Exploring the Genetic and Morphological Basis of Biofilm-Linked Drug Resistance in Clinical Isolates of Acinetobacter baumannii

Background Acinetobacter baumannii is a major nosocomial pathogen combining multidrug resistance (MDR) with strong biofilm-forming ability, enabling persistence on medical devices. Studying the correlation between biofilm-related genes and antibiotic resistance is critical for successful infection management. This study aimed to determine the prevalence of antibiotic resistance, phenotypic biofilm formation (by Congo red agar (CRA) and tissue culture plate (TCP) methods), and selected biofilm-associated genes (bap, csuD, ompA, blaper-1) in 153 clinical A. baumannii isolates from respiratory specimens, which were further characterized using scanning electron microscopy (SEM) analysis. In addition, the study aimed to evaluate the association between these genes, biofilm strength, and drug resistance patterns. Methodology In this study, an investigation was performed on 153 respiratory isolates from the laboratory of the Department of Microbiology at a tertiary care hospital (2022-2024). The Kirby-Bauer method was used for antibiotic susceptibility testing and minimum inhibitory concentration for colistin following the 2022 Clinical and Laboratory Standards Institute norms. Biofilm testing was performed using the CRA and TCP methods and validated by SEM and genetic analysis of biofilm association genes such as bap, csuD, ompA, and blaPER-1. Results The present study demonstrated an extremely high rate of antibiotic resistance, with meropenem resistance observed in 152 (99.3%) isolates and ceftriaxone resistance in 148 (96.7%) isolates. Regarding biofilm formation, the TCP method identified 85 (55.6%) isolates as biofilm producers, whereas the CRA method detected 57 (37.3%) isolates. Strong biofilm-producing isolates identified by the TCP method were confirmed by SEM to exhibit dense, mature biofilm structures. Genotypic analysis revealed csuD (99, 64.7%) and bap (82, 53.6%) as the most prevalent genes, both significantly associated with strong biofilm formation (p < 0.05). The combined presence of bap + csuD (51, 33.3%) showed a strong correlation with enhanced biofilm strength in the TCP assay (p < 0.05). Conclusions High MDR and strong biofilm formation were observed in A. baumannii, with a significant association between biofilm and antibiotic resistance. The csuD gene and bap + csuD combination correlated with increased resistance and biofilm production. SEM confirmed dense biofilm architecture, highlighting their role in virulence and persistence.