The objective of this study was to analyse proteomic profiles of antibiotic-susceptible E. coli MG1655, K. pneumoniae NCTC418, E. faecium NCTC13169, and S. aureus NCTC8325 under sub-inhibitory antibiotic stress. Gram-negative bacteria were exposed to cefotaxime, ciprofloxacin, kanamycin, and imipenem, while Gram-positive bacteria were treated with chloramphenicol, vancomycin, or oxacillin.