During routine microbiological examination of milk samples from dairy cows without clinical signs of mastitis, quarter milk samples of 231 dairy cows from 12 herds were investigated for the presence of coagulase-negative staphylococci (CNS). The isolates were identified on the basis of colony morphology, Gram staining, catalase and coagulase test and the commercial kit, API Staph. CNS was detected in 29% (67/231) of the cows. A total of seven CNS species were identified with the most prevalent being Staphylococcus (Staph.) chromogenes (30%) and Staph. haemolyticus (28·8%), followed by Staph. simulans (11·2%), Staph. xylosus (11·2%), Staph. epidermidis (7·5%), Staph. hyicus (6·3%) and Staph. sciuri (5%). The predominant species, Staph. chromogenes and Staph. haemolyticus, were further characterized by antibiotic susceptibility testing using the agar disc diffusion method (Kirby-Bauer) and by pulsed-field gel electrophoresis (PFGE). Considerable resistance to ampicillin and penicillin was observed in both species. Isolates with identical or highly similar PFGE profiles were detected at the herd level despite a marked heterogeneity seen for both species. On the basis of somatic cell count, absence of clinical signs of inflammation and heterogeneity of genotypes, we assume that CNS isolated in this study could not be considered as important causative agents of the bovine mammary gland inflammation.

Staphylococcus haemolyticus is a pathogen frequently isolated from dairy cows and small ruminants. However, it always appears in only a few animals and not as a major pathogen. Recently, in a dairy goat herd of approximately 250 milking animals, 25·6% (46/180 goats) had milk cultures with atypical highly mucoid colonies accompanied by elevated somatic cell counts. The isolates were identified as Staph. haemolyticus. The present study describes the steps used in an attempt to identify the bacterium and to compare it with other coagulase-negative staphylococci (CNS) including Staph. haemolyticus. Species identification performed with the API STAPH-IDENT 32 kit showed >99·4% identity confirmed by 16S rDNA sequencing tests. Microscopically the atypical Staph. haemolyticus strains showed unique cuboidal tetrad clusters reminiscent of those of the genus Sarcina. The outbreak caused by an atypical CNS underlines the need for accurate biochemical and genetic methods for ultimate identification of CNS to the species level.