Chlamydia trachomatis clinical isolates identified as tetracycline resistant do not exhibit resistance in vitro: whole-genome sequencing reveals a mutation in porB but no evidence for tetracycline resistance genes

Abstract

Chlamydia trachomatis is the most common bacterial sexually transmitted infection worldwide and the leading cause of preventable blindness in developing countries. Tetracycline is commonly the drug of choice for treating C. trachomatis infections, but cases of antibiotic resistance in clinical isolates have previously been reported. Here, we used antibiotic resistance assays and wholegenome sequencing to interrogate the hypothesis that two clinical isolates (IU824 and IU888) have acquired mechanisms of antibiotic resistance. Immunofluorescence staining was used to identify C. trachomatis inclusions in cell cultures grown in the presence of tetracycline; however, only antibiotic-free control cultures yielded the strong fluorescence associated with the presence of chlamydial inclusions. Infectivity was lost upon passage of harvested cultures grown in the presence of tetracycline into antibiotic-free medium, so we conclude that these isolates were phenotypically sensitive to tetracycline. Comparisons of the genome and plasmid sequences for the two isolates with tetracycline-sensitive strains did not identify regions of low sequence identity that could accommodate horizontally acquired resistance genes, and the tetracycline binding region of the 16S rRNA gene was identical to that of the sensitive control strains. The porB gene of strain IU824, however, was found to contain a premature stop codon not previously identified, which is noteworthy but unlikely to be related to tetracycline resistance. In conclusion, we found no evidence of tetracycline resistance in the two strains investigated, and it seems most likely that the small, aberrant inclusions previously identified resulted from the high chlamydial load used in the original antibiotic resistance assays.

Chronic Chlamydial Diseases: From Atherosclerosis to Urogenital Infections

“…Second, tetracycline resistance in chlamydiae may be possible. Evidence of antibiotic resistance in human pathogenic chlamydiae is lacking, based on the observation that suspected tetracycline resistant strains lost the resistant phenotype during culture and failed to exhibit genomic evidence of resistance [101]. However, isolation of tetracycline resistant C. suis from pigs demonstrates an adaptive ability of chlamydiae to acquire antibiotic resistance under selective pressure [102], with implications for continued use of antibiotic treatment of chlamydial disease.…”

Comprehensive global genome dynamics of Chlamydia trachomatis show ancient diversification followed by contemporary mixing and recent lineage expansion

“…This is despite the ease at which mutations conferring a high level antimicrobial resistance to most clinically relevant antimicrobials can be generated in vitro (for review, see Sandoz and Rockey 2010) and sporadic reports of clinical resistance (Hogan et al 2004;Sandoz and Rockey 2010), including a case of phenotypic but not genotypic resistance (O'Neill et al 2013). Although none of the isolates in this study were deemed clinically resistant, in order to understand whether any of these mutations were present in a circulating population, we performed a systematic search for known resistance alleles, either fixed or heterozygous.…”

The effects of pig manure application on the spread of tetracycline resistance in bulk and cucumber rhizosphere soils: a greenhouse experiment

“…Soil genomic DNA was extracted according to the protocol of the Power-Soil TM DNA Isolation Kit (MO BIO Laboratories Inc., Carlsbad, CA) and amplified for tetC and tetZ genes, encoding an efflux pump, which were predominantly found in gram-negative and -positive bacteria (Aminov et al 2002;Benacer et al 2010;O'Neill et al 2013;Tauch et al 2000). Q-PCR assay for the detection D r a f t of TRGs was the same as that described previously (Kang et al 2016b).…”