IN VITRO EVALUATION OF ANTIBIOTIC SYNERGY AGAINST BIOFILM-FORMING PSEUDOMONAS AERUGINOSA ISOLATED FROM POST-CESAREAN SURGICAL SITE INFECTIONS AND ITS MOLECULAR RESISTANCE PROFILE

Abstract

Background: Biofilm-associated Pseudomonas aeruginosa infections complicate post-cesarean surgical site infections (SSIs) and contribute to treatment failure. Objective: To evaluate antimicrobial susceptibility, disc-diffusion–based synergy of selected antibiotic pairs against biofilm-forming P. aeruginosa, and molecular detection of a carbapenemase gene (blaVIM) and a biofilm-associated gene (pelA). Methodology: This prospective in-vitro study was conducted after the approval of IRB of Azra Naheed Dental College, Superior University, from Aug 25 to Feb 26, on 100 cultured pus swabs from post-cesarean SSIs. Isolates were identified using standard microbiological methods. Biofilm formation was assessed using crystal violet ring assay. Antimicrobial susceptibility testing was done by Kirby–Bauer disc diffusion on Mueller–Hinton agar following CLSI guidance. Synergy testing involved paired discs, 20mm apart, interpreted qualitatively and by an interaction-zone size (≥18 mm) indicating synergy. PCR was used for blaVIM and pelA detection in a subset of biofilm-forming isolates. Results: Seventy-seven (77%) samples were culture-positive, and P. aeruginosa were 32/77 (41.5%), and biofilm was seen in 24/32 (75%). Resistance among P. aeruginosa was high to meropenem (83%) and imipenem (75%), and ciprofloxacin (75%). Among biofilm-forming isolates (n=24), synergy was most frequent with meropenem+gentamicin (22/24, 91.7%) and meropenem+ciprofloxacin (20/24, 83.3%), while cefixime-based combinations reported limited synergy (≤12.5%). blaVIM was detected in 5/8 tested isolates and pelA in 5/8. Conclusions: Biofilm-forming P. aeruginosa was common in post-cesarean SSIs and reported significant resistance to tested antipseudomonal agents. Meropenem combined with gentamicin or ciprofloxacin reported strong in-vitro synergistic activity, indicating further validation using quantitative synergy, biofilm-eradication assays and in-vivo studies.