METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (MRSA): GROWTH DYNAMICS AND RESISTANCE MECHANISMS

Methicillin-Resistant Staphylococcus aureus (MRSA) represents a critical public health threat due to its multidrug resistance and capacity to cause persistent infections. This study investigates the growth dynamics and resistance mechanisms of MRSA under varying antibiotic stress conditions using a multi-modal approach. Three isolates—H9, H52, and a reference strain—were exposed to Cefoxitin and Vancomycin at both minimum inhibitory concentrations (MIC) and sub-lethal levels. A resazurin-based viability assay was employed to determine MIC values, while digital microscopy was used to observe morphological changes over time intervals (6, 12, 24, and 48 hours). Quantitative PCR (qPCR) targeting the icaD gene, a biofilm-associated gene, was used to assess molecular responses to antibiotic exposure. Results revealed strain-specific differences in antibiotic susceptibility and morphological adaptations. H9 showed strong upregulation of icaD under Cefoxitin stress, indicating a potential biofilm-mediated survival strategy, whereas H52 and the reference strain exhibited downregulation. Microscopic analysis confirmed structural adaptations such as cell thickening, aggregation, and deformation under sub-lethal exposures. The study highlights the dynamic response of MRSA to antimicrobial stress and underscores the importance of integrating phenotypic and molecular techniques to understand resistance development. These findings support the need for more nuanced antimicrobial stewardship and may inform future therapeutic strategies targeting biofilm-associated resistance Keywords: health, infections, mechanisms, microscopic, cell.