Objectives

To investigate various stress responses of triclosan selected Staphylococcus aureus small colony variants in comparison to their parent strains.

Methods

Methicillin resistant S. aureus (MRSA) and methicillin sensitive S. aureus (MSSA) SCV strains and their parents were exposed to:

•Hydrogen peroxide (H202) and peracetic acid to examine oxidative stress.
•Increasing NaCl concentrations to examine salt tolerance.
•Increasing temperatures (50, 60 and 70°C) to investigate heat tolerance and heat shock response.
•Increasing exposure to UV light.

Samples were taken at set time points in all experiments and viable counts performed on Mueller-Hinton agar.

Results
SCVs showed reduced salt tolerance and also reduced rates of survival when exposed to oxidative stress. Parent cultures survived at 10 and 12.5 % w/v NaCl, whilst SCV cultures lost viability. SCVs also displayed reduced survival in hydrogen peroxide and peracetic acid. SCVs however showed prolonged survival at extreme temperatures and exposure to UV light when compared to their parent strains.

Conclusions
These results show a clear difference between SCV and parent responses to a variety of stresses. The ability of SCVs to withstand higher temperatures and longer exposure to UV light suggests SCVs up regulate or overexpress the genes involved in the heat shock or SOS response of S. aureus. This may be a direct result of the SCV phenotype. The reduced survival at high salt concentrations and oxidative stresses may be related to reduced levels of ATP that SCVs produce, resulting in decreased levels of active transport and enzyme production.