| Chapter one:Analysis on susceptibility of gentamicin against Neisseria gonorrhoeae isolated in Nanjing,ChinaObjective:The aim of our study was to investigate the antimicrobial susceptibility profiles of gonococcal strains isolated in Nanjing in 2016-2017,collect information on the in vitro susceptibility of gentamicin against clinical N.gonorrhoeae;analyse the susceptible trend of gentamicin from 2016 to 2017.Methods:N.gonorrhoeae isolates were collected consecutively from men with symptomatic urethritis attending the Nanjing STD Clinic between 2016 and 2017.The minimum inhibitory concentrations(MICs)for gentamicin,ceftriaxone,cefixime,penicillin,tetracycline,spectinomycin,ciprofloxacin and azithromycin were determined by agar dilution for each isolate.Chi-square(x2)testing was used to compare the resistance rates of N.gonorrhoeae to antimicrobials in different years.The p values of<0.05 were considered as statistically significant.Results:A total of 407 clinical N.gonorrhoeae isolates were collected and tested.84.3%(343/407)and 86.7%(353/407)of isolates were resistant to tetracycline and penicillin.12.0%(49/407)of isolates were azithromycin non-wild-type(NWT)strains,as the azithromycin MICs were>2mg/L.19.7%(80/407)of isolates displayed reduced susceptibility to ceftriaxone,14.5%(59/407)to cefixime.All strains were susceptible to spectinomycin,gentamicin and resistant to ciprofloxacin.100(24.6%)multi-drug resistant(MDR)strains were detected.Gentamicin MICs ranged from<4mg/L to 16mg/L;MIC50 was 8 mg/L,and MIC90 was 16mg/L.MIC50 and MIC90 of gentamicin for MDR strains were 8 mg/L.Conclusions:The gonococcal strains prevalent in Nanjing are generally sensitive to gentamicin,which may be used as an alternative to future gonorrhea treatment.Chapter two:Synergy testing of gentamicin in combination with three other antimicrobials against multidrug-resistant Neisseria gonorrhoeae strainsObjective:We aimed to evaluate the in vitro efficacy of gentamicin combined with azithromycin,ceftriaxone or ertapenem against multi drug-resistant(MDR)N.gonorrhoeae strains.Methods:103 N.gonorrhoeae strains(97 MDR strains and 6 strains with decreased susceptibility of ceftriaxone or cefixime)were selected.The antimicrobial gradient epsilometer test(E-test)method was used to evaluate the efficacy of three antimicrobial combinations against MDR isolates,namely gentamicin plus ceftriaxone,gentamicin plus azithromycin,and gentamicin plus ertapenem.The fractional inhibitory concentration index(FICI)was determined,and the FICI values were interpreted using the following criteria:synergy:?0.5;additivity:>0.5 to<1.0;indifference:>1.0 to<4.0 and antagonism:>4.0.The differences of the MICs of antimicrobial in alone and in combination were analyzed by applying the nonparametric Mann-Whitney's U-test.The P values of<0.05 were considered as statistically significant.Results:No antagonism was observed for any of the antimicrobial combinations against the 103 isolates.The MIC values of each antibiotic showed statistical difference(P<0.05)in the combination with other antibiotics.The combination of gentamicin with ertapenem displayed the highest level of synergistic effect(28.2%),its mean FICI value was 0.665,which is the lowest geometric mean FICI among all combinations.Gentamicin in combination with ceftriaxone or azithromycin showed synergistic effects in 14.6%or 7.8%of strains,and the geometric mean FICI value was 0.745,1.022,respectively.Conclusions:Combinations of gentamicin with azithromycin,ceftriaxone,and ertapenem did not show any antagonistic effects.Gentamicin combined with ertapenem displayed the highest rate of synergistic effect.These antimicrobial combinations may be used as alternative treatment for patients with gonorrhea,especially multidrug-resistant gonorrhea. |
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