Absence of Association of Autoinducer-2-Based Quorum Sensing with Heat and Acid Resistance of Salmonella

This study used various approaches to investigate the potential association of autoinducer-2 (AI-2) presence with thermal and acid resistance of Salmonella cultures. Salmonella Thompson strains RM1987N (luxS-positive; AI-2 positive) and RM1987NLUX (luxS-negative; AI-2 negative) were exposed to 55 degrees C (6 h) in Luria-Bertani (LB) broth, while the luxS-negative S. Thompson strain and a Salmonella Typhimurium luxS-positive strain were exposed to 55 degrees C in AI-2-positive or -negative preconditioned (PC) media derived from S. Thompson and Escherichia coli O157:H7 luxS-positive and -negative strains. In addition, the luxS-negative S. Thompson strain was subjected to pH 3.5 PC media (35 degrees C, 6 h) with or without AI-2 activity, and acid-adapted or nonadapted S. Thompson strains were exposed to pH 3.0 LB broth (35 degrees C, 6 h). Surviving bacterial populations during exposure to 55 degrees C LB were not different between luxS-negative and -positive S. Thompson strains. In addition, heating at 55 degrees C of the luxS-negative S. Thompson strain in AI-2-positive and -negative PC media resulted in similar (P >= 0.05) survivor counts. Furthermore, surviving cell counts of S. Typhimurium (luxS-positive) in 55 degrees C AI-2-positive PC media were not different (P >= 0.05) than those in AI-2 negative PC media. No differences in surviving cell counts of the luxS-negative S. Thompson strain was found when exposed to pH 3.5 AI-2-positive and -negative PC media. Also, survivors of acid-adapted or nonadapted cells of luxS-negative and -positive S. Thompson strains were not different following exposure to pH 3.0 LB. The results indicated that, under the conditions of this study, AI-2-based quorum sensing did not appear to be associated with heat and acid resistance of Salmonella.