Investigation into potential cross-resistance of Enterococcus faecalis OG1RF induced by adaptation to NaCl and subsequent SDS challenge
The gram-positive, non-spore forming bacteria Enterococcus faecalis has been the interest of numerous stress studies due to its ability to survive a range of harsh environments. Its highly adapted membrane replete with specialized proteins enable E. faecalis to maintain homeostasis in such conditions as bile salts, low pH, and low oxygen encountered in the human gastrointestinal tract (12). Bile is a bacteriostatic agent because of its amphipathic nature and toxic amino acid moiety when in its conjugated bile acid form. Similarly, the detergent SDS (sodium dodecyl sulfate) exhibits toxic effects on the bacterial membrane of E. faecalis and for this reason is a comparable stressor to bile (4). Previous studies have explored the existence of cross-protection by exposure of bile salts stress to test growth in subsequent stress challenges such as heat, bile salts, SDS, and varied pH (9). We predicted that growth in NaCl may confer similar resistance to E. faecalis OG1RF when challenged to low concentrations of SDS in rich growth media. To examine the effects of such cross-protection by NaCl, OG1RF was grown with varying concentrations (%w/v) of NaCl then subjected to 0.01% SDS. Dilutions plated at various time points of the challenge revealed that rather than providing cross-protection, growth in salt only served to prolong the death of cells in the SDS challenge.