Identification and characterization of gram negative glucose nonfermenting bacilli from clinical veterinary specimens

Abstract

Gram negative, glucose nonfermenting bacilli (NFB) have recently been shown to be significant opportunistic pathogens of man. Very little is known about the occurrence of these bacteria in clinical veterinary specimens. Generally, only the following NFB species are considered to be etiologically significant: Pseudomonas aeruginosa, Pseudomonas mallei, Pseudomonas pseudomallei, Bordetella bronchiseptica, and Moraxella bovis. In this study, 347 NFB isolates were cultured during a 1 year period in the Clinical Microbiology Laboratory of the Texas A&M University Veterinary Teaching Hospital. NFB isolates were recovered from 10% of the specimens submitted to this laboratory. The following species were isolated from animals in order of prevalence: P. aeruginosa (67.4%), Acinetobacter calcoaceticus (14.5%), B. bronchiseptica (4.9%), and Pseudomonas pseudoalcaligenes (2.3%). In all, 19 species of NFB were cultured from clinical veterinary specimens. The prevalance of each nonfermenter species by both animal species and anatomical site was determined. The NFB isolates were identified and characterized using a system consisting of 33 conventional tests. The characteristics of each NFB species is also presented. In general, they were similar to those reported for human isolates. The minimum inhibitory concentration (MIC) of 16 antimicrobial agents was determined for each of 160 clinical veterinary NFB isolates by using a commercial microdilution system. Few strict patterns were observed suggesting that each clinically significant strain be individually tested for antimicrobial susceptibility. Most NFB isolates are not completely identified in the clinical veterinary laboratory for 2 reasons: (1) most are not considered to be animal pathogens, and (2) they require a large number of tests for identification. If commercial identification systems used for human NFB isolates could accurately identify animal isolates, then more veterinary laboratories might identify their NFB isolates. In the third section of this study, 2 commercial identification systems (API 20E and MicroScan) were evaluated to determine if they could accurately identify 182 NFB strains. The API 20E identified 69% of the strains correctly and the MicroScan panel identified 72% correctly.