This study found widespread acquired resistance to penicillin among C. diphtheriae isolates and identified a novel penicillin-binding protein gene (pbp2m) associated with resistance. This gene is located on a large multidrug resistance plasmid and its expression in C. glutamicum demonstrated its effect against several beta-lactams, potentially impacting treatment strategies for diphtheria.

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This research provides a valuable overview of antimicrobial resistance, particularly penicillin, in C. diphtheriae. It identifies a novel penicillin-binding protein associated with resistance and describes its genomic context on a plasmid carrying other resistance genes, providing important information for understanding the evolution of resistance. While the study acknowledges limitations and uses tentative ecological cut-offs, it offers a comprehensive analysis of the genetic and phylogenetic dynamics of resistance in C. diphtheriae, enhancing our understanding of this re-emerging pathogen.