High-level resistance to class IIa bacteriocins is associated with one general mechanism in Listeria monocytogenes

Abstract

Class IIa bacteriocins may be used as natural food preservatives, yet resistance development in the target organisms is still poorly understood. In this study, the understanding of class IIa resistance development in Listeria monocytogenes is extended, linking the seemingly diverging results previously reported. Eight resistant mutants having a high resistance level (at least a 10 3 -fold increase in MIC), originating from five wild-type listerial strains, were independently isolated following exposure to four different class IIa bacteriocin-producing lactic acid bacteria (including pediocin PA-1 and leucocin A producers). Two of the mutants were isolated from food model systems (a saveloy-type sausage at 10 SC, and salmon juice at 5 SC). Northern blot analysis showed that the eight mutants all had increased expression of EII Bgl and a phospho-β-glucosidase homologue, both originating from putative β-glucosidespecific phosphoenolpyruvate-dependent phosphotransferase systems (PTSs). However, disruption of these genes in a resistant mutant did not confer pediocin sensitivity. Comparative two-dimensional gel analysis of proteins isolated from mutant and wild-type strains showed that one spot was consistently missing in the gels from mutant strains. This spot corresponded to the MptA subunit of the mannose-specific PTS, EII Man t , found only in the gels of wild-type strains. The mptACD operon was recently shown to be regulated by the σ 54 transcription factor in conjunction with the activator ManR. Class IIa bacteriocin-resistant mutants having defined mutations in mpt or manR also exhibited the two diverging PTS expression changes. It is suggested here that high-level class IIa resistance in L. monocytogenes and at least some other Gram-positive bacteria is developed by one prevalent mechanism, irrespective of wild-type strain, class IIa bacteriocin, or the tested environmental conditions. The changes in expression of the β-glucoside-specific and the mannose-specific PTS are both influenced by this mechanism. The current understanding of the actual cause of class IIa resistance is discussed.

Expression of mptC of Listeria monocytogenes induces sensitivity to class IIa bacteriocins in Lactococcus lactis

“…This observation substantiates previous suggestions of a common mode of action for the class IIa bacteriocins against Ls. monocytogenes based on cross-resistance to these compounds (Ennahar et al, 2000a;Rasch & Knöchel, 1998) and also agrees with the general high-level resistance mechanism proposed for class IIa bacteriocins (Gravesen et al, 2002).…”

“…lactis MG-ACD was insignificant at 156 ng leucocin ml 21 , which is similar to concentrations required for inhibition of Ls. monocytogenes (Gravesen et al, 2002;Vadyvaloo et al, 2002). Thus, the sensitivity to leucocin A increased at least 2500-fold when expression of mptACD was induced in Lc.…”

“…The same observation was made for a number of spontaneous mutants of Ls. monocytogenes showing highlevel resistance to class IIa bacteriocins (Gravesen et al, 2002). This IIAB is part of the EII Man t permease encoded by the mptACD operon (Dalet et al, 2001).…”

Influence of Peptide P34 on Gene Expression of Listeria Monocytogenes and Listeria Seelegeri

“…The L. monocytogenes used in this study is a collection strain (ATCC) and the decrease of mptA gene expression has been reported only for resistant or mutant strains of L. monocytogenes [38,40,41]. Therefore the result of a non-significant increase in mptA gene expression in L. monocytogenes ATCC 7644 is consistent with the literature.…”

“…The expression of this gene was highly suppressed after incubation for 240 h at 4 °C, and the treatment with nisin resulted in lower dltA expression as compared with the peptide P34. Previous studies have shown that a 1000-fold increased resistance to class IIa bacteriocins in L. monocytogenes and Enterococcus faecalis resulted from the loss of mptA expression [38,42,43]. The cell wall of L. monocytogenes is composed by a thick peptidoglycan layer containing two types of anionic polymers: teichoic acids (TA), which are covalently linked to the peptidoglycan, and lipoteichoic acids (LTAs), which are poly phosphoglycerols substituted with a Dalanyl ester or a glycosyl residue and anchored in the membrane by their glycolipid moiety [44].…”