<p>Growing environmental and health concerns related to microplastics (MPs) exposure have prompted increasing attention, yet the toxicological impacts of polyethylene terephthalate microplastics (PET-MPs) remain poorly understood. This study investigated the dose-dependent physiological and antimicrobial susceptibility responses of four pathogenic bacteria (<i>Escherichia coli</i>, <i>Pseudomonas aeruginosa</i>, <i>Salmonella typhimurium</i>, and <i>Staphylococcus aureus</i>) to PET-MPs exposure. The results revealed species- and dose-dependent responses. <i>E. coli</i> and <i>P. aeruginosa</i> exhibited a consistent stimulatory effect on growth and biomass with increasing PET-MPs concentrations, whereas <i>S. aureus</i> and <i>S. typhimurium</i> displayed biphasic behavior with growth inhibition at lower concentrations and significant stimulation at higher levels. Furthermore, protein disruption and upregulation of catalase (CAT) activity were observed in all bacterial strains across the tested concentrations. Notably, bacteria acclimated to 3% PET-MPs exhibited enhanced resistance to multiple antibiotics, indicating adaptive cellular mechanisms promoting multidrug resistance. Microscopic examination of the DNA extraction solutions revealed particles with a morphology consistent with PET-MPs; however, definitive molecular associations between MPs and genomic DNA require confirmation through advanced co-localization analyses. Overall, these findings offer new insights into the biological and adaptive responses of pathogenic bacteria to exposure to microplastics.</p> Graphical Abstract <p></p>