Phenotypic And Molecular Characterization of Acinetobacter Species Isolated from Bloodstream Infections in Intensive Care Unit Patients

Abstract Background: In the demanding environment of intensive care units (ICUs), bloodstream infections (BSIs) attributed to Acinetobacter species represent a formidable clinical challenge. This is primarily driven by the pathogen's escalating multidrug-resistant (MDR) phenotypes, which severely restrict effective therapeutic avenues. Objective: The primary aim of this investigation was to comprehensively characterize Acinetobacter strains recovered from the blood of ICU patients exhibiting clinical signs of septicemia, with a specific focus on determining their phenotypic antibiotic susceptibility profiles and genotypically identifying key resistance determinants. Methods: A cross-sectional observational study was executed between July 2021 and June 2024 across the ICUs of two prominent tertiary care centers in Dhaka, Bangladesh: Combined Military Hospital and Kurmitola General Hospital. Blood specimens from a cohort of 301 patients with suspected septicemia were cultured. The resulting Acinetobacter isolates were subjected to rigorous antimicrobial susceptibility testing and polymerase chain reaction (PCR) analysis to detect underlying resistance genes. Results: Acinetobacter species were successfully isolated from 46 of the 301 patients, corresponding to a prevalence rate of 15.3%. Phenotypically, these isolates demonstrated alarmingly high resistance levels against ceftazidime (76.1%), followed closely by ceftriaxone and cotrimoxazole (both at 71.7%), cefixime (69.6%), and levofloxacin (63%). Moderate levels of resistance were noted for gentamicin (52.2%), amikacin (50%), netilmicin (47.8%), and piperacillin-tazobactam (43.5%). Notably, 28.3% of isolates were resistant to meropenem. Conversely, colistin and tigecycline retained high efficacy, with resistance rates of 0% and 2.2%, respectively. Molecular analysis of five representative isolates indicated a universal (100%) presence of blaNDM-1, blaCTX-M, and blaTEM-793 genes. Furthermore, blaOXA-48, blaCTX-M-15, blaSHV, and mphA were identified in 80% of these samples, while blaCMY-2 and blaCTX-M-2 were found in 40% and 20%, respectively. Genes such as blaCMY, blaKPC, and other CTX-M variants were absent. Conclusion: The findings highlight a substantial burden of MDR Acinetobacter spp. in ICU-related bloodstream infections, underpinned by intricate genetic mechanisms that include both ESBL and carbapenemase genes. While colistin and tigecycline currently remain viable therapeutic options, their long-term utility is threatened. These results advocate for continuous resistance surveillance, rigorous infection prevention protocols, and the incorporation of routine molecular diagnostics to steer targeted treatment and effective containment measures.