Experimental mastitis in mice induced by coagulase-negative staphylococci isolated from cases of mastitis in nursing women.

Coagulase-negative staphylococci are frequently isolated from the milk of women with signs of puerperal mastitis. In order to evaluate the pathogenicity of these bacteria, strains of S. epidermidis and S. saprophyticus isolated from cases of mastitis in nursing women were inoculated into the mammary glands of lactating mice. Although clinical signs of mastitis were absent, by histological examination, mastitis was demonstrated in 78-93% of the glands. Abscesses were found in a few cases only. The inoculated bacteria were re-isolated in 41-61% of the cases, and when inoculated in numbers of 10(2) to 10(4) c.f.u. the bacteria multiplied above input levels in several cases. It is concluded that coagulase-negative staphylococci isolated from the milk of women with puerperal mastitis can produce mastitis in mice and should be considered as a possible etiologic agent of mastitis in nursing women.