Cell-surface alterations in class IIa bacteriocin-resistant Listeria monocytogenes strains

Abstract

Strains of the food-borne pathogen Listeria monocytogenes, showing either intermediate or high-level resistance to class IIa bacteriocins, were investigated to determine characteristics that correlated with their sensitivity levels. Two intermediate and one highly resistant spontaneous mutant of L. monocytogenes B73, a highly resistant mutant of L. monocytogenes 412, and a highly resistant, defined (mptA) mutant of L. monocytogenes EGDe were compared with their respective wild-type strains in order to investigate the contribution of different factors to resistance. Decreased mannose-specific phosphotransferase system gene expression (mptA, EIIAB Man component) was implicated in all levels of resistance, confirming previous studies by the authors' group. However, a clear correlation between D-alanine content in teichoic acid (TA), in particular the alanine : phosphorus ratio, and a more positive cell surface, as determined by cytochrome c binding, were found for the highly resistant strains. Furthermore, two of the three highly resistant strains showed a significant increase in sensitivity towards D-cycloserine (DCS). However, real-time PCR of the dltA (D-alanine esterification), and dal and ddlA genes (peptidoglycan biosynthesis) showed no change in transcriptional levels. The link between DCS sensitivity and increased D-alanine esterification of TA may be that DCS competes with alanine for transport via the alanine transporter. A possible tendency towards increased lysinylation of membrane phospholipid in the highly resistant strains was also found. A previous study reported that cell membranes of all the resistant strains, including the intermediate resistant strains, contained more unsaturated phosphatidylglycerol, which is an indication of a more fluid cell membrane. The results of that study correlate with the possible lysinylation, decreased mptA expression, D-alanine esterification of TA and more positive cell surface charge found in this study for resistant strains. The authors' findings strongly indicate that all these factors could contribute to class IIa bacteriocin resistance and that the combination and contribution of each of these factors determine the level of bacteriocin resistance.

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

“…For the expression levels of dltA and Imo1965, our results are consistent with those proposed by [40], who also found no significant changes in expression of these genes in wild-type strains of L. monocytogenes. 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].…”

“…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.…”

Target recognition, resistance, immunity and genome mining of class II bacteriocins from Gram-positive bacteria

“…Moreover, there are also cases where class IIa bacteriocinresistant cells show normal or even elevated Man-PTS expression (Kjos et al, 2011;Tessema et al, 2009;Vadyvaloo et al, 2004b). The exact resistance mechanism in these cases is unknown, but changes in the cell envelope (e.g.…”

“…The exact resistance mechanism in these cases is unknown, but changes in the cell envelope (e.g. membrane fluidity or cell surface charge) have been found to be associated with these resistant cells (Vadyvaloo et al, 2002(Vadyvaloo et al, , 2004b. Probably, such changes can mask or interfere with the bacteriocin-receptor interaction, thereby rendering cells resistant to bacteriocins.…”

“…In this context, it is interesting to note that class IIa bacteriocin-resistant Li. monocytogenes (Vadyvaloo et al, 2004b) and E. faecalis (Opsata et al, 2010) display altered metabolic profiles. Whether such a stochastic mechanism contributes to bacteriocin resistance development remains to be investigated experimentally.…”