Different CprABC amino acid sequences affect nisin A susceptibility in Clostridioides difficile isolates

Abstract

Clinical isolates of Clostridioides difficile sometimes exhibit multidrug resistance and cause diarrhea after antibiotic administration. Metronidazole and vancomycin are often used as therapeutic agents, but resistance to these antibiotics has been found clinically. Therefore, the development of alternative antimicrobial agents is needed. Nisin A, produced by Lactococcus lactis, has been demonstrated to be effective against C. difficile infection. In this study, we evaluated the susceptibility of 11 C. difficile clinical isolates to nisin A and found that they could be divided into 2 groups: high and low susceptibility. Since CprABC and DltDABC, which are responsible for nisin A efflux and cell surface charge, respectively, have been reported to be related to nisin A susceptibility, we investigated the expression of cprA and dltA among the 11 strains. cprA expression in all strains was induced by nisin A, but dltA expression was not. The expression levels of both genes did not correlate with nisin A susceptibility in these clinical isolates. To evaluate cell surface charge, we performed a cytochrome C binding assay and found no relationship between charge and nisin A susceptibility. Then, we determined the whole genome sequence of each clinical isolate and carried out phylogenetic analysis. The 11 isolates separated into two major clusters, which were consistent with the differences in nisin A susceptibility. Furthermore, we found common differences in several amino acids in the sequences of CprA, CprB, and CprC between the two clusters. Therefore, we speculated that the different amino acid sequences of CprABC might be related to nisin A susceptibility. In addition, C. difficile strains could be divided in the same two groups based on susceptibility to epidermin and mutacin III, which are structurally similar to nisin A. These results suggest that genotypic variations in C. difficile strains confer different susceptibilities to bacteriocins.

After a century of nisin research - where are we now?

“…Ultimately, NGS technologies will facilitate resistance-guided genome mining, which in combination with sequence-based functional metagenomics will not only assist in establishing how prevalent nisin and lantibiotic resistance determinants are within microbiome populations, but also improve the prospects for the discovery of genetic variants or new structurally related homologs of known resistance mechanisms. For example, a whole-genome analysis and evaluation of clinical isolates of C. difficile established a link between strains exhibiting high or low nisin resistance to genetic variants in the cpr ABC nisin resistance module (Ide et al 2023 ). Such knowledge will be invaluable to accelerate the development of strategies that could eventually counteract or avoid nisin resistance action.…”