Phenotypic Activity of Efflux Pumps by Carbonyl Cyanide M-Chlorophenyl Hydrazone (CCCP) and Mutations in GyrA and ParC Genes Among Ciprofloxacin-Resistant Acinetobacter baumannii Isolates

Acinetobacter baumannii is one of the major bacteria causing nosocomial infections. The emergence of multidrug-resistant (MDR) isolates causes morbidity and mortality and lead to financial burdens for patients and public health systems.

Regarding the use of ciprofloxacin and increase of ciprofloxacin resistance, this study was aimed to investigate the role of the efflux pump and mutations in gyrA and parC genes as the mechanisms of ciprofloxacin-resistance.

This study was conducted on 55 strains of A. baumannii isolated from the patients hospitalized in Milad Hospital, Tehran. The isolates were identified by biochemical tests, and their antibiotic susceptibility was assessed by the disc diffusion method. To investigate the role of the efflux pump, minimum inhibitory concentration (MIC) of ciprofloxacin was determined in the presence and absence of the carbonyl cyanide m-chlorophenyl hydrazone (CCCP) inhibitor. The PCR was used for amplification of gyrA, and parC genes and sequencing of its products was carried out to track the mutations.

The highest and lowest antibiotic resistance were observed in ciprofloxacin (100%) and tobramycin (52.7%), respectively. Moreover, 96% of the A. baumannii isolates exhibited MDR. Five percent of strains showed 4-fold MIC reduction after the use of the inhibitor and were reported as the strains with high activity efflux pump. In 100% of the isolates, gyrA and parC genes were detected, and only one mutation was observed in parC and gyrA genes in the studied isolates that altered amino acid type.

Reduction in MIC in the presence of an efflux pump inhibitor confirmed its role in enhancing the resistance to ciprofloxacin in some isolates. The results of this study also revealed no significant relationship between the ciprofloxacin resistance of the studied isolates and mutation in the encoding region of parC and gyrA genes. Thus, the significance of other mechanisms, such as the expression of genes encoding efflux pump proteins, should not be neglected.