Determination of Different Fluoroquinolone Mechanisms Among Clinical Isolates of Acinetobacter baumannii in Tehran, Iran

Acinetobacter baumannii isolates resistant to fluoroquinolones, such as levofloxacin and ciprofloxacin are being increasingly developed every day.
In this study, ciprofloxacin resistance in A. baumannii isolates was determined by the presence or absence of efflux pump inhibitors, as the efflux pumps play an important role in the creation of ciprofloxacin resistance.
One hundred and three Acinetobacter isolates were collected from ventilator-associated pneumonia (VAP) and burn patients of Tehran hospitals, Iran, during six months of 2014. Susceptibility rates of the isolates to levofloxacin and ciprofloxacin antibiotics were assessed using the agar disk diffusion and broth microdilution. The effects of the efflux pump inhibitors including phenylalanine-arginine β-naphthylamide (PAβN) and 1-(1-naphtylmethyl)-piperazine (NMP) on ciprofloxacin resistance were investigated. Further, the quinolone resistance qnrA, qnrB, qnrS, and adeABC genes were evaluated using the polymerase chain reaction (PCR) test. Finally, to examine the mutation in quinolone resistance-determining regions, the PCR products of the gyrA and parC genes were sequenced.
According to the results of the antibiogram test, 74.7% and 33% of the studied isolates were resistant to ciprofloxacin and levofloxacin, respectively. Also, there was a significant relationship between the type of the specimen and resistance to ciprofloxacin (P = 0.02) and resistance to levofloxacin (P = 0.04). As for the synergistic study of the inhibitors with ciprofloxacin, the reduction of minimum inhibitory concentration (MIC) was observed in 40% and 56.6% of the isolates in the presence of PAβN and NMP, respectively. The prevalence rates of qnrA, qnrB, qnrS, AdeA, AdeB, and AdeC genes were 0%, 0%, 3.9%, 100%, 100% and 100%, respectively. In all the resistant isolates, mutation of in the gyrA gene was observed, but no mutation was seen in the parC gene.
The presence of the efflux pumps and the gyrA gene mutation are still considered as the most important factors causing fluoroquinolone resistance; however, identification of the qnr genes for the first time in Tehran hospitals, Iran, can lead to further concerns in the future.