Microtube Method for Identification of Neisseria Species

Neisseria species are identified in most diagnostic microbiology laboratories by using carbohydrate degradation methods. Conventional methods require 24 to 48 h of incubation for completion of the test (15). A number of rapid methods which employ various agar bases, growth factors, sugar concentrations, agar concentrations, inoculum sizes, filter paper disks, radiometry, gas chromatography, spectrophotometry, etc., and which use solid, semisolid, or liquid media have been reported in the literature (2, 4-7, 11, 12, 14, 16-19, 22, 23, 25-27). Some inherent disadvantages exist with several of these methods. For example, radiometric methods (7, 24) require the purchase of expensive equipment and the use of 14C-labeled substrates. Gas-liquid chromatography (17) involves not only extraction procedures, but also the purchase of gas chromatography equipment. The identification of bacteria by genetic transformation (4) requires techniques, such as the preparation of wild-type deoxyribonucleic acid, which are not feasible in many diagnostic laboratories. Methods involving CO2 release from fermentable carbohydrates (23) require the use of spectrophotometry and preliminary preparation methodology which may not be practical in many clinical laboratories. The New York City fermentation media require horse blood and the preparation of a yeast dialysate. The Minitek system (BBL Microbiology Systems, Cockeysville, Md.) uses the manufacturer's equipment and has shown a sensitivity of around 92% within 4 h (2, 16). In this paper we report on the evaluation of a commercially available rapid carbohydrate degradation (RCD) microtube system that does not require any prior preparation or purchase of special equipment and yields accurate results in 0.5 to 4.0 h. We used 386 strains of gonococci, meningococci, Neisseria lactamica, Neisseria sicca, Neisseria subflava, Neisseria flavescens, and Brahmanella catarrhalis. The method uses preformed enzymes as well as those synthesized by bacteria during growth in an enriched medium.