The pH-responsive SmrR-SmrT system modulatesC. difficileantimicrobial resistance, spore formation, and toxin production

Abstract

ABSTRACTClostridioides difficileis an anaerobic gastrointestinal pathogen that spreads through the environment as dormant spores. To survive, replicate, and sporulate in the host intestine,C. difficilemust adapt to a variety of conditions in its environment, including changes in pH, the availability of metabolites, host immune factors, and a diverse array of other species. Prior studies showed that changes in intestinal conditions, such as pH, can affectC. difficiletoxin production, spore formation, and cell survival. However, little is understood about the specific genes and pathways that facilitate environmental adaptation and lead to changes inC. difficilecell outcomes. In this study, we investigated two genes,CD2505andCD2506,that are differentially regulated by pH to determine if they impactC. difficilegrowth and sporulation. Using deletion mutants, we examined the effects of both genes (hereinsmrRandsmrT) on sporulation frequency, toxin production, and antimicrobial resistance. We determined that SmrR is a repressor ofsmrRTthat responds to pH and suppresses sporulation and toxin production through regulation of the SmrT transporter. Further, we showed that SmrT confers resistance to erythromycin and lincomycin, establishing a connection between the regulation of sporulation and antimicrobial resistance.IMPORTANCEC. difficileis a mammalian pathogen that colonizes the large intestine and produces toxins that lead to severe diarrheal disease.C. difficileis a major threat to public health due to its intrinsic resistance to antimicrobials and its ability to form dormant spores that are easily spread from host to host. In this study, we examined the contribution of two genes,smrRandsmrTon sporulation, toxin production, and antimicrobial resistance. Our results indicate that SmrR repressessmrTexpression, while production of SmrT increases spore and toxin production, as well as resistance to antibiotics.