Novel insights into the newly described Corynebacterium hesseae: first molecular and genomic characterization of a multidrug-resistant strain from blood culture.

The genus Corynebacterium comprises several valid species, yet most studies focus on Corynebacterium diphtheriae. Infections by non-diphtherial species are increasingly reported, despite limited genomic and pathogenicity data. Corynebacterium hesseae was recently described and isolated from clinical samples, warranting further investigation into its phenotypic characteristics and potential clinical significance. In the context, this study aimed to investigate the first reported case of systemic infection caused by C. hesseae in an elderly patient from south-central Brazil. The study focused on identifying the isolate using genomic tools, characterizing its antimicrobial resistance (AMR) profile, and assessing its virulence through phenotypic and genomic analyses. The isolate, misidentified as Corynebacterium aurimucosum by MALDI-TOF MS, was confirmed as C. hesseae through genomic analyses (ANI: 96.36%, dDDH: 84.9%). The genome (2.8 Mb, 60.84% G + C content) revealed virulence genes (sapD, srtB, fagBCD) and AMR genes (ermX, tetA, tetW, aph(3')-Ia, aph(6)-Id, and cmx). The strain exhibited multidrug resistance (MDR) to penicillin, clindamycin, ciprofloxacin, and tetracycline, with resistance linked to AMR genes and gyrA mutations. Biofilm assays showed strong adhesion, and Galleria mellonella testing demonstrated 70% mortality, confirming pathogenicity. Further studies are needed to elucidate penicillin resistance mechanisms. This study confirms C. hesseae as an emerging pathogen with MDR and significant virulence potential. The misidentification by MALDI-TOF MS emphasizes the importance of genomic tools for accurate pathogen identification and characterization. The findings underscore the critical need for enhanced genomic monitoring, updated microbial identification databases, and continued surveillance of MDR pathogens. These efforts are essential to mitigate the rising threat of AMR and improve infection control strategies, particularly in healthcare settings managing emerging pathogens like C. hesseae.