Investigation of mutations in adeR and adeS gene regions in gentamicine resistant Acinetobacter baumannii isolates

This study evaluated the relationship between aminoglycoside resistance and the active efflux pump and investigated the role of the active efflux pump in resistance mechanisms. In addition, the mutations related to aminoglycoside resistance were investigated in Acinetobacter baumannii isolates obtained from different clinical specimens. The study included 32 A. baumannii isolates. They were identified and their susceptibilities were determined using conventional techniques and an automated system. Total genomic RNA, DNA and cDNA were obtained using commercial extraction kits. Primers for adeR and adeS were designed using sequences in GenBank. All isolates were subjected to polymerase chain reaction (PCR) to determine the presence of adeR and adeS. The PCR products were electrophoresed for the optimization study. Subsequently, real-time PCR was performed to determine the expression levels of the adeR and adeS genes. Sequence analysis of the two adeRS operons in our isolates showed five mutations differing from those of other isolates. Isolate A21 had three mutations: (Tyr31Phe), (Val136Ala) and (Leu142Ile); isolate A24 had two mutations: (Asn115His) and (Leu142Ile). In our study, the examined gene regions that play a role in the resistance mechanisms of A. baumannii were considered important. The results indicated that adeR and adeS expression clearly affect aminoglycoside resistance. However, gene expression alone does not seem sufficient to explain that. These results could help to design improved active efflux pump inhibitors.