Characterization and Antibiotic Resistance Profile of Biofilm Forming Pseudomonas aeruginosa Isolated from Infected Wounds

Abstract

Pseudomonas aeruginosa is a leading cause of chronic and hard-to-heal wound infections due to its strong ability to form biofilms and develop multidrug resistance. Biofilm-associated growth significantly limits antibiotic penetration and promotes persistent infection, making treatment challenging. This study aimed to determine the prevalence, biofilm-forming ability, and antimicrobial susceptibility patterns of P. aeruginosa isolated from infected wounds. A total of 248 wound swab samples were aseptically collected from in-patients and out-patients presenting with clinical evidence of wound infection in hospitals within Enugu metropolis. Samples were cultured on Blood agar and MacConkey agar plates and incubated aerobically at 37 °C for 24–48 hours and isolates were identified using standard microbiological and biochemical tests. Antibiotic susceptibility testing was performed using the Kirby–Bauer disk diffusion method following CLSI guidelines. Also, biofilm formation was detected using Congo Red Agar (CRA). A total of 248 wound swab samples were collected from patients with clinically diagnosed wound infections and analyzed. Out of these, 184 samples (74.2%) yielded significant bacterial growth, while 64 samples (25.8%) showed no bacterial growth after 24–48 hours of incubation. Among the positive cultures, Gram –negative bacteria were 61.4% and Pseudomonas aeruginosa had 56 isolates (30.4%) which were the predominant isolates. Out of the 248 samples that were analysed, 184 samples (74.2%) showed significant bacterial growth, and P. aeruginosa had 56 isolates (30.4%) which were the predominant isolates. Antimicrobial susceptibility testing of all P. aeruginosa isolates was performed using the Kirby–Bauer disk diffusion method. High resistance was observed against commonly used antibiotics: Cefotaxime (80.4%), Ceftazidime (75.0%), Ciprofloxacin (69.6%), Gentamicin (62.5%) and Ofloxacin (58.9%). Moderate susceptibility was observed with Piperacillin–tazobactam (59.0%), Imipenem (55.4%) and Meropenem (51.8%) while the highest susceptibility was seen in amikacin, with 64.3% sensitivity. All 56 P. aeruginosa isolates were screened for biofilm formation using the Congo Red Agar (CRA) method. It was observed that 24 isolates (42.9%) were strong biofilm formers, 18 (32.1%) were moderate/weak while 14 (25.0%) isolates did not form biofilms. The high prevalence of biofilm formation shows the organism’s inherent ability to establish persistent infection, particularly in chronic wound environments where biofilm facilitates adhension, protects bacteria from host defenses and significantly reduces antibiotic penetration which will lead to resistance. These findings emphasize the clinical relevance of biofilm formation as a key virulence mechanism contributing to antimicrobial resistance and treatment failure in Pseudomonas aeruginosa wound infections.