Screening of quinolone resistance determinants in ciprofloxacin-resistant Acinetobact-er baumannii isolates / 军事医学

ABSTRACT

Objective To investigate the quinolone resistance determinants in ciprofloxacin-resistant Acinetobacter bau-mannii (ABA)clinical isolates.Methods One hundred and fourteen ciprofloxacin-resistant ABA strains were collected from six Chinese hospitals .The quinolone resistance determining region ( QRDR) of 4 target genes ( gyrA, gyrB, parC and parE) was amplified , sequenced and compared with the reference genome of ATCC 17978 to identify possible resistance-related mutations.Nine plasmid-mediated quinolone resistance (PMQR) genes (qnrA, qnrB, qnrC, qnrD, qnrS, qepA, aac(6′)-Ⅰb-cr, oqxA and oqxB) were also amplified, and the amplicons were then sequenced to determine their character-istics.Results Almost all isolates (113/114, 99.1%) harbored a substitution in codon 83 of gyrA gene, leading to a Ser83Leu mutation.Meanwhile,58.8%(67/114) of the isolates possessed dual mutations of GyrA-Ser83Leu and GyrA-Ser80Leu, which were known determinants for ciprofloxacin resistance .There were also multiple non-synonymous substitu-tions in gyrB, leading to Arg393Ser, Arg393Cys, Thr401Ala, Pro406Ser, Val430Phe, Cys440Ser and Gly480Arg muta-tions with prevalence rates of 95.6%, 0.9%, 96.5%, 96.5%, 100%, 96.5%and 96.5%,respectively.For parE, all the seven mutations were synonymous and found in more than 96%of the tested isolates.For PMQR genes, although 83.3%(95/114) of the isolates were positive for aac(6′)-Ⅰb, nocrmutations were identified.None of the other eight PMDR genes were found in our strain collection .Conclusion Although multiple mutations are identified in gyrB and parE, these mutations might be the characteristic SNP markers for specific clones , unlikely linked to quinolone resistance .No PMQR is found in the tested isolates.Mutations in chromosomal QRDR (GyrA-Ser83Leu and ParC-Ser80Leu) are the main determi-nants of ciprofloxacin resistance in our ABA collection .