Antimicrobial Susceptibility And Resistance Mechanism Of Macrolide And Tetracycline Class Drugs Against Clinical Moraxella Catarrhalis Isolates

[Objective]1.To investigate the antimicrobial susceptibility of macrolide class drugs against the clinical Moraxella catarrhalis isolates and study the resistance mechanism of the macrolide class drugs in clinical Moraxella catarrhalis isolates.2.To investigate the antimicrobial susceptibility of tetracycline class drugs against the clinical Moraxella catarrhalis isolates and study the resistance mechanism of tetracycline class drugs in clinical Moraxella catarrhalis isolates.[Methods]1.Source of Clinical Bacterial Strains: In this study,The source of 207 clinical isolates of Moraxella catarrhalis were from the inpatients in Shenzhen Nanshan people’s Hospital.The isolates species were identified by the Phoenix 100 automated microbiology system and mass spectrometer.2.Antimicrobial Susceptibility Testing: We determined the MICs of Moraxella catarrhalis to the macrolide class drugs,including erythromycin,telithromycin,solithromycin and cethromycin,and the tetracycline class drugs,including minocycline,doxycycline,tigecycline,omadacycline and eravacycline by the agar dilution method in vitro.3.Bacteria DNA Isolation: the bacterial DNA were extracted according to the manufacturer’s protocol with DNeasy Blood and Tissue Kits(QIAGEN China,Zhang jiang Hi-Tech Park Pudong,Shanghai,PR China).The DNA were eluted by 100μl AE buffer(Qiagen)then stored at﹣20℃.4.PCR assay: Macrolide resistance genes(erm A,erm B,erm C,msr A,msr B and mef E/A)and tetracycline resistance genes(tet B,tet L,tet M,tet W,tet Q,tet O and tet K)were detected by PCR assay.[Results]1.The antimicrobial activity of the macrolide class drugs against clinical Moraxella catarrhalis isolates in vitro: According to the EUCAST standards,The resistance rate of strains to erythromycin was 23%,the resistance rate of strains to telithromycin was 2%.The MIC90 of Moraxella catarrhalis to solithromycin and cethromycin were 0.125μg/ml.2.Distribution of the macrolide class drugs resistance genes in clinical Moraxella catarrhalis isolates: No erythromycin resistance genes were found in this study.3.The antimicrobial activity of the tetracycline class drugs against clinical Moraxella catarrhalis isolates in vitro: According to the EUCAST standards,the frequence of clinical Moraxella catarrhalis isolates susceptible to doxycycline and minocycline were 97% and98%,respectively.The MIC90 of Moraxella catarrhalis to tigecycline,omadacycline and eravacycline were 0.125μg/ml.4.Distribution of the tetracycline class drugs resistance genes in clinical Moraxella catarrhalis isolates: In this study 136 Moraxella catarrhalis isolates(include resistence strains and sensitive strains)were carried with tet B;and 15 sensitive isolates were carried with tet L.[Conclusions]1.According to the EUCAST standards,The frequence of clinical Moraxella catarrhalis isolates from our hospital nonsusceptible to erythromycin should be alert.The clinical Moraxella catarrhalis isolates showed high susceptibility to the new macrolide class drugs.2.The commonly reported erythromycin resistance genes,including erm A,erm B,erm C,msr A,msr B and mef E/A,shouldn’t be responsible for the nonsusceptibility to erythromycin in clinical Moraxella catarrhalis from our hospital.3.The clinical Moraxella catarrhalis isolates showed high susceptibility to the new tetracycline class drugs.4.The tetracycline resistance genes,tet B or tet L,can be detected in some Moraxella catarrhalis stains,however their impact on the antibiotics susceptibility need to be further studied.