Capsule-negative Staphylococcus aureus induces chronic experimental mastitis in mice

TUCHSCHERR, LPN; BUZZOLA, FR; ALVAREZ, LP; LEE, JC; SORDELLI, DO

INFECTION AND IMMUNITY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2005 vol. 73 p. 7932 - 7937

0019-9567

Staphylococcus aureuscapsular polysaccharides (CP) have been shown to enhance 3staphylococcal virulence in numerous animal models of infection. Although serotypes 5 CP 4(CP5) and 8 (CP8) predominate among S. aureusisolates from humans, most 5staphylococcal isolates from bovines with mastitis in Argentina are capsule-negative. This 6study was designed to evaluate the effects of CP5 and CP8 expression on the pathogenesis 7of experimental murine mastitis. Lactating mice were challenged by the intramammary 8route with one of three isogenic S. aureusstrains producing CP5, CP8, or no capsule. 9Significantly greater numbers of the acapsular mutant were recovered from the infected 10glands 8 and 12 days after bacterial challenge compared with the encapsulated strains. 11Histopathological analyses revealed greaterpolymorphonuclear and mononuclear leukocyte 12infiltration and congestion in the mammary glands of mice infected with the encapsulated 13strains compared with the acapsular mutant, and the serotype 5 strain elicited more 14inflammation than the serotype 8 strain. In vitro experiments revealed that the acapsular S. 15aureus strain was internalized by MAC-T bovine epithelial cellsin significantly greater 16numbers than the CP5- or CP8-producing strains. Taken together, the results suggest that S. 17aureuslacking a capsule were able to persist in the murine mammary gland, whereas 18encapsulated strains elicited more inflammation and were eliminated faster. Loss of CP5 or 19CP8 expression may enhance the persistence of staphylococci in the mammary gland of 20chronically infected hosts. 21