Key findings from the 2024 Mycoplasma genitalium Antimicrobial Resistance Surveillance (MARS) programme

Abstract

Background

Mycoplasma genitalium is a sexually transmitted pathogen of public health concern due to antimicrobial resistance to the recommended first- and second-line treatments, azithromycin and moxifloxacin. The M. genitalium Antimicrobial Resistance Surveillance (MARS) programme monitors resistance trends in England to inform clinical management and public health policy. Here, we summarise key findings from MARS 2024.

Methods

From 1^st March to 30^th June 2024, M. genitalium-positive specimens were collected at 32 sentinel sexual health services across England. Specimens were tested for molecular markers predictive of macrolide and fluoroquinolone resistance in the 23S rRNA and parC genes, respectively. In non-wildtype parC specimens, the gyrA gene was also sequenced. AMR data were linked to patient demographic, clinical, and behavioural data.

Results

The MARS 2024 sample included 1,049 individuals; 65.6% were male. Where resistance results were available, 63.6% of specimens were macrolide-resistant, 16.7% were fluoroquinolone resistant, and 13.7% were dual-resistant to both antimicrobials. Compared to MARS 2023, high levels of macrolide resistance remain, with increasing fluoroquinolone (p = 0.008) and dual resistance (p = 0.024).

Most individuals (87.3%) were prescribed the recommended first- or second-line treatments and 80.8% received doxycycline as a pre-treatment. Resistant genotypes were common among those with a positive test-of-cure (TOC): 90.9% of individuals with a positive TOC following azithromycin were infected with a macrolide-resistant strain, and 51.6% of those with a positive TOC following moxifloxacin were infected with a fluoroquinolone-resistant strain. However, genotype did not consistently predict TOC outcome, as 14.6% of those with negative TOCs following azithromycin had macrolide-resistant infections and 16.6% of those with negative TOCs following moxifloxacin had fluoroquinolone-resistant infections.

Conclusions

MARS 2024 is the largest dataset examining antimicrobial resistance in M. genitalium in England, confirming widespread macrolide resistance and increasing levels of fluoroquinolone and dual resistance, underscoring the importance of national surveillance to inform management guidelines.

Keywords

NGU (Non-gonococcal urethritis) < Bacterial disease Urethritis (bacterial) < Bacterial disease Europe < Location Epidemiology < Other Antibiotic < Other

Background

M. genitalium is a sexually transmitted pathogen that is often asymptomatic but is an established cause of non-gonococcal urethritis (NGU) and is associated with cervicitis and pelvic inflammatory disease (PID).¹ Although M. genitalium may present with a range of symptoms, it is often non-pathological and for this reason, asymptomatic screening for M. genitalium is not recommended in the UK. Instead, indications for testing are based on specific clinical syndromes such as PID and NGU, or in sexual partners.² Routine screening outside of these indications may lead to overdiagnosis and overtreatment.³

Treatment of M. genitalium infections is challenging due to intrinsically limited antimicrobial options and acquired antimicrobial resistance (AMR). Doxycycline has limited effectiveness as a monotherapy but can be used to reduce bacterial load in combination with another agent.⁴ Azithromycin, a macrolide antibiotic, is used as first-line therapy. However, its extensive use has been linked to a rise in macrolide resistance, with rates exceeding 50% in several regions globally.^5,6 Macrolide resistance is conferred by single base mutations in region V of the 23S rRNA gene, specifically at positions A2058 or A2059, that inhibit macrolide binding and are strongly associated with clinical treatment failure.⁷

The fluoroquinolone moxifloxacin is the recommended alternative treatment for macrolide-resistant infections, but moxifloxacin resistance is also a growing threat, with a recent review showing the resistance rate in the European non-Nordic region rising from 8.1% in 2015–2017 to 12.3% in 2018–2021.⁸ The effect of specific mutations on fluoroquinolone resistance in M. genitalium is not fully elucidated. Amino acid substitutions in the quinolone resistance-determining region (QRDR) of the parC gene, particularly at positions S83 and D87 (M. genitalium numbering), are associated with elevated moxifloxacin MICs and clinical treatment failure.^9–11 However, it is unclear whether parC substitutions beyond positions S83 and D87 confer moxifloxacin resistance, due to their rarity and insufficient phenotypic MIC and associated clinical outcome data.¹¹

Substitutions in the QRDR of the gyrA gene are less common and usually occur alongside a parC substitution, but their contribution to fluoroquinolone resistance is not well established. The combined presence of the parC S83I and gyrA M95I substitutions appears to be of particular importance, as individuals infected by ‘double mutation’ strains were twice as likely to fail treatment with moxifloxacin than those with parC substitutions alone.¹²

In the UK, the British Association for Sexual Health and HIV (BASHH) recommends a resistance-guided sequential approach.² This consists of doxycycline 100 mg twice daily for 7 days followed by azithromycin (1 g orally as a single dose, then 500 mg once daily for 2 days) where the organism is macrolide-sensitive or resistance status is unknown. Where macrolide resistance is confirmed, or azithromycin has failed, doxycycline is followed by moxifloxacin 400 mg once daily for 7 days. However, access to assays that detect macrolide resistance varies across UK sexual health services, meaning empiric therapy is often required. At the time of this analysis, a test-of-cure (TOC) was recommended 3-5 weeks after treatment initiation to confirm microbiological clearance, although more recent guidance no longer recommends a TOC where symptoms have resolved.^2,13

The M. genitalium Antimicrobial Resistance Surveillance (MARS) Programme was established by the UK Health Security Agency (UKHSA) to monitor annual trends in macrolide and fluoroquinolone resistance in England and examine the distribution of key demographic factors such as gender identity, sexual orientation, and age. Data are intended to support evidence-based updates to national treatment recommendations and guide clinical practice in the management of M. genitalium.² MARS was run as a pilot in 2019 and 2020, providing estimates of the prevalence of macrolide (69%) and fluoroquinolone resistance (8 to 11%). MARS has been perfomed as an annual programme at a larger scale since 2023. In the MARS 2023 sample, macrolide and fluoroquinolone resistance were detected in 62.2% and 12.1% of sequenced specimens, respectively, with increased resistance to both antibiotics in gay, bisexual, and other men who have sex with men (GBMSM).¹⁴ Here, we present the key findings from MARS 2024, the second year of MARS as a routine sentinel surveillance programme.

Methods

From 1^st March to 30^th June 2024, M. genitalium-positive specimens were collected from patients who attended 32 sexual health services (SHSs) and their associated 12 laboratories across England. Testing and treatment decisions were made at the discretion of clinicians at the participating SHSs, and specimens were collected as part of routine patient care.

M. genitalium positivity was confirmed at the UKHSA STI Reference Laboratory (STIRL) using an RT-PCR assay, which targets 2 intrinsic M. genitalium genes (MgPa and gap).^15,16 Sanger sequencing was performed on M. genitalium-positive specimens to establish molecular markers of resistance. Macrolide resistance was inferred from the detection of mutations in Region V of the 23S rRNA gene and fluoroquinolone resistance was inferred from amino acid substitutions within the QRDR of the parC gene. In specimens where the parC genotype was non-wildtype, the QRDR of the gyrA gene was also sequenced. Sequence data was analysed using BioNumerics v6.1 (Applied Maths).

Antimicrobial susceptibility results were securely linked to pseudonymised GUMCAD STI surveillance data to obtain demographic and clinical details. GUMCAD comprises a pseudonymised, depersonalised dataset of all SHS attendances in England. Data regarding services, tests, and diagnoses are coded by healthcare practitioners in keeping with surveillance reporting specifications. This data was further enriched with additional demographic, clinical, and behavioural information provided by SHSs.

Data analysis was performed using STATA v17.0 (StataCorp LP, College Station, TX) and the Sankey diagram (Figure 3) was generated using the SankeyMATIC tool.¹⁷ For the treatment analysis, test-of-cure (TOC) outcomes were categorised as positive or negative following treatment, with a positive TOC indicating persistence of M. genitalium infection and a negative TOC suggesting microbiological clearance. Some patients did not have a TOC, in some cases because they did not respond to recall or if the SHS did not offer them. Patients whose treatment journey was incomplete within the MARS sampling period and who would not yet have been offered a TOC were excluded from the treatment outcome analysis.

Differences in the prevalence of macrolide, fluoroquinolone, and dual resistance between MARS 2023 and 2024 were assessed using two-sample tests of proportions (z-test). A p-value of <0.05 was considered statistically significant.

Results

Full results are available in the MARS 2024 Report.¹⁸

Sample characteristics

A total of 1,049 individuals were diagnosed with M. genitalium and included in the MARS 2024 sample (Table 1). Among these, 65.6% were male, 68.1% of whom were heterosexual. Individuals most frequently belonged to the White ethnic group (50.6%) and the modal age group was 25–34 years (43.9%), with ages ranging from 15 to 73 years. The majority of individuals were born in the UK (66.5%) and just below half (47.7%) of individuals attended a SHS in London.

Table 1.

Demographic characteristics of individuals included in the MARS 2024 sample, by gender identity and sexual orientation, England [note 1, 2].

Characteristic		GBMSM	Heterosexual men	Women [note 3]	Other [note 4]	Total
Metric		n (% of N)	n (% of N)	n (% of N)	n (% of N)	n (% of N)
Number of individuals		212 (20.2%)	469 (44.7%)	358 (34.1%)	10 (1.0%)	1,049 (100.0%)
Age group (years)	15–24	24 (11.3%)	140 (29.9%)	159 (44.4%)	1 (10.0%)	324 (30.9%)
	25–34	101 (47.6%)	209 (44.6%)	142 (39.7%)	8 (80.0%)	460 (43.9%)
	35–44	71 (33.5%)	84 (17.9%)	46 (12.9%)	1 (10.0%)	202 (19.3%)
	≥45	16 (7.6%)	36 (7.7%)	11 (3.1%)	0 (0.0%)	63 (6.0%)
Ethnic group [note 5]	Asian	19 (9.4%)	35 (7.9%)	39 (11.3%)	0 (0.0%)	93 (9.3%)
	Black	33 (16.3%)	158 (35.7%)	51 (14.8%)	3 (42.9%)	245 (24.6%)
	Mixed	20 (9.9%)	51 (11.5%)	33 (9.6%)	1 (14.3%)	105 (10.6%)
	Other	8 (4.0%)	27 (6.1%)	13 (3.8%)	1 (14.3%)	49 (4.9%)
	White	122 (60.4%)	171 (38.7%)	208 (60.5%)	2 (28.6%)	503 (50.6%)
World region of birth	UK	114 (56.2%)	297 (67.4%)	243 (71.1%)	6 (85.7%)	660 (66.5%)
World region of birth	Outside of the UK	89 (43.8%)	144 (32.7%)	99 (29.0%)	1 (14.3%)	333 (33.5%)
Sexual health service location	London	138 (65.1%)	216 (46.1%)	142 (39.7%)	4 (40.0%)	500 (47.7%)
Sexual health service location	Outside of London	74 (34.9%)	253 (53.9%)	216 (60.3%)	6 (60.0%)	549 (52.3%)
HIV status	Living with HIV	21 (10.1%)	4 (0.9%)	2 (0.7%)	0 (0.0%)	27 (2.8%)
HIV status	Negative	186 (89.9%)	425 (99.1%)	307 (99.4%)	9 (100.0%)	927 (97.2%)
Use of HIV PrEP [note 6]	No	67 (37.6%)	418 (99.1%)	322 (99.4%)	8 (100.0%)	815 (87.4%)
Use of HIV PrEP [note 6]	Yes	111 (62.4%)	4 (0.9%)	2 (0.6%)	0 (0.0%)	117 (12.6%)
M. genitalium symptoms at diagnosis	No	35 (16.5%)	105 (22.4%)	207 (57.8%)	4 (40.0%)	351 (33.5%)
M. genitalium symptoms at diagnosis	Yes	177 (83.5%)	364 (77.6%)	151 (42.2%)	6 (60.0%)	698 (66.5%)
Concurrent STI diagnosis [note 7]	No	156 (78.0%)	389 (85.1%)	280 (81.6%)	8 (80.0%)	833 (82.5%)
	Yes	44 (22.0%)	68 (14.9%)	63 (18.4%)	2 (20.0%)	177 (17.5%)
	Gonorrhoea	25 (11.8%)	13 (2.8%)	18 (5.0%)	1 (10.0%)	57 (5.4%)
	Chlamydia	17 (8.0%)	50 (10.7%)	29 (8.1%)	0 (0.0%)	96 (9.2%)
	Syphilis	6 (2.8%)	4 (0.9%)	0 (0.0%)	0 (0.0%)	10 (1.0%)
	Other	6 (2.8%)	10 (2.1%)	21 (5.9%)	1 (10.0%)	38 (3.6%)
Previous STI diagnosis (last 12 months) [note 7]	No	100 (57.5%)	322 (81.5%)	256 (84.8%)	5 (71.4%)	683 (77.8%)
	Yes	74 (42.5%)	73 (18.5%)	46 (15.2%)	2 (28.6%)	195 (22.2%)
	Gonorrhoea	48 (22.6%)	23 (4.9%)	16 (4.5%)	1 (10.0%)	88 (8.4%)
	Chlamydia	28 (13.2%)	38 (8.1%)	22 (6.2%)	0 (0.0%)	88 (8.4%)
	Syphilis	6 (2.8%)	0 (0.0%)	1 (0.3%)	0 (0.0%)	7 (0.7%)
	Other	13 (6.1%)	26 (5.5%)	15 (4.2%)	1 (10.0%)	55 (5.2%)
Total sexual partners (past 3 months)	0–1	62 (32.1%)	269 (61.3%)	249 (76.4%)	6 (66.7%)	586 (60.6%)
	2–5	88 (45.6%)	160 (36.4%)	66 (20.2%)	2 (22.2%)	316 (32.7%)
	≥6	43 (22.3%)	10 (2.3%)	11 (3.4%)	1 (11.1%)	65 (6.7%)
Sexual partners whilst abroad (past 3 months)	No	78 (88.6%)	264 (90.4%)	210 (92.1%)	7 (87.5%)	559 (90.7%)
Sexual partners whilst abroad (past 3 months)	Yes	10 (11.4%)	28 (9.6%)	18 (7.9%)	1 (12.5%)	57 (9.3%)

Note 1. these percentages reflect the distribution of these characteristics among people attending the 32 sentinel SHSs participating in MARS 2024.

Note 2. individuals where demographic data was not reported are not included.

Note 3. includes women who have sex with men and women who have sex with women.

Note 4. includes individuals who are gender diverse and males where sexual orientation was not reported.

Note 5. ethnic categories are as specified by the Office for National Statistics (ONS).¹⁹

Note 6. HIV PrEP use is only shown among individuals who are HIV negative or where HIV status is unknown.

Note 7. some individuals had more than one concurrent or previous STI diagnosis, so appear in more than one total.

At diagnosis, 66.5% of individuals had signs and symptoms indicative of M. genitalium infection, with 83.5% of GBMSM and 77.6% of heterosexual men presenting with symptoms, compared to 42.2% of women. Of those who were asymptomatic or had symptoms not indicative of M. genitalium, 50.4% were tested because they were a contact.

At the time of M. genitalium diagnosis, 17.5% of individuals had a concurrent STI, most frequently chlamydia (9.2%) or gonorrhoea (5.4%). Over one fifth had been diagnosed with another STI in the past 12 months (22.2%), again most commonly chlamydia (8.4%) or gonorrhoea (8.4%). Individuals most frequently reported having 0–1 (60.6%) or 2–5 (32.7%) sexual partners in the 3 months prior to their M. genitalium diagnosis, and 9.3% reported having a sexual partner outside of the UK in the same time interval. Almost all (97.7%) specimens included in the sentinel surveillance sample were genital samples (including urine samples).

Antimicrobial resistance

Of the 1,049 specimens, 23S rRNA sequence data was available for 89.9%; parC sequence data was available for 83.3%; and data for both were available for 81.1% of specimens. The gyrA genotype was successfully investigated in 93.2% (n = 151) of eligible specimens.

Of all sequenced specimens, 63.6% had a 23S rRNA mutation associated with macrolide resistance, most commonly A2058G (50.0%) or A2059G (37.7%; Table 2). Fluoroquinolone resistance-associated parC substitutions were detected in 16.7% of all specimens, consisting of S83I (66.4%), D87N (19.9%), S83R (7.5%), D87Y (5.5%) or D87N and S83I (mixed; 0.7%). Other parC substitutions were identified in 1.8% of specimens and are currently of unknown clinical significance.

Table 2.

Frequency of 23S rRNA mutations and parC and gyrA amino acid substitutions associated with antimicrobial resistance in M. genitalium specimens included in the MARS 2024 sample, England (23S rRNA, n = 943; parC, n = 874; gyrA, n = 151).

Gene	Genotype/substitution	n (% of N)
23S rRNA	Susceptible	343 (36.4%)
	Resistant (total)	600 (63.6%)
	A2058G	300 (50.0%)
	A2059G	226 (37.7%)
	A2058T	56 (9.3%)
	A2059C	14 (2.3%)
	A2058C	2 (0.3%)
	Mixed A2058G and A2059G	2 (0.3%)
parC	Susceptible	712 (81.5%)
	Resistant (total)	146 (16.7%)
	S83I	97 (66.4%)
	D87N	29 (19.9%)
	S83R	11 (7.5%)
	D87Y	8 (5.5%)
	Mixed D87N and S83I	1 (0.7%)
	Unknown [note 1]	16 (1.8%)
gyrA	Susceptible	139 (92.1%)
	Resistant (total)	12 (7.9%)
	D99G	4 (33.3%)
	D99N	3 (25.0%)
	M95I	3 (25.0%)
	D99Y	2 (16.7%)

Note 1. Includes S83N (n = 6), G81C (n = 3), S84P (n = 3), D82N (n = 1), N91I (n = 1), P62S and G81C (mixed; n = 1), and S83I and S83N (mixed; n = 1) amino acid substitutions.

Among the 162 specimens with parC substitutions, 7.9% (n = 12) also harboured substitutions in the gyrA gene that may act synergistically with parC substitutions to confer fluoroquinolone resistance. The gyrA substitutions were D99G (n = 4), D99N (n = 3), M95I (n = 3), and D99Y (n = 2) while the corresponding parC substitutions were S83I (n = 10), D87Y (n = 1) and S83R (n = 1). All specimens with both parC and gyrA substitutions were also genotypically resistant to macrolides.

Dual resistance, defined as the presence of both macrolide resistance and fluoroquinolone resistance-associated parC substitutions, was detected in 13.7% of specimens. Of the specimens with parC substitutions, 83.0% also carried mutations predictive of macrolide resistance (where 23S rRNA testing was successful).

In MARS 2024, macrolide resistance (63.6%) remained stable when compared with 2023 (62.2%; p = 0.53); resistance levels in both years remained lower than those observed in the pilot years (∼69%; Figure 1). Fluoroquinolone resistance increased significantly to 16.7% in 2024, rising from 12.1% in 2023 (p = 0.008). Similarly, dual resistance increased significantly to 13.7% in 2024, an increase from 10.1% in 2023 (p = 0.024).

Figure 1.

The percentage of M. genitalium specimens with genetic markers predictive of macrolide, fluoroquinolone, and dual resistance in the MARS pilots (2019 and 2020), MARS 2023 and 2024 sentinel surveillance sample, England.

Demographic differences

Differences in resistance patterns were seen across demographic groups in MARS 2024, as in 2023 (Figure 2). In 2024, both macrolide and fluoroquinolone resistance were most prevalent in specimens from GBMSM at 79.6% and 29.8%, respectively (Figure 2a). Specimens from individuals reporting an STI diagnosis in the previous 12 months were more frequently macrolide (76.0%) and fluoroquinolone (20.9%) resistant in 2024, compared to those without a previous STI diagnosis in the last 12 months (Figure 2b). The prevalence of macrolide resistance was lowest among specimens from the oldest age group (50.0% in those aged ≥45), whereas fluoroquinolone resistance was highest in the older age groups (20.8% in those aged ≥45 and 20.6% in those aged 35–44; Figure 2c).

Figure 2.

The percentage of macrolide- and fluoroquinolone-resistant M. genitalium specimens in the MARS 2023 and 2024 sentinel surveillance sample by (a) gender identity and sexual orientation, (b) previous STI diagnosis (last 12 months), and (c) age group, England.

Prescribing practices

Antimicrobial prescribing data was available for all individuals and is summarised up to the second treatment prescribed (Figure 3).

Figure 3.

Sankey diagram showing the number of individuals prescribed each antimicrobial (combination) as their first or second treatment for M. genitalium infection in the MARS 2024 sentinel surveillance sample, England.

First treatment

Most individuals (87.3%; n = 916) were prescribed the recommended first- or second-line treatments of azithromycin (n = 546) or moxifloxacin (n = 374), either as monotherapy or in combination with other antibiotics. Over three-quarters of all patients were initially pre-treated with doxycycline (80.8%; n = 835). Among those who received azithromycin monotherapy as their first treatment, 95.4% (n = 514) received doxycycline pre-treatment, compared with 60.4% (n = 223) of those treated with moxifloxacin monotherapy. Of all patients, 7.5% (n = 77) received only doxycycline with no further treatment.

Doxycycline pre-treatment was not given to 19.2% (n = 198) of individuals. Of these, 9.5% (n = 19) received azithromycin, 69.2% (n = 137) received moxifloxacin, and 3.0% (n = 6) received other antibiotics or antibiotic combinations at their first SHS attendance noted within MARS 2024. Additionally, 3.4% (n = 36) of patients did not receive any treatment. A small number of patients were not prescribed the recommended first- or second-line therapy or were prescribed them in combination with another antibiotic (2.2%; n = 23).

Second treatment

Among patients who received azithromycin as their first treatment, 69.0% (n = 372) had no further treatment; 83.0% (n = 274) of those who received only azithromycin had a macrolide-susceptible infection. A small number of patients (1.7%; n = 9) received a second course of azithromycin, while 27.6% (n = 149) were switched to moxifloxacin. Of the patients who were switched to moxifloxacin, 95.1% (n = 137) had a macrolide-resistant specimen (where resistance data was available).

Similarly, among those who received moxifloxacin as their first treatment, 94.3% had no further treatment (n = 348); 79.2% (n = 236) of those who received only moxifloxacin had a fluoroquinolone-susceptible infection. The remaining patients either received a second course of moxifloxacin (3.0%; n = 11), were switched to azithromycin (0.5%; n = 2), or were switched to another antibiotic (2.2%; n = 8). Of individuals who received a second treatment after moxifloxacin, 65.0% (n = 13) had a fluoroquinolone-resistant infection (11 S83I, 1 D87N, and 1 D87N and S83I (mixed) substitutions in parC). Additionally, 30.8% (n = 4) had a concurrent gyrA mutation (M95I, n = 2; D99G, n = 1; D99Y, n = 1) and all of these occurred in specimens with an S83I parC substitution (where sequence data was available).

Subsequent treatments

Treatment beyond a second course was uncommon, with 2.2% (n = 23) of patients receiving a third or subsequent treatment. In total, 37 such treatment courses were prescribed: 23 third courses, 8 fourth courses, 3 fifth courses, 2 sixth courses, and 1 seventh course. These treatments were predominantly azithromycin, moxifloxacin, minocycline and pristinamycin. Among patients who received a third or subsequent treatment, 90.9% (n = 20) had macrolide-resistant infections, 45.0% (n = 9) had fluoroquinolone-resistant infections, and 39.1% (n = 9) had dual-resistant infections. Following these treatments, 35.1% (n = 13) returned a positive TOC, 27.0% (n = 10) returned a negative TOC, 27.0% (n = 10) had no TOC and 10.8% (n = 4) had no TOC information available.

Resistance-associated mutations and treatment outcomes

A TOC result was available for 54.5% (n = 224) of patients prescribed azithromycin. Of those with a TOC result available, 29.5% (n = 66) had a positive TOC and 90.9% of these individuals had a macrolide-resistant infection (n = 60; Figure 4(a)). Where data was available, 71.0% (n = 39) of patients with a positive TOC experienced clinical failure, i.e. remained symptomatic. However, macrolide resistance mutations were not unequivocally associated with treatment failure; 14.6% (n = 23) of individuals with a known negative TOC also had infections with these mutations. Among patients where a TOC result wasn’t available, 26.7% (n = 50) had a macrolide-resistant infection. The most common reason that a TOC was not conducted among these patients was because they did not respond to recall (76.9%; n = 30).

Figure 4.

M. genitalium resistance genotype by TOC result following treatment with (a) azithromycin and (b) moxifloxacin in the MARS 2024 sentinel surveillance sample, England.

A TOC result following moxifloxacin treatment was available for 58.9% (n = 242) of patients. When a TOC result was available, 12.8% of patients had a positive TOC (n = 31). The highest percentage of resistant specimens, 51.6%, was observed among this group (n = 16; Figure 4(b)). Of these 16 individuals, 35.7% (n = 5) were infected with a gyrA-mutated strain. ParC amino acid substitutions were not fully predictive of TOC outcomes: among those with a negative TOC, 16.6% (n = 35) had a resistant specimen. Where a TOC result wasn’t available, the percentage of resistant specimens was similar to those with a negative TOC (18.3%; n = 31). In most cases (60.9%; n = 14), the reason a TOC wasn’t conducted was because the patient didn’t respond to recall, whereas reported symptom resolution accounted for only 4.3% (n = 1). A TOC was also not conducted among 34.8% of patients (n = 8) because the SHS did not routinely offer them for M. genitalium infection.

Discussion

The MARS 2024 collection is the largest dataset to examine the pattern of AMR in M. genitalium in England. Macrolide resistance remains high in 2024, with no significant change since 2023. Fluoroquinolone resistance showed a significant increase from 2023, and a year-on-year rise since 2019. Dual resistance to both antimicrobial classes also increased significantly compared to 2023, predominantly due to the rise in fluoroquinolone resistance. Specimens from GBMSM had higher rates of macrolide and fluoroquinolone resistance compared with other gender identity and sexual orientation groups. These findings are consistent with recent international surveillance data reporting persistently high macrolide resistance and increasing fluoroquinolone resistance in M. genitalium populations worldwide.⁸

In the MARS 2024 sample, almost half of diagnoses among those who were asymptomatic or those with non-M. genitalium symptoms were from individuals not identified as contacts of an M. genitalium case, suggesting some testing contrary to current BASHH guidance, which does not recommend asymptomatic screening.² Most individuals were prescribed the recommended first- or second-line treatments recommended by BASHH, azithromycin and moxifloxacin. While the prescribing data may not be complete for all individuals due to the sentinel time period of MARS, our data provides useful insight into how AMR is shaping real-world prescribing practices. The findings from MARS suggest that AMR results were used to guide treatment decisions: most patients whose first recorded treatment in MARS 2024 was moxifloxacin were infected with a macrolide-resistant strain. This aligns with current guidance recommending fluoroquinolones as a first-line option when macrolide resistance is detected or when a patient has previously experienced treatment failure.²

Although most patients with a positive TOC following azithromycin treatment had a macrolide- resistant infection, 14.6% of those with a negative TOC were also infected with a resistant strain. Almost all patients who were treated with azithromycin also received doxycycline, which may have contributed to azithromycin treatment success by reducing bacterial load.⁴ Spontaneous self-clearance – reported as 55% at 3 months in a Ugandan cohort – could also have influenced observed outcomes but could not be assessed within MARS.²⁰

Other studies have reported high cure rates with empiric azithromycin therapy (defined as either a negative TOC or symptom resolution) in populations with high resistance or among cohorts with resistant infections.^21–23 These observations are consistent with our data and suggest that 23S rRNA mutations are not entirely specific predictors of treatment outcome. In these studies, however, treatment outcomes were assessed 2–4 weeks after completion of therapy, whereas our data do not include information on the timing of a TOC.

For moxifloxacin, the correlation between parC amino acid substitutions and TOC outcome was less well defined in MARS 2024. Of the patients with a positive TOC, just over half had mutations in the parC gene and approximately one third of the parC mutants also had mutations in the gyrA gene. This is consistent with studies that have shown that the presence of mutations in both genes is a strong predictor of moxifloxacin treatment failure.¹² However, almost half of patients with a positive TOC result had a fluoroquinolone-sensitive genotype, which could reflect incomplete adherence to treatment, reinfection, or if a TOC was performed before all residual DNA had been cleared.²⁴ Despite this, the percentage of parC-mutated specimens was lower among those with a negative TOC (16.6%), suggesting that fluoroquinolone resistance-associated mutations likely contribute to moxifloxacin treatment failure, but are not sufficient as a sole predictor, consistent with findings from clinical studies.²⁵ Preliminary data has suggested that there may be an association between other par genes and elevated moxifloxacin MICs, however more data is required to fully delineate their role.²⁶

Treatment outcomes were difficult to accurately ascertain as a TOC result was not always available. The most common reason a TOC wasn’t performed was because the patient did not respond to recall. It is likely that some individuals did not return as their symptoms had resolved and clinical cure had been achieved. The 2025 BASHH guidelines no longer recommend a TOC in cases of symptom resolution.² Supporting this, the percentages of macrolide- and fluoroquinolone-resistant specimens were similar between patients with a negative TOC and those with an unknown TOC outcome, suggesting that assuming treatment success in the absence of a TOC provides a reasonable proxy for treatment success.

A limitation of MARS is possible selection bias; SHS participation was largely determined by the availability of local M. genitalium testing and subsequent reporting to GUMCAD. However, comparison with GUMCAD data suggests the MARS sample is broadly representative of national M. genitalium diagnoses.²⁷

Conclusions

The MARS 2024 sentinel surveillance programme provides the most comprehensive picture to date of the AMR landscape in M. genitalium in England, building on previous MARS findings from 2023. High levels of macrolide resistance remain, with evidence of increasing fluoroquinolone and dual resistance. Despite this, some genotypically resistant infections appear to respond to the corresponding antimicrobial.

The inclusion of detailed demographic data within MARS enables analysis of AMR patterns across different population groups, offering valuable insight into disparities, with GBMSM being most affected by M. genitalium AMR. Longitudinal monitoring of AMR in M. genitalium will provide better understanding of changes in resistance patterns and guide future management strategies, such as appropriate testing for M. genitalium.

Footnotes

ORCID iD

Kirsty F. Bennet

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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