An unclassified gram-negative rod isolated from the pharynx on Thayer-Martin medium (selective agar)

Abstract

An oxidase-positive, small gram-negative rod was isolated on Thayer-Martin medium (TM) inoculated with pharyngeal swabs obtained during surveys to detect Neisseria carriers. In one survey, this organism was isolated from 48% of the subjects, and 50 or more colonies were present on the majority of the primary isolation plates. Other characteristics of the organism, which has been given the provisional designation "TM-1," include: delayed production (2 to 10 days) of acid from glucose, formation of gas during nitrate reduction, and the frequent formation of "pits" in the agar surface. On TM, nonpitting colonies of TM-1 are morphologically similar to colonies of Neisseria gonorrhoeae and N. lactamica. Comparison of the characteristics of TM-1 strains with other similar fastidious gram-negative organisms encountered in clinical laboratories indicates that TM-1 is a distinct species. Further studies are required before proper taxonomic placement can be made.