MOST CORYNEBACTERIUM-XEROSIS STRAINS IDENTIFIED IN THE ROUTINE CLINICAL LABORATORY CORRESPOND TO CORYNEBACTERIUM-AMYCOLATUM

A comprehensive study was performed on 25 bacterial clinical isolates originally identified as Corynebacterium xerosis. Three reference stra ins of C. xerosis were also included in the study, On the basis of a v ariety of phenotypic characteristics tested, all strains could be divi ded into two separate clusters: reference strains ATCC 373 (the type s train of C. xerosis) and ATCC 7711 showed yellow-pigmented, dry, rough colonies, fermented 5-keto-gluconate, exhibited strong leucine arylam idase and alpha-glucosidase activities, produced lactate as the major end product of glucose metabolism, were susceptible to most of the 19 antimicrobial agents tested, and showed an inhibition zone around disk s containing the vibriocidal compound O/129. In contrast, the remainin g 26 strains including reference strain NCTC 7243 as well as all clini cal isolates formed white-grayish, dry, slightly rough colonies, did n ot ferment 5-keto-gluconate, exhibited only weak leucine arylamidase a nd no cy-glucosidase activity, produced large amounts of propionic aci d as the end product of glucose metabolism, and were resistant to most antimicrobial agents tested, including O/129. Chemotaxonomic (cellula r fatty acids, mycolic acids, and G+C content) and molecular genetic ( 16S rRNA gene sequence) investigations revealed that the strains of th e second cluster unambiguously belonged to the species C. amycolatum. Our data suggest that most strains reported in the literature as C. xe rosis are probably misidentified and correspond to C. amycolatum.