The effects of active efflux pumps on antibiotic resistance in Pseudomonas aeruginosa.

In this study, we investigated the roles of active efflux pumps in antibiotic resistance. The transcription efflux pump genes were analyzed by real-time polymerase chain reaction (qPCR) to determine their role in drug resistance. Antibiotic sensitivity testing was carried out using the Vitek 2 automated system (bioMérieux, France). Isolates were divided into four groups according to their resistance status: multiple-drug resistant (MDR), isolated carbapenem resistant (ICR), isolated quinolone resistant (IQR), and carbapenem and quinolone resistant (CQR). Transcript levels of mexB, mexD, mexF, and mexY were analyzed by qPCR using a LightCycler instrument (Roche, Germany). The genetic similarity between isolates was determined using arbitrarily primed PCR (AP-PCR). Among the 50 isolates investigated, the frequency of genes classified as overexpressed were 88 % for mexD, 76 % for mexB, 46 % for mexF, and 40 % for mexY. Within the MDR group, mexB was overexpressed in 15 of 22 isolates, mexD in 20 of 22, mexF in 15 of 22, and mexY in 19 of 22. In the ICR group, isolates mexB and mexD were each overexpressed in five isolates. mexD overexpression was observed in all seven CQR isolates. Within the IQR group, mexB and mexD were overexpressed in all 12 isolates. mexF overexpression was detected in 7 of 12 isolates in this group. 18 distinct banding patterns were determined by AP-PCR. Increased transcription of mexB was directly correlated with meropenem resistance in the majority of isolates tested, while MexCD-OprJ and MexEF-OprN were related to quinolone resistance; the MexCD-OprJ efflux pump was also related to multidrug resistance. Increased transcription of mexY may contribute to the gentamicin resistance.