Stress resistance assays. A Sensitivity to H2O2 at concentrations of 0.5, 1 or 1.5 mM. B Sensitivity to polymyxin B at concentrations of 50, 100 or 200 μg/mL. C Sensitivity to bovine serum (BS) and heat inactivated bovine serum (HIBS). D Resistance to low pH. Values are means ± standard errors for triplicate samples. * p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001; ns: no significant difference.