Antimicrobial susceptibility of Treponema pallidum subspecies pallidum: an in-vitro study

Long-term in vitro exposure of Treponema pallidum to sub-bactericidal doxycycline did not induce resistance: Implications for doxy-PEP and syphilis

Doxycycline post-exposure prophylaxis (doxy-PEP) could significantly reduce syphilis incidence. However, the increase in intermittent doxycycline usage might select resistant Treponema pallidum ( T. pallidum ) strains. To assess whether resistance to doxycycline could be induced in this pathogen, we exposed the SS14 strain in vitro both intermittently and continuously to a sub-bactericidal doxycycline concentration that still exerts antibiotic pressure. During and after each exposure experiment, we assessed the doxycycline minimal inhibitory concentration in test and control treponemes and performed whole genome sequencing, concluding that no resistance developed. This work suggests that doxycycline-resistant T. pallidum is not an immediate threat for doxy-PEP implementation.

Prevalence and Treatment Outcomes of Syphilis among People with Human Immunodeficiency Virus (HIV) Engaging in High-Risk Sexual Behavior: Real World Data from Northern Greece, 2019-2022

In this study, we aimed to assess the prevalence of syphilis among people with human immunodeficiency virus (HIV; PWH) engaging in high-risk sexual behavior, determine the stage of syphilis, and evaluate treatment efficacy. A retrospective single-center cohort study was conducted at the AHEPA University General Hospital of Thessaloniki, focusing on PWH at high risk for sexually transmitted infections (STIs) attending outpatient care from January 2019 to December 2022. Sociodemographic and clinical data were collected, incident syphilis rates were identified, associations with HIV-related characteristics were explored, and the treatment response was assessed. Among 991 participants, 94 PWH were diagnosed with syphilis, representing 9.4% of the cohort. Incident syphilis cases experienced a decrease in the early COVID-19 era compared to 2019, followed by a gradual increase leading up to 2022. The majority of syphilis cases were asymptomatic latent syphilis (71.1%). Men who have sex with men (MSM) and younger individuals exhibited higher rates of co-infection during the study period. No significant association was found between incident syphilis and HIV-related factors. Most syphilis cases (86%) were treated with benzathine penicillin G (BPG). Treatment with BPG and doxycycline showed an increased success rate (96.7% vs. 92.9%), with no statistically significant difference observed between them (p = 0.438). This study highlights the alarming incidence of syphilis among PWH engaging in high-risk sexual behavior, particularly among younger MSM. BPG remains effective, and alternative regimens like doxycycline show promise, especially in settings with penicillin shortages or patient allergies.

A Retrospective Cohort Study on Treponema pallidum Infection: Clinical Trends and Treatment Outcomes for Congenital Syphilis in Guangxi, China (2013-2023)

Background

Syphilis, a prevalent sexually transmitted infection, poses severe risks, especially during pregnancy. This study aimed to elucidate the trends and impacts of syphilis in Guangxi, China, focusing on prevalence, clinical manifestations, and treatment outcomes in pregnant women and newborns. The objectives included understanding the demographic characteristics of affected pregnant women, analysing the clinical manifestations in newborns, and assessing the effectiveness of the treatment protocol.

Methods

Conducted in adherence to ethical guidelines, a retrospective cohort study from January 2013 to December 2023 included 54,048 pregnant women tested for T. pallidum. Diagnosis involved a comprehensive approach, utilizing tests like the Toluidine Red Unheated Serum Test (TRUST) and the Treponema pallidum Particle Agglutination (TPPA) assay. Infant diagnosis and clinical manifestations were evaluated through a decade-long follow-up. Treatment protocols, including Benzathine penicillin, were implemented. Statistical analyses were conducted using SAS version 9.4.

Results

Among 54,048 pregnant women, 0.10% were syphilis positive, correlating with a rise in hospitalizations. Newborns exhibited varied clinical manifestations, with neonatal pneumonia and jaundice being prevalent. The treatment protocol, especially with Benzathine penicillin, achieved a remarkable 100% cure success rate. The study noted a significant reduction in mother-to-child transmission. Syphilis in mothers and babies was diagnosed at different clinical stages, including primary, secondary, latent, and tertiary.

Conclusion

This study underscores the escalating impact of syphilis on pregnant women and newborns in Guangxi, China. The findings highlight the necessity for robust preventive measures, early diagnosis, and effective treatment strategies. The observed 100% cure success rate with Benzathine penicillin emphasizes the importance of strict treatment protocols in mitigating the adverse effects of congenital syphilis and reducing its transmission.

Congenital Syphilis: A Re-Emerging but Preventable Infection

Congenital syphilis presents a significant global burden, contributing to fetal loss, stillbirth, neonatal mortality, and congenital infection. Despite the target established in 2007 by the World Health Organization (WHO) of fewer than 50 cases per 100,000 live births, the global incidence is on the rise, particularly in low- and middle-income regions. Recent data indicate a rate of 473 cases per 100,000 live births, resulting in 661,000 total cases of congenital syphilis, including 355,000 adverse birth outcomes such as early fetal deaths, stillbirths, neonatal deaths, preterm or low-birth-weight births, and infants with clinical congenital syphilis. Alarmingly, only 6% of these adverse outcomes occurred in mothers who were enrolled, screened, and treated. Unlike many neonatal infections, congenital syphilis is preventable through effective antenatal screening and treatment of infected pregnant women. However, despite available screening tools, affordable treatment options, and the integration of prevention programs into antenatal care in various countries, congenital syphilis remains a pressing public health concern worldwide. This review aims to summarize the current epidemiology, transmission, and treatment of syphilis in pregnancy, as well as to explore global efforts to reduce vertical transmission and address the reasons for falling short of the WHO elimination target.

Bright New Resources for Syphilis Research: Genetically Encoded Fluorescent Tags for Treponema pallidum and Sf1Ep Cells

The recently discovered methodologies to cultivate and genetically manipulate Treponema pallidum subsp. pallidum ( T. pallidum ) have significantly helped syphilis research, allowing the in vitro evaluation of antibiotic efficacy, performance of controlled studies to assess differential treponemal gene expression, and generation of loss-of-function mutants to evaluate the contribution of specific genetic loci to T. pallidum virulence. Building on this progress, we engineered the T. pallidum SS14 strain to express a red-shifted Green Fluorescent Protein (GFP) and Sf1Ep cells to express mCherry and blue fluorescent protein (BFP) for enhanced visualization. These new resources improve microscopy- and cell sorting-based applications for T. pallidum , better capturing the physical interaction between the host and pathogen, among other possibilities. Continued efforts to develop and share new tools and resources are required to help our overall knowledge of T. pallidum biology and syphilis pathogenesis reach that of other bacterial pathogens, including spirochetes.

Graphical abstract

By employing genetic engineering, T. pallidum was modified to express GFP, and Sf1Ep cells to express mCherry on the cytoplasmic membrane and BFP in the nucleus. These new resources for syphilis research will facilitate experimental designs to better define the complex interplay between T. pallidum and the host during infection.

Update on syphilis in pregnancy: marrying basic science advances and clinical perseverance to solve an ancient public health problem

PURPOSE OF REVIEW

While the clinical disease of syphilis, its consequences in pregnancy, and its sensitivity to penicillin treatment have remained relatively unchanged for a century or more, new technologies and basic discoveries in syphilis research have translated into tangible advances in clinical diagnosis, treatment, and prevention. The purpose of this review is to help the reader understand some of the recent relevant scientific publications on syphilis and its causative organism in a clinical obstetric context.

RECENT FINDINGS

Rates of adult and congenital syphilis have risen dramatically in the last decade despite public health efforts. Penicillin shortages and lack of screening or adequate treatment have all contributed to global disease burden. Advances in genomic and microbiological characterization of this spirochete have led to new developments in serologic and molecular diagnosis as well as evaluation of potential vaccine candidates. Until a syphilis vaccine is available, substance use disorders and lack of screening in pregnancy are associated with increased congenital syphilis, and these challenges will require novel solutions to fully address this public health crisis.

SUMMARY

Addressing the burden of congenital syphilis demands that obstetricians stay well informed of new tools and resources for diagnosis, treatment, and prevention of syphilis now and in the future.

Oral linezolid compared with benzathine penicillin G for treatment of early syphilis in adults (Trep-AB Study) in Spain: a prospective, open-label, non-inferiority, randomised controlled trial

BACKGROUND

Management of syphilis, a sexually transmitted infection (STI) with increasing incidence, is challenged by drug shortages, scarcity of randomised trial data, an absence of non-penicillin alternatives for pregnant women with penicillin allergy (other than desensitisation), extended parenteral administration for neurosyphilis and congenital syphilis, and macrolide resistance. Linezolid was shown to be active against Treponema pallidum, the causative agent of syphilis, in vitro and in the rabbit model. We aimed to assess the efficacy of linezolid for treating early syphilis in adults compared with the standard of care benzathine penicillin G (BPG).

METHODS

We did a multicentre, open-label, non-inferiority, randomised controlled trial to assess the efficacy of linezolid for treating early syphilis compared with BPG. We recruited participants with serological or molecular confirmation of syphilis (either primary, secondary, or early latent) at one STI unit in a public hospital and two STI community clinics in Catalonia (Spain). Participants were randomly allocated in a 1:1 ratio using a computer-generated block randomisation list with six participants per block, to receive either oral linezolid (600 mg once per day for 5 days) or intramuscular BPG (single dose of 2·4 million international units) and were assessed for signs and symptoms (once per week until week 6 and at week 12, week 24, and week 48) and reagin titres of non-treponemal antibodies (week 12, week 24, and week 48). The primary endpoint was treatment response, assessed using a composite endpoint that included clinical response, serological response, and absence of relapse. Clinical response was assessed at 2 weeks for primary syphilis and at 6 weeks for secondary syphilis following treatment initiation. Serological cure was defined as a four-fold decline in rapid plasma reagin titre or seroreversion at any of the 12-week, 24-week, or 48-week timepoints. The absence of relapse was defined as the presence of different molecular sequence types of T pallidum in recurrent syphilis. Non-inferiority was shown if the lower limit of the two-sided 95% CI for the difference in rates of treatment response was higher than -10%. The primary analysis was done in the per-protocol population. The trial is registered at ClinicalTrials.gov (NCT05069974) and was stopped for futility after interim analysis.

FINDINGS

Between Oct 20, 2021, and Sept 15, 2022, 62 patients were assessed for eligibility, and 59 were randomly assigned to linezolid (n=29) or BPG (n=30). In the per-protocol population, after 48 weeks' follow-up, 19 (70%) of 27 participants (95% CI 49·8 to 86·2) in the linezolid group had responded to treatment and 28 (100%) of 28 participants (87·7 to 100·0) in the BPG group (treatment difference -29·6, 95% CI -50·5 to -8·8), which did not meet the non-inferiority criterion. The number of drug-related adverse events (all mild or moderate) was similar in both treatment groups (five [17%] of 29, 95% CI 5·8 to 35·8 in the linezolid group vs five [17%] of 30, 5·6 to 34·7, in the BPG group). No serious adverse events were reported during follow-up.

INTERPRETATION

The efficacy of linezolid at a daily dose of 600 mg for 5 days did not meet the non-inferiority criteria compared with BPG and, as a result, this treatment regimen should not be used to treat patients with early syphilis.

FUNDING

European Research Council and Fondo de Investigaciones Sanitarias.

Treatment of bacterial sexually transmitted infections in Europe: gonorrhoea, Mycoplasma genitalium, and syphilis

This review explores the therapeutic challenges of sexually transmitted infections (STI) in Europe, which include increasing antimicrobial resistance and limited progress in drug discovery. We primarily focus on gonorrhoea, Mycoplasma genitalium, and syphilis infections. For gonorrhoea with escalating resistance rates we explore the possibility of combining ceftriaxone with another antibiotic or using alternative antibiotics to mitigate resistance emergence, and we provide insights on the ongoing evaluation of new antimicrobials, like gepotidacin and zoliflodacin. In the case of M. genitalium, which exhibits high resistance rates to first and second-line treatments, we emphasize the importance of resistance-guided therapy in regions with elevated resistance levels, and highlight the limited alternative options, such as pristinamycin and minocycline. Furthermore, we address the challenges posed by syphilis, where the primary treatment consists of penicillin or doxycycline, with challenges arising in neurosyphilis, allergy, pregnancy, and supply shortages and discuss the ongoing evaluation of alternative antimicrobials (e.g., ceftriaxone, cefixime, linezolid). Our findings identify priority actions and provide concrete solutions for long-term effective management of STIs and antimicrobial resistance mitigation.

Prevention strategies for sexually transmitted infections, HIV, and viral hepatitis in Europe

The current prevention efforts for STIs, HIV and viral hepatitis in the WHO European Region, especially in the Central and Eastern subregions, are hindered by healthcare disparities, data gaps, and limited resources. In this comprehensive narrative review, we aim to highlight both achievements and persisting challenges while also exploring new developments that could significantly impact the prevention of these infections in the near future. While pre-exposure prophylaxis (PrEP) for HIV has been broadly approved and implemented in 38 out of 53 countries in the region, challenges remain, including cost, limited licensing, and incomplete adherence. We explore innovative approaches like on-demand PrEP, long-acting injectable cabotegravir, and intravaginal rings that have shown promising results, alongside the use of six-monthly lenacapavir, the outcomes of which are pending. Additionally, the potential of doxycycline post-exposure prophylaxis has been discussed, revealing efficacy in reducing chlamydia and syphilis risk, but effectiveness against gonorrhoea being contingent on tetracycline resistance rates, and the need of further data to determine potential resistance development in other bacteria and its impact on the gut microbiome. We examine successful vaccination campaigns against HBV and HPV, the ongoing development of vaccines for chlamydia, syphilis, herpesvirus, and gonorrhoea, and challenges in HIV vaccine research, including lines of research with significant potential like sequential immunization, T-cell responses, and mRNA technology. This review underscores the research endeavors that pave the way for a more resilient and robust approach to combating STIs, HIV, and viral hepatitis in the region.