Cold Shock Protein Functions Contribute to Listeriolysin O Production and Antibiotic Stress Tolerance in Listeria monocytogenes

Introduction: Cold shock proteins (Csps) are small multifunctional nucleic acid binding proteins used to regulate various gene expression and stress adaptation responses in bacteria. Listeria monocytogenes is a gram-positive foodborne pathogenic bacterium causing serious illness (listeriosis) and high mortality among those with diminished immunity. This bacterium harbours three Csps whose contribution to virulence and stress resistance responses is not yet fully investigated.

Purpose: Our aims in the present study were to investigate the contribution of the Csps to the regulation Listeriolysin O (LLO) production and antibiotic stress resistance in L. monocytogenes.

Methods: L. monocytogenes EGDe and its isogenic triple deletion mutant (EGDe ΔcspABD) lacking csp genes (cspA, cspB and cspD) were compared in terms of LLO expression and sensitivity to different antibiotics.

Results:  The EGDe ΔcspABD mutant was impaired in hemolysis and LLO production compared to the parental EGDe strain. In addition this mutant was more sensitive than the parental strain to various antibiotics including those used to treat listeriosis (ampicillin and gentamicin). The decreased LLO synthesis in EGDe ΔcspABD was associated with reduced expression and stability of hly mRNA. Deletion of csp genes was not associated with decreased expression of selected multidrug resistance (MDR) transporter genes examined. The EGDe ΔcspABD mutant however displayed differences in the expression of genes encoding putative peptidoglycan synthesis proteins (lmo1438, lmo2754, lmo2039, lmo0540 and lmo1892) compared to the parental strain suggesting that loss of Csp functions might have caused alterations to the composition and integrity of the cell wall in this mutant.

Significance: Our results thus indicate that, besides documented roles in cold and osmotic stress adaptation, the csp gene family also contributes to the regulation of virulence and antibiotic stress responses in L. monocytogenes.