Identification and Susceptibility Testing of Non-lactose Fermenting Gram-Negative Bacilli in Urinary Tract Infection

Abstract

Background: Urinary tract infections are one of the most common bacterial infections in humans both in community and hospital settings. The etiology of UTIs and the antimicrobial susceptibility of urinary pathogens have been changing over the years. Objectives: This work aimed to compare the accuracies of API 20E, Vitek1 system with GNI card with conventional reference biochemical tests for the identification of non-lactose fermenting Gram-negative bacilli in patients with urinary tract infection. Methodology: This study was conducted on 320 patients attending outpatient urology clinic. Physical, chemical, and microscopic examinations were done first to urine samples. Then, urine samples with pus cells <10 per high power field (HPF) or with bacterial cells or yeast were chosen for culture. These samples were 142 out 320 urine samples. These urine samples were isolated on nutrient, blood & MacConkey's agar media. Results: Standard bacteriological identification was done for all isolates (187 isolates) by colony morphology and microscopic examination. Only non-lactose fermenting Gram-negative bacilli (60 isolates) were further examined. Other growths were excluded. Motility test, biochemical reactions by conventional methods, API 20E, and vitek1 system with GNI card were done on non-lactose fermenting Gram-negative bacilli. Antibiotic susceptibility test by reference broth microdilution MIC procedure and Vitek1 system with GNI-108 card were done on non-lactose fermenting Gram-negative bacilli. One hundred thirty-five strains isolated from 94 hospitalized catheterized patients and fifty-two strains isolated from 48 outpatients sixty isolates (32.1%) were non-lactose fermenting Gram-negative bacilli. Out of them (thirty-one (16.5%) Pseudomonas aeruginosa, twenty (10.7%) Proteus mirabilis, six (3.2%) Proteus vulgaris, and three (1.6%) Providencia stuartii). After completion of supplemental tests, there was no difference between API 20E and vitek1 system in their ability to correctly identify Proteus mirabilis, Proteus vulgaris, and Providencia stuartii to the species level with there was difference between identifying isolates from Pseudomonas aeruginosa with vitek1 system. Conclusion: API 20E needs more time than vitek1 for identification of Proteus mirabilis, Proteus vulgaris, Providencia stuartii, and Pseudomonas aeruginosa, the most effective antibiotic against Pseudomonas aeruginosa isolates was ticarcillin/clavulant (77.4%), for Proteus mirabilis isolates were aztreonam and imipenem (each with 100%), for Proteus vulgaris isolates was imipenem (100%), and for Providencia stuartii isolates were amikacin, aztreonam, ciprofloxacin, imipenem, and TMP/SMX (100%).