Purpose: The objectives of this study were to determine the role of sigB and inlA gene expression levels in L. monocytogenes biofilm formation and their role on the antimicrobial efficacy of NECAW treatment.
Methods: Liquid cultures and biofilms grown on stainless steel coupon surface of four L. monocytogenes strains (wild type (WT) 10403S, isogenic ΔinlA, ΔinlB, and ΔinlAΔsigBmutants) were treated with NECAW for 10 min. Sanitizing efficacy of NECAW was determined by counting the survivors after treatment using standard plate count. Gene expression levels were determined using qPCR.
Results: Isogenic inlA and sigB mutants were able to form biofilms. After NECAW treatment, both gene expressions increased for the WT. While sigB gene expression of ΔinlA strain increased comparable to the WT, inlA gene expression of ΔsigB strain did not significantly increase. Both genes were expressed more in biofilms than in liquid cultures. The level of inlA gene expression in WT increased by 4.28 and 5.51-fold with treatment with 4 mg/l NECAW for 10 min in liquid cultures and biofilms, respectively, while the corresponding values were 5.91 and 10.05-fold for sigB gene. Mutant strains were more sensitive to NECAW treatment than WT strain. For liquid culture, 10 mg/l NECAW for 10 min resulted in 0.79 and 1.17 more log CFU/ml reductions for ΔinlA and ΔsigBstrains, respectively, than WT strain while there was no significant difference in biofilms under the same condition.
Significance: The sigB gene was more important than inlA for surviving NECAW treatment. Surviving L. monocytogenes cells post sublethal NECAW treatment might become resistant to further sanitizer treatment.