vanI : a novel d ‐ A la‐ d ‐ L ac vancomycin resistance gene cluster found in D esulfitobacterium hafniense

Summary The glycopeptide vancomycin was until recently considered a drug of last resort against Gram‐positive bacteria. Increasing numbers of bacteria, however, are found to carry genes that confer resistance to this antibiotic. So far, 10 different vancomycin resistance clusters have been described. A chromosomal vancomycin resistance gene cluster was previously described for the anaerobic D esulfitobacterium hafniense   Y 51. We demonstrate that this gene cluster, characterized by its d ‐ A la‐ d ‐ L ac ligase‐encoding vanI gene, is present in all strains of D .  hafniense , D . chlororespirans and some strains of D esulfosporosinus spp. This gene cluster was not found in vancomycin‐sensitive D esulfitobacterium or D esulfosporosinus spp., and we show that this antibiotic resistance can be exploited as an intrinsic selection marker for D esulfitobacterium hafniense and D . chlororespirans . The gene cluster containing vanI is phylogenetically only distantly related with those described from soil and gut bacteria, but clusters instead with vancomycin resistance genes found within the phylum A ctinobacteria that include several vancomycin‐producing bacteria. It lacks a vanH homologue, encoding a D ‐lactate dehydrogenase, previously thought to always be present within vancomycin resistance gene clusters. The location of vanH outside the resistance gene cluster likely hinders horizontal gene transfer. Hence, the vancomycin resistance cluster in D .  hafniense should be regarded a novel one that we here designated vanI after its unique d ‐ A la‐ d ‐ L ac ligase.