Gentamicin Susceptibility in Neisseria gonorrhoeae and Treatment Outcomes for Urogenital Gonorrhea After 25 Years of Sustained Gentamicin Use in Malawi

Abstract

Background: Gentamicin has been used for the treatment of gonorrhea in Malawi since 1993. However, declining clinical cure rates have been suspected. We evaluated current Neisseria gonorrhoeae susceptibility to gentamicin in vitro and clinically.Methods: Men with acute urethritis were recruited at the Bwaila District Hospital STI Clinic in Lilongwe, Malawi, between January 2017 and August 2019. All men provided urethral swabs for etiological testing at enrollment and test of cure (TOC), 1 week later, using Gram-stained microscopy and culture. We used Etest to determine minimum inhibitory concentrations (MICs) of gentamicin, azithromycin, cefixime, ceftriaxone, ciprofloxacin, and spectinomycin; disc diffusion for tetracycline susceptibility; and whole-genome sequencing (WGS) to verify/refute treatment failure.Results: Among 183 N. gonorrhoeae culture-positive men enrolled, 151 (82.5%) had a swab taken for TOC. Of these 151 men, 16 (10.6%) had a positive culture at TOC. One hundred forty-one baseline isolates were tested for gentamicin susceptibility using Etest: 2 (1.4%), MIC = 2 μg/ mL; 111 (78.7%), MIC = 4 μg/mL; and 28 (19.9%), MIC = 8 μg/mL. All isolates were susceptible to azithromycin, cefixime, ceftriaxone, and spectinomycin, whereas 63.1% had intermediate susceptibility or resistance to ciprofloxacin. Almost all (96.1%) isolates were resistant to tetracycline. All examined isolates cultured at TOC (n = 13) had gentamicin MICs ≤8 μg/mL. Ten men had pretreatment and posttreatment isolates examined by whole-genome sequencing; 2 (20%) were verified new infections (4119 and 1272 single-nucleotide polymorphisms), whereas 8 (80%) were confirmed treatment failures (0-1 single-nucleotide polymorphism).Conclusions: Gentamicin MICs poorly predict gonorrhea treatment outcome with gentamicin, and treatment failures are verified with gonococcal strains with in vitro susceptibility to gentamicin. The first-line treatment of gonorrhea in Malawi should be reassessed.

A Single Amino Acid Substitution in Elongation Factor G Can Confer Low-Level Gentamicin Resistance in Neisseria gonorrhoeae

“…However, we stress that if Gen usage for treating gonorrheal infection becomes more prominent worldwide, compensatory mutations which relieve the fitness cost without changing Gen R may develop, allowing the proliferation of fusA2 -bearing strains in communities. Furthermore, based on our studies and those of others ( 21 – 24 , 42 – 46 ), it will also become critical to include Gen in routine antimicrobial susceptibility testing so that Ng isolates with decreased susceptibility to this aminoglycoside can be identified and studied.…”

“…Additionally, compared to FA19, this spontaneous mutant also exhibited a 4-fold decrease in susceptibility to tobramycin (Tob) and a 2-fold decrease in susceptibility to kanamycin (Kan), but was equally susceptible to erythromycin (Ery), polymyxin B (Pmb), spectinomycin (Spt), and streptomycin (Str) ( Table 1 ). Because the MIC of Gen against this mutant was at the previously suggested breakpoint ( 20 , 21 ), this phenotype was termed low-level Gen R .…”

“…Presently, the prevalence of Gen susceptibility depends largely on the region of study. In Malawi, China, Europe, and the U.S., Ng isolates showed universal susceptibility to Gen (MICs of ≤8 μg/mL) ( 21 – 24 , 42 ). In contrast, intermediate or reduced susceptibility to Gen has been seen in Jamaica, India, South Africa, and Côte d’Ivoire ( 43 – 46 ).…”

“…The emergence of MDR Ng clinical isolates has prompted the development and clinical testing of new antibiotics, the use of molecular diagnostics to identify isolates susceptible to previously used antibiotics (e.g., ciprofloxacin), and the use of existing antibiotics in new gonorrheal treatment regimens ( 6 , 18 , 19 ). With respect to existing antibiotics which have been used to treat other bacterial infections, gentamicin (Gen) is known to have anti-gonococcal action and has been used in many countries when recommended first-line gonorrheal therapy fails ( 6 ) and in Malawi as front-line empirical gonorrheal therapy, i.e., in combination with doxycycline ( 20 , 21 ). However, there are currently no interpretative criteria for Gen MICs set by the Clinical and Laboratory Standards Institute (CLSI) or the European Committee on Antimicrobial Susceptibility Testing (EUCAST).…”

“…MICs of ≥32 μg/mL have been used by the World Health Organization and in Malawi as the Gen resistance breakpoint for gonococci. In Malawi, Gen has been routinely used to treat suspected gonococcal infections for over 25 years, and isolates have mainly been uniformly susceptible to Gen in vitro ( 20 ); Gen treatment failures have been verified, likely due to pharmacokinetic/pharmacodynamic reasons ( 21 ). Similarly, a study of 1,366 gonococcal isolates from 17 European countries showed that most isolates were Gen-susceptible ( 22 ).…”