Propionic Acid-Producing Strains Previously Designated as Corynebacterium xerosis, C. minutissimum, C. striatum, and CDC Group I2 and Group F2 Coryneforms Belong to the Species Corynebacterium amycolatum

Abstract

Propionic acid-producing Corynebacterium strains that lacked mycolic acids and were formerly identified as Corynebacterium minutissimum, Corynebacterium xerosis, Corynebacterium striatum, and CDC group I2 and F2 strains were studied to determine their relatedness to Corynebacterium amycolatum. A total of 60 strains were used for phenotypic characterization studies, and 26 of these strains were used for genetic studies. DNA-DNA hybridization experiments performed at 65°C revealed that the levels of relatedness between the propionic acid-producing strains and the type strain of C. amycolatum were more than 70% and that the ΔT m values ranged from 0 to 5°C (ΔT m is the difference between the denaturation temperature of a homoduplex and the denaturation temperature of a heteroduplex); these values are consistent with inclusion of these strains in the species C. amycolatum. Currently used conventional tests, such as urease, nitrate reduction, and sugar fermentation tests, were not suitable for accurate identification of C. amycolatum. Phenotypic differentiation of this species from related taxa should be based on the following characteristics in addition to propionic acid production: Lipid requirement, Tween esterase activity, tyrosine clearing, alkaline phosphatase activity, α-glucosidase activity, and β-glucuronidase activity.