Abstract
This research was carried out to investigate the differences in adhesion and growth during biofilm formation of L. monocytogenes from different sources and clonal complexes. Biofilm by L. monocytogenes (isolates CLIST 441 and 7: both lineage I, serotype 1/2b, CC3; isolates 19 and 508: both lineage II, serotype 1/2c, CC9) was grown on stainless steel coupons under different stressing conditions (NaCl, curing salts and quaternary ammonium compounds-QAC), to determine the expression of different genes involved in biofilm formation and stress response. CLIST 441, which carries a premature stop codon (PMSC) in agrC, formed high-density biofilms in the presence of QAC (7.5% w/v) or curing salts (10% w/v). Reverse Transcriptase-qPCR results revealed that L. monocytogenes isolates presented differences in transcriptional profile of genes related to biofilm formation and adaptation to environmental conditions. Our results demonstrated how L. monocytogenes can survive, multiply and form biofilm under adverse conditions related to food processing environments. Differences in transcriptional expression were observed, highlighting the role of regulatory gene networks for particular serotypes under different stress responses.
Highlights
Listeria monocytogenes is the causative agent of listeriosis, a foodborne disease that affects mainly children, pregnant women, the elderly and immunocompromised individuals (Radoshevich and Cossart 2018)
Absorbance values obtained for adhesion assays on stainless steel microtiter plates showed that in the presence of quaternary ammonium compounds (QAC) or curing salts (7.5%, and 10%) the isolate CLIST 441 formed higher-density biofilms, when compared to the other isolates tested (Fig. 1)
Based on absorbance values recorded by crystal violet assay, specific treatments were employed in further testing, where the isolates 7 and CLIST 441 were exposed to cure salts while isolates 19 and 508 were exposed to QAC treatment, on stainless steel microtiter plates and coupons
Summary
Listeria monocytogenes is the causative agent of listeriosis, a foodborne disease that affects mainly children, pregnant women, the elderly and immunocompromised individuals (Radoshevich and Cossart 2018). Due to its capacity to adhere and to form biofilms, L. monocytogenes can colonize food processing facilities and often persist in this environment for years, leading to cross contamination of foodstuffs (Møretrø and Langsrud 2004; RodríguezMelcón et al 2019). L. monocytogenes can adhere and form biofilms on different materials, such as stainless steel, glass and polymers, favoring its environmental persistence (Carpentier and Cerf 2011). L. monocytogenes is known for other features that contributes for its persistence in the food processing environments, such as tolerance to disinfectants, to cold storage temperatures and to high salt concentrations (Ryan et al 2010; Belessi et al 2011; Pieta et al 2014; Lee et al 2017). The increasing use of advanced molecular tools, like whole genome sequencing (WGS), is allowing deeper studies on L. monocytogenes genomics and the proper understanding of the relatedness between persistent and transient strains at sub species level (Jagadeesan et al 2019)
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