Effects of Salt Stress on the Antimicrobial Drug Resistance and Protein Profile of Staphylococcus aureus

Background: staphylococcus aureus is the causative agent of a high percentage of nosoco- mially acquired infections and food-borne illnesses. antimicrobial resistance of s. aureus, especially methicillin-resistant s. aureus (mrsa), continues to be a concernfor clinicians worldwide. objectives: the aim of this study was to investigate the effects of salt stress on the antimi- crobial drug resistance and protein profile of s. aureus. materials and methods: staphylococcus aureus (atcc 25823) was grown in trypticase soy broth at 37°c. cells in the exponential growth phase were gradually exposed to sub-lethal salt stress with concentrations ranging from 5% to35% (wt/vol). there after, these cells were harvested and re-suspended in a tube containing 0.5ml of saline. to standardize the num- ber of bacteria, the bacterial suspension was compared to the 0.5 mcfarland standard sus- pension. antibiotic susceptibility was determined using the disk diffusion method, and the method involved plating of cell suspensions with stressed cells and unstressed cells on mueller-hinton agar plates. the pooled proteins from each condition were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (sds-page). results: compared to the unstressed cells, the cells exposed to salt showed signifi- cant changes in resistance to rifampicin (p=0.032), penicillin (p=0.02) and methicillin (p=0.001). furthermore, sds-page analysis of pooled proteins from cells exposed to salt showed changes in the protein profile. conclusions: we conclude that salt stress is responsible for the changes in protein profile- and antimicrobial resistance of s. aureus, especially to methicillin.