Abstract
We detected Corynebacterium spp. in raw milk samples of three farms by means of a selective, tellurite-containing medium. The isolated strains were identified based on full 16S rRNA gene sequences and partial rpoB gene sequences as C. xerosis, C. variabile, C. lactis, C. callunae, C. confusum, C. glutamicum and C. crudilactis. The identification based on 16S rRNA and rpoB sequences was not reliable for isolates of C. xerosis. Chemotaxonomic markers of the isolates, fatty acids, acyl type of peptidoglycan, presence and length of mycolic acids, quinone patterns, and polar lipids, were in accord with the known characteristics of these species. Biochemical profiles, analyzed with the API Coryne system, were able to differentiate all groups, but were unable to identify the strains due to an inappropriate database for raw-milk associated corynebacteria. Most of the tested isolates showed a single-substance resistance against oxacillin, but three single isolates were classified as multidrug resistant.
Highlights
Species of the genus Corynebacterium were found ubiquitously in the environment, often their natural habitat—especially the habitat of nonmedical Corynebacterium species— remains unknown [1]
Pathogenic corynebacteria were detected in raw milk samples and Corynebacterium spp. are known to cause subclinical mastitis in dairy cows [2]
Potassium tellurite trihydrate (Merck KGaA, Darmstadt, Germany) was dissolved in distilled water and added filter-sterilized to the autoclaved medium in concentrations of 0.15 g/L [21], 0.25 g/L [22] or 0.36 g/L [16]. Selectivity of this medium was tested with type strains and isolates of the genus Corynebacterium and with isolates of other non-target genera: C. frankenforstense ST18T, C. lactis RW2-5T, C. glutamicum DSM 20300T, C. amycolatum DSM 6922T, C. camporealensis NS1-11, C. flavescens TS21, C. xerosis M3_I15, C. confusum M3_I13, C. casei M3_I10, Lactococcus lactis subsp. lactis JZ RK-40, Bacillus subtilis M3_I11, Staphylococcus chromogenes M3_I12, Escherichia coli M3_I20, Acinetobacter guillouiae M3_I21 and Pseudomonas gessardii M3_I22
Summary
Species of the genus Corynebacterium were found ubiquitously in the environment, often their natural habitat—especially the habitat of nonmedical Corynebacterium species— remains unknown [1]. Pathogenic corynebacteria were detected in raw milk samples and Corynebacterium spp. are known to cause subclinical mastitis in dairy cows [2]. Non-pathogenic Corynebacterium species were frequently isolated from raw milk or raw milk products [7,8]. Among them were some species with beneficial functions in food processing. The species C. glutamicum and C. variabile are well-known aminoacid producers [9] and the species C. casei, C. mooreparkense, C. ammoniagenes and C. stationis, have been detected on the surface of smear ripened cheese and are supposed to contribute to the flavor of the cheese [10,11]
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