Growing Staphylococcus aureus in synthetic cystic fibrosis medium promotes colonization in a murine pneumonia model

Staphylococcus aureus is a leading cause of bacterial infections worldwide and can lead to diseases, such as osteomyelitis, skin, and lung infections in humans. Murine infection models have been an essential tool to the study of S. aureus virulence, although they do have their limitations. In murine pneumonia models, S. aureus infections are generally not well maintained. We hypothesize that culturing S. aureus under different conditions, such as in Synthetic CF Medium 2 (SCFM2), would increase bacterial respiratory loads compared to growing the bacteria on standard rich medium agar plates. We observed that culturing six S. aureus strains from various sources in SCFM2 resulted in a neutral or increased level of bacterial lung load compared with those cultured on agar plates. Focusing on one strain, WU1, we found that culturing in SCFM2 improved bacterial persistence in the oropharynx and led to a sustained long-term lung infection compared with agar plates. We further noted that mice experienced increased inflammation in both lobes of the lungs when infected with WU1 cultured in SCFM2 compared with agar plates. Overall, we have shown that culturing S. aureus under different conditions prior to infection impacts the level of colonization and host response.