EVALUATION OF PHENOTYPIC AND GENOTYPIC METHODS FOR EPIDEMIOLOGIC TYPING OF STAPHYLOCOCCUS-AUREUS ISOLATES FROM BOVINE MASTITIS IN DENMARK

The value of five different typing methods (antibiogram typing, biotyp ing, phage typing, plasmid profiling and restriction fragment length p olymorphism of the gene encoding 16S and 23S ribosomal RNA (ribotyping )), in discriminating 105 Staphylococcus aureus strains from bovine mi lk samples obtained from 105 different Danish dairy herds was investig ated. A total of 85 strains (81%) proved susceptible to all of the 11 antibiotics tested, and the remaining 20 strains could be divided into 5 different antibiogram patterns. The predominant resistance pattern, penicillin resistance, was observed in 15 (75%) of the 20 antibiotic resistant strains. Biotyping assigned the strains to 14 different type s, with the most common type accounting for 25.7% of the strains. Nine ty eight (93.3%) strains could be typed by phages, assigning them to 1 9 different phage types. The predominant phage type accounted for 31.4 % of the strains. Eight different plasmid profiles was observed among 24 (23%) strains harbouring plasmids. Ribotyping yielded 30 different types, with the most common accounting far 29.5% of the strains. The s ingle most discriminatory typing method was ribotyping (0.863) followe d by biotyping (0.842) and phage typing (0.795). Plasmid profiling (0. 395) and antibiogram typing (0.327) had low discriminatory indices. Co rrespondence among ribotypes and the presence or absence of plasmids w ere observed, as was some degree of correspondence between ribotype, p hage type and biotype. In general the correspondence between phage typ e and ribotype were stronger than between biotype and ribotype and bet ween biotype and phage type. All combinations of two or more methods l ed to an improved index of discrimination compared to the individual m ethods indicating, that some subdivision of types had taken place. The combination of phage, bio- or ribotyping or all three methods in comb ination are considered to be an efficient combination of typing method s for epidemiological investigation of S. aureus mastitis.