Molecular Characterization and Clonal Analysis of Carbapenem-Resistant Acinetobacter baumannii: Insights Into Biofilm-Related Gene Coexistence in Clinical Isolates.

Abstract

The emergence of multidrug-resistant Acinetobacter baumannii (MDR A. baumannii) and biofilm-producing ability have become a worldwide serious concern. This study is aimed at investigating the clonal relationships, coexistence of carbapenemase-resistant and biofilm-related genes, and biofilm biomass capacity in 57 A. baumannii isolates obtained from patients in intensive care units (ICUs). Antibiotic resistance patterns to 11 antibiotics were determined using the disc diffusion test. The minimum inhibitory concentrations (MICs) of imipenem and colistin were evaluated by the microdilution method. All isolates were subjected to PCR for the detection of carbapenemase- and biofilm-related genes and examined for the biofilm-forming ability using crystal violet staining methods. The clonality relationship was identified by rep-PCR. Overall, 49 (86%) isolates were characterized as extensively drug-resistant (XDR) with a high MIC for imipenem. Eight isolates were resistant to colistin (MIC>64 μg/mL). Additionally, 86.21% of isolates were strong biofilm formers, which correlated with the PDR phenotype. All isolates carried at least three genes related to biofilm formation. Genotypically, 100% of isolates had bla _OXA-51-like, bla _OXA-24-like, and bla _TEM genes, followed by bla _VIM (61.4%), bla _OXA-23-like (24.6%), bla _SHV (1.8%), and bla _KPC (1.8%), whereas bla _CTX-M and bla _OXA-58-like genes were not found in the isolates. The rep-PCR analysis identified 10 distinct genotypes, among which GTG Type 3 showed a significant correlation with strong biofilm formation. Moreover, the greatest number of colistin-resistant isolates (MIC>64 μg/mL) were located in this cluster. This study highlights the emergence of PDR A. baumannii strains carrying a variety of β-lactamase and biofilm-related genes in ICUs, underscoring the urgent need for improved infection control measures and antimicrobial stewardship programs to address the spread of these formidable pathogens.