Is gentamicin a viable therapeutic option for treating resistant Neisseria gonorrhoeae in New South Wales?

ABSTRACT: The key issues with Neisseria gonorrhoeae infections, in Australia and elsewhere, are coincident increases in disease rates and in antimicrobial resistance (AMR), although these factors have not been shown to be correlated. Despite advances in diagnosis, control of this disease remains elusive, and incidence in Australia continues to increase. Of the Australian jurisdictions, New South Wales (NSW) has the highest N. gonorrhoeae notifications, and over the five-year period 2015-2019, notifications in NSW have increased above the national average (by 116% versus 85%, respectively). Gonococcal disease control is reliant on effective antibiotic regimens. However, escalating AMR in N. gonorrhoeae is a global health priority, as the collateral injury of untreated infections has substantive impacts on sexual and newborn health. Currently, our first-line therapy for gonorrhoea is also our last line, with no ideal alternative identified. Despite some limitations, gentamicin is licensed and readily available in Australia, and is proposed for treatment of resistant N. gonorrhoeae in national guidelines; however, supportive published microbiological data are lacking. Analysis of gonococcal resistance patterns within Australia for the period 1991-2019, including 35,000 clinical isolates from NSW, illustrates the establishment and spread of population-level resistance to all contemporaneous therapies. An analysis of gentamicin susceptibility on 2,768 N. gonorrhoeae clinical isolates from NSW, for the period 2015-2020, demonstrates that the median minimum inhibitory concentration (MIC) for gentamicin in NSW has remained low, at 4.0 mg/L, and resistance was not detected in any isolate. There has been no demonstration of MIC drift over time (p = 0.91, Kruskal-Wallis test), nor differences in MIC distributions according to patients' sex or site of specimen collection. This is the first large-scale evaluation of gentamicin susceptibility in N. gonorrhoeae in Australia. No gentamicin resistance was detected in clinical isolates, 2015-2020, hence this is likely to be an available treatment option for resistant gonococcal infections in NSW.

Australian Meningococcal Surveillance Programme annual report, 2019.

Invasive meningococcal disease (IMD) is a notifiable disease in Australia, and both probable and laboratory-confirmed cases of IMD are reported to the National Notifiable Diseases Surveillance System (NNDSS). In 2019, there were 206 notifications of IMD. Of these, 202 were laboratory-confirmed cases analysed by the reference laboratories of the Australian National Neisseria Network (NNN). Of the 202 laboratory-confirmed cases of IMD, 167 were confirmed by bacterial culture and 35 by nucleic acid amplification testing, and all had the serogroup determined. Fine typing was available on 146 samples (146/202, 72%). Neisseria meningitidis serogroup B (MenB) infections accounted for 50.0% (101/202); MenW for 26.2% (53/202); MenY for 20.8% (42/202) and MenC for 3.0% of cases (6/202). Of the MenW cases, 88% were PorA antigen type P1.5,2, and 65% of these (24/37) were sequence type 11, the hypervirulent strain reported in recent outbreaks in Australia and overseas. The primary peaks of IMD notifications in Australia in 2019 were observed in infants less than 1 year of age (36/202, 18%) and in adults aged 65 years or older (39/202, 19%). MenB infections predominated in those aged less than 5 years and those aged 15-19 years, whereas MenW and MenY infections predominated in those aged 45 years or more. All 167 IMD isolates were tested for antimicrobial susceptibility. One isolate out of these 167 (0.6%) was resistant to penicillin with an MIC ≥ 1mg/L; 154/167 isolates (92%) had decreased susceptibility to penicillin. All isolates were susceptible to ceftriaxone and ciprofloxacin, and one isolate was resistant to rifampicin.

Australian Meningococcal Surveillance Programme annual report, 2018.

Invasive meningococcal disease (IMD) is a notifiable disease in Australia, and both probable and laboratory-confirmed cases of IMD are reported to the National Notifiable Diseases Surveillance System (NNDSS). In 2018, there were 281 IMD cases notified to the NNDSS. Of these, 278 were laboratory-confirmed cases analysed by the reference laboratories of the Australian National Neisseria Network (NNN). On investigation, the serogroup was able to be determined for 98.6% (274/278) of laboratory-confirmed cases. Serogroup B infections accounted for 44.2% of cases (123 cases); serogroup W for 36.3% of cases (101 cases); serogroup Y infections for 15.8% (44 cases) and serogroup C 1.4% (4 cases); and there were two unrelated cases (0.7%) of IMD attributable to serogroup E. Using molecular methods, 181/278 IMD cases were able to be typed. Of note was that 89% of typed serogroup W IMD cases (66/74) were porA antigen type P1.5,2; of this number, 44% (29/66) were sequence type 11, the hypervirulent strain reported in recent outbreaks in Australia and overseas. The primary age peak of IMD in Australia in 2018 was again observed in adults aged 45 years or more; a secondary disease peak was observed in children and infants aged less than 5 years. Serogroup B infections predominated in those aged less than 5 years, whereas serogroup W and serogroup Y infections predominated in those aged 45 years or more. Of the IMD isolates tested for antimicrobial susceptibility, 1.4% (3/210) were resistant to penicillin with an MIC ≥ 1 mg/L, and decreased susceptibility to penicillin was observed in a further 93.8% (197/210) of isolates. All isolates were susceptible to ceftriaxone and rifampicin; there was one isolate less susceptible to ciprofloxacin.

Genetic relatedness of ceftriaxone-resistant and high-level azithromycin resistant Neisseria gonorrhoeae cases, United Kingdom and Australia, February to April 2018.

Between February and April 2018, three ceftriaxone-resistant and high-level azithromycin-resistant Neisseria gonorrhoeae cases were identified; one in the United Kingdom and two in Australia. Whole genome sequencing was used to show that the isolates from these cases belong to a single gonococcal clone, which we name the A2543 clone.

Azithromycin-resistant Neisseria gonorrhoeae spreading amongst men who have sex with men (MSM) and heterosexuals in New South Wales, Australia, 2017.

Objectives: To identify the genetic basis of resistance as well as to better understand the epidemiology of a recent surge in azithromycin-resistant Neisseria gonorrhoeae in New South Wales, Australia. Methods: Azithromycin-resistant N. gonorrhoeae isolates (n = 118) collected from 107 males, 10 females and 1 transsexual between January and July 2017 were genotyped using a previously described iPLEX method. The results were compared with phenotypic resistance profiles and available patient data. Results: The iPLEX results revealed 10 different N. gonorrhoeae genotypes (designated AZI-G1 to AZI-G10) of which three were responsible for the majority of infections; AZI-G10 (74.6%, 88 isolates; 87 males and 1 transsexual), AZI-G4 (11.0%, 13 isolates; 7 males and 6 females) and AZI-G7 (6.8%, 8 isolates; 7 males and 1 female). The observed resistance was attributable to one of two different azithromycin resistance mechanisms; the 23S rRNA C2611T mutation was identified in 24% of isolates, whereas the majority of resistance (76%) was associated with a meningococcal-type mtrR variant. Additionally, one isolate was found to harbour both the 23S rRNA C2611T mutation and a type XXXIV mosaic penA sequence associated with cephalosporin resistance. Conclusions: These data indicate outbreaks of azithromycin-resistant gonococci amongst networks of MSM and heterosexuals in New South Wales. The results also provide further evidence that azithromycin may soon be an ineffective treatment option for gonococcal infection and highlight the urgent need to explore alternative therapies.

Molecular Antimicrobial Resistance Surveillance for Neisseria gonorrhoeae, Northern Territory, Australia.

Neisseria gonorrhoeae antimicrobial resistance (AMR) is a globally recognized health threat; new strategies are needed to enhance AMR surveillance. The Northern Territory of Australia is unique in that 2 different first-line therapies, based primarily on geographic location, are used for gonorrhea treatment. We tested 1,629 N. gonorrhoeae nucleic acid amplification test-positive clinical samples, collected from regions where ceftriaxone plus azithromycin or amoxicillin plus azithromycin are recommended first-line treatments, by using 8 N. gonorrhoeae AMR PCR assays. We compared results with those from routine culture-based surveillance data. PCR data confirmed an absence of ceftriaxone resistance and a low level of azithromycin resistance (0.2%), and that penicillin resistance was <5% in amoxicillin plus azithromycin regions. Rates of ciprofloxacin resistance and penicillinase-producing N. gonorrhoeae were lower when molecular methods were used. Molecular methods to detect N. gonorrhoeae AMR can increase the evidence base for treatment guidelines, particularly in settings where culture-based surveillance is limited.

The Molecular Epidemiology and Antimicrobial Resistance of Neisseria gonorrhoeae in Australia: A Nationwide Cross-Sectional Study, 2012.

BACKGROUND: Antimicrobial resistance (AMR) by Neisseria gonorrhoeae is considered a serious global threat. METHODS: In this nationwide study, we used MassARRAY iPLEX genotyping technology to examine the epidemiology of N. gonorrhoeae and associated AMR in the Australian population. All available N. gonorrhoeae isolates (n = 2452) received from Australian reference laboratories from January to June 2012 were included in the study. Genotypic data were combined with phenotypic AMR information to define strain types. RESULTS: A total of 270 distinct strain types were observed. The 40 most common strain types accounted for over 80% of isolates, and the 10 most common strain types accounted for almost half of all isolates. The high male to female ratios (>94% male) suggested that at least 22 of the top 40 strain types were primarily circulating within networks of men who have sex with men (MSM). Particular strain types were also concentrated among females: two strain types accounted for 37.5% of all isolates from females. Isolates harbouring the mosaic penicillin binding protein 2 (PBP2)-considered a key mechanism for cephalosporin resistance-comprised 8.9% of all N. gonorrhoeae isolates and were primarily observed in males (95%). CONCLUSIONS: This large scale epidemiological investigation demonstrated that N. gonorrhoeae infections are dominated by relatively few strain types. The commonest strain types were concentrated in MSM in urban areas and Indigenous heterosexuals in remote areas, and we were able to confirm a resurgent epidemic in heterosexual networks in urban areas. The prevalence of mosaic PBP2 harboring N. gonorrhoeae strains highlight the ability for new N. gonorrhoeae strains to spread and become established across populations.

Australian Gonococcal Surveillance Programme annual report, 2013.

The Australian Gonococcal Surveillance Programme has continuously monitored antimicrobial resistance in clinical isolates of Neisseria gonorrhoeae from all states and territories since 1981. In 2013, 4,897 clinical isolates of gonococci from public and private sector sources were tested for in vitro antimicrobial susceptibility by standardised methods. Decreased susceptibility to ceftriaxone (MIC value 0.06-0.125 mg/L) was found nationally in 8.8% of isolates, double that reported in 2012 (4.4%). The highest proportions were reported from New South Wales and Victoria (both states reporting 11.8%), with a high proportion of strains also reported from Tasmania but a low number of isolates were tested. In addition, there was a multi-drug-resistant strain of N. gonorrhoeae isolated from a traveller to Australia, with a ceftraixone MIC value of 0.5 mgL-the highest ever reported in Australia. These antimicrobial resistance data from Australia in 2013 are cause for considerable concern. With the exception of remote Northern Territory where penicillin resistance rates remain low (1.3%) the proportion of strains resistant to penicillin remained high in all jurisdictions ranging from 15.6% in the Australian Capital Territory to 44.1% in Victoria. Quinolone resistance ranged from 16% in the Australian Capital Territory to 46% in Victoria. Azithromycin susceptibility testing was performed in all jurisdictions and resistance ranged from 0.3% in the Northern Territory to 5.7% in Queensland. High level resistance to azithromycin (MIC value was > 256 mg/L) was reported for the first time in Australia, in 4 strains: 2 each from Queensland and Victoria. Azithromycin resistant gonococci were not detected in the Australian Capital Territory, Tasmania or from the remote Northern Territory. Nationally, all isolates remained susceptible to spectinomycin.

Persistence of Neisseria gonorrhoeae DNA following treatment for pharyngeal and rectal gonorrhea is influenced by antibiotic susceptibility and reinfection.

BACKGROUND: To guide interpretation of gonorrhea tests of cure using nucleic acid amplification testing, this study examined the persistence of Neisseria gonorrhoeae DNA following treatment for pharyngeal and rectal gonorrhea. METHODS: Men who had sex with men diagnosed with pharyngeal or rectal gonorrhea underwent swabbing from the pharynx or rectum 7 and 14 days following treatment. Repeat testing for N. gonorrhoeae was undertaken using real-time polymerase chain reaction (PCR) assays targeting the opa gene and porA pseudogene. RESULTS: One hundred pharyngeal and 100 rectal gonorrhea infections in 190 men were included. For pharyngeal gonorrhea, positivity of N. gonorrhoeae DNA on both PCR assays was present at days 7 or 14 in 13% (95% confidence interval [CI], 6.4%-19.6%) and 8% (95% CI, 2.7%-13.3%), respectively. For rectal gonorrhea, DNA positivity was present in 6% (95% CI, 1.4%-10.7%) and 8% (95% CI, 2.7%-13.3%), respectively. Among 200 baseline pharyngeal and rectal isolates, there were 10 with ceftriaxone minimum inhibitory concentration (MIC) ≥0.06 mg/L and azithromycin MIC ≥0.5 mg/L, of which 3 (30%) had DNA detected at day 14; among the 190 isolates with lower ceftriaxone and azithromycin MICs, only 13 (7%) had persistent DNA (odds ratio, 5.8 [95% CI, 1.3-25.4]; P = .019). One man initially infected with N. gonorrhoeae multiantigen sequence type 2400 had type 4244 infection at day 14, indicating reinfection. CONCLUSIONS: Pharyngeal and rectal gonorrhea DNA persisted in 8% of men 14 days after treatment. Persistence was associated with elevated ceftriaxone and azithromycin MICs. Persistence can also reflect reinfection.

In vitro activity of ertapenem versus ceftriaxone against Neisseria gonorrhoeae isolates with highly diverse ceftriaxone MIC values and effects of ceftriaxone resistance determinants: ertapenem for treatment of gonorrhea?

Clinical resistance to the currently recommended extended-spectrum cephalosporins (ESCs), the last remaining treatment options for gonorrhea, is being reported. Gonorrhea may become untreatable, and new treatment options are crucial. We investigated the in vitro activity of ertapenem, relative to ceftriaxone, against N. gonorrhoeae isolates and the effects of ESC resistance determinants on ertapenem. MICs were determined using agar dilution technique or Etest for international reference strains (n = 17) and clinical N. gonorrhoeae isolates (n = 257), which included the two extensively drug-resistant (XDR) strains H041 and F89 and additional isolates with high ESC MICs, clinical ESC resistance, and other types of clinical high-level and multidrug resistance (MDR). Genetic resistance determinants for ESCs (penA, mtrR, and penB) were sequenced. In general, the MICs of ertapenem (MIC(50) = 0.032 µg/ml; MIC(90) = 0.064 µg/ml) paralleled those of ceftriaxone (MIC(50) = 0.032 µg/ml; MIC(90) = 0.125 µg/ml). The ESC resistance determinants mainly increased the ertapenem MIC and ceftriaxone MIC at similar levels. However, the MIC ranges for ertapenem (0.002 to 0.125 µg/ml) and ceftriaxone (<0.002 to 4 µg/ml) differed, and the four (1.5%) ceftriaxone-resistant isolates (MIC = 0.5 to 4 µg/ml) had ertapenem MICs of 0.016 to 0.064 µg/ml. Accordingly, ertapenem had in vitro advantages over ceftriaxone for isolates with ceftriaxone resistance. These in vitro results suggest that ertapenem might be an effective treatment option for gonorrhea, particularly for the currently identified ESC-resistant cases and possibly in a dual antimicrobial therapy regimen. However, further knowledge regarding the genetic determinants (and their evolution) conferring resistance to both antimicrobials, and clear correlates between genetic and phenotypic laboratory parameters and clinical treatment outcomes, is essential.