Purpose: To understand the mechanism of stress response in these serotypes, six strains of each serotype were selected in this study to differentiate L. monocytogenes under oxidative stress from physiological and genetic response.
Methods: Oxidative stress tolerance was examined by plate count during exponential phase, long-term-survival phase and biofilm state. The capability of forming biofilm in two serotypes was also compared with crystal violet assay after 3 days of incubation. Three oxidation resistance genes (kat, sod, fri), two stress-regulator encoding genes (sigB, perR), and one DNA repair gene (recA) were selected for transcription analysis by quantitative RT-PCR.
Results: Most serotype 4b strains exhibited a stronger resistance to 0.6% H2O2 than did serotype 1/2a during exponential phase and long-term-survival phase, while the later demonstrated a relatively hyper-biofilm in BHI broth at 37°C. At the genetic level, there were significant differences in the expression of three genes (sod, fri and perR) under oxidative stress between two serotypes, which suggests their importance of serotype variation in stress resistance. In addition, recA appeared to be critical for survival under stress in L. monocytogenes but not important for the difference among serotypes.
Significance: Our data gave a primary conclusion on the mechanism of two common serotype strains under oxidative stress. Further investigation is required to focus on sod, fri, and in particular perR, to elucidate the factors caused the different resistance in two common serotypes to stress.