Mastitis can be caused by a number of bacteria (Philpot & Pankey, 1975), among
which Staphylococcus aureus is one of the most important, responsible for considerable
economic loss to the dairy industry (Jasper et al. 1982). Carrier rates have been
studied extensively in dairy herds suffering from mastitis (Davidson, 1961, 1963).
Subtyping bacteria is an important epidemiological tool; for example, antimicrobial
susceptibility patterns (antibiograms) have been used for typing Staph.
aureus in human medicine (Gillespie et al. 1990). Staph. aureus of bovine origin can
be divided into several categories by biotyping (Devriese, 1984). Phage typing has
proved useful in differentiating mastitis strains (Mackie et al. 1987) and plasmid
profiling has been valuable in epidemiological studies of bovine Staph. aureus
(Baumgartner et al. 1984).
During the last 5 years genomic fingerprinting of Staph. aureus became a powerful
tool for epidemiological typing. Numerous techniques for comparison of staphylococcal
isolates have been developed and are becoming important in investigations
of strain origin, clonal relatedness and epidemiology.
The aim of this study was to determine the epidemiology of Staph. aureus isolates
from mammary glands of cows from a single herd using modern molecular typing
techniques, and to assess whether the same strain constantly colonizes the udder or
cows are repeatedly infected by different strains. We investigated 26 Staph. aureus
isolates obtained from quarter milk samples from 16 cows. These isolates were
characterized biochemically, by their antibiotic resistance pattern, by two
polymerase chain reaction (PCR) methods on the basis of coagulase (Coa) gene and
protein A (Spa) gene (X region) polymorphism and by macrorestriction analysis of
chromosomal DNA using pulsed-field gel electrophoresis (PFGE).