Neisseria mule, horse, or donkey

In a recent note (3), Hodge et al. reported a problem isolate which demonstrated characteristics of both Neisseria gonorrhoeae and Neisseria meningitidis. The authors suggested that the isolate might be a genetically transformed gonococcus with the ability to utilize maltose or a meningococcus which acquired antigenic determinants of N. gonorrhoeae. Either is a reasonable hypothesis, as a close genetic relationship has been well established (8). Indeed, DNADNA hybridization studies have demonstrated a homology value of 93% (4), which on a genetic basis is sufficient to consider them a single species (4, 8). The biochemical reactions of the isolate of Hodge et al. are identical to those of N. gonorrhoeae transformed in vitro by exposure to Neisseria lactamica DNA. These organisms retain other gonococcal characteristics but acquire the ability to make glutamyl aminopeptidase and to degrade maltose (5). N. lactamica has been sporadically isolated from the female genital tract (1, 6), and in vivo transformation is an intriguing possibility in that Neisseria spp. readily undergo autolysis with the release of DNA. Although at times it may be difficult to distinguish N. gonorrhoeae from N. meningitidis in the laboratory, correct species identification is nonetheless important from clinical, therapeutic, epidemiologic, and legal standpoints. This is a particular problem for laboratories which rely solely on biochemical identification, because serologic methods are more costly and require different expertise and equipment. It is currently the policy of the Denver Disease Control laboratory to identify genital isolates presumptively as recommended by the Centers for Disease Control (Gram stain, oxidase test, and growth with typical colonial morphology on selective agar) (2). The source of the organism and the probability of gonococcal infection are taken into account, and all nongenital or questionable isolates are confirmed by immunologic as well as biochemical methods. Although the isolate of Hodge et al. would have been subjected to further study in our laboratory, we differ with some of their conclusions. Specifically, distinct smalland large-colony variants are characteristic of freshly isolated N. gonorrhoeae cultures and are found only rarely in cultures of N. meningitidis, while lack of growth at 22°C in air and no growth on nutrient agar at 36°C in 5% C02 is typical of both species, not just the meningococcus (7, 8). Both species are oxidase and catalase positive and give negative reactions for the production of ,-galactosidase and tributyrinase and synthesis of polysaccharide from 5% sucrose. Finally, we have tested 942 isolates of N. gonorrhoeae for susceptibility to spectinomycin, with a resulting geometric mean MIC of 19.4 ,ug/ml. Obviously, an isolate for which the MIC is 21 ,ug/ml would not be considered unusual, as implied in the note. The results of four tests reported by Hodge et al. are most important. Sugar degradation, gamma-glutamyl aminopeptidase production, and growth on media without cysteine are all compatible with N. meningitidis. The fluorescent-antibody technique with the Syva MicroTrak fluorescent monoclonal antibody for confirmation of N. gonorrhoeae has been highly specific in our hands, with 90 isolates of N. meningitidis tested and no cross-reactions seen (B. E. Laughon, J. M. Ehret, H. H. Handsfield, R. B. Jones, F. N. Judson, T. Tanino, B. Van Der Pol, and E. W. Hook II, submitted for publication). The positive reaction of this isolate with Syva gonococcal antisera is indeed significant. Thus, theirs is an isolate meriting sophisticated molecular analysis. Is it a transformed gonococcus, a newly recognized Neisseria species or subspecies, or an altered meningococcus, i.e., mule, horse, or donkey? The answer to this, as well as to the pathogenic potential of such isolates and the frequency with which they occur, is important to both laboratorians and clinicians.