The bile salt deoxycholate induces Campylobacter jejuni genetic point mutations that promote increased antibiotic resistance and fitness

Authors: TALUKDAR, PRABHAT - Washington State University; CROCKETT, TORIN - Washington State University; GLOSS, LISA - Washington State University; Huynh, Steven; ROBERTS, STEVEN - Washington State University; TURNER, KYRAH - Washington State University; LEWIS, SEBASTIEN - Washington State University; HERUP-WHEELER, TRISTIN - Washington State University; Parker, Craig; KONKEL, MICHAEL - Washington State University

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2022
Publication Date: 12/21/2022
Citation: Talukdar, P., Crockett, T.M., Gloss, L.M., Huynh, S., Roberts, S.A., Turner, K.L., Lewis, S.T., Herup-Wheeler, T.L., Parker, C.T., Konkel, M. 2022. The bile salt deoxycholate induces Campylobacter jejuni genetic point mutations that promote increased antibiotic resistance and fitness. Frontiers in Microbiology. 13. Article 1062464. https://doi.org/10.3389/fmicb.2022.1062464.
DOI: https://doi.org/10.3389/fmicb.2022.1062464

Interpretive Summary: Reactive oxygen species, such as hydrogen peroxide, can damage DNA in ways that prevent DNA replication. This type of DNA damage must be repaired to ensure that bacteria replicate their genomes and survive. During the repair process, errors are often made in the DNA sequence that may contribute to mutations and the evolution of the bacteria. Previous work has revealed that C. jejuni growth in a medium containing the bile salt deoxycholate (DOC) causes an increase in reactive oxygen species. The fundamental goal of this project was to determine if C. jejuni growth in a medium containing DOC contributes to DNA mutations that provide a fitness advantage to the bacterium. Co-culture experiments revealed that C. jejuni growth in a DOC-supplemented medium increases the total number of increased fitness mutants, ciprofloxacin-resistant (CiproR) isolates, compared to C. jejuni grown in the absence of the detergent. In addition, we recovered an isolate grown in a medium with DOC that had a point mutation in the gene encoding the phosphoethanolamine transferase. Isolates possessing the variant gene showed enhanced resistance to the antimicrobial agent polymyxin B and DOC. Finally, we found that a deletion of mutY, which encodes a critical enzyme involved in the DNA base-excision repair pathway and repair of oxidative DNA damage, results in a mutator phenotype demonstrated by an increased number of CiproR isolates. Based on our findings, we postulate that DOC is a driver for DNA mutations (adaptations) and that the variants with enhanced fitness are enriched in animals, including poultry.

Technical Abstract: Oxidative damage to DNA is a significant source of mutations in living organisms. While DNA damage must be repaired to maintain the integrity of the genome and cell survival, errors made during DNA repair may contribute to evolution. Previous work has revealed that C. jejuni growth in the presence of bile salt deoxycholate (DOC) causes an increase in reactive oxygen species and the occurrence of 8-oxo-deoxyguanosine (8-oxo-dG) DNA lesions. The fundamental goal of this project was to determine if C. jejuni growth in a medium containing DOC contributes to DNA mutations that provide a fitness advantage to the bacterium. Co-culture experiments revealed that C. jejuni growth in a DOC-supplemented medium increases the total number of ciprofloxacin-resistant isolates compared to C. jejuni grown in the absence of DOC. We recovered two individual isolates grown in a medium with DOC that had a point mutation in the gene encoding the EptC phosphoethanolamine transferase. Transformants harboring the EptC variant protein showed enhanced resistance to the antimicrobial agent polymyxin B and DOC when compared to an eptC deletion mutant or the isolate complemented with a wild-type copy of the gene. Finally, we found that the base excision repair (BER), homologous recombination repair (HRR), and nucleotide excision repair (NER) are involved in general oxidative damage repair in C. jejuni, but that the BER pathway plays the primary role in the repair of the 8-oxo-dG lesion. We postulate that bile salts drive C. jejuni mutations (adaptations) and enhance bacterial fitness in animals.