Important considerations regarding the widespread use of doxycycline chemoprophylaxis against sexually transmitted infections

Exceedingly high levels of tetracycline resistance in Neisseria gonorrhoeae in eight WHO Enhanced Gonococcal Antimicrobial Surveillance Programme countries in three WHO regions, 2021-2024-doxycycline post-exposure prophylaxis will unlikely impact gonorrhoea burdens

OBJECTIVES

Doxycycline post-exposure prophylaxis (doxycycline-PEP) can reduce incident cases of syphilis, chlamydia and possibly gonorrhoea especially among men who have sex with men with recent bacterial sexually transmitted infections (STIs). Owing to potential implementation of doxycycline-PEP internationally, global tetracycline/doxycycline resistance data for contemporary Neisseria gonorrhoeae isolates has become imperative. We report tetracycline resistance data for gonococcal isolates (n = 2993) from eight WHO Enhanced Gonococcal Antimicrobial Surveillance Programme (EGASP) countries in three WHO regions in 2021-2024, i.e. to estimate potential impact of doxycycline-PEP on the incident gonorrhoea cases in these WHO EGASP countries.

METHODS

WHO EGASP isolates cultured from men with urethral discharge in Cambodia (n = 482), Indonesia (n = 101), Malawi (n = 121), The Philippines (n = 843), South Africa (n = 597), Thailand (n = 250), Uganda (n = 350) and Vietnam (n = 249) in 2021-2024 were examined. MICs (mg/L) of tetracycline were determined using Etest.

RESULTS

The tetracycline resistance (range) using the current EUCAST (MIC > 0.5 mg/L) and CLSI (MIC > 1 mg/L) clinical resistance breakpoints in the eight WHO EGASP countries was 92.2% (83.5%-99.6%) and 80.6% (66.3%-98.6%), respectively. Using a previous minocycline-PEP resistance breakpoint (MIC > 2 mg/L) and breakpoint for high-level plasmid (tetM)-mediated tetracycline resistance (MIC > 8 mg/L), the tetracycline resistance (range) was 77.3% (47.4%-98.6%) and 74.3% (31.3%-98.6%), respectively.

CONCLUSIONS

The exceedingly high levels of gonococcal tetracycline resistance (independent of resistance breakpoint used) in the eight WHO EGASP countries elucidate that doxycycline-PEP will unlikely significantly reduce the gonorrhoea cases in these countries. Furthermore, doxycycline-PEP might rapidly select for additional gonococcal strains with tetracycline resistance (low- and high-level) and MDR/XDR strains, i.e. because these strains are mostly resistant to tetracycline.

Revisiting the potential impact of doxycycline post-exposure prophylaxis on the selection of doxycycline resistance in Neisseria commensals

Doxycycline post-exposure prophylaxis (doxy-PEP) is a strategy to reduce bacterial sexually transmitted infections. However, the impact of doxy-PEP on resistance emergence is as of yet unclear. Commensal Neisseria are known reservoirs of resistance for gonococci through horizontal gene transfer (HGT), and are more likely to experience bystander selection from doxy-PEP as they are universally carried. The consequences of doxycycline selection on commensal Neisseria will be critical to investigate to understand possible resistance mechanisms that may be transferred to an important human pathogen. Here, collection of commensals from human hosts demonstrated 46% of isolates carry doxycycline resistance; and doxycycline resistance was significantly greater in participants self-reporting doxycycline use in the past 6 months. High-level doxycycline resistance (> 8 µg/mL) was always associated with the ribosomal protection protein (tetM) and pConj. In vitro selection of Neisseria commensals (N. cinerea, N. canis, N. elongata, and N. subflava) resulted in 12 of 16 lineages evolving doxycycline resistance (> 1 µg/mL). An A46T substitution in the repressor of the Mtr efflux pump (MtrR) and a V57M substitution in the 30 ribosomal protein S10 were associated with elevated MICs. Mutations in ribosomal components also emerged (i.e., 16 S rRNA G1057C, RplX A14T). We find the MtrR 46T, RpsJ 57M, and RplX 14T in natural commensal populations. In vitro co-evolution of N. gonorrhoeae with Neisseria commensals demonstrated rapid transfer of the pConj plasmid to N. subflava and N. cinerea, and pbla to N. cinerea. This work underscores the importance of commensal Neisseria as reservoirs of doxycycline resistance, and demonstrates a link between doxycycline use and the emergence of resistance. Though novel chromosomal resistance mutations are nominated herein, resistance emergence in natural commensal populations appears to be mainly associated with acquisition of the tetM gene. A secondary danger to pConj acquisition, is spread of pbla and β-lactam resistance, which we demonstrate here in vitro. Ultimately, characterizing the contemporary prevalence of doxycycline resistance, and underlying resistance mechanisms, in commensal communities may help us to predict the long-term impact of doxy-PEP on Neisseria, and the likelihood of transferring resistance across species' boundaries.

A Qualitative Study of Doxycycline Postexposure Prophylaxis Knowledge, Attitudes, and Practices Among Health Care Providers in New York City

BACKGROUND

Three randomized controlled trials have demonstrated the efficacy of doxycycline for bacterial sexually transmitted infection postexposure prophylaxis (Doxy PEP). Few studies have assessed provider knowledge, attitudes, and practices (KAP) regarding Doxy PEP implementation. Between July of 2023 and January 2024, this study qualitatively assessed KAP and intention to prescribe Doxy PEP among health care providers in the New York City area.

METHODS

In-depth, semistructured individual interviews were conducted with 18 health care provider key informants including physicians, nurse practitioners, and physician assistants from various practice settings. Transcripts were analyzed using inductive KAP codes, with additional deductive coding used to identify emergent subthemes.

RESULTS

The following themes were identified: (1) STI Disparities, (2) Doxy PEP Experience, (3) Doxy PEP Benefits, (4) Doxy PEP Concerns, and (5) Doxy PEP Implementation. Doxy PEP knowledge was high, with all providers being aware and most (78%) having prescribed it to at least one patient at the time of interview. Providers were knowledgeable of factors contributing to high rates of STIs. Benefits included reducing STI anxiety. Concerns included contributing to antimicrobial resistance and impacts on microbiota. Practice implications included challenges getting Doxy PEP approved by the pharmacy. These factors were shown to affect Doxy PEP's perceived acceptability.

CONCLUSIONS

To ensure that Doxy PEP is implemented safely and equitably, KAP factors that may influence provider decision making should be examined. Understanding providers' KAP and how they affect intention to prescribe Doxy PEP, and to what patients, has important implications for successful implementation.

DOXY do, or DOXY Don't? Syphilis and doxycycline post-exposure prophylaxis: A case report

The resurgence of syphilis across Europe has led to a growing number of atypical cases, often characterised by varied symptoms that can delay diagnosis. We report the case of a young man who has sex with men (MSM), presenting with persistent headaches and swelling of the forehead suggestive of giant cell arteritis (GCA). Despite a recent negative syphilis test, further investigations confirmed the diagnosis of neurosyphilis. The patient had been using doxycycline post-exposure prophylaxis (DoxyPEP), which is suspected to have delayed the diagnosis by masking the typical antibody response. This case highlights concerns about DoxyPEP's impact on syphilis detection and disease progression. Further research is warranted to explore its effects on antimicrobial resistance, the human microbiome, and clinical outcomes.

Doxycycline Postexposure Prophylaxis and Bacterial Sexually Transmitted Infections Among Individuals Using HIV Preexposure Prophylaxis

Importance

Doxycycline postexposure prophylaxis (doxyPEP) has been shown to decrease the incidence of bacterial sexually transmitted infections (STIs) among people assigned male sex at birth in clinical trials, but data from clinical practice are limited.

Objective

To describe early uptake of doxyPEP and evaluate changes in STI incidence following doxyPEP initiation.

Design, Setting, and Participants

This retrospective cohort study of adults (aged ≥18 years) dispensed HIV preexposure prophylaxis (PrEP) at Kaiser Permanente Northern California during November 1, 2022, to December 31, 2023, examined electronic health record data to compare HIV PrEP users dispensed and not dispensed doxyPEP and rates of bacterial STIs before and after starting doxyPEP. Individuals were followed up from their first recorded STI test on or after November 1, 2020, until December 31, 2023, or discontinuation of health plan membership.

Exposure

Pharmacy dispensing data were used to define doxyPEP recipients.

Main Outcomes and Measures

Demographic and clinical characteristics were compared between individuals dispensed and not dispensed doxyPEP. Primary outcomes were incident chlamydia, gonorrhea, or infectious syphilis measured as quarterly STI positivity (proportion of individuals testing positive at least once per quarter). Among doxyPEP recipients, rate ratios (RRs) compared mean quarterly STI positivity from 24 months before to 12 months after starting doxyPEP. In an exploratory analysis, STI trends were evaluated for the full cohort, stratified by receipt of doxyPEP.

Results

Among 11 551 HIV PrEP users (mean [SD] age, 39.9 [12.1] years; 95.1% male), 2253 (19.5%) were dispensed doxyPEP, of whom 2228 (98.9%) were male and 1096 (48.6%) had an STI in the year before starting doxyPEP. Compared with individuals not dispensed doxyPEP, doxyPEP recipients were older (mean [SD] age, 40.4 [10.8] vs 39.8 [12.4] years; P = .04) and had used HIV PrEP longer (mean [SD], 4.2 [2.8] vs 3.4 [2.6] years; P < .001), and a higher proportion were commercially insured (2091 [92.8%] vs 8270 [88.9%]; P < .001). Among doxyPEP recipients, quarterly chlamydia positivity decreased from 9.6% (95% CI, 9.0%-10.3%) before starting doxyPEP to 2.0% (95% CI, 1.5%-2.6%) after starting doxyPEP (RR, 0.21; 95% CI, 0.16-0.27; P < .001), with significant declines for each anatomic site of infection. Quarterly gonorrhea positivity decreased from 10.2% (95% CI, 9.6%-10.9%) before starting doxyPEP to 9.0% (95% CI, 8.0%-10.1%) after starting doxyPEP (RR, 0.88; 95% CI, 0.77-1.00; P = .048); site-specific declines were significant for rectal (RR, 0.81; 95% CI, 0.67-0.97; P = .02) and urethral (RR, 0.56; 95% CI, 0.40-0.79; P = .001) gonorrhea, but not pharyngeal gonorrhea. Quarterly syphilis positivity decreased from 1.7% (95% CI, 1.4%-1.9%) before starting doxyPEP to 0.3% (95% CI, 0.2%-0.6%) after starting doxyPEP (RR, 0.20; 95% CI, 0.11-0.37; P < .001). Positivity for STIs remained stable in individuals not dispensed doxyPEP.

Conclusions and Relevance

This study found that receipt of doxyPEP was associated with substantial declines in chlamydia and syphilis incidence and modest declines in urethral and rectal gonorrhea incidence among individuals using HIV PrEP. These findings suggest that doxyPEP may offer substantial benefits for reducing population-level STI transmission with broader implementation.

Acceptability and feasibility of pre-exposure prophylaxis for bacterial STIs: a systematic review

BACKGROUND

A recent resurgence of bacterial sexually transmitted infections (STIs) is placing a major burden on high-risk populations, physicians, and the healthcare system. Treatment in the form of antibiotic pre-exposure prophylaxis (STI PrEP) is a potential solution. However, little is known about the acceptability and feasibility of this approach in high-risk populations.

METHODS

A comprehensive search strategy was developed and executed in October 2024 across six databases adhering to PRISMA guidelines.

RESULTS

Eight studies met the inclusion criteria. These studies were all conducted in high-income countries, used various methods, and all focussed on sexual minority men. Findings consistently identified moderate to high levels of acceptability among GBMSM (54.3% - 67.5%). Factors such as engagement in perceived 'high risk' sexual encounters, and past diagnosis of STIs strengthened acceptability, while others (e.g., antimicrobial resistance concerns and stigma) act as barriers. Only one study included the perspectives of healthcare workers, indicating a moderate willingness to prescribe, which would increase under governing-body endorsement.

DISCUSSION

Overall, while there is some promise of STI PrEP acceptability among GBMSM, vast gaps in knowledge remain. Knowledge transfer and feasibility and, hence, the sustainability and capacity needed for the success of STI PrEP is yet to be examined and understood. However, for STI PrEP to be successfully adopted, it is essential not only to assess its acceptability and feasibility but also to focus on knowledge transfer. Knowledge transfer is a dynamic and iterative process, involving the synthesis, dissemination, exchange, and application of knowledge in an ethically sound manner. This process supports the improvement of health outcomes, strengthens healthcare systems, and ensures that healthcare interventions, such as STI PrEP, are effectively understood and implemented by both healthcare providers and at-risk populations. Similarly, the perspectives of populations beyond GBMSM have been omitted, and there is little understanding of the impact of their differing socio-cultural contexts around sex-related behaviour and Western pharmaceutical healthcare interventions on their acceptance and uptake.

CONCLUSION

Further research into acceptability, feasibility and knowledge transfer among diverse high-risk groups, healthcare professionals, and policymakers is necessary to create a strong foundation for implementing STI PrEP.

Doxycycline as Post-Exposure Prophylaxis: Awareness, Beliefs, and Interest Among Patients with and at Risk for HIV

Recent studies have demonstrated the efficacy of doxycycline as post-exposure prophylaxis (doxy-PEP) for sexually transmitted infection (STI) prevention, but little is known regarding patient beliefs and interest in doxy-PEP. We conducted a cross-sectional survey of adults (≥ 19 years) receiving care for HIV treatment (PWH) or prevention (pre-exposure prophylaxis, PrEP) between May-October 2023. The 32-question survey was organized into three parts: doxy-PEP awareness/beliefs/interest/concerns, sexual history, and demographics. Fishers Exact and Wilcoxon rank sum tests were used to compare responses between groups. Multivariate logistic regression identified predictive factors for doxy-PEP interest and concern(s). 166 participants completed the survey. Mean age was 43 years, 83% were male, 22% Black, and 13% Hispanic. Forty-one participants (25%) were on PrEP. Most respondents (75%) were unaware of doxy-PEP. Factors associated with doxy-PEP interest were respondents prescribed PrEP (aOR 2.67; 95% CI, 1.15-6.21) and belief of high risk for STI (aOR, 4.50; 95% CI, 2.24-9.07). Higher doxy-PEP concerns were associated with age ≤40 years (aOR, 3.10; 95% CI, 1.47-6.52), > high school education (aOR, 3.47; 95% CI, 1.64-7.33), and belief of high risk for STI (aOR, 2.58; 95% CI, 1.21-5.50). In this single-site cohort survey study, most respondents were unaware of doxy-PEP but expressed interest and low levels of overall concern. Clinicians should offer doxy-PEP access to all patients at high risk for STIs or requesting the treatment after shared decision-making discussions.

Doxycycline post-exposure prophylaxis among men who have sex with men and transgender women in Belgium: awareness, use and antimicrobial resistance concerns in a cross-sectional online survey

OBJECTIVES

We aimed to assess the awareness, willingness to use and use of doxycycline post-exposure prophylaxis (doxyPEP) among men who have sex with men (MSM) and transgender women (TGW) in Belgium. Additionally, we aimed to identify factors associated with doxyPEP use and concerns regarding antimicrobial resistance (AMR).

METHODS

Cross-sectional online survey among MSM and TGW in Belgium in April 2024. Participants were recruited through sexual networking applications and social media of community-based organisations. Numerical variables were compared with Wilcoxon rank-sum test and categorical variables with χ2 or Fisher's exact tests. Factors associated with doxyPEP use were assessed using logistic regression. Willingness to use doxyPEP and concerns about side effects/AMR were assessed before and after presenting a brief paragraph on the potential effects of doxyPEP on AMR.

RESULTS

875 individuals initiated the survey. Almost all identified as men (860/875, 98.3%) with a median age of 40 years (IQR 32-48), 40.4% (n=352/875) had heard of doxyPEP and 9.4% (n=82/875) had used it, among whom the majority used it within the previous 6 months (70/81, 86.4%). In multivariable logistic regression, doxyPEP use was associated with reporting ≥1 sexually transmitted infection (STI) in the previous 12 months, engagement in chemsex, HIV status and pre-exposure prophylaxis use, and education level.About 80% of the participants initially reported being willing to use doxyPEP, and about 50% reported being concerned about side effects. After reading about the potential effects of doxyPEP on AMR, willingness to use decreased to 60% and concerns of side effects/AMR increased to around 70%.

CONCLUSIONS

Approximately 1 in 10 MSM in Belgium reported using doxyPEP. A recent history of STIs and STI risk factors were positively associated with doxyPEP use. Importantly, concerns about AMR and side effect influenced willingness to use doxyPEP. If doxyPEP is introduced, informing patients about doxyPEP benefits and risks is crucial to enable informed decision-making.

Re-visiting the potential impact of doxycycline post-exposure prophylaxis (doxy-PEP) on the selection of doxycycline resistance in Neisseria commensals

Doxycycline post-exposure prophylaxis (doxy-PEP) is a preventative strategy demonstrated to reduce bacterial sexually transmitted infections in high-risk populations. However, the impact of doxy-PEP on antibiotic resistance acquisition in key members of our microbiomes, is as of yet unclear. For example, commensal Neisseria are known reservoirs of resistance for gonococci through horizontal gene transfer (HGT), and are more likely to experience bystander selection due to doxy-PEP as they are universally carried. Thus, the consequences of doxycycline selection on commensal Neisseria will be critical to investigate to understand possible resistance mechanisms that may be transferred to an important human pathogen. Here, we use in vitro antibiotic gradients to evolve four Neisseria commensals (N. cinerea, N. canis, N. elongata, and N. subflava, n=4 per species) across a 20-day time course; and use whole genome sequencing to nominate derived mutations. After selection, 12 of 16 replicates evolved doxycycline resistance (> 1 μg/mL). Across resistant lineages: An A46T substitution in the repressor of the Mtr efflux pump (MtrR) and a V57M substitution in the 30 ribosomal protein S10 were clearly associated with elevated MICs. Additional mutations in ribosomal components also emerged in strains with high MICs (i.e., 16S rRNA G1057C, RplX A14T). We find the MtrR 46T, RpsJ 57M, and RplX 14T circulating in natural commensal populations. Furthermore, in vitro co-evolution of N. gonorrhoeae with Neisseria commensals demonstrated rapid transfer of the pConj plasmid to N. subflava and N. cinerea, and pbla to N. cinerea. Finally, collection of novel commensals from human hosts reveals 46% of isolates carrying doxycycline resistance; and doxycycline resistance was significantly greater in participants self-reporting doxycycline use in the past 6 months. High-level doxycycline resistance (> 8 μg/mL) was always associated with carriage of the ribosomal protection protein (tetM) and pConj. Ultimately, characterizing the contemporary prevalence of doxycycline resistance, and underlying resistance mechanisms, in commensal communities may help us to predict the long-term impact of doxy-PEP on Neisseria, and the likelihood of transferring particular genotypes across species' boundaries.

Long-term 4CMenB Vaccine Effectiveness Against Gonococcal Infection at Four Years Post-Program Implementation: Observational Case-Control Study

Background

A 4-component meningococcal B (4CMenB) vaccine program was introduced in adolescents in 2019 in South Australia. We aimed to evaluate long-term vaccine effectiveness (VE) and impact (VI) on gonococcal infection 4 years after implementation of the program.

Methods

Disease notification data were provided by SA Health. VE was estimated as the reduction in the odds of infection using the screening and case-control methods. Time-to-event analyses assessed vaccine effect on reinfections. VI was estimated as incidence rate ratios (IRRs) using negative binomial regression models.

Results

At 4 years after implementation of the program, 2-dose VE against gonococcal infection was 44.3% (95% CI, 35.1%-52.2%) using chlamydia patients as controls. Lower VE estimates were demonstrated in those >48 months post-4CMenB vaccination (26.2%; 95% CI, -2.6% to 47.0%) compared with those who had been vaccinated within ≤48 months (46.0%; 95% CI, 36.3%-54.2%). Slightly higher VE estimates were observed in females (48.7%; 95% CI, 36.9%-58.2%) compared with males (38.0%; 95% CI, 22.0%-50.7%). The risk of a second episode of gonococcal infection was lower in vaccinated gonococcal cases (adjusted hazard ratio, 0.682; 95% CI, 0.450-1.034). The adjusted IRR was 0.635 (95% CI, 0.421-0.957), with an observed 36.5% reduction in gonococcal infection.

Conclusions

4CMenB demonstrates moderate effectiveness against gonococcal infection, with a lower VE estimate after 4 years postvaccination. 4CMenB may reduce the risk of recurrent gonococcal infection. The requirement for a booster dose and dosing interval warrants evaluation.

Knowledge, uptake and intention to use antibiotic post-exposure prophylaxis and meningococcal B vaccine (4CMenB) for gonorrhoea among a large, online community sample of men and gender-diverse individuals who have sex with men in the UK

Novel STI prevention interventions, including doxycycline post-exposure prophylaxis (doxyPEP) and meningococcal B vaccination (4CMenB) against gonorrhoea, have been increasingly examined as tools to aid STI control. There is evidence of the efficacy of doxyPEP in preventing bacterial STIs; however, limited data exist on the extent of use in the UK. We examined self-reported knowledge and use of antibiotic post-exposure prophylaxis (PEP), and intention to use (ITU) doxyPEP and 4CMenB among a large, community sample of men and gender-diverse individuals who have sex with men in the UK. Using data collected by the RiiSH survey (November/December 2023), part of a series of online surveys of men and other gender-diverse individuals in the UK, we describe (%, [95% CI]) self-reported knowledge and use of antibiotic PEP (including doxyPEP) and doxyPEP and 4CMenB ITU. Using bivariate and multivariable logistic regression, we examined correlates of ever using antibiotic PEP, doxyPEP ITU, and 4CMenB ITU, respectively, adjusting for sociodemographic characteristics and a composite marker of sexual risk defined as reporting (in the last three months): ≥5 condomless anal sex partners, bacterial STI diagnosis, chemsex, and/or meeting partners at sex-on-premises venues, sex parties, or cruising locations. Of 1,106 participants (median age: 44 years [IQR: 34-54]), 34% (30%-37%) knew of antibiotic PEP; 8% (6%-10%) ever reported antibiotic PEP use. Among those who did, most reported use in the last year (84%, 73/87) and exclusively used doxycycline (69%, 60/87). Over half of participants reported doxyPEP ITU (51% [95% CI: 47%-56%], 568/1,106) while over two-thirds (64% [95% CI: 60%-69%], 713/1,106) reported 4CMenB ITU. Participants with markers of sexual risk and with uptake of other preventative interventions were more likely to report ever using antibiotic PEP as well as doxyPEP and 4CMenB ITU, respectively. HIV-PrEP users and people living with HIV (PLWHIV) were more likely to report antibiotic PEP use and doxyPEP and 4CMenB vaccination ITU than HIV-negative participants not reporting recent HIV-PrEP use. Findings demonstrate considerable interest in the use of novel STI prevention interventions, more so for 4CMenB vaccination relative to doxyPEP. Fewer than one in ten participants had reported ever using antibiotic PEP, with most using appropriate, evidence-based antibiotics. The use of antibiotic PEP and the report of doxyPEP ITU and 4CMenB ITU was more common among those at greater risk of STIs.

From Cure to Prevention: Doxycycline's Potential in Prophylaxis for Sexually Transmitted Infections

Over the past two decades, the global incidence of sexually transmitted infections (STIs) such as gonorrhea, chlamydia, and syphilis have increased significantly, particularly among cisgender men who have sex with men (MSM) and transgender women (TGW). This rise in STIs has spurred interest in new preventive measures, including doxycycline post-exposure prophylaxis (DoxyPEP). Clinical trials in the United States and France have demonstrated the effectiveness of DoxyPEP in reducing both chlamydia and syphilis incidence among MSM and TGW; although, its efficacy against gonorrhea remains limited, and it was further found to be ineffective among cisgender women in Kenya. Due to the promising results, the CDC and the German STI Society have incorporated DoxyPEP into their guidelines for specific high-risk groups. However, the broader implementation of DoxyPEP presents several challenges and ethical concerns. Key issues involve the potential development of antimicrobial resistance, particularly among common STI pathogens like C. trachomatis, M. genitalium, and N. gonorrhoeae, as well as other bacteria such as S. aureus and K. pneumoniae. Additionally, questions concerning equitable healthcare access, the potential impact on adherence to safer sex practices, and broader public health implications warrant careful consideration. Addressing these challenges necessitates a careful balance between the benefits and risks of DoxyPEP, as well as the implementation of strategies to mitigate negative outcomes while maximizing the impact on public health. Lastly, future research should explore the integration of DoxyPEP with other preventive strategies, such as vaccines, to enhance its effectiveness and reduce the global burden of STIs.

IUSTI Europe position statement on use of DoxyPEP: June 2024

This position statement is aimed at front-line clinical practitioners and public health authorities in WHO European Region providing services for people wishing to reduce their risk of acquiring sexually transmitted infections (STIs), including HIV.

High increase of Nichols-like clade circulating Treponema pallidum subsp. pallidum in Barcelona from 2021 to 2023

Worldwide, more than 90% of contemporary syphilis strains belong to SS14-like clade. This study aimed to describe the molecular profile of circulating Treponema pallidum subsp. pallidum (TPA) strains in Barcelona, Spain, from 2021 to 2023 building upon our report in 2015 which showed that 94.8% of typed strains belonged to the SS14 clade. Multilocus sequence typing (MLST) was conducted on TPA-positive samples obtained from swab samples by sequencing the tp0136, tp0548, and tp0705 loci. Strains were classified as Nichols-like or SS14-like clade. Macrolide and tetracycline resistance‑associated mutations were determined through analysis of 23S rDNA and 16S rRNA gene sequences. Of the 96 typeable samples, 47.9% belonged to SS14-like and 52.1% to the Nichols-like. Fourteen haplotypes were identified, with ST26 representing 43.8% of the samples, distributed across 11 haplotypes in the SS14-like and 3 haplotypes in the Nichols-like. All the samples showed macrolide resistance-associated mutations, while none exhibited tetracycline-associated mutations. Our findings revealed a substantial shift in the proportion of TPA clades within the Barcelona population from 2021 to 2023, characterized by a higher proportion of Nichols-like strains compared to 2015 and international trends. The varying temporal and geographical trends underscore the need for regular surveillance to understand regional variations in syphilis and strengthen control programs.

Doxycycline prophylaxis for the prevention of sexually transmitted infections: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVES

To investigate the effects of doxycycline pre- and post-exposure prophylaxis (doxy-PrEP/PEP) on bacterial sexually transmitted infections (STIs) by conducting a systematic review and meta-analysis.

METHODS

PubMed, Embase, and CENTRAL were searched for randomized controlled trials (RCTs), including ongoing studies published until November 7, 2023. Our primary endpoint was the incidence of bacterial STIs measured as the number of visits with an STI per total number of visits. Random-effects model was used to estimate pooled effect sizes. The study was registered with PROSPERO, CRD42023478486.

RESULTS

We identified six eligible studies containing data from seven articles and four conference abstracts, enrolling men who have sex with men (MSM), transgender women (TGW), and cisgender women (CGW). The pooled analysis of 1,766 participants with 602 newly diagnosed STIs showed a 56% decrease in the overall STI incidence using doxy-PrEP/PEP (RR = 0.44; 95% CI: 0.30-0.65; I2 = 73%). For doxy-PEP, including MSM and TGW only, the RR observed for overall STI incidence was 0.40 (95% CI: 0.28-0.57; I² = 37%), 0.19 (95% CI: 0.08-0.44; I² = 39%) for chlamydia, 0.23 (0.14-0.36; I² = 0%) for syphilis and 0.55 (95% CI: 0.34-0.87; I² = 41%) for gonorrhea. No serious adverse events were reported in the studies. The certainty of evidence regarding the efficacy of doxy-PEP among MSM and TGW was graded as high.

CONCLUSION

Doxy-PEP significantly reduces the number of new cases of chlamydia and syphilis and is potentially effective against gonorrhea, influenced by local resistance patterns. Thus, it is a promising tool in the prevention of bacterial STIs among MSM and TGW.

Interaction of the Atypical Tetracyclines Chelocardin and Amidochelocardin with Renal Drug Transporters

Antimicrobial resistance is expected to increase mortality rates by up to several million deaths per year by 2050 without new treatment options at hand. Recently, we characterized the pharmacokinetic (PK) and pharmacodynamic properties of two atypical tetracyclines, chelocardin (CHD) and amidochelocardin (CDCHD) that exhibit no cross-resistance with clinically used antibacterials. Both compounds were preferentially renally cleared and demonstrated pronounced effects in an ascending urinary tract infection model against E. coli. Renal drug transporters are known to influence clearance into the urine. In particular, inhibition of apical transporters in renal tubular epithelial cells can lead to intracellular accumulation and potential cell toxicity, whereas inhibition of basolateral transporters can cause a higher systemic exposure. Here, selected murine and human organic cation (Oct), organic anion (Oat), and efflux transporters were studied to elucidate interactions with CHD and CDCHD underlying their PK behavior. CHD exhibited stronger inhibitory effects on mOat1 and mOat3 and their human homologues hOAT1 and hOAT3 compared to CDCHD. While CHD was a substrate of mOat3 and mOct1, CDCHD was not. By contrast, no inhibitory effect was observed on Octs. CDCHD rather appeared to foster enhanced substrate transport on mOct1. CHD and CDCHD inhibited the efflux transporter hMRP2 on the apical side. In summary, the substrate nature of CHD in conjunction with its autoinhibition toward mOat3 rationalizes the distinct urine concentration profile compared to CDCHD that was previously observed in vivo. Further studies are needed to investigate the accumulation in renal tubular cells and the nephrotoxicity risk.

Antimicrobial treatment and resistance in sexually transmitted bacterial infections

Sexually transmitted infections (STIs) have been part of human life since ancient times, and their symptoms affect quality of life, and sequelae are common. Socioeconomic and behavioural trends affect the prevalence of STIs, but the discovery of antimicrobials gave hope for treatment, control of the spread of infection and lower rates of sequelae. This has to some extent been achieved, but increasing antimicrobial resistance and increasing transmission in high-risk sexual networks threaten this progress. For Neisseria gonorrhoeae, the only remaining first-line treatment (with ceftriaxone) is at risk of becoming ineffective, and for Mycoplasma genitalium, for which fewer alternative antimicrobial classes are available, incurable infections have already been reported. For Chlamydia trachomatis, in vitro resistance to first-line tetracyclines and macrolides has never been confirmed despite decades of treatment of this highly prevalent STI. Similarly, Treponema pallidum, the cause of syphilis, has remained susceptible to first-line penicillin.

Effect of mass treatment on the long-term prevalence of gonorrhoea, chlamydia and syphilis-a systematic review

BACKGROUND

Selective mass treatment of STIs may lead to a durable reduction in the prevalence of STIs or a temporary reduction associated with an increased probability of antimicrobial resistance emerging.

METHODS

We searched PubMed and Google Scholar for studies evaluating the impact of mass STI treatment on the long-term prevalence of chlamydia, gonorrhoea, syphilis and chancroid. The primary outcomes were the long term (≥3 months post the intervention) impact of the intervention on prevalence/incidence of the STI and on antimicrobial resistance.

RESULTS

Our search yielded 269 studies, of which 4 met the inclusion criteria. With the exception of the Carletonville study, where this was not assessed, three of the four studies found that intensive STI treatment was associated with a reduced prevalence of the targeted STI during or immediately after the intervention. In all four studies, there was no evidence that the intense treatment had a long-term effect on prevalence. In the only study where this was assessed, the intensive use of penicillin to reduce gonococcal prevalence was associated with the emergence of reduced susceptibility to penicillin in N. gonorrhoeae.

CONCLUSION

The available evidence suggests that mass treatment of chlamydia, gonorrhoea and syphilis in high prevalence populations is only associated with a temporary reduction in the prevalence of these infections and may select for antimicrobial resistance.

Pleasurable and problematic receptive anal intercourse and diseases of the colon, rectum and anus

The ability to experience pleasurable sexual activity is important for human health. Receptive anal intercourse (RAI) is a common, though frequently stigmatized, pleasurable sexual activity. Little is known about how diseases of the colon, rectum, and anus and their treatments affect RAI. Engaging in RAI with gastrointestinal disease can be difficult due to the unpredictability of symptoms and treatment-related toxic effects. Patients might experience sphincter hypertonicity, gastrointestinal symptom-specific anxiety, altered pelvic blood flow from structural disorders, decreased sensation from cancer-directed therapies or body image issues from stoma creation. These can result in problematic RAI - encompassing anodyspareunia (painful RAI), arousal dysfunction, orgasm dysfunction and decreased sexual desire. Therapeutic strategies for problematic RAI in patients living with gastrointestinal diseases and/or treatment-related dysfunction include pelvic floor muscle strengthening and stretching, psychological interventions, and restorative devices. Providing health-care professionals with a framework to discuss pleasurable RAI and diagnose problematic RAI can help improve patient outcomes. Normalizing RAI, affirming pleasure from RAI and acknowledging that the gastrointestinal system is involved in sexual pleasure, sexual function and sexual health will help transform the scientific paradigm of sexual health to one that is more just and equitable.

Sexual behaviour and incidence of sexually transmitted infections among men who have sex with men (MSM) using daily and event-driven pre-exposure prophylaxis (PrEP): Four-year follow-up of the Amsterdam PrEP (AMPrEP) demonstration project cohort

BACKGROUND

An increasing number of countries are currently implementing or scaling-up HIV pre-exposure prophylaxis (PrEP) care. With the introduction of PrEP, there was apprehension that condom use would decline and sexually transmitted infections (STIs) would increase. To inform sexual health counselling and STI screening programmes, we aimed to study sexual behaviour and STI incidence among men who have sex with men (MSM) and transgender women who use long-term daily or event-driven PrEP.

METHODS AND FINDINGS

The Amsterdam PrEP demonstration project (AMPrEP) was a prospective, closed cohort study, providing oral daily PrEP and event-driven PrEP to MSM and transgender women from 2015 to 2020. Participants could choose their PrEP regimen and could switch at each three-monthly visit. STI testing occurred at and, upon request, in-between 3-monthly study visits. We assessed changes in numbers of sex partners and condomless anal sex (CAS) acts with casual partners over time using negative binomial regression, adjusted for age. We assessed HIV incidence and changes in incidence rates (IRs) of any STI (i.e., chlamydia, gonorrhoea, or infectious syphilis) and individual STIs over time using Poisson regression, adjusted for age and testing frequency. A total of 367 participants (365 MSM) commenced PrEP and were followed for a median 3.9 years (interquartile range [IQR] = 3.4-4.0). Median age was 40 years (IQR = 32-48), 315 participants (85.8%) self-declared ethnicity as white and 280 (76.3%) had a university or university of applied sciences degree. Overall median number of sex partners (past 3 months) was 13 (IQR = 6-26) and decreased per additional year on PrEP (adjusted rate ratio [aRR] = 0.86/year, 95% confidence interval [CI] = 0.83-0.88). Overall median number of CAS acts with casual partners (past 3 months) was 10 (IQR = 3-20.5) and also decreased (aRR = 0.92/year, 95% CI = 0.88-0.97). We diagnosed any STI in 1,092 consultations during 1,258 person years, resulting in an IR of 87/100 person years (95% CI = 82-92). IRs of any STI did not increase over time for daily PrEP or event-driven PrEP users. Two daily PrEP users, and no event-driven PrEP users, were diagnosed with HIV during their first year on PrEP. Study limitations include censoring follow-up due to COVID-19 measures and an underrepresentation of younger, non-white, practically educated, and transgender individuals.

CONCLUSIONS

In this prospective cohort with a comparatively long follow-up period of 4 years, we observed very low HIV incidence and decreases in the numbers of casual sex partners and CAS acts over time. Although the STI incidence was high, it did not increase over time.

TRIAL REGISTRATION

The study was registered at the Netherlands Trial Register (NL5413) https://www.onderzoekmetmensen.nl/en/trial/22706.

Preventive and Sexual Health in LGBTQ+ Older Adults

Sexual health is an important but often overlooked health concern of LGBTQ + older adults. Multiple factors influence sexual health including intersecting identities; adverse life events; coping mechanisms; and psychological, social, and physical health domains. Thus, the use of a culturally competent and comprehensive person-centered approach to sexual health is warranted. In this review, we discuss approaches to engaging LGBTQ + older adults to ensure they are able to achieve their sexual health priorities and prevent new human immunodeficiency virus infections. We also discuss doxycycline postexposure prophylaxis to prevent other sexually transmitted infections and the impact of chemsex.

Impact of screening and doxycycline prevention on the syphilis epidemic among men who have sex with men in British Columbia: a mathematical modelling study

Background

Men who have sex with men (MSM) in British Columbia (BC) are disproportionately affected by infectious syphilis and HIV. In this study, we developed a co-interaction model and evaluated the impact and effectiveness of possible interventions among different MSM subgroups on the syphilis epidemic.

Methods

We designed a deterministic compartmental model, which stratified MSM by HIV status and HIV pre-exposure prophylaxis (HIV-PrEP) usage into (1) HIV-negative/unaware MSM (HIV-PrEP not recommended, not on HIV-PrEP), (2) HIV-negative/unaware MSM with HIV-PrEP recommended (not on HIV-PrEP), (3) HIV-negative/unaware MSM actively on HIV-PrEP, and (4) MSM diagnosed with HIV. We estimated the effect of scaling up syphilis testing frequency from Status Quo to six-, four-, and three-months, increasing the percentage of MSM using doxycycline prevention (Doxy-P) to 25%, 50%, and 100% of the target level, and a combination of both among subgroups (2)-(4). We also assessed the impact of these interventions on the syphilis incidence rates from 2020 to 2034 in comparison to the Status Quo scenario where no intervention was introduced.

Findings

Under the Status Quo scenario, with the expansion of the HIV-PrEP program to improve syphilis testing, the syphilis incidence rate was estimated to peak at 16.1 [Credible Interval (CI):14.2-17.9] per 1,000 person-years (PYs) in 2023 and decrease to 6.7 (CI:3.8-10.9) per 1,000 PYs by 2034. The syphilis incidence rate in 2034 was estimated at 0.7 (0.3-1.3) per 1,000 PYs if MSM diagnosed with HIV could be tested every four months, and at 1.5 (0.7-3.0) per 1,000 PYs if HIV-negative/unaware MSM actively on HIV-PrEP could be tested every three months. By achieving 100% of the target coverage of Doxy-P, the syphilis incidence rate was estimated at 1.4 (0.5-3.4) if focusing on MSM diagnosed with HIV, and 2.6 (1.2-5.1) per 1,000 PYs if focusing on HIV-negative/unaware MSM actively on HIV-PrEP. Under the combined interventions, the syphilis incidence rate could be as low as 0.0 (0.0-0.1) and 0.8 (0.3-1.8) per 1,000 PYs, respectively.

Interpretation

The HIV-PrEP program in BC plays a crucial role in increasing syphilis testing frequency among high-risk MSM and reducing syphilis transmission among this group. In addition, introducing Doxy-P can be an effective complementary strategy to minimize syphilis incidence, especially among MSM diagnosed with HIV.

Funding

This work was funded by the Canadian Institutes of Health Research.

Four recent insights suggest the need for more refined methods to assess the resistogenicity of doxycycline post exposure prophylaxis

Two recently published randomized trials of doxycycline post exposure prophylaxis (PEP) have concluded that this intervention is highly effective at reducing the incidence of bacterial sexually transmitted infections (STIs) and has little or no risk of promoting the spread of antimicrobial resistance (AMR). In this perspective piece, we review four types of evidence that suggest that the risk of promoting AMR has been inadequately assessed in these studies. 1) The studies have all used proportion resistant as the outcome measure. This is a less sensitive measure of resistogenicity than MIC distribution. 2) These RCTs have not considered population-level pathways of AMR selection. 3) In populations with very high antimicrobial consumption such as PrEP cohorts, the relationship between antimicrobial consumption and resistance may be saturated. 4) Genetic linkage of AMR means that increased tetracycline use may select for AMR to not only tetracyclines but also other antimicrobials in STIs and other bacterial species. We recommend novel study designs to more adequately assess the AMR-inducing risk of doxycycline PEP.

45 years of tetracycline post exposure prophylaxis for STIs and the risk of tetracycline resistance: a systematic review and meta-analysis

There is considerable interest in the use of doxycycline post exposure prophylaxis (PEP) to reduce the incidence of bacterial sexually transmitted infections (STIs). An important concern is that this could select for tetracycline resistance in these STIs and other species. We searched PubMed and Google Scholar, (1948-2023) for randomized controlled trials comparing tetracycline PEP with non-tetracycline controls. The primary outcome was antimicrobial resistance (AMR) to tetracyclines in all bacterial species with available data. Our search yielded 140 studies, of which three met the inclusion criteria. Tetracycline PEP was associated with an increasedprevalence of tetracycline resistance in Neisseria gonorrhoeae, but this effect was not statistically significant (Pooled OR 2.3, 95% CI 0.9-3.4). PEP had a marked effect on the N. gonorrhoeae tetracycline MIC distribution in the one study where this was assessed. Prophylactic efficacy was 100% at low MICs and 0% at high MICs. In the one study where this was assessed, PEP resulted in a significant increase in tetracycline resistance in commensal Neisseria species compared to the control group (OR 2.9, 95% CI 1.5-5.5) but no significant effect on the prevalence of tetracycline resistance in Staphylococcus aureus. The available evidence suggests that PEP with tetracyclines could be associated with selecting tetracycline resistance in N. gonorrhoeae and commensal Neisseria species.

Sexually transmitted coinfections among at-risk HIV-positive MSM: implications for optimal preemptive treatment

Background

Concurrent sexually transmitted infections (STIs) are common in sexually active populations. We aimed to estimate the prevalence and coinfection rates of bacterial STIs among sexually active, HIV-positive men who have sex with men (MSM), and to assess the potential benefits of different combination treatment regimens in managing concurrent bacterial STIs.

Methods

From September 2021 to September 2023, HIV-positive MSM underwent STI testing when they had symptoms suggestive of STIs or recently acquired hepatitis C virus (HCV) infection or early syphilis. The oral rinse, rectal swab, and urethral swab specimens were tested for Chlamydia trachomatis, Neisseria gonorrhoeae, Mycoplasma spp., Ureaplasma spp., and Trichomonas vaginalis with the use of multiplex real-time polymerase-chain-reaction assays. The estimated coinfection rates were used to evaluate the benefits of different combination treatment regimens for managing coinfections.

Results

During the study period, 535 participants (median age, 37 years; and CD4 count, 615 cells/mm3) were enrolled. On their first visits, at least one bacterial pathogen was detected in 57.9% and concomitant bacterial infections were found in 32.9% of the participants. The most commonly identified pathogen was U. urealyticum (36.3%), followed by C. trachomatis (22.8%), and N. gonorrhoeae (19.8%). The factors associated with any bacterial STIs included older age (per 1-year increase, adjusted odds ratio [AOR], 0.97; 95% confidence interval [CI], 0.95-1.00), early syphilis (AOR, 1.87; 95% CI, 1.22-2.84), and having more than 5 sex partners in the preceding 3 months (AOR, 2.08, 95% CI, 1.07-4.06). A combination therapy of benzathine penicillin G with a 7-day course of doxycycline could simultaneously treat 27.1% of C. trachomatis coinfections in participants with early syphilis, while a combination therapy of ceftriaxone with doxycycline could simultaneously treat 40.6% of chlamydial coinfections in participants with gonorrhea.

Conclusion

Bacterial STIs were prevalent and concomitant infections were not uncommon among sexually active, HIV-positive MSM, supporting regular screening for bacterial STIs. The effectiveness of preemptive use of doxycycline as combination therapy for concurrent STIs warrants more investigations.

Filling in the Gaps: Updates on Doxycycline Prophylaxis for Bacterial Sexually Transmitted Infections

Over the past two decades, cases of sexually transmitted infections (STIs) due to syphilis, gonorrhea, and chlamydia have been rising in the United States, disproportionately among gay, bisexual, and other men who have sex with men (MSM), as well as racial and ethnic minorities of all genders. In this review, we address updates about the evidence on doxycycline post-exposure prophylaxis (doxy-PEP) for prevention of bacterial STIs, including efficacy, safety, antimicrobial resistance (AMR), acceptability, modeling population impact, and evolving guidelines for use. Equitable implementation of doxy-PEP will require evaluation of who is offered and initiates it, understanding patterns of use and longer-term STI incidence and AMR, provider training, and tailored community education.

Single-dose cefixime 800 mg plus doxycycline 100 mg twice a day for 7 days compared with single-dose ceftriaxone 1 g plus single-dose azithromycin 2 g for treatment of urogenital, rectal, and pharyngeal gonorrhoea: a randomised clinical trial

OBJECTIVES

To evaluate the efficacy and tolerability of a single dose of oral cefixime 800 mg plus oral doxycycline 100 mg twice a day for 7 days, compared with a recommended single dose of ceftriaxone plus single dose of oral azithromycin, for treatment of uncomplicated urogenital, rectal, or pharyngeal gonorrhoea.

METHODS

A noninferiority, open-label, multicentre randomized controlled trial was conducted in Prague, Czech Republic. Some 161 patients, 18-65 years of age diagnosed with uncomplicated urogenital, rectal, or pharyngeal gonorrhoea by nucleic acid amplification test (NAAT) were randomized to treatment with single dose of cefixime 800 mg plus doxycycline 100 mg twice a day for 1 week or a single dose of ceftriaxone 1 g intramuscularly plus single dose of azithromycin 2 g. The primary outcome was the number of participants with negative culture and NAAT at 1 week and 3 weeks, respectively, after treatment initiation.

RESULTS

In all, 161 patients were randomized and 152 were included in per-protocol analyses. All 76 (100%; 95% CI, 0.95-1.00) patients treated with ceftriaxone plus azithromycin achieved negative cultures and NAAT after treatment. In the cefixime plus doxycycline arm at week 1, culture was negative in all 76 (100%) patients; at week 3, culture was negative in 70 of the 76 patients (92%; 95% CI, 0.84-0.97) and NAAT negative in 66 of the 76 patients (87%; 95% CI, 0.77-0.94). At week 3, culture and NAAT were negative in 65 of the 76 patients (86%; 95% CI, 0.76-0.93). Per-protocol risk difference was 14.5%; 95% CI, 6.56-22.38. All treatment failures observed in the cefixime arm were pharyngeal gonorrhoea cases.

DISCUSSION

The combination of cefixime and doxycycline did not achieve noninferiority to ceftriaxone and azithromycin for treatment of gonorrhoea when including pharyngeal gonorrhoea. It did, however, show high efficacy for urogenital and rectal gonorrhoea.

STI pathogens in the oropharynx: update on screening and treatment

PURPOSE OF REVIEW

The rise in antimicrobial resistance in several STI pathogens such as Neisseria gonorrhoeae has become a public health threat as only one first-line treatment remains. Reducing screening interval for gonorrhoea and chlamydia in high-prevalence populations has been proposed to address antimicrobial stewardship, but this remains controversial. This review aimed to revisit the epidemiology of infections at the oropharynx and review the current screening recommendations and treatment guidelines in different populations.

RECENT FINDINGS

Emerging evidence suggests that the oropharynx is the primary anatomical site for gonorrhoea transmission but maybe not for chlamydia transmission. Most international guidelines recommend 3-monthly oropharyngeal gonorrhoea and chlamydia screening for high-prevalence populations (e.g. men who have sex with men) but not low-prevalence populations (e.g. heterosexuals) given the clinical and public health benefits of screening in low-prevalence populations are still unclear. Doxycycline remains the first-line treatment for oropharyngeal chlamydia in most guidelines. However, some countries have moved from dual therapy (ceftriaxone and azithromycin) to monotherapy (ceftriaxone) for oropharyngeal gonorrhoea treatment to address antimicrobial stewardship.

SUMMARY

The transmission of gonorrhoea and chlamydia is still not fully understood. Further work will be required to evaluate the benefits and harms of reducing screening in high-prevalence populations.

Estimating changes in antibiotic consumption with the introduction of doxycycline post-exposure prophylaxis in the United States

Doxycycline as post-exposure prophylaxis (doxy-PEP) reduces the risk of gonorrhea, chlamydia, and syphilis in studies of men who have sex with men (MSM) and transgender women (TGW) on HIV Pre-exposure Prophylaxis (PrEP) and people living with HIV (PLWH)). Doxy-PEP is an important tool to address the increasing burden of sexually transmitted infections (STIs), but there is concern that increased consumption of doxycycline may drive antimicrobial resistance. We estimated the expected increase in antibiotic use in the US under several doxy-PEP prescribing scenarios. We accounted for doses of antibiotics that may be averted due to the prevention of chlamydia, gonorrhea, and syphilis infections by doxy-PEP. Under a scenario of 75% adoption among the eligible population, with rates of consumption similar to the DoxyPEP trial population, monthly antibiotic consumption would increase by around 2.52 million doses, driven by doxy-PEP consumption of 2.58 million doses and less 62.1 thousand antibiotic doses that would otherwise have been used for chlamydia, gonorrhea, and syphilis treatment.

Doxycycline PEP can induce doxycycline resistance in Klebsiella pneumoniae in a Galleria mellonella model of PEP

Background

Four randomized controlled trials have now established that doxycycline post exposure (sex) prophylaxis (PEP) can reduce the incidence of chlamydia and syphilis in men who have sex with men. These studies have concluded that the risk of selecting for antimicrobial resistance is low. We evaluated this risk in vitro and in vivo using a Galleria mellonella infection model.

Methods

We evaluated how long it took for doxycycline resistance to emerge during passage on doxycycline containing agar plates in 4 species - Escherichia coli, Klebsiella pneumoniae, Neisseria gonorrhoeae and Neisseria subflava. We then assessed if K. pneumoniae could acquire resistance to doxycycline (and cross resistance to other antimicrobials) during intermittent exposure to doxycycline in a Galleria mellonella model of doxycycline PEP.

Results

In our passage experiments, we found that resistance first emerged in K. pneumoniae. By day 7 the K. pneumoniae MIC had increased from 2 mg/L to a median of 96 mg/L (IQR 64-96). Under various simulations of doxycycline PEP in the G. mellonella model, the doxycycline MIC of K. pneumoniae increased from 2 mg/L to 48 mg/L (IQR 48-84). Ceftriaxone and ciprofloxacin MICs increased over ten-fold. Whole genome sequencing revealed acquired mutations in ramR which regulates the expression of the AcrAB-TolC efflux pump.

Conclusion

Doxycycline PEP can select for doxycycline, ceftriaxone and ciprofloxacin resistance in K. pneumoniae in a G. mellonella model. The emergent ramR mutations were similar to those seen in circulating strains of K. pneumoniae. These findings suggest that we need to assess the effect of doxycycline PEP on resistance induction on a broader range of bacterial species than has hitherto been the case.