Paeniclostridium sordellii and Clostridioides difficile encode similar and clinically relevant tetracycline resistance loci in diverse genomic locations.

BACKGROUND: With the current rise of antibiotic resistance in bacteria, it is important to monitor the efficacy of antimicrobials in clinical use. Paeniclostridium sordellii (previously Clostridium sordellii) is a bacterial pathogen that causes human uterine infection after spontaneous or medically induced abortion, for which mortality rates approach 100%. Prophylactic antibiotics have been recommended for individuals undergoing medically-induced abortion, one of which is doxycycline, a member of the tetracycline antibiotic family. However, tetracycline resistance had not been well characterized in P. sordellii. This study therefore aimed to determine the levels of tetracycline resistance in P. sordellii isolates, and to identify associated loci and their genomic locations.

RESULTS: Using a MIC assay, five of 24 P. sordellii isolates were found to be resistant to tetracycline, minocycline, and importantly, doxycycline. Analysis of genome sequence data from 46 isolates found that phenotypically resistant isolates encoded a variant of the Clostridium perfringens tetracycline resistance determinant Tet P. Bioinformatic analysis and comparison of the regions surrounding these determinants found variation in the genomic location of Tet P among P. sordellii isolates. The core genome comparison of the 46 isolates revealed genetic diversity and the absence of dominant genetic types among the isolates. There was no strong association between geographic location of isolation, animal host or Tet P carriage with isolate genetic type. Furthermore, the analysis of the Tet P genotype revealed that Tet P is encoded chromosomally, or on one of two, novel, small plasmids, all consistent with multiple acquisition and recombination events. BLAST analysis of Clostridioides difficile draft genome sequences also identified a Tet P locus, the genomic location of which demonstrated an evolutionary relationship with the P. sordellii locus.

CONCLUSIONS: The Tet P determinant is found in variable genomic locations within diverse human and animal isolates of P. sordellii and C. difficile, which suggests that it can undergo horizontal transfer, and may disseminate tetracycline resistance between clostridial species. Doxycycline is a suggested prophylactic treatment for P. sordellii infections, however, a small sub-set of the isolates tested are resistant to this antibiotic. Doxycycline may therefore not be an appropriate prophylactic treatment for P. sordellii infections.