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Gradient diffusion susceptibility testing for Neisseria gonorrhoeae: an accurate alternative to agar dilution in high-MIC strains?

ABSTRACT: Introduction:The correlation of antimicrobial susceptibility testing (AST) between agar dilution and gradient diffusion for Neisseria gonorrhoeae is not well established, especially in strains with high MICs. Aim:The objective of this study was to evaluate the accuracy of gradient diffusion for N. gonorrhoeae . Methods:Fifty strains of N. gonorrhoeae , all tested by the agar dilution method according to CLSI methods and confirmed to be genetically distinct using molecular typing (NG-MAST), were selected. Isolates with high MICs were targeted. Gradient diffusion was performed for ceftriaxone (CRO), cefixime (CFX), azithromycin (AZT), tetracycline (TET) and fosfomycin (FOS) using two different commercial antimicrobial strips on different culture media (a non-commercial GC agar base with 1?% defined growth supplement and two commercial media). The performance of agar gradient diffusion was assessed based on accuracy, using essential and category agreements (EA and CA). Results:Essential and categorical agreement were over 90?% for CRO, CFX and AZT on the two commercial agar media tested. Category disagreements were seen for CFX and AZT, mostly just very major errors. For TET, EA ranged from 80 to 96?% and CA ranged from 38 to 76?%, most of the misclassifications being minor errors. Finally, EA for FOS ranged between 80 and 98?%. Conclusion:Gradient diffusion is an accurate and acceptable alternative for CRO, CFX and AZT. Caution is advised when MICs are reported by gradient diffusion approach breakpoints because of the possibility of very major errors. The use of gradient diffusion is limited for TET because of the high rate of minor errors.

SUBMITTER: Desjardins M

PROVIDER: S-EPMC7494190 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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Gradient diffusion susceptibility testing for <i>Neisseria gonorrhoeae</i>: an accurate alternative to agar dilution in high-MIC strains?

Desjardins Michaël M Lefebvre Brigitte B Lavallée Christian C Labbé Annie-Claude AC Mauffrey Florian F Martin Irene I Longtin Jean J Fortin Claude C

Access microbiology 20200325 5

<h4>Introduction</h4>The correlation of antimicrobial susceptibility testing (AST) between agar dilution and gradient diffusion for <i>Neisseria gonorrhoeae</i> is not well established, especially in strains with high MICs.<h4>Aim</h4>The objective of this study was to evaluate the accuracy of gradient diffusion for <i>N. gonorrhoeae</i> .<h4>Methods</h4>Fifty strains of <i>N. gonorrhoeae</i> , all tested by the agar dilution method according to CLSI methods and confirmed to be genetically disti ...[more]

PMID: 32974579

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Project description:OBJECTIVE:To investigate the in vitro antimicrobial susceptibility and resistant trends of Neisseria gonorrhoeae strains isolated in Guangzhou, from 1996 to 2001. METHODS:The agar dilution method was used to determine the minimum inhibitory concentrations (MICs) to four antimicrobials, penicillin G, ciprofloxacin, ceftriaxone, and spectinomycin. The resistance of all strains to four antibiotics was interpreted according to criteria used in the project of surveillance of gonococcal antibiotic susceptibility in the WHO Western Pacific Region. Penicillinase producing N gonorrhoeae (PPNG) was analysed by the paper acidometric method. RESULTS:793 consecutive N gonorrhoeae isolates collected in Guangzhou were studied from 1996 to 2001. A total of 55 strains of PPNG were identified and the prevalence rapidly spread from 2% to 21.8%. Of the four antibiotics examined, ceftriaxone and spectinomycin appeared to be the most effective agents although two spectinomycin resistant strains were isolated in 1996. Their MIC(50), MIC(90), and geometric mean MIC (MICmean) were all between the sensitive ranges of the interpretative criteria and remained stable over the years. However, resistance increased continuously to penicillin G and dramatically to ciprofloxacin. In 1996-2001, MIC(50), MIC(90), and MICmean of penicillin G increased from 1 micro g/ml to 2 micro g/ml, 4 micro g/ml to 32 micro g/ml, and 0.68 micro g/ml to 2.35 micro g/ml, respectively; those of ciprofloxacin steeply increased from 0.12 micro g/ml to 4 micro g/ml, 2 micro g/ml to 32 micro g/ml, and 0.14 micro g/ml to 2.62 micro g/ml in 1996-9, respectively, and then declined slightly in 2000-1. The prevalence of resistant isolates spread from 57.2% to 81.8% for penicillin G and from 17.6% to 72.7% for ciprofloxacin over the 6 years. CONCLUSION:Resistance to penicillin and ciprofloxacin increased greatly during 1996-2001. Ceftriaxone and spectinomycin should be used as the first line agents in treating gonorrhoea. It is of great importance to continuously survey the susceptibilities of N gonorrhoeae to antibiotics in controlling the spread of gonococcal infections.

Dataset Information

Gradient diffusion susceptibility testing for Neisseria gonorrhoeae: an accurate alternative to agar dilution in high-MIC strains?

Publications

Gradient diffusion susceptibility testing for <i>Neisseria gonorrhoeae</i>: an accurate alternative to agar dilution in high-MIC strains?

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