CONCURRENT ESBL PRODUCTION AND BIOFILM-FORMING POTENTIAL IN GRAM-NEGATIVE CLINICAL ISOLATES FROM A TERTIARY CARE HOSPITAL IN KARNATAKA WITH IMPLICATIONS FOR ANTIMICROBIAL STEWARDSHIP

Abstract

Extended-spectrum beta-lactamase (ESBL)-producing Gram-negative bacteria complicate empirical treatment and elevate healthcare costs in tertiary care settings. This prospective, single-center laboratory-based study aimed to evaluate eight classified culture media for Gram-negative recovery, confirm ESBL production using a comprehensive six-method phenotypic panel, quantify biofilm formation by three validated methods, analyze the statistical association between ESBL production and biofilm-forming capacity, and determine the antibiotic susceptibility and multidrug resistance (MDR/XDR) profile of ESBL-confirmed isolates. Of 125 consecutive clinical specimens, 100 (80.0%) yielded Gram-negative growth across seven species; the remaining 25 yielded no growth or non-qualifying organisms. Escherichia coli predominated (46.0%). MacConkey agar achieved the highest recovery (96.0%). ESBL production was phenotypically confirmed in 77 of 100 isolates (77.0%) using a comprehensive six-method panel comprising double disc synergy test (DDST), combination disc test (CDT), E-test for ESBL, MIC by agar dilution, inhibitor potentiated disc diffusion test (IPDD), and modified CLSI phenotypic confirmatory method using phenylboronic acid and EDTA (Boronic Acid-EDTA method). Biofilm was detected in 86 isolates (86.0%) by the microtiter plate reference method; ESBL-positive isolates showed significantly greater biofilm-forming capacity than ESBL-negative isolates (93.5% vs. 60.9%; OR = 9.26; 95% CI: 2.81-30.50; p < .001). Colistin susceptibility was universal (100%), and tigecycline retained high activity (94.8%). MDR was identified in 80.5% and XDR in 13.0% of ESBL-confirmed isolates. Consequently, tracking concurrent ESBL and biofilm profiles is crucial for effective antibiotic stewardship in Karnataka.