Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/27/2006
Publication Date: 4/1/2007
Citation: Widmer, K.W., Jesudhasan, P.R., Dowd, S.E., Pillai, S.D. 2007. Differential expression of virulence-related genes in a Salmonella enterica serotype Typhimurium luxS mutant in response to autoinducer AI-2 and poultry meat-derived AI-2 inhibitor. Foodborne Pathogens and Disease. 4(1):5-15. Interpretive Summary: ARS scientists in Lubbock, Texas, as part of research related to the National Program 108 on Food Safety and its Performance Measure 3.2.1: Provide scientific information to protect animals from pests, infectious diseases, and other disease-causing entities that affect animal and human health performed in collaborations with Texas A&M Dr. Suresh D. Pillai to evaluate the modulation of genes related to virulence and how they are affected by natural inhibitors found in poultry meat. Poultry meat contains bacterial communication inhibitors that interfere with the bacterial communication hormone (AI-2) signaling and cause increases in genes that cause disease. Expression of 1136 disease-related genes in Salmonella Typhimurium wild type and a mutant strain of this bacteria that is unable to produce communication hormone AI-2 was monitored when the cells were exposed to different treatments containing purified AI-2, cell-free supernatants (simulate AI-2-like activity), and the natural inhibitor. The results indicate that the inhibitor increases the expression of important disease causing genes. Understanding the interaction of AI-2 and AI-2 inhibitors found in poultry meat may explain Salmonella survival and potential increases in virulence on poultry products. The further classification of naturally occurring AI-2 inhibitors and how to counteract them could limit the relative danger these pathogens pose when they contaminate our food supply.
Technical Abstract: Bacterial cells communicate amongst each other and respond to external stimuli using signal molecules termed autoinducers. Poultry meat contains inhibitors that interfere with AI-2 signaling. The objective was to understand the expression of Salmonella Typhimurium genes (using spotted microarrays) in response to AI-2 in the presence, and absence, of poultry meat (PM) derived AI-2 inhibitors. Expression of 1136 virulence-related genes in Salmonella Typhimurium wild type and its isogenic luxS mutant strain (unable to produce AI-2) was monitored when the cells were exposed to different treatments containing purified AI-2, cell-free supernatants (CFS) having AI-2-like activity, and the PM inhibitor. The treatments contained AI-2, AI-2 + PM, CFS, or CFS + PM. Total RNA was extracted from the cells after exposing the cells to the different treatments for 3 hours. Out of 1136 genes on the array, 14 genes were differentially expressed (3 up regulated and 11 down regulated) at least 2-fold when comparing the AI-2 treatment to the AI-2 + PM inhibitor treatment. Thirty one genes were differentially expressed at least 2-fold with 21 genes up-regulated, and 10 genes down regulated when comparing the CFS treatment to the CFS + PM inhibitor treatment. The differential expression of the genes was statistically significant (p < 0.05). The results indicate a varied expression of virulence genes in Salmonella when comparing purified AI-2 to that of CFS when combined with the PM inhibitor. Understanding the interaction of AI-2 and AI-2 inhibitors in poultry meat may explain Salmonella survival and virulence in poultry products.