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This study was conducted to determine the in vitro activities of gentamicin alone and in combination with ceftriaxone, ertapenem, and azithromycin against multidrug-resistant (MDR) Neisseria gonorrhoeae isolates. A total of 407 clinical isolates from Nanjing, China, obtained in 2016 to 2017, had MICs determined for gentamicin using the agar dilution method. MDR status was ascribed to 97 strains that displayed decreased susceptibility or resistance to extended-spectrum cephalosporins (ESCs) (ceftriaxone [MIC, ≥0.125 mg/liter] and cefixime [MIC, ≥0.25 mg/liter]), plus resistance to at least two of the following antimicrobials: penicillin (MIC, ≥2 mg/liter), ciprofloxacin (MIC, ≥1 mg/liter), and azithromycin (MIC, ≥1 mg/liter). MDR strains underwent MIC determinations for antimicrobial combinations using the antimicrobial gradient epsilometer test (Etest). Results that ranged from synergy to antagonism were interpreted using the fractional inhibitory concentration (FICI). All 407 gonococcal isolates were susceptible to gentamicin; MICs ranged from 2 mg/liter to 16 mg/liter. Synergy was demonstrated in 16.5% (16/97), 27.8% (27/97), and 8.2% (8/97) of MDR strains when gentamicin was combined with ceftriaxone (geometric mean [GM] FICI, 0.747), ertapenem (GM FICI, 0.662), and azithromycin (GM FICI, 1.021), respectively. No antimicrobial antagonism was observed with any combination tested against MDR strains; overall, antimicrobial combinations were indifferent. The GM MICs of gentamicin were reduced by 2.63-, 3.80-, and 1.98-fold when tested in combination with ceftriaxone, ertapenem, and azithromycin, respectively. The GM MICs of the three additional antimicrobials individually were reduced by 3-, 2.57-, and 1.98-fold, respectively, when each was tested in combination with gentamicin. Gentamicin alone was effective in vitro against N. gonorrhoeae, including MDR isolates. Combination testing of MDR strains showed lower MICs against gentamicin and each of three antimicrobials (ceftriaxone, ertapenem, and azithromycin) when used in combination. IMPORTANCE Antimicrobial-resistant Neisseria gonorrhoeae is a major global public health concern. New treatment options are urgently needed to successfully treat multidrug-resistant (MDR) Neisseria gonorrhoeae infections. This study showed that gentamicin maintained excellent in vitro susceptibility against clinical gonococcal isolates collected in 2016 and 2017, including MDR isolates. Combinations of gentamicin plus ertapenem, ceftriaxone, and azithromycin produced synergistic effects against certain MDR isolates. No antagonism was observed in any of the antimicrobial combinations, which may prove useful to guide clinical testing of combination therapies.

ObjectivesTo determine in vitro activities of gentamicin alone and in combination with ceftriaxone, ertapenem and azithromycin against multidrug-resistant (MDR) N. gonorrhoeae isolates.Methods407 isolates from Nanjing, China, obtained in 2016 and 2017, had minimum inhibitory concentrations (MICs) determined for gentamicin using the agar dilution method. Antimicrobial combinations were also tested in 97 MDR strains using the antimicrobial gradient epsilometer test (Etest); results ranging from synergy to antagonism were interpreted using the fractional inhibitory concentration (FICI).ResultsAll 407 gonococcal isolates were susceptible to gentamicin. MICs ranged from 2 mg/L to 16 mg/L. Synergy was demonstrated in 16.5%(16/97), 27.8%(27/97) and 8.2%(8/97) MDR strains when gentamicin was combined with ceftriaxone [geometric mean (GM) FICI; 0.747], ertapenem (GM FICI; 0.662) and azithromycin (GM FICI; 1.021), respectively. No antimicrobial antagonism was observed with any combination. The three antimicrobial combinations were indifferent overall. The overall GM MICs of gentamicin were reduced by 2.63-, 3.80- and 1.98-fold when tested in combination with ceftriaxone, ertapenem and azithromycin, respectively. The GM MICs of the three antimicrobials by themselves were reduced by 3-, 2.57- and 1.98-fold respectively, when each was tested in combination with gentamicin. No antimicrobial antagonism was observed with any combination.ConclusionsGentamicin alone was effective in vitro against MDR N. gonorrhoeae and in combination with ceftriaxone, ertapenem or azithromycin. Combination testing of resistant strains, overall, showed lower effective MICs against gentamicin itself and each of the three antimicrobials when used in combination with gentamicin.

Previously, we reported the potent activity of a novel spiropyrimidinetrione, zoliflodacin, against Neisseria gonorrhoeae isolates collected in 2013 from symptomatic men in Nanjing, China. Here, we investigated trends of susceptibilities to zoliflodacin in 986 isolates collected from men between 2014 and 2018. N. gonorrhoeae isolates were tested for susceptibility to zoliflodacin and seven other antibiotics. Mutations in the gyrA, gyrB, parC, parE, and mtrR genes were determined by PCR and sequencing. The MICs of zoliflodacin ranged from ≤0.002 to 0.25 mg/liter; the overall MIC50 and MIC90 were 0.06 mg/liter and 0.125 mg/liter, respectively, in 2018, increasing 2-fold from 2014. However, the percentage of isolates with lower zoliflodacin MICs declined in each year sequentially, while the percentage with higher MICs increased yearly (P ≤ 0.00001). All isolates were susceptible to spectinomycin but resistant to ciprofloxacin (MIC ≥ 1 mg/liter); 21.2% (209/986) were resistant to azithromycin (≥1 mg/liter), 43.4% (428/986) were penicillinase-producing N. gonorrhoeae (PPNG), 26.9% (265/986) were tetracycline-resistant N. gonorrhoeae (TRNG), and 19.4% (191/986) were multidrug-resistant (MDR) isolates. 202 isolates with the lowest (≤0.002 to 0.015 mg/liter) and highest (0.125 to 0.25 mg/liter) zoliflodacin MICs were quinolone resistant with double or triple mutations in gyrA; 193/202 (95.5%) also had mutations in parC There were no D429N/A and/or K450T mutations in GyrB identified in the 143 isolates with higher zoliflodacin MICs; an S467N mutation in GyrB was identified in one isolate. We report that zoliflodacin continues to have excellent in vitro activity against clinical gonococcal isolates, including those with high-level resistance to ciprofloxacin, azithromycin, and extended-spectrum cephalosporins.

Previously, we reported potent activity of a novel spiropyrimidinetrione, zoliflodacin, against N. gonorrhoeae isolates from symptomatic men in Nanjing, China, collected in 2013. Here, we investigated trends of susceptibilities of zoliflodacin in 986 gonococcal isolates collected from men between 2014 and 2018. N. gonorrhoeae isolates were tested for susceptibility to zoliflodacin and seven other antibiotics. Mutations in gyrA, gyrB, parC and parE genes were determined by PCR and DNA sequencing. The MIC of zoliflodacin for N. gonorrhoeae ranged from ≤0.002 to 0.25 mg/L; the overall MIC50s and MIC90s were 0.06 mg/L and 0.125mg/L in 2018, increasing two-fold from 2014. However, the percent of isolates with lower zoliflodacin MICs declined in each year sequentially while the percent with higher MICs increased yearly (P≤0.00001). All isolates were susceptible to spectinomycin but resistant to ciprofloxacin (MIC ≥1 μg/ml); 21.2% (209/986) were resistant to azithromycin (≥1 μg/ml), 43.4% (428/986) were penicillinase-producing (PPNG), 26.9% (265/986) tetracycline-resistant (TRNG) and 19.4% (191/986) were multi-drug resistant (MDR) isolates. Among 143 isolates with higher zoliflodacin MICs (0.125-0.25 mg/L), all had quinolone resistance associated double or triple mutations in gyrA; 139/143 (97.2%) also had mutations in parC. There were no D429N/A and/or K450T mutations in GyrB identified in the 143 isolates with higher zoliflodacin MICs; a S467N mutation in GyrB was identified in one isolate. We report that zoliflodacin has excellent in vitro activity against clinical gonococcal isolates, including those with high-level resistance to ciprofloxacin, azithromycin and extended spectrum cephalosporins.

Previously, we reported the potent activity of a novel spiropyrimidinetrione, zoliflodacin, against Neisseria gonorrhoeae isolates collected in 2013 from symptomatic men in Nanjing, China. Here, we investigated trends of susceptibilities to zoliflodacin in 986 isolates collected from men between 2014 and 2018. N. gonorrhoeae isolates were tested for susceptibility to zoliflodacin and seven other antibiotics., Previously, we reported the potent activity of a novel spiropyrimidinetrione, zoliflodacin, against Neisseria gonorrhoeae isolates collected in 2013 from symptomatic men in Nanjing, China. Here, we investigated trends of susceptibilities to zoliflodacin in 986 isolates collected from men between 2014 and 2018. N. gonorrhoeae isolates were tested for susceptibility to zoliflodacin and seven other antibiotics. Mutations in the gyrA, gyrB, parC, parE, and mtrR genes were determined by PCR and sequencing. The MICs of zoliflodacin ranged from ≤0.002 to 0.25 mg/liter; the overall MIC50 and MIC90 were 0.06 mg/liter and 0.125 mg/liter, respectively, in 2018, increasing 2-fold from 2014. However, the percentage of isolates with lower zoliflodacin MICs declined in each year sequentially, while the percentage with higher MICs increased yearly (P ≤ 0.00001). All isolates were susceptible to spectinomycin but resistant to ciprofloxacin (MIC ≥ 1 mg/liter); 21.2% (209/986) were resistant to azithromycin (≥1 mg/liter), 43.4% (428/986) were penicillinase-producing N. gonorrhoeae (PPNG), 26.9% (265/986) were tetracycline-resistant N. gonorrhoeae (TRNG), and 19.4% (191/986) were multidrug-resistant (MDR) isolates. 202 isolates with the lowest (≤0.002 to 0.015 mg/liter) and highest (0.125 to 0.25 mg/liter) zoliflodacin MICs were quinolone resistant with double or triple mutations in gyrA; 193/202 (95.5%) also had mutations in parC. There were no D429N/A and/or K450T mutations in GyrB identified in the 143 isolates with higher zoliflodacin MICs; an S467N mutation in GyrB was identified in one isolate. We report that zoliflodacin continues to have excellent in vitro activity against clinical gonococcal isolates, including those with high-level resistance to ciprofloxacin, azithromycin, and extended-spectrum cephalosporins.

Background The aim of this study is to monitor the trend in antimicrobial resistance in Neisseria gonorrhoeae in Nanjing, China. Gonococcal strains isolated during 2015–2018 were examined for susceptibility to seven antibiotics and compared with results from 2013–14 (Antimicrob Agents Chemother, 2018) Methods 1173 gonococcal strains were isolated from men with urethritis; n=789 (2015–18), compared with n=384 (2013–14). MICs for seven antibiotics were determined by agar dilution method. Criteria for decreased susceptibility to ceftriaxone (MIC≥0.125 mg/L) and cefixime (MIC≥0.25 mg/L) were defined by WHO. Using CLSI and EUCAST (for azithromycin only) criteria, the following MIC breakpoints were used to ascertain resistance: ≥128 mg/L, spectinomycin; ≥2 mg/L, penicillin and tetracycline and ≥1 mg/L, ciprofloxacin and azithromycin. Resistance determinants were investigated using WGS of two isolates which were resistant to both ceftriaxone and cefixime. Results The percentage of isolates with decreased susceptibility to ceftriaxone rose from 9.9% in 2013–14 to 23% in 2016 and decreased to 16.7% in 2018 (P=0.01). The percentage of isolates with decreased susceptibility to cefixime rose from 0.3% (2013–14) to 15.7% in 2016 and decreased to 13.7% in 2018 (P Conclusion The proportion of N. gonorrhoeae isolates with decreased susceptibility to extended-spectrum cephalosporins increased significantly from 2013 to 2018. Ceftriaxone-resistant strain has emerged in Nanjing, China. Disclosure No significant relationships.