Increasing antimicrobial resistance in Neisseria gonorrhoeae has become a major global public health concern. The World Health Organization (WHO) estimated that 106.1 million new cases occur worldwide in 2008, and up to 42 million cases in the WHO Western Pacific region (e.g., China, Japan, Philippines, Malaysia, Vietnam, and Australia).1 Treatment with effective antimicrobial drugs successfully prevented serious sequelae and further transmission. However, N. gonorrhoeae has a remarkable ability to develop antimicrobial resistance to all previously recommended first-line drugs, including sulfonamides, penicillins, tetracyclines, and fuoroquinolones (e.g., ciprofloxacin).2 Extended-spectrum cephalosporins cefixime and ceftriaxone are currently the only remaining options for first-line empiric antimicrobial monotherapy in many countries worldwide. Unfortunately, clinical treatment failures with ceftriaxone and particularly cefixime have been verified in several countries,3 and the first extensively drug-resistant gonococcal strains with high-level extended-spectrum cephalosporin resistance were reported recently.4
Our previous report showed the levels of resistance as follows: penicillin, 59.6%; ciprofloxacin, 60.6%; ceftriaxone, 0%; spectinomycin, 0%; penicillinase-producing N. gonorrhoeae (PPNG), 5.8%; and tetracycline-resistant N. gonorrhoeae (TRNG), 3.4%, between September 1997 and August 1998.5 These surveillance data have been useful in guiding local clinicians in the use of appropriate antibiotics for gonorrhea treatment. This study complements and extends our previous work aimed at understanding the trend of antimicrobial resistance in N. gonorrhoeae isolated from Guangzhou in 2 periods, 2000 to 2005 and 2008 to 2013, where sexually transmitted infections are mostly prevalent in China.5
N. gonorrhoeae isolates were collected from outpatients with gonorrhea attending sexually transmitted disease clinic in Guangzhou, China, in 2000 to 2005 and 2008 to 2013, respectively. Male urethral or female endocervical swab specimens were directly inoculated onto modified Thayer-Martin medium. The plates were incubated in a 5% CO2 atmosphere at 35 °C for 48 hours. All the isolates were identified through colony morphology, Gram staining, oxidase, and carbohydrate degradation tests. Second-generation strains were suspended with skim milk and stored in a freezer at −70 °C until further testing.
All isolates were examined for minimum inhibitory concentrations (MICs) of penicillin, ciprofloxacin, ceftriaxone, and spectinomycin by the agar plate dilution method using GC agar base supplemented with 10% defibrinated fresh sheep blood, as described in our previous publication.5 Each MIC determination was performed in duplicate and included WHO N. gonorrhoeae reference strains A to E used as controls. A β-lactamase assay was performed by the paper acidometric method to screen PPNG, and WHO reference strains A and E were used as negative and positive controls, respectively. The results were interpreted according to the WHO Western Pacific Region Program criteria,6 except for ceftriaxone according to the criteria defined by WHO in 20127: penicillin and ciprofloxacin (susceptibility MIC ≤0.03 μg/mL, intermediate MIC of 0.06–0.50 μg/mL, resistance MIC ≥1.0 μg/mL), ceftriaxone (susceptibility MIC <0.125 μg/mL, intermediate MIC ≥0.125 μg/mL), spectinomycin (susceptibility MIC ≤64 μg/mL, resistance MIC ≥128 μg/mL), PPNG (β-lactamase positive), and TRNG (tetracycline MIC ≥16 μg/mL).
A total of 1224 N. gonorrhoeae isolates were studied, including 665 samples from 2000 to 2005 and 559 samples from 2008 to 2013. Between 2000–2005 and 2008–2013, the rates of PPNG and TRNG isolates significantly increased from 23.5% (156/665) to 38.3% (214/559; P < 0.001) and from 33.4% (222/665) to 45.1% (252/559; P < 0.001), respectively. The proportion of resistant strains to penicillin remarkably rose from 71.1% to 90.1% (P < 0.001). Like penicillin, the percentage of resistant strains to ciprofloxacin significantly increased from 88.9% to 98.0% (P < 0.001). Intermediate susceptible isolates to ceftriaxone (MIC ≥0.125 μg/mL) increased from 12.3% to 22.0% (P < 0.001). No isolates resistant to spectinomycin (MIC ≥128 μg/mL) were identified over the years. Minimum inhibitory concentrations (MIC range, MIC50, MIC90, or MICmean) of the four antibiotics to N. gonorrhoeae isolates were elevated in different degree, as detailed in Table 1, Figure 1, and supplementary Tables 1 and 2, http://links.lww.com/OLQ/A92.
Similar to the previous study in Guangzhou,8 Shanghai,9 and Nanjing,10 China, the present study showed that the level of penicillin resistance generally increased in 2008 to 2013 (90.1%) as compared with those in 2000 to 2005 (71.1%), and there was no N. gonorrhoeae isolates susceptible to penicillin from the year 2001. With the increasing spread of the resistant worldwide, penicillin and tetracycline have not been recommended for the treatment of gonorrhea; however, prevalence of PPNG/TRNG remains key index of resistance surveillance. According to data from the current study, PPNG and TRNG had been as prevalent as 38.3% and 45.1% in 2008 to 2013, nearly 7-fold and 13-fold compared with our surveillance starting year,5 respectively, and were substantially higher than those in 2000 to 2005. Consistent with other reports from Guangzhou, the prevalence of PPNG rapidly spread from 2% to 21.8% between 1996 and 2001.8 The proportions of PPNG and TRNG that were detected in Shanghai within November 2004 and May 2005 were 37.8% and 20.1%, respectively.9 Similar ascending trend was observed between 1999 and 2006 in Nanjing (for PPNG from 8.0% to 44.4% and for TRNG from1.8% to 32.8%).10 However, in Korea, the proportions of PPNG decreased from 64% in 2000 to 21% in 2006, whereas TRNG increased from 3% to 9% over the 7 years.11 Surveillance results from Canada showed PPNG (from 3.0% to 0.9%) and TRNG (from 3.4% to1.6%), both had a declining trend in 2000 and 2009.12 These changes have been explained by association with whether more effective diagnosis and treatment with penicillinase stable antibiotics, more effective contact tracing, a change in sexual activity and behavior, or a more subtle biological change in the gonococci.13
Fluoroquinolones were introduced and effectively used to treat gonorrhea since the late 1980s, but after that, fluoroquinolone-resistant N. gonorrhoeae sharply increased during 2 decade years in many countries around the world. Very high levels of resistance to ciprofloxacin were detected in this surveillance study, with staying more than 93% annually from 2002 and increasing from 88.9% in 2000 to 2005 to 98% in 2008 to 2013, and most of the resistance was at a high level (MIC50 ≥8 μg/mL and MIC90 ≥32 μg/mL). The similar increase in ciprofloxacin resistance over time has been serially documented in other parts of China,9,10 and third-generation cephalosporins are currently preferred; therefore, ciprofloxacin was no longer recommended for the treatment of gonorrhea in China now.
In contrast to our findings for penicillin and ciprofloxacin, there was no resistant (MIC ≥128 μg/mL) to spectinomycin in the 2 time periods. Nevertheless, the isolates with MIC (64 μg/mL) near the resistance breakpoint has appeared for the first time, rapidly increased from none in 2000–2005 to 7.2% (40/665) in 2008–2013, indicating that continued surveillance is critical. Although spectinomycin resistance was rare after the mid-1980s, a small number of gonococcal isolates has been reported in some countries, such as in Colombia and Venezuela between 1990 and 1998,14 and in Vietnam, Korea, and Papua New Guinea in 2000.15 Some spectinomycin-resistant strains have also been detected in Guangzhou (2/793 in 1996–2001) and Nanjing (8/1208 in 1999–2006), China.8,10 The WHO recommends discontinuation of empirical use of an antibiotic once 5% of locally acquired gonococcal isolates are resistant. Accordingly, despite occasional reports of resistance from other studies in China and some other countries, spectinomycin is still effective and can be used as primary treatment of gonorrhea in Guangzhou and is an alternative therapeutic option for treatment for people with allergies to cephalosporins.16
Although not yet at MIC levels associated with loss of clinical efficacy, increasing ceftriaxone MICs and emergence of clinical treatment failure in recent decade have posed a public health challenge—the threat of untreatable gonorrhea. In the current study, the rate of intermediate susceptible (also known as probably resistance, MIC ≥0.125 μg/mL) strains to ceftriaxone, as well as its MIC rang, MIC50, and the geometric mean MICs, significantly increased from 2000–2005 to 2008–2013, which was similar to the findings in Shanghai (11.9% in November 2004 and May 2005),9 but lower than a recent report in Nanning, China (32.9% in 2000–2012).17 Moreover, it was noteworthy that the proportion of intermediate susceptible strains to ceftriaxone has been more than 5% since the early 2000s and 1.1% (6/559) of isolates firstly showed an MIC 0.5 μg/mL in 2008 to 2013, suggesting an ongoing rise in MIC values and probably resistance for ceftriaxone among Guangzhou gonococci. Higher doses of intramuscular ceftriaxone for gonorrhea in some countries have been advised to slow down the spread of cephalosporin-resistant gonococci.18 China has recommended using a single dose of 250 mg ceftriaxone administered intramuscularly as a first-line treatment of gonorrhea since 2007. Based on the information from other international guidelines, we recommend, like that in Nanning of China,17 a higher dose (≥500 mg) of intramuscular ceftriaxone be used for gonorrhea treatment in Guangzhou.
In conclusion, N. gonorrhoeae isolates in Guangzhou exhibited the prevalence of resistance to penicillin and ciprofloxacin, and plasmid-mediated resistance (PPNG and TRNG) increased rapidly from 2000–2005 to 2008–2013. No resistance was still identified; however, high levels of MICs for ceftriaxone (MIC 0.5 μg/mL) and spectinomycin (MIC 64 μg/mL) were firstly discovered during the second period. It is of great importance to strengthen the N. gonorrhoeae surveillance of antimicrobial resistance as well as gonorrhea treatment failures in the future in Guangzhou.
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