INRA scientists at Jouy-en-Josas have been using Lactococcus lactis to study the mechanisms by which bacteria can resist the deterioration of their cell wall by lysozyme.  The type of resistance thus demonstrated is of particular interest because lysozyme is used as an antibacterial agent in the agrifood industry.  Consequently, this research opens the way to a broad range of applications that will enable the effective control of lysozyme use in the manufacture of food products.

The results obtained by these scientists show that Lactococcus lactis is capable of resisting lysozyme. They thus reveal the existence of a sophisticated regulatory mechanism that involves the interlinked and concerted action of several regulators in response to different types of stress.

Indeed, the response to numerous stress conditions in Gram-positive bacteria is regulated by a family of general transcription factors: Spx-related proteins.  Study of this protein family has enabled researchers to identify one of them – SpxB – as mediating the response to stress affecting the cell wall.

By causing the over-expression of SpxB in bacteria, the scientists observed a chemical modification to a bacterial wall component, peptidoglycan, which ensures mechanical and physical protection of the bacterium.  This modification allows the bacterium to better resist the damage caused by attack from lysozyme.


Work is ongoing to study how other Spx-related proteins participate in this regulation of the different types of stress to which lactococci and non-pathogenic bacteria are subjected.

The knowledge acquired could then be transposed to pathogenic or opportunistic bacteria belonging to the streptococcal, staphylococcal or enterococcal genera, which are phylogenetically close to lactococci.  The results will throw new light on the mechanisms which allow the orchestration of cell responses to numerous environmental signals.  They will also help to elucidate how these mechanisms are involved when bacteria enter a dormant phase (the ultimate bacterial strategy to enable their survival under conditions of stress), and in the acquisition of resistance against antimicrobial agents in foods.