Growth in cecal mucus facilitates colonization of the mouse intestinal tract by methicillin-resistant Staphylococcus aureus

Intestinal colonization by methicillin-resistant Staphylococcus aureus (MRSA) is common in some groups of hospitalized patients and has been associated with an increased risk of staphylococcal infection. We tested the hypothesis that growth of MRSA in the colonic mucus layer is required for establishment of intestinal colonization. Mice treated with oral streptomycin before oral administration of MRSA developed persistent intestinal colonization, and the cecal mucus layer contained high concentrations of MRSA. MRSA strains grew rapidly when inoculated into cecal mucus in vitro but were unable to replicate under anaerobic conditions in cecal contents of saline- or streptomycin-treated mice. Oral vancomycin treatment reduced the density of 1 MRSA strain in stool but had no effect on a second strain. These results suggest that the cecal mucus layer provides an important niche that facilitates intestinal colonization by MRSA. Oral nonabsorbed antibiotics may be ineffective in eradicating some MRSA strains from the intestinal tract.