Molecular and epidemiological characterization of toxigenic and non-toxigenic C. diphtheriae, C. belfantii and C. ulcerans isolates identified in Spain from 2014 to 2019. Corynebacterium isolates identified in Spain (2014-2019).

We present a molecular and epidemiological review of the characteristics of toxigenic and non-toxigenic Corynebacterium isolates submitted to the national reference laboratory in Spain, between 2014 and 2019. This work is the first to describe the diphtheria isolates, after the implementation of the new surveillance guidelines in 2014, which now includes surveillance of C. ulcerans cases and cases of diphtheria of any localisation. Thirty-nine isolates were analysed, of which the majority were non-toxigenic including one non-toxigenic tox gene-bearing C. diphtheriae biovar mitis. Similar to other studies, a higher proportion of toxigenicity was observed in C. ulcerans. A quarter of the isolates harboured antimicrobial resistance genes in addition to the high prevalence of penicillin resistance phenotypically demonstrated. Whole genome sequence analysis also demonstrated that all the isolates analysed harboured the dtxR regulator meaning the currently non-toxigenic isolates are capable of becoming fulling toxigenic upon the acquisition of the phage-harboured tox gene. This retrospective work provides evidence for a need to strengthen the current surveillance in Spain by collecting more microbiological and epidemiological information on non-toxigenic Corynebacterium infections and the merits of using WGS for characterisation over traditional techniques.