A Biochemical and Serological Study of a Group of Identical Unidentifiable Gram-negative Bacilli from Human Sources

Abstract

A study was made of 15 unidentified identical strains of Gram-negative bacilli, most of them from urine cultures. These organisms are short and plump, show marked bi-polar staining and have a small capsule. They are strict aerobes, growing heavily on simple media. Glucose, galactose, and arabinose are fermented, other carbohydrates are negative. Although 1% lactose broth is not fermented, an acid reaction is produced on 10% lactose agar slants; this is an unique characteristic of these bacilli. Another outstanding characteristic is their failure to reduce nitrates. Other biochemical reactions are: indol negative, methyl red positive, Voges-Proskauer negative, citrate positive, malonate positive, hydrogen sulfide negative. In the mucoid (M) encapsulate phase, these organisms are serologically homogeneous, showing complete cross agglutination and agglutinin absorption. They may be rapidly identified by the Quellung reaction with specific antiserum. Smooth (S), rough (R) and small colony variants were observed, which variants differ morphologically, biochemically and serologically from the typical M form. Since no serological relationship to any recognized genera or species could be demonstrated and since they differ biochemically from any recognized forms, it was proposed that these bacilli be included in the genera Bacterium and, because of their failure to reduce nitrates, that they called Bacterium anitratum n. sp.