Efficacy of linezolid on Treponema pallidum, the syphilis agent: A preclinical study

Abstract

Background Penicillin G, the current standard treatment for syphilis, has important drawbacks, but virtually no preclinical or clinical studies have been performed to identify viable alternatives. We tested, both in vitro and in vivo, three marketed antibiotics with adequate pharmacological properties to treat syphilis. Methods We used an in vitro culturing system of T. pallidum to perform drug susceptibility testing and applied quantitative PCR targeting the tp0574 gene to measure bacterial growth. To confirm in vivo efficacy, fifteen rabbits were infected intradermally with T. pallidum at eight sites each and randomly allocated to an experimental treatment (linezolid, moxifloxacin, clofazimine) or a control arm (benzathine penicillin G [BPG], untreated). The primary outcome was treatment efficacy defined as the time to lesion healing measured from the date of treatment start. Secondary outcomes were absence of treponemes or treponemal mRNA in injection sites, absence of seroconversion, and cerebrospinal fluid (CSF) abnormalities and negative rabbit infectivity tests (RIT). Findings Linezolid showed in vitro bactericidal activity at concentrations of 0.5 µg/mL or higher. When administered orally to experimentally infected rabbits, it induced healing of early lesions at a time similar to BPG (hazard ratio 3.84; 95% CI 2.05–7.17; p < 0.0001 compared to untreated controls). In linezolid-treated animals, dark-field microscopy and qPCR assessment showed no presence of treponemes after day 3 post-treatment start, serologic test did not convert to positive, CSF had no abnormalities, and RIT was negative. Moxifloxacin and clofazimine failed to inhibit bacterial growth in vitro and could not cure the infection in the rabbit model. Interpretation Linezolid, a low-cost oxazolidinone, has in vitro and in vivo activity against T. pallidum , with efficacy similar to BPG in treating treponemal lesions in the animal model. Our findings warrant further research to assess the efficacy of linezolid as an alternative to penicillin G to treat syphilis in human clinical trials. Funding European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant agreement No. 850450).

Longitudinal TprK profiling of in vivo and in vitro-propagated Treponema pallidum subsp. pallidum reveals accumulation of antigenic variants in absence of immune pressure

“…At the same time, treponemal culture medium (TpCM2) was prepared according to the Edmondson et al . protocol [ 25 ], and incubated overnight at 34°C in a microaerophilic atmosphere (1.5% O 2 , 5% CO 2 and 93.5% N 2 ) to deplete the medium of oxygen.…”

“…One day prior to in vitro inoculation of the Chicago C strain of T. pallidum, 10 5 rabbit Sf1 epithelial cells were plated into each well of a 6-well plate and incubated at 37˚C overnight in a 5% CO2 atmosphere within a HeraCell 150 incubator (Thermo Fisher Scientific, Waltham, MA). At the same time, treponemal culture medium (TpCM2) was prepared according to the Edmondson et al protocol [25], and incubated overnight at 34˚C in a microaerophilic atmosphere (1.5% O 2 , 5% CO 2 and 93.5% N 2 ) to deplete the medium of oxygen.…”

Comparison of transcriptional profiles of Treponema pallidum during experimental infection of rabbits and in vitro culture: Highly similar, yet different

“…This culture system uses a modified culture medium (TpCM-2, containing CMRL 1066 medium as its basal medium) in combination with Sf1Ep cells grown under microaerobic conditions to successfully cultivate T . pallidum continuously in vitro , with retention of infectivity in the rabbit model [ 22 – 25 ].…”

Longitudinal accumulation of in vivo and in vitro-grown Treponema pallidum subsp. pallidum TprK variants in the presence and absence of immune pressure

“…At the same time, treponemal culture medium (TpCM2) was prepared according to the Edmondson et al protocol [25], and incubated overnight at 34ºC in a microaerophilic atmosphere (1.5% O 2 , 5% CO 2 and 93.5% N 2 ) to deplete the medium of oxygen.…”