The Influence of the Toxin/Antitoxin mazEF on Growth and Survival of Listeria monocytogenes under Stress

Abstract

A major factor in the resilience of Listeria monocytogenes is the alternative sigma factor B (σB). Type II Toxin/Antitoxin (TA) systems are also known to have a role in the bacterial stress response upon activation via the ClpP or Lon proteases. Directly upstream of the σB operon in L. monocytogenes is the TA system mazEF, which can cleave mRNA at UACMU sites. In this study, we showed that the mazEF TA locus does not affect the level of persister formation during treatment with antibiotics in lethal doses, but exerts different effects according to the sub-inhibitory stress added. Growth of a ΔmazEF mutant was enhanced relative to the wildtype in the presence of sub-inhibitory norfloxacin and at 42 °C, but was decreased when challenged with ampicillin and gentamicin. In contrast to studies in Staphylococcus aureus, we found that the mazEF locus did not affect transcription of genes within the σB operon, but MazEF effected the expression of the σB-dependent genes opuCA and lmo0880, with a 0.22 and 0.05 fold change, respectively, compared to the wildtype under sub-inhibitory norfloxacin conditions. How exactly this system operates remains an open question, however, our data indicates it is not analogous to the system of S. aureus, suggesting a novel mode of action for MazEF in L. monocytogenes.

Occurrence, Diversity of Listeria spp. Isolates from Food and Food-Contact Surfaces and the Presence of Virulence Genes

“…The presence in most isolates of the mazEF toxin-antitoxin system, which indicates efficient heat-shock-adaptation capacity [15], underlines the need to reinforce contamination prevention to reduce the risk that these bacteria pose to consumers.…”

“…nih.gov) and Clustal Omega (https://www.ebi.ac.uk/Tools/msa/clustalo/) for their ability to target mazF homologs in Listeria species other than L. monocytogenes. The amplification conditions were those reported by Curtis et al [15].…”

“…An analysis of the distribution of the mazF gene, a component of the type II toxin-antitoxin system mazEF, conferring increased tolerance to heat shock [15], was carried out to obtain indications of the tolerance of the isolates to a key stress factor applied in food production.…”

Large-Scale Comparison of Toxin and Antitoxins in Listeria monocytogenes

“…In silico predictions using TADB2 reveal only two TASs in L. monocytogenes EGD-e: lmo0113-0114 and lmo0887-0888 [19]. There are a few studies investigating TAS systems in L. monocytogenes [20][21][22] focusing only on a few L. monocytogenes strains and a few TAS pairs. The following TAS pairs were identified mainly using in silico methods in the strain ATCC19117 (with their corresponding gene names in L. monocytogenes EGD-e): lmo0113-0114, lmo0887-0888, and lmo1301-1302, predicting their 3D structure and potential inhibitory peptides.…”

“…Another report investigated the TAS lmo0887-888 of L. monocytogenes EGD-e in more detail, ruling out the classical MazF action, but without demonstrating the exact role of this TAS in L. monocytogenes [20]. They showed that lmo0887-888 does not affect the level of persister formation upon antibiotic treatment, but the expression of σ B -dependent genes opuCA and lmo0880 under sub-inhibitory norfloxacin treatment [20].…”