Mechanisms of resistance to bacteriocins targeting the mannose phosphotransferase system

Area of Science:

• Microbiology
• Bacteriology
• Molecular Biology

Background:

• The mannose phosphotransferase system (Man-PTS) membrane proteins IIC and IID act as receptors for bacteriocins, including class IIa and IIc types.
• Bacterial strains sensitive to bacteriocins often develop resistance rapidly upon exposure, necessitating an understanding of resistance mechanisms.

Purpose of the Study:

• To investigate the mechanisms of resistance to lactococcin A in Lactococcus lactis mutants and Listeria monocytogenes isolates.
• To identify the genetic and metabolic basis for bacteriocin resistance in these bacterial species.

Main Methods:

• Analysis of lactococcin A-resistant mutants of Lactococcus lactis.
• Examination of natural food isolates of Listeria monocytogenes with varying susceptibilities to class IIa bacteriocins.
• Investigation of gene expression and metabolic shifts associated with resistance phenotypes.

Main Results:

• Two primary mechanisms of bacteriocin resistance were identified: downregulation of Man-PTS gene expression and an unknown mechanism with normal Man-PTS expression.
• Downregulation of Man-PTS gene expression was observed in both spontaneous resistant mutants and natural resistant isolates.
• In some resistant strains, reduced Man-PTS expression led to decreased glucose metabolism but enhanced growth on alternative sugars like galactose.

Conclusions:

• Bacteriocin resistance in Lactococcus lactis and Listeria monocytogenes is mediated by distinct mechanisms, primarily involving the mannose phosphotransferase system.
• The development of resistance can lead to significant metabolic heterogeneity within bacterial populations, impacting their adaptation and survival.
• Understanding these resistance mechanisms is crucial for controlling bacteriocin efficacy in food preservation and managing bacterial infections.