, 1996; Bearson et al., 1998). In addition, Bearson et al. (2006) have recently identified the phoP, rpoS, fur and pnp genes as being involved Selleck Natural Product Library in protecting serovar Typhimurium against

exposure to lactic acid. Our group has previously reported that, at the concentration present in Lactobacillus CFCSs, lactic acid plays no role in the anti-Salmonella activities of L. johnsonii NCC533, L. rhamnosus GG, Lactobacillus casei Shirota YT9029, L. casei DN-114 001, L. rhamnosus GR1 or Lactobacillus acidophilus LB strains (Bernet et al., 1994; Coconnier et al., 1997, 2000; Hudault et al., 1997; Lievin-Le Moal et al., 2002; Fayol-Messaoudi et al., 2005). Here, we found that at the concentration present in Lactobacillus CFCS lactic acid alone plays no role in the killing effect of L. johnsonii NCC533 or vaginal L. gasseri KS120.1 against two other pathogens: UPEC CFT073 and G. vaginalis DSM 4944 strains. The observation that the killing activity of lactic acid develops at high concentrations is consistent with Makras et al. (2006), who

have shown that activities of lactic acid started at 100 mM. In contrast, based on the fact that the activity of L. rhamnosus GG CFCS against the growth and survival of serovar Typhimurium disappears after dialysis eliminating lactic acid, whereas it is still present after dialysis against a lactic acid solution, De Keersmaecker et al. (2006) have concluded that lactic acid is responsible for the activity of L. rhamnosus GG. However, eliminating Ivacaftor mw lactic acid could have an effect on some other molecule(s) secreted by Lactobacillus that kill pathogens in co-operation with lactic acid. Consistent with this hypothesis, Niku-Paavola et al. (1999) have proposed that compounds secreted by Lactobacillus plantarum act synergistically with lactic acid, and Makras et al. (2006) observed that L. johnsonii NCC533 CFCS was effective against serovar Typhimurium by unknown inhibitory substance(s) that are only active in the presence of lactic acid. These nonlactic acid, heat-resistant anti-Salmonella molecule(s) present in the CFCSs of probiotic Lactobacillus strains have not yet been identified (McGroarty & Reid, 1988; Bernet-Camard

et al., 1997; Coconnier et al., 1997; Hudault et al., 1997; Ocana et al., 1999; Aroutcheva et al., Protirelin 2001b; van de Guchte et al., 2001; Sgouras et al., 2004, 2005; Fayol-Messaoudi et al., 2005, 2007; Atassi et al., 2006a). It has already been suggested that pyroglutamic acid may be responsible for the antimicrobial activity of L. rhamnosus GG and L. casei strains LC-10 and LB1931 (Silva et al., 1987; Huttunen et al., 1995; Yang et al., 1997), but it has been found to be intrinsically present in MRS medium and it does not increase during bacterial growth (De Keersmaecker et al., 2006). Adding increasing concentrations of acetic or formic acid to MRS medium has no effect on the viability of serovar Typhimurium (De Keersmaecker et al., 2006).