Determining the in vitro susceptibility of Neisseria gonorrhoeae isolates from 8 cities in Guangdong Province through an improved microdilution method

[Establishment and Evaluation of a Resazurin-Based Microdilution Assay for Microbial Sensitivity Test of Neisseria gonorrhoeae]

Objective

To establish and evaluate a microbial sensitivity test method for Neisseria gonorrhoeae based on resazurin coloration.

Methods

Based on the broth microdilution method, resazurin was added as a live bacteria indicator. WHO G, a WHO gonococcal reference strain, was used to optimize the incubation time for resazurin-stained bacteria and the color change was visually observed to obtain the results. Agar dilution method (the gold standard) and resazurin-based microdilution assay were used to determine the minimum inhibitory concentration (MIC) of azithromycin, ceftriaxone, and spectinomycin for 3 reference strains and 32 isolates of Neisseria gonorrhoeae. The results were analyzed based on essential agreement (EA), which reflected the consistency of the MIC values, category agreement (CA), which reflected the consistency in the determination of drug resistance, intermediary, and sensitivity, very major error (VME), which reflected false sensitivity, and major error (ME), which reflected pseudo drug resistance, to evaluate the accuracy of resazurin-based microdilution assay as a microbial sensitivity test of of Neisseria gonorrhoeae. CA and EA rates≥90% and VME and ME rates≤3% were found to be the acceptable performance rates.

Results

The results obtained 6 hours after resazurin was added were consistent with those of the agar dilution method and the resazurin-based microdilution assay was established accordingly based on this parameter. The EA of resazurin-based microdilution assay for measuring the MIC results of azithromycin, ceftriaxone, and spectinomycin was 97.1%, 91.5%, and 94.3%, respectively, and the CA was 88.6%, 94.3%, and 94.3%, respectively. The VME was 0% for all three antibiotics, while the ME was 11.4%, 5.7%, and 5.7%, respectively.

Conclusion

The resazurin-based microdilution assay established in this study showed good agreement with agar dilution method for measuring the MIC of antibiotics against Neisseria gonorrhoeae. Moreover, the sensitivity results of this method were highly reliable and could be easily obtained through naked eye observation. Nonetheless, the results of drug resistance should be treated with caution and the optimization of parameters should be continued.

Antimicrobial effects of Medicines for Malaria Venture Pathogen Box compounds on strains of Neisseria gonorrhoeae

Therapeutic options for Neisseria gonorrhoeae are limited due to emerging global resistance. New agents and treatment options to treat patients with susceptible and multi-extensively drug-resistant N. gonorrhoeae is a high priority. This study used an in vitro approach to explore the antimicrobial potential, as well as synergistic effects of Medicine for Malaria Venture (MMV) Pathogen Box compounds against ATCC and clinical N. gonorrhoeae strains. Microbroth dilution assay was used to determine pathogen-specific minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the Pathogen Box compounds against susceptible and resistant N. gonorrhoeae strains, with modification, by adding PrestoBlue HS Cell Viability Reagent. A checkerboard assay was used to determine synergy between the active compounds and in conjunction with ceftriaxone. Time-kill kinetics was performed to determine if the compounds were either bactericidal or bacteriostatic. The Pathogen Box compounds: MMV676501, MMV002817, MMV688327, MMV688508, MMV024937, MMV687798 (levofloxacin), MMV021013, and MMV688978 (auranofin) showed potent activity against resistant strains of N. gonorrhoeae at an MIC and MBC of ≤10 µM. Besides the eight compounds, MMV676388 and MMV272144 were active against susceptible N. gonorrhoeae strains, also at MIC and MBC of ≤10 µM. All the compounds were bactericidal and were either synergistic or additive with fractional inhibitory concentration index ranging between 0.40 and 1.8. The study identified novel Pathogen Box compounds with potent activity against N. gonorrhoeae strains and has the potential to be further investigated as primary or adjunctive therapy to treat gonococcal infections.

Markedly Increasing Antibiotic Resistance and Dual Treatment of Neisseria gonorrhoeae Isolates in Guangdong, China, from 2013 to 2020

The emergence of multidrug resistance in Neisseria gonorrhoeae is concerning, especially the cooccurrence of azithromycin resistance and decreased susceptibility to extended-spectrum cephalosporin. This study aimed to confirm the antibiotic resistance trends and provide a solution for N. gonorrhoeae treatment in Guangdong, China. A total of 5,808 strains were collected for assessment of antibiotic MICs. High resistance to penicillin (53.80 to 82%), tetracycline (88.30 to 100%), ciprofloxacin (96 to 99.8%), cefixime (6.81 to 46%), and azithromycin (8.60 to 20.03%) was observed. Remarkably, spectinomycin and ceftriaxone seemed to be the effective choices, with resistance rates of 0 to 7.63% and 2.00 to 16.18%, respectively. Moreover, the rates of azithromycin resistance combined with decreased susceptibility to ceftriaxone and cefixime reached 9.28% and 8.64%, respectively. Furthermore, genotyping identified NG-STAR-ST501, NG-MAST-ST2268, and MLST-ST7363 as the sequence types among representative multidrug-resistant isolates. Evolutionary analysis showed that FC428-related clones have spread to Guangdong, China, which might be a cause of the rapid increase in extended-spectrum cephalosporin resistance currently. Among these strains, the prevalence of N. gonorrhoeae was extremely high, and single-dose ceftriaxone treatment might be a challenge in the future. To partially relieve the treatment pressure, a susceptibility test for susceptibility to azithromycin plus extended-spectrum cephalosporin dual therapy was performed. The results showed that all the representative isolates could be effectively killed with the coadministration of less than 1 mg/liter azithromycin and 0.125 mg/liter extended-spectrum cephalosporin, with a synergistic effect according to a fractional inhibitory concentration (FIC) of <0.5. In conclusion, dual therapy might be a powerful measure to treat refractory N. gonorrhoeae in the context of increasing antibiotic resistance in Guangdong, China.

Development and application of Cas13a-based diagnostic assay for Neisseria gonorrhoeae detection and azithromycin resistance identification

BACKGROUND

Gonorrhoea, caused by Neisseria gonorrhoeae, has spread worldwide. Strains resistant to most antibiotics, including ceftriaxone and azithromycin, have emerged to an alarming level. Rapid testing for N. gonorrhoeae and its antimicrobial resistance will therefore contribute to clinical decision making for early diagnosis and rational drug use.

METHODS

A Cas13a-based assay (specific high-sensitivity enzymatic reporter unlocking; SHERLOCK) was developed for N. gonorrhoeae detection (porA gene) and azithromycin resistance identification (A2059G, C2611T). Assays were evaluated for sensitivity with purified dsDNA and specificity with 17 non-gonococcal strains. Performance of SHERLOCK (porA) was compared with Roche Cobas 4800 using 43 urine samples. Identification of azithromycin resistance mutations (A2059G, C2611T) was evaluated using a total of 84 clinical isolates and 18 urine samples. Lateral flow was tested for this assay as a readout tool. Moreover, we directly assayed 27 urethral swabs from patients with urethritis to evaluate their status in terms of N. gonorrhoeae infection and azithromycin resistance.

RESULTS

The SHERLOCK assay was successfully developed with a sensitivity of 10 copies/reaction, except 100 copies/reaction for A2059G, and no cross-reaction with other species. Comparison of the SHERLOCK assay with the Cobas 4800 revealed 100% concordance within 18 positive and 25 negative urine samples. Of the 84 isolates, 21 strains with azithromycin resistance mutations were distinguished and further verified by sequencing and MIC determination. In addition, 62.96% (17/27) strains from swab samples were detected with no mutant strains confirmed by sequencing.

CONCLUSIONS

The SHERLOCK assay for rapid N. gonorrhoeae detection combined with azithromycin resistance testing is a promising method for application in clinical practice.

Comparison of Microdilution Method with Agar Dilution Method for Antibiotic Susceptibility Test of Neisseria gonorrhoeae

Introduction

Antimicrobial resistance (AMR) of Neisseria gonorrhoeae (N. gonorrhoeae) becomes a grave public health problem in the world. A strengthened Antimicrobial Resistance Surveillance Program is needed to track the trend of AMR development. However, the lack of a proper antimicrobial susceptibility test (AST) method is a barrier to expand the AMR surveillance in China. Traditional agar dilution (AD) method is laborious and E-test strips have no approval license for clinical use. Herein, a Chinese group modified the microdilution (MD) method for clinical ASTs. The objective of this study is to compare the MD method with the AD method for N. gonorrhoeae AST.

Materials and Methods

A total of 166 clinical isolates were tested for antimicrobial susceptibility of ceftriaxone, spectinomycin, azithromycin, ciprofloxacin, tetracycline, and penicillin using MD and AD method simultaneously. Results of MD method were read manually or automatically. Rates of essential agreement (EA), category agreement (CA), minor error, and very major error were compared.

Results

The total EAs (compared with results read manually) of penicillin, tetracycline, ciprofloxacin, spectinomycin, ceftriaxone, and azithromycin were 90.4%, 97.0%, 85.5%, 100.0%, 94%, and 72.3%; and CAs were 82.5%, 94.0%, 100%, 100%, 95.2%, and 94%, respectively.

Conclusion

We conclude that the MD method might be an alternative for clinical AST of N. gonorrhoeae in China. In particular, MD method has the potency of accurate differentiation of isolates resistant to ceftriaxone or azithromycin, which were empirically recommended for gonococcal treatment, but its quality remained suboptimal, and further improvement is needed for clinical use.

<p>Disk-Diffusion Testing Is an Inappropriate Screening Tool for Cephalosporin-Resistant Gonorrhoea Strains in Clinical Practice in China</p>

Purpose

Injectable ceftriaxone and oral cefixime are the last agents effective against Neisseria gonorrhoeae. In vitro antimicrobial-susceptibility testing (AST) is done to identify the most efficacious antibiotic needed to combat the infection in that particular individual. The objective of this study was to evaluate whether Kirby–Bauer (KB) disk-diffusion tests can detect N. gonorrhoeae isolates that have decreased susceptibility to ceftriaxone and cefixime for appropriate clinical management.

Methods

A total of 1,633 consecutive clinical isolates of N. gonorrhoeae were collected from January 1, 2013 to December 31, 2017 from seven dermatology clinics located in five provinces in China. Consistency between KB disk-diffusion tests and the agar-dilution method, as well as sensitivity of the KB test for detecting N. gonorrhoeae isolates with decreased susceptibility to ceftriaxone and cefixime, were determined using 1,306 clinical isolates that had been recovered to complete agar-dilution AST.

Results

The prevalence of isolates with decreased susceptibility to ceftriaxone and cefixime was 12.1% (198 of 1,633) and 12.7% (208 of 1,633), respectively, using KB disk-diffusion tests. The prevalence of isolates with decreased susceptibility was 9.9% (129 of 1,306) for ceftriaxone and 9.9% (129 of 1,305) for cefixime using agar-dilution AST. The categorical agreement of these two methods was 80.9% for both ceftriaxone and cefixime. Compared to agar-dilution AST, the sensitivity of the KB test for detecting N. gonorrhoeae isolates with decreased susceptibility was 22.5% (29 of 129) for ceftriaxone and 29.5% (38 of 129) for cefixime, and its specificity 87.3% (1,028 of 1,177) for ceftriaxone and 86.7% (1,018 of 1,176) for cefixime.

Conclusion

Although KB tests are easy to carry out in clinical practice, their ability to detect cephalosporin-resistant gonorrhoea strains is limited. This method is not an appropriate selection for screening cephalosporin-resistant gonorrhoea strains in clinical practice in China.

Antimicrobial resistance of Neisseria gonorrhoeae in Jakarta, Indonesia: a cross-sectional study

Background Neisseria gonorrhoeae has developed resistance to various antimicrobials. At least 10 countries have reported treatment failures with extended-spectrum cephalosporins. Periodic surveillance is essential to determine local treatment guidelines. This study was conducted to determine the resistance of N. gonorrhoeae to penicillin, tetracycline, levofloxacin, cefixime and ceftriaxone among the high-risk population for acquiring STIs in Jakarta and to identify factors associated with resistance.

METHODS

A cross-sectional study was conducted in Jakarta, Indonesia, from September to November 2018. In all, 98 high-risk males and females who fulfilled the study criteria were included. Specimens were collected from urethral or endocervical swabs, put into Amies transport medium and then transported to the Laboratory of Clinical Microbiology, Universitas Indonesia for culture and identification. Proven gonococcal isolates were examined for susceptibility to various antimicrobials using the disk diffusion method according to Clinical and Laboratory Standard Institute guidelines.

RESULTS

Of the 98 specimens, 35 were confirmed to be N. gonorrhoeae. The proportion of N. gonorrhoeae specimens resistant to penicillin, tetracycline, levofloxacin, cefixime and ceftriaxone among the high-risk population was 97.1%, 97.1%, 34.3%, 0% and 0% respectively. The possible factors associated with resistance could only be analysed for levofloxacin. Age, sexual orientation and a history of orogenital sexual activity during the past month were not associated with N. gonorrhoeae resistance to levofloxacin.

CONCLUSION

This study detected no resistance of N. gonorrhoeae to cefixime and ceftriaxone. Further studies with larger samples are needed to obtain more representative results of N. gonorrhoeae resistance and the possible factors associated with resistance.

Changing antimicrobial susceptibility and molecular characterisation of Neisseria gonorrhoeae isolates in Guangdong, China: in a background of rapidly rising epidemic

The prevalence of Neisseria gonorrhoeae infections has increased rapidly since 2015 in China. Antimicrobial resistance and molecular mobilisation in N. gonorrhoeae are two important factors driving this increasing prevalence. This study explored changes in antimicrobial susceptibility and molecular characteristics of N. gonorrhoeae collected in Guangdong, China (2013-2017). A total of 704 isolates were collected in two cities in Guangdong. MICs of major antimicrobials were determined. Penicillinase-producing N. gonorrhoeae (PPNG) and tetracycline-resistant N. gonorrhoeae (TRNG) were characterised, and N. gonorrhoeae multiantigen sequence typing (NG-MAST) was performed. High resistance to penicillin (68.2%), tetracycline (85.7%) and ciprofloxacin (98.2%) was observed. Spectinomycin, ceftriaxone and azithromycin appeared effective, with susceptibilities of 100%, 96.4% and 90.7%, respectively. Resistance to penicillin decreased significantly from 78.4% to 73.6% and to azithromycin from 11.9% to 3.7%. Total prevalence of PPNG, TRNG and PPNG/TRNG was 25.4%, 33.1% and 13.4%, respectively. Rates of PPNG decreased significantly from 37.3% to 23.9%, TRNG from 50.0% to 31.3%, and PPNG/TRNG from 23.5% to 11.7%. However, the ratio of African-type PPNG increased significantly (18.4% to 64.1%) compared with decreasing Asian-type PPNG (81.6% to 33.3%), and the ratio of American-type TRNG increased significantly (0% to 13.7%) compared with decreasing Dutch-type TRNG (100% to 86.3%). A total of 271 sequence types (STs) were identified by NG-MAST from 380 isolates collected in 2013, 2014 and 2017, with 145 novel STs. African-type PPNG is increasing and replacing Asian-type, and novel STs have emerged. Gonococcal isolates with new genotypes might contribute to the rising gonorrhoea epidemic in this area.