Regulation of para-cresol production in Clostridioides difficile

•p-cresol selectively inhibits growth of certain taxa in the gut microbiome.•p-cresol production provides C. difficile with a competitive advantage in vivo.•p-cresol can be produced from fermentation of tyrosine or using exogenous p-HPA.•Elevated p-HPA induces production of p-cresol.•HpdBCA decarboxylase, encoded by hpdBCA operon converts p-HPA to p-cresol.