Development and characterization of a Staphylococcus aureus nasal colonization model in mice

Staphylococcus aureus nasal carriage is a risk factor for infection in huma ns, particularly in the hospital environment. Attenuation of carriage has p roven effective in reducing the prevalence of infection in some high-risk g roups. To study staphylococcal factors that influence nasal colonization, a mouse model of S. aureus nasal colonization was developed. Mice were inocu lated intranasally,vith S. aureus Reynolds, and nasal carriage was evaluate d by quantitating cultures of the nasal tissues from mice sacrificed at var ious time points after inoculation. The majority of mice inoculated with 10 (8) CFU of S. aureus maintained nasal carriage for at least 20 days. Nasal colonization rates were similar for inbred (BALB/c and C57BL/6) and outbred (ICR) mice. Colonization was not affected by mouse passage of strain Reyno lds. Lower inoculum doses (<10(7) CFU) resulted in reduced colonization aft er 7 days. However, mice given streptomycin in their drinking water develop ed long-term carriage of S. aureus, and they were colonized with inocula as low as 10(5) CFU. Nasal colonization was also established with two other S . aureus strains tone strain each of human and murine origins). S. aureus r ecovered from the nares of experimentally colonized mice expressed high lev els of capsule, and the ability of a capsule-defective mutant to persist in the nares was reduced in comparison to that of the parent strain. This nas al colonization model should prove useful for studies of factors that media te S. aureus colonization and for assessment of targets for antimicrobial i ntervention or vaccine development.