A Point Mutation in carR Is Involved in the Emergence of Polymyxin B-Sensitive Vibrio cholerae O1 El Tor Biotype by Influencing Gene Transcription

• Published in: Infection and immunity 2020-04, Vol.88 (5)
• Main Authors: Samanta, Prosenjit, Mandal, Rahul Shubhra, Saha, Rudra Narayan, Shaw, Sreeja, Ghosh, Priyanka, Dutta, Shanta, Ghosh, Amit, Imamura, Daisuke, Morita, Masatomo, Ohnishi, Makoto, Ramamurthy, Thandavarayan, Mukhopadhyay, Asish Kumar
• Format: Article
• Language: English
• Subjects: Bacterial Infections
• ISSN: 0019-9567; 1098-5522
• DOI: 10.1128/IAI.00080-20

Antimicrobial peptides play an important role in host defense against Generally, the O1 classical biotype is polymyxin B (PB) sensitive and El Tor is relatively resistant. Detection of classical biotype traits like the production of classical cholera toxin and PB sensitivity in El Tor strains has been reported in recent years, including in the devastating Yemen cholera outbreak during 2016-2018. To investigate the factor(s) responsible for the shift in the trend of sensitivity to PB, we studied the two-component system encoded by , regulating the lipid A modification of El Tor vibrios, and found that only contains a single nucleotide polymorphism (SNP) in recently emerged PB-sensitive strains. We designated the two alleles present in PB-resistant and -sensitive strains and alleles, respectively, and replaced the allele of a sensitive strain with the allele, using an allelic-exchange approach. The sensitive strain then became resistant. The PB-resistant strain N16961 was made susceptible to PB in a similar fashion. Our CarR protein models suggested that the D89N substitution in the more stable CarR protein brings the two structural domains of CarR closer, constricting the DNA binding cleft. This probably reduces the expression of the -regulated operon, inducing PB susceptibility. Expression of in PB-sensitive strains was found to be downregulated under natural culturing conditions. In addition, the expression of and decreased in all strains with increased concentrations of extracellular Ca but increased with a rise in pH. The downregulation of in CarR strains confirmed that the G265A mutation is responsible for the emergence of PB-sensitive El Tor strains.