Effect of Phenylalanine-arginine-beta-naphthylamide to Ciprofloxacin Minimum Inhibitory Concentration Values and Expression of Efflux Pump System Genes in Acinetobacter baumannii Isolates

The most realistic approach in recent years is researching the resistance inhibition rather than synthesizing new compounds. In this study, we aimed to determine i) the effect of phenylalanine-argininebeta-naphthylamide (PAβN), on minimum inhibition concentrations (MICs) of ciprofloxacin (CIP), ii) to obtain the CIP+PAβN concentration that inhibits CIP resistance and iii) to show that this inhibition is caused by the effect of PAβN on the expression of efflux pump (EF) system genes. Acinetobacter baumannii isolates were collected from Trakya University Hospital. In 67 isolates determined to be resistant to CIP, CIP susceptibility was investigated in presence of PAβN once again. Isolates determined to have four or more fold decrease in ciprofloxacin MIC values were included in checkerboard assay and quantitative real-time reverse transcriptase polymerase chain reaction (qrRT-PCR). Fractional inhibition concentrations (FICs) were calculated through the PAßN concentrations that inhibit ciprofloxacin resistance, by the checkerboard assay results. With the combination of CIP+PAβN, the effect of the concentrations at which inhibition occurs, to the expression levels of EF system genes (adeA, adeB, adeR, adeS, adeF, adeG, adeH, adeL) was investigated by qrRT-PCR. By the checker board assay, a synergistic effect was determined between PAßN and CIP in 11 isolates, while in other isolates the effect was determined to be additive. In some isolates resistant to CIP, CIP + PAβN combination inhibited the resistance and increased CIP susceptibility. In the presence of 25 mg/L and 100 mg/L PAβN, 22 (32.83%) and 27 (40.3%) of 67 isolates became sensitive to CIP, respectively. In seven isolates, 12.5 µg/ml PAβN concentration eliminated CIP resistance by decreasing CIP MIC value to 1 µg/ml. Also, in one isolate the MIC value was 0.5 µg/ml in the presence of 25 µg/ml PAβN and 1 µg/ml in the presence of 1.5625 µg/ml PAβN. After analyzing the expression levels of EF genes (adeA, adeB, adeC, adeF, adeG, adeH, adeL, adeR and adeS) by the qRt-PCR method, it was determined that with the addition of PAβN to media containing CIP, the expression levels of the genes decreased (p<0.05). The aim of the study has been achieved with the results obtained. These results highlighted the importance of research on the inhibition of resistance, as well as the synthesis of new antimicrobial compounds. Combined use of inhibitors and antibiotics should be considered as an alternative treatment method. Thus, existing antibiotics can be included in the treatment again, saving time and money. It will be possible to use these findings in further studies to elucidate the mechanism of action of new inhibitor candidate compounds and associate them with the expression of DAP genes, also by investigating mutations in the regulatory gene regions in isolates with over-expression levels.