The location of Staphylococcus aureus in experimental chronic mastitis in the mouse and the effect on the action of sodium cloxacillin.

Chronic staphylococcal mastitis was established in the mouse and electron miscroscopic examination of mammary tissue showed that the staphylococci were within epithelial cells, neutrophils and macrophages. Suspensions of cells containing staphylococci were prepared from chronically infected glands and incubated with sodium cloxacillin in vitro. This procedure resulted in a reduction in bacterial numbers, but a significantly greater reduction was obtained if the somatic cells were disrupted by sonication before the addition of cloxacillin. The results imply that the intracellular location of the staphylococci protects them against the action of the antibiotic.