ARS | Publication request: Role of anionic charges of osmoregulated periplasmic glucans of Salmonella enterica Serovar Typhimurium SL1344 in mice virulence

Submitted to: Archives Of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 4, 2012
Publication Date: January 26, 2012
Citation: Bhagwat, A.A., Kannan, P., Leow, Y., Dharne, M., Smith, A.D. 2012. Role of anionic charges of osmoregulated periplasmic glucans of Salmonella enterica Serovar Typhimurium SL1344 in mice virulence. Archives Of Microbiology. 194(6):541-548.

Interpretive Summary: The ability to survive under environmental stress conditions enables Salmonella spp. to successfully enter the food chain. Survival of human pathogens in vegetable wash waters is a persistent cause of food borne infections. We have identified two genes, in the glucans gene family, opgB and opgC which are essential to overcome detergent and sanitation agents which are used in produce wash steps. Genetic mutation in the corresponding gene rendered Salmonella strains incapable of rapid growth in the presence of detergents however they remained fully virulent. Identification of genes essential for stress tolerance is crucial in designing specific sanitation agents to wash vegetables. The development of better cleaning agents to eliminate Salmonella spp. in food would be extremely beneficial to the food processing industry.

Technical Abstract: Osmoregulated periplasmic glucans (OPGs) are important periplasmic constituents of Salmonella spp. and are required for optimal growth in hypoosmotic environments such as irrigation and vegetable wash waters as well as for mice virulence. opgB gene of Salmonella enterica serovar Typhimurium was identified earlier in a genome-wide screen for mice virulence (Valentine et al., Infect. Immun. 66:3378-3383, 1998). Although mutation in opgB resulted in avirulent Salmonella strain, how this gene contributes to pathogenesis remains unclear. Based on DNA homology, opgB and opgC genes are predicted to be responsible for adding phosphoglycerate and succinate residues respectively on OPGs and giving them anionic characteristics. We constructed opgB, opgC and opgBC double mutants Salmonella enterica serovar Typhimurium strain SL1344. As predicted opgBC mutant synthesized neutral OPGs which were devoid of any anionic substituents. However opgB, C and opgBC mutations had no significant impact on mice virulence as well as on competitive organ colonization. In low osmotic conditions, opgB, opgC and opgBC mutants exhibited delay in growth initiation in the presence of sodium deoxycholate. Anionic OPG characteristics as well as delayed growth phenotype observed in presence of deoxycholate were restored to wild type levels when cloned wild type genes, opgB, C and BC were mobilized to respective mutants. Anionic substituents of OPGs from Salmonella although appear to be needed to overcome resistance of deoxycholate in hypoosmotic growth media however no evidence was found for their role in mice virulence.