Genome-wide analysis of fitness determinants of Staphylococcus aureus during growth in milk

Bovine mastitis caused by Staphylococcus aureus remains a major challenge to the dairy industry. Knowing which genetic determinants that facilitate S. aureus proliferation and persistence in milk, as well as the genes that influence antibiotic susceptibility in this environment could open the door to improved treatment strategies and novel antimicrobial targets, including targets for new synergistic drug combinations. In this work we employ CRISPRi-seq to identify genes that affects S. aureus fitness in milk, identifying pathways and mechanisms that are neccessary for S. aureus growth in milk, in addition to pathways that seem less important. Importantly, some of these genes could not have been detected by more conventional knock-out approaches because they are essential for growth under normal laboratory settings. By additional exposure of the library to sublethal concentrations of trimethoprim-sulfamethoxazole (TMP-SMX) we identify genes that influence S. aureus susceptibility to TMP-SMX.