Genomic characterization of the most barotolerant Listeria monocytogenes RO15 strain compared to reference strains used to evaluate food high pressure processing

Abstract

Background: High pressure processing (HPP; i.e. 100-600 MPa pressure depending on product) is a non-thermal preservation technique adopted by the food industry to decrease significantly foodborne pathogens, including Listeria monocytogenes, from food. However, susceptibility towards pressure differs among diverse strains of L. monocytogenes and it is unclear if this is due to their intrinsic characteristics related to genomic content. Here, we tested the barotolerance of 10 different L. monocytogenes strains, from food and food processing environments and widely used reference strains including clinical isolate, to pressure treatments with 400 and 600 MPa. Genome sequencing and genome comparison of the tested L. monocytogenes strains were performed to investigate the relation between genomic profile and pressure tolerance. Results: None of the tested strains were tolerant to 600 MPa. A reduction of more than 5 log 10 was observed for all strains after 1 min 600 MPa pressure treatment. L. monocytogenes strain RO15 showed no significant reduction in viable cell counts after 400 MPa for 1 min and was therefore defined as barotolerant. Genome analysis of so far unsequenced L. monocytogenes strain RO15, 2HF33, MB5, AB199, AB120, C7, and RO4 allowed us to compare the gene content of all strains tested. This revealed that the three most pressure tolerant strains had more than one CRISPR system with self-targeting spacers. Furthermore, several anti-CRISPR genes were detected in these strains. Pan-genome analysis showed that 10 prophage genes were significantly associated with the three most barotolerant strains. Conclusions: L. monocytogenes strain RO15 was the most pressure tolerant among the selected strains. Genome comparison suggests that there might be a relationship between prophages and pressure tolerance in L. monocytogenes.

HPP-induced transcriptome response during recovery of Listeria monocytogenes

“…For example, it has been shown that a mutation in ctsR causes barotolerance and a ctsR deletion mutant of L. monocytogenes shows increased expression of Clp protease and PTS system genes after HPP [31]. Similarly, we previously reported that heat-shock and Clp protease family genes were upregulated after HPP [12]. In contrast, Bowman et al [32] reported downregulation of heat-shock and PTS system genes after HPP.…”

“…The previous studies used relatively higher temperatures for storage after HPP (⩾ 15 °C) compared to common coldstorage applications in the food industry. We recently showed genetic differences between barotolerant and barosensitive L. monocytogenes strains, which may explain their different HPP sensitivity [12]. Hence, in the present study, we investigate the transcriptional response to HPP and the differences in gene expression pro les between barotolerant and barosensitive L. monocytogenes strains during recovery.…”

“…We previously reported that strain RO15 is more resistant to treatment of 400 MPa for 1 minute compared to several other L. monocytogenes strains including strain ScottA [12]. Here, we sought to test the susceptibility of both strains to pressure treatment at 200 and 400 MPa for 8 minutes at 8 °C.…”

“…It has been reported that HPP causes morphological, structural, physiological, and genetic changes or damages to L. monocytogenes cells [9]. However, the susceptibility of L. monocytogenes to HPP varies between growth phase [10], strength of the cellular envelope [11], genomic features [12], and individual strains [13]. In addition, food matrix type, temperature, water activity, compression and decompression rates, applied pressure and holding time, and other extrinsic factors have an impact on inactivation of L. monocytogenes cells by HPP [9].…”

“…Hence, in the present study, we investigate the transcriptional response to HPP and the differences in gene expression pro les between barotolerant and barosensitive L. monocytogenes strains during recovery. We selected L. monocytogenes strains RO15 (barotolerant) and ScottA (barosensitive) that were already analysed previously [12]. This is the rst study to perform time-series RNA-seq using both barosensitive and barotolerant strains monitoring gene expression pro les during recovery of an HPP insult at 8 °C.…”