Insights on carbapenem-resistant Acinetobacter baumannii: Phenotypic characterization of relevant isolates

Abstract

Acinetobacter baumannii (A. baumannii) is an important nosocomial pathogen, which may be a causative agent in a wide-range of human pathologies. Carbapenems are usually considered the last safe and eff ective choice of drugs for the treatment of Gram-negative infections. The emergence of carbapenem-resistant A. baumannii (CRAB) is a critical public health issue as they leave clinicians with limited therapeutic options. In this study, phenotypic methods were used to characterize sixty-Two (n = 62) A. baumannii isolates, which were included based on their suspected non-susceptibility to meropenem. Minimum inhibitory concentrations (MICs) of meropenem, levofl oxacin, gentamicin, sulfamethoxazole/trimethoprim, tigecycline were determined using E-Tests, while colistin MICs were determined using broth microdilution. The isolates were subjected to the modifi ed Hodge test (MHT), the modifi ed carbapenem-inactivation method (mCIM) and the imipenem/EDTA combined disk test (CDT). Effl ux pump overexpression was studied using agar plates containing phenylalanine-Arginine ?-naphthylamide (PA?N). Assessment of biofi lm-formation was carried out using the crystal violet tube-Adherence method. 64.5% of the strains showed meropenem MICs in the resistant range (8 mg/L), resistance rates were similarly high to the other tested antibiotics. The MHT and mCIM assay were positive in 79.0% and 67.7% of cases, respectively; the presence of an MBL was suggested for 29.0% of isolates. Effl ux-pump overexpression was seen in 12.9% of isolates. 54.8% of the isolates were characterized as strong biofi lm-producers. Microbiology laboratories have an important role in diff erentiating the distinct mechanisms by which these pathogens develop the CRAB phenotype, as plasmid-borne carbapenemases are signifi cant from the standpoint of public health microbiology.