Differential ability of Staphylococcus aureus from diverse agr groups to invade mammary epithelial cells.

BUZZOLA FR; ALVAREZ, LP; TUCHSCHERR, LPN; BARBAGELATA, MS; LATTAR, SM; CALVINHO, L; SORDELLI, DO

Maastricht, Holanda

Simposio; 12th International Symposium on Staphylococci & Staphylococcal Infections; 2006

Staphylococcus aureus is the most frequently isolated bacteria from milk of bovines with mastitis. Four allelic groups, which interfere with the regulatory activity among the different groups, have been identified in the accessory gene regulator (agr) system. The aim of this study was to ascertain the prevalence of the different agr groups in S. aureus isolated from mastitic bovines and whether a given agr group was associated with capsular polysaccharide (CP) production, MAC-T cell invasion and in vivo persistence. Seventy-five percent of bovine S. aureus strains were classified as agr group I. The remainder belonged in agr groups III, II and IV (10, 7.5 and 7.5%, respectively). By restriction fragment length polymorphism analysis after PCR amplification of the agr locus variable region, 7 agr restriction types were identified. All agr group I strains presented an unique allele (A/1), whereas strains from groups II, III and IV exhibited higher diversity. Bovine S. aureus strains defined as agr group I showed a significantly increased ability to be internalized within MAC-T cells, compared with isolates from agr groups II, III and IV. Agr-groups II or IV S. aureus strains were cleared more efficiently than agr-group I strains from the murine mammary gland. The absence of CP expression in agr group I S. aureus demonstrated to be an important phenotype that favored internalization into MAC-T cells.  The results suggest that agr-group I S. aureus strains persist more efficiently in mammary gland tissue than S. aureus strains classified as agr groups II, III or IV.