42-5

C.-Y. CHEN, Microbial Food Safety Research Unit, USDA-ARS-Eastern Regional Research Center, 600 E. Mermaid Ln., Wyndmoor, PA 19038-8598

Quorum sensing has been shown to control many physiological attributes, such as bacterial virulence/pathogenesis, competence, and biofilm formation, when the bacterial population has reached a cretain threshold. Among the various signaling compounds, autoinducer-2 (AI-2) is present in most bacterial species, and is capable of cross-species signaling. Campylobacter species, an important foodborne pathogen, was also shown to carry the luxS gene, which encodes the enzyme involved in AI-2 synthesis, and can produce AI-2-like compounds detectable by the Vibrio harveyi bioluminescence assay. The production of AI-2 in C. jejuni strain 81-176 (a clinical isolate) was shown to be related to population density, with the maximal levels of AI-2 detected at the late log-phase to early stationary phase of bacterial growth (1 x 10⁸ CFU/ml or higher). The levels of AI-2 in the culture supernatants decrease after prolonged culture time (30 hours or longer) at 42^oC, even though the cell concentrations remained constant; a negative feedback control is apparently involved. We also constructed a luxS deletion mutant in C. jejuni strain 81-176 and studied the effects of AI-2 on bacterial growth and survival under various oxygen levels (5-21%). Our results showed that the growth and survival of the luxS mutant was similar to that of the wild type under either microaerobic or aerobic conditions. On the other hand, the survival of both wild type and luxS mutant strains showed a population density-dependent effect, i.e. survived longer at higher cell densities (10⁷-10⁸ CFU/ml) than at lower cell densities (10⁶ CFU/ml or lower), under aerated conditions. Supernatants collected from older cultures (24-50 hours) also prolonged the aerobic survival of C. jejuni strains at lower cell densities (10⁴-10⁶ CFU/ml). This protective effect is not dependent on the AI-2/luxS gene. Whether this protective effect is a true quorum sensing phenomenon requires further study.

Session 42, Control of quorum sensing signals and antimicrobial effects on foods
2:30 PM - 5:30 PM, Monday PM Room 296

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana