species are gram-negative, oxidase-positive bacteria. All are catalase positive, except some strains of N. bacilliformis and N. elongata . All are diplococci, except N. bacilliformis and N. elongata . Whereas meningococci and gonococci require additional carbon dioxide for optimal growth and grow only at temperatures between 30°C and 37°C, the other species are less fastidious, growing without added carbon dioxide and at 22°C–25°C. Unlike N. gonorrhoeae and N. meningitidis, the other Neisseria species (except N. lactamica ) generally do not grow on selective media such as Thayer-Martin agar; LBVT.SNR medium is used to isolate commensal species. Commensal and pathogenic species usually can be distinguished by biochemical and serologic tests. Carbohydrate use reactions, production of polysaccharide from sucrose, and reduction of nitrate are commonly used for identification ( Table 127.1 ). Difficulties in accurate identification of certain species resulted in some confusion and incorrect identifications in earlier published reports.
TABLE 127.1
Selected Characteristics of Neisseria Species
| Acid Produced From | ||||||||
|---|---|---|---|---|---|---|---|---|
| Species | Morphology | Pigment | Polysaccharide Synthesis | Reduction of Nitrate | Glucose | Maltose | Sucrose | Lactose |
| Neisseria gonorrhoeae | Diplococci | − | − | + a | − | − | − | − |
| Neisseria meningitidis | Diplococci | − | − | + | + | − | − | − |
| Neisseria bacilliformis | Bacilli | + | − | − | − | − | − | +/− |
| Neisseria cinerea | Cocci in pairs or clusters | +/− | − | − | − | − | − | − |
| Neisseria elongata | Bacilli | + | − | +/− | − | − | − | − |
| Neisseria flavescens | Cocci in pairs or tetrads | + | + | − | − | − | − | − |
| Neisseria lactamica | Diplococci | + | − | + | + | − | + | − |
| Neisseria mucosa | Diplococci | +/− | + | + | + | + | − | + |
| Neisseria oralis | Cocci in chains | + | ? | +/− | +/− | +/− | +/− | + |
| Neisseria polysaccharea | Diplococci | − | + | + | + | − | − | − |
| Neisseria sicca | Cocci in pairs or tetrads | +/− | + | + | + | + | − | − |
| Neisseria skkuensis | Cocci | + | ? | + | − | + | − | − |
| Neisseria subflava | Cocci in pairs or tetrads | + | +/− | + | + | +/− | − | − |
+, strains typically are positive, but mutations lacking the specific enzyme activity are found occasionally; −, most strains are negative; +/−, strains are variable.
a Some N. gonorrhoeae strains are weak acid producers and may appear to be glucose negative.
Epidemiology
Neisseria species commonly colonize the upper respiratory tract and occasionally the genital tract. In a study evaluating carriage rates of two Neisseria species in healthy infants and children, the prevalence of N. lactamica carriage was 3.8% at 3 months of age, peaked at 21% at 18 months of age, and declined to 1.8% by early adolescence. In contrast, the rate of N. meningitidis carriage was 0.7% in the first 4 years of life and increased to 5.4% by early adolescence. Similarly, among 1400 healthy children 0–10 years of age in Turkey, 17.7% of children were colonized with N. lactamica, whereas only 1.2% were colonized with N. meningitidis. Similar results were found in a study of 1- to 29-year-old male and female study subjects in Burkina Faso. Carriage of nonpathogenic strains can be important because N. meningitidis and N. lactamica share cross-reactive carbohydrate antigens; carriage of N. lactamica is likely associated with the development of “natural” immunity against N. meningitidis . Cross-reacting antibodies to N. meningitidis were found in 66% of children who had asymptomatic colonization with N. lactamica, compared with 5% of children who were not colonized. Moreover, inhibition of meningococcal carriage of multiple sequence types was demonstrated following nasal inoculation of N. lactamica into university students. N. lactamica– based vaccines are being evaluated as a potential strategy to prevent meningococcal disease.
Most adults are colonized, either densely or sparsely, by two or three Neisseria strains. For example, oropharyngeal cultures from patients in a clinic for sexually transmitted infections revealed N. subflava (biovar perflava ) in >95%; N. cinerea, N. mucosa, and N. subflava (biovar flava ) were found in 25%; and N. lactamica in 1%.
Clinical Manifestations of Infection
Information on clinical disease caused by commensal Neisseria species is accrued primarily through case reports. Characteristics of various species of human origin and some infections caused by the organisms are briefly described here; species of animal origin causing human disease (e.g., N. animaloris , N. canis , N. weaver, and N. zoodegmatis ) are not discussed. Antibiotic susceptibility testing should be performed on all clinically relevant isolates because some organisms are penicillin resistant secondary to β-lactamase production or altered penicillin binding proteins.
Neisseria bacilliformis
Strains of N. bacilliformis grow as light grey colonies that resemble N. elongata on sheep blood agar or chocolate agar at 35°C with 5% carbon dioxide. N. bacilliformis is one of a few bacillary Neisseria species isolated from humans. N. bacilliformis does not produce indole, and reactions in catalase, nitrate reduction, and tributilin tests vary by strain. Sequencing of the 16S ribosomal RNA (rRNA) gene is the most reliable way to identify N. bacilliformis .
N. bacilliformis predominantly causes infections of the oral cavity and respiratory tract in immunocompromised people, but cases of native valve endocarditis have been reported in previously healthy men. ,
Neisseria cinerea
N. cinerea grows as translucent yellow colonies that closely resemble N. gonorrhoeae . Misidentification as N. gonorrhoeae also can occur when these strains are grown on gonococcus-selective media (e.g., Martin-Lewis medium) or when the Bactec (Becton, Dickinson, Franklin Lakes, NJ) radiometric system is used for detection of glucose use. However, susceptibility to colistin and the ability to grow in trypticase soy broth or Mueller-Hinton agar are characteristics of N. cinerea and not N. gonorrhoeae .
N. cinerea has been isolated from the oropharynx and nasopharynx and, rarely, from the genital tract. Infections attributed to this species include hospital-associated pneumonia, cavitary pneumonia and chronic cervical lymphadenitis in immunocompromised patients, dialysis-associated peritonitis, bloodstream infection (particularly in immunocompromised patients and those taking the terminal complement inhibitor eculizumab), endocarditis, proctitis, orbital cellulitis, and conjunctivitis (including neonatal disease). , In some cases, the isolate was initially misidentified as N. gonorrhoeae.
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