Submitted to: Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2008
Publication Date: 1/1/2009
Citation: Bhagwat, A.A., Jun, W., Liu, L., Porteen, K., Dharne, M., Pheh, B., Tall, B.D., Kothary, M.H., Gross, K.C., Angle, S., Jianghong, M., Smith, A.D. 2009. Osmoregulated periplasmic glucans of Salmonella enterica serovar Typhimurium are required for optimal virulence in mice. Microbiology. 155:229-237. Interpretive Summary: The ability of Salmonella enterica serovar Typhimurium strains to survive environmental stress conditions plays a crucial role in the spread of salmonelosis. Fresh and fresh-cut produce has been implicated in recent outbreaks of infections caused by Salmonella sp. In this study we show that the ability to make specific glucose-polymer offers growth advantage to Salmonella strains under nutritionally challenging conditions. Salmonella strains synthesizing this glucose-polymer were more virulent in mice. Understanding how pathogens overcome various stress conditions during produce processing and handling will advance our knowledge of how enteric human pathogens enter our food chain. The research will benefit the fresh produce industry, as well as increasing the microbial food safety of the Americans food supply.
Technical Abstract: We purified osmoregulated periplasmic glucans (OPGs) from Salmonella enterica serovar Typhimurium and found them to be composed of 100% glucose with 2-linked glucose as the most abundant residue with terminal glucose, 2,3-linked and 2,6-linked glucose also present in high quantities. The two structural genes for OPGs biosynthesis, opgG and opgH form a bicistronic operon and insertion of kanamycin gene cassette in this operon resulted in a strain devoid of OPGs. The opgGH mutant strain was impaired in motility and growth under low osmolarity-low nutrient conditions. The opgGH mutation resulted in a 2 log increase in the LD50 in mice compared to the wild-type strain SL1344. Inability to synthesize OPGs had no significant impact on the organism’s lipopolysaccharide pattern or its ability to survive antimicrobial peptides-, detergent-, pH, and nutrient-stress conditions. We observed that the opgGH-defective strain respired at a reduced rate under acidic growth conditions (pH 5.0) and had lower ATP levels compared to the wild type strain. These data indicate that OPGs of S. enterica serovar Typhimurium contribute towards mouse virulence as well as growth and motility under low osmolarity growth conditions.