NONFERMENTATIVE BACILLI: PHENOTYPIC FEATURES, DNA-DNA HYBRIDIZATIONS, AND TAXONOMY OF CDC'S IIK GROU

Nonfermentative organisms that were once thought to be normal human flora or of environmental origin are increasingly being implicated as agents of disease. Elizabeth King at the Center for Disease Control (CDC) collected organisms that did not fit known biochemical profiles and placed them into groups based on their distinct phenotypic features. Among these organisms were CDC's yellow pigmented IIk group, which was divided into two biotypes. Recently, IIk biotype 1 was placed in the genus Pseudomonas as Pseudomonas paucimobilis. The IIk biotype 2 group has not been extensively characterized.;Twenty-two strains of CDC's IIk-2 group of nonfermentative bacilli and nineteen strains of Pseudomonas paucimobilis were studied. Phenotypic characterization, nutritional studies, and DNA hybridization were used to examine these two groups.;Our strains of IIk-2 fell into two clusters based on biochemical data and DNA-DNA hybridization. The major cluster (18 strains) was homogeneous, giving identical results for 37 of 40 phenotypic features. Representative strains from this cluster showed a high level (75% or more) of DNA-DNA homology. The minor cluster of 4 strains reduced nitrate to nitrite, grew at 42(DEGREES)C, and showed no DNA homology with the major cluster. In an attempt to assign the major cluster to an established genus, representative strains from genera with similar guanine plus cytosine contents (37-43%) were selected for hybridization. DNA from the major cluster was not related to the DNA of Flavobacterium meningosepticum, Flavobacterium group IIb, Acinetobacter anitratus, and Moraxella phenylpyruvica. Although IIk-2 was not closely related to either Flavobacterium species tested, examination of a new definition of the genus Flavobacterium, fatty acid composition studies, and flagella morphology, led to the decision to place the IIk-2 group in the genus Flavobacterium.;Nineteen strains of Pseudomonas paucimobilis were studied to confirm and expand the phenotypic results of Holmes et al., International Journal of Systematic Bacteriology 27: 133-146, 1977. After examination of 37 tests, we, too, find Pseudomonas paucimobilis to be a phenotypically homogeneous group. Nine phenotypically identical, representative strains of Pseudomonas paucimobilis were studied using DNA-DNA hybridization. Two groups emerged. The majority of the isolates were highly related (85% or above homology). Two strains were only slightly related to the reference strain. Since, at this time, no biochemical features have been found to differentiate these two groups, we feel they should remain as a single species.;When IIk-1 (Pseudomonas paucimobilis) was first described it was thought to be related to the genus Xanthomonas, Holmes et al, investigated the biochemical profile of some Xanthomonas species and found them to be similar to Pseudomonas paucimobilis although certain biochemical features could be used to differentiate the two groups. No DNA homology studies were done by them. Hence, in order to investigate the genetic relationship between these two groups, strains of Xanthomonas phaseoli were hybridized to Pseudomonas paucimobilis. No homology was found; this emphasizes that these are two distinct taxa.