Project description:Staphylococcus aureus (S. aureus) is a Gram-positive opportunistic bacterium commonly isolated on the skin and in the nasal cavity of many healthy individuals. It can cause infections, from local skin and soft tissue infections (SSTIs) like wound infections, abscesses, and cellulitis, to more severe conditions such as endocarditis, pneumonia, sepsis, and toxic shock syndrome. Its pathogenicity is due to its numerous virulence factors and its adaptability to environmental changes, including pH, oxygen, CO2, and temperature during host infections. Understanding metabolic adaptation is a complex step for identifying new therapeutic targets to combat antibiotic-resistant pathogens. Proteomic approaches are essential for studying microbial protein expression during environmental changes to understand metabolic pathways and antibiotic resistance mechanisms. We investigated the protein expression of two MRSA strains under three experimental conditions (ECs) to simulate the variations in pH, temperature, and NaCl concentration expected during a wound infection. One strain is Livestock-Associated (LA-MRSA) ST398, which colonizes the nasal cavity of pigs and has also been reported in other animals and used in the food industry. It poses a risk for farmers and people in direct contact with animals, such as veterinarians. The other strain is Community Associated (CA-MRSA), JE2 strain (USA300 isolate), one of the major causes of SSTI and the main cause of CA infections in the USA. The selected ECs mimic the stress conditions occurring on the skin during infection with S. aureus. These ECs were named experimental condition 1 (EC1), characterized by pH 7 at 37°C and considered as a control condition; experimental condition 2 (EC2), characterized by pH 6 at 35°C; and experimental condition 3 (EC3), characterized by pH 6 at 35°C with 5% NaCl added to the medium. The comparative analysis of bacterial proteomes under these diverse in vitro exposures provided evidence of metabolic reshaping and highlighted strain-specific and environmental-specific variations in critical bacterial functions.