Impact of target site mutations and plasmid associated resistance genes acquisition on resistance of Acinetobacter baumannii to fluoroquinolones

Abstract

Among bacterial species implicated in hospital-acquired infections are the emerging Pan-Drug Resistant (PDR) and Extensively Drug-Resistant (XDR) Acinetobacter (A.) baumannii strains as they are difficult to eradicate. From 1600 clinical specimens, only 100 A. baumannii isolates could be recovered. A high prevalence of ≥ 78% resistant isolates was recorded for the recovered isolates against a total of 19 tested antimicrobial agents. These isolates could be divided into 12 profiles according to the number of antimicrobial agents to which they were resistant. The isolates were assorted as XDR (68; 68%), Multi-Drug Resistant (MDR: 30; 30%), and PDR (2; 2%). Genotypically, the isolates showed three major clusters with similarities ranging from 10.5 to 97.8% as revealed by ERIC-PCR technique. As a resistance mechanism to fluoroquinolones (FQs), target site mutation analyses in gyrA and parC genes amplified from twelve selected A. baumannii isolates and subjected to sequencing showed 12 profiles. The selected isolates included two CIP-susceptible ones, these showed the wild-type profile of being have no mutations. For the ten selected CIP-resistant isolates, 9 of them (9/10; 90%) had 1 gyrA/1 parC mutations (Ser 81 → Leu mutation for gyrA gene and Ser 84 → Leu mutation for parC gene). The remaining CIP-resistant isolate (1/10; 10%) had 0 gyrA/1 parC mutation (Ser 84 → Leu mutation for parC gene). Detection of plasmid-associated resistance genes revealed that the 86 ciprofloxacin-resistant isolates carry qnrA (66.27%; 57/86), qnrS (70.93%; 61/86), aac (6')-Ib-cr (52.32%; 45/86), oqxA (73.25%; 63/86) and oqxB (39.53%; 34/86), while qepA and qnrB were undetected in these isolates. Different isolates were selected from profiles 1, 2, and 3 and qnrS, acc(6,)-ib-cr, oqxA, and oqxB genes harbored by these isolates were amplified and sequenced. The BLAST results revealed that the oqxA and oqxB sequences were not identified previously in A. baumannii but they were identified in Klebsiella aerogenes strain NCTC9793 and Klebsiella pneumoniae, respectively. On the other hand, the sequence of qnrS, and acc(6,)-ib-cr showed homology to those of A. baumannii. MDR, XDR, and PDR A. baumannii isolates are becoming prevalent in certain hospitals. Chromosomal mutations in the sequences of GyrA and ParC encoding genes and acquisition of PAFQR encoding genes (up to five genes per isolate) are demonstrated to be resistance mechanisms exhibited by fluoroquinolones resistant A. baumannii isolates. It is advisable to monitor the antimicrobial resistance profiles of pathogens causing nosocomial infections and properly apply and update antibiotic stewardship in hospitals and outpatients to control infectious diseases and prevent development of the microbial resistance to antimicrobial agents.