Variations in stress tolerance abilities of diverse Listeria monocytogenes isolates

Abstract

Listeria monocytogenes is an important foodborne pathogen with the ability to survive and grow in different foods and food processing environments. The variability in innate stress tolerance abilities of L. monocytogenes strains (n=104) isolated from clinical (n=35), environment (n=28) and food (n=41) sources was investigated against salt (2.5 percent to 12.5 percent), pH (pH 4.0 to 9.5) and low temperature (down to 4 degrees C). The stress tolerance abilities were correlated with the source of isolation, serogroups and identifying the prevalent stress tolerant genotype. A total of 37 (35.57 percent) strains could tolerate different stresses of which 19 (18.26 percent) strains showed multi-stress tolerance capability. No correlation was observed among tolerance pattern and sources of isolation, while, 46.55 percent strains of L. monocytogenes serogroup 4b, 4d, 4e were tolerant to different stresses. The subtyping of stress tolerant strains employing pulsed-field gel electrophoresis revealed 15 pulsotypes. Multiple stress tolerant strains belonging to serogroup 4b, 4d, 4e (n=21) revealed to be clonal with unique pulsotypes. However, no correlation was observed for particular stress and pulsotypes. The data showed that strains varied remarkably with respect to stress tolerance abilities under different stresses without any correlation between stress tolerance pattern and origin of the strains for all studied stresses. This study is a significant step towards dissecting the variability of stress response in L. monocytogenes and understanding the dominance and prevalence of particular serogroup among different niches.