Speciation of oxidase-positive non-fermentative gram-negative bacilli

Background: Due to lack of simple and economic methods for speciation of oxidase-positive non-fermentative gram-negative bacilli (NFGNB) and the belief that most of them are saprophytes, the oxidase-positive isolates are reported as Pseudomonas aeruginosa without further testing for identification. Any commensal or saprophyte can cause infections when a suitable opportunity arises. This is also true for oxidase-positive NFGNBs which are widely being reported from different clinical settings among immunocompromised as well as immunocompetent patients. There are contrasting differences in the antibiotic sensitivities of these organisms making identification and sensitivity testing a necessity. Objectives: This study was conducted to speciate various oxidase-positive NFGNBs from different clinical samples and to study their antibiotic sensitivity profile. Materials and Methods: Oxidase-positive clinical isolates from various samples were characterized by biochemical analysis using a battery of tests. Antibiotic sensitivity was done according to National Committee on Clinical Laboratory Standards (NCCLS) guidelines for antibiotic susceptibility testing for P. aeruginosa. Results: We isolated 78 different types of oxidase-positive species from different clinical samples. The various samples included urine, sputum, Bronchoalveolar lavage, Cerebrospinal fluid (BAL, CSF), blood, pus, catheter tips, and body fluid. P. aeruginosa was the commonest isolate comprising 25 (32%), followed by Moraxella catarrhalis (11.5%), Pseudomonas sp. CDC group 17 (8.9%), and Moraxella osloensis and CDC Vb - 3 (each 5.1%) among others. Conclusions: Identification and antibiotic sensitivity testing of oxidase-positive NFGNBs are necessary for apt therapy as they are widely prevalent in the environment and can cause a wide spectrum of infections.