Nontypeable Haemophilus influenzae isolates from the lower respiratory tract in Western Sichuan, China: MIC value of ofloxacin and Mutation characteristics of Quinolones Resistance determining region gene

Abstract Background: Fluoroquinolones are one of the most widely used antibiotics in the treatment of respiratory tract infections, and the mechanism of resistance to fluoroquinolones is considered to be related to the amino acid substitution of gyrA, gyrB, parC, and parE, the Quinolone Resistance-Determining Regions (QRDRs) of DNA cyclase type II topoisomerase and IV topoisomerase. The purpose of this study was to explore the molecular mechanism of quinolone resistance of Nontypeable Haemophilus influenzae(NTHi ) isolates and analyze the mutation law of the QRDRs gene. Results: MIC value of ofloxacin of 280 NTHi isolates from lower respiratory tract secretions in children group during 2003~2004 and in whole age group during 2013~2014 in Western Sichuan, China were monitored and the amino acid sequences of gyrA, gyrB, parC and parE gene in QRDRs were detected. The resistance rate of ofloxacin in adult group was 1.92% (n=52), while the NTHi strains with ofloxacin MIC value≥0.5 showed an upward trend in all age groups. No ofloxacin-resistant strains were found in 57 NTHi strains isolated from the children patient. Four amino acid substitutions were found in GyrA genes, four in GyrB, three in parC and nine in parE genes. The results showed that different amino acid replacement patterns of the gyrA , gyrB, parC and parE gene had different effects on ofloxacin MIC values. Conclusions: Ser-84-leu and asp-88-tyr/asn mutation of the gyrA, ser-84-lys/ile and ser -133-ala mutations of the parC and ala-400-val variation of the gyrB were the main factors leading to the increase of MIC value of ofloxacin of NTHi strains in Western Sichuan, China. It can be predicted that with the increase of quinolones exposure, the susceptibility of isolates from children to quinolones will be further reduced.