The vaginal microbial NVP-BKM120 in vivo flora plays a role in maintaining human health (Pybus & Onderdonk, 1999; Aroutcheva et al., 2001a, b), and within this flora, resident Lactobacillus species exercise antibacterial activity by producing metabolites, including hydrogen peroxide, lactic acid and other antibacterial molecules (Eschenbach et al., 1989; Klebanoff et al., 1991; Hillier et al., 1992; Saunders

et al., 2007). Hydrogen peroxide-producing lactobacilli that colonize the vagina have been reported to reduce the prevalence of bacterial vaginosis (Wilks et al., 2004; Antonio et al., 2005). For women with recurrent urinary tract infections (UTIs), who often display persistent vaginal colonization by Escherichia coli (Johnson & Russo, 2005), the absence of hydrogen peroxide-producing strains of Lactobacillus appears to be important in the pathogenesis of recurrent UTI by facilitating colonization

by E. coli (Gupta et al., 1998). In the intestine, the role of hydrogen peroxide-producing strains in killing enteric pathogens has been poorly documented. Recently, Pridmore et al. (2008) reported for the first time that the human intestinal isolate Lactobacillus johnsonii NCC533, which exhibits antimicrobial properties against Salmonella typhimurium (Bernet et al., 1994; Bernet-Camard et al., 1997; Fayol-Messaoudi et al., 2005; Makras et al., 2006) and Helicobacter pylori (Michetti et al., 1999; Felley et al., 2001; Cruchet et al., 2003; Gotteland & Cruchet,

2003; Sgouras et al., 2005), produced hydrogen peroxide that was effective in killing S. typhimurium. Here, we investigate the respective contributions of hydrogen peroxide selleck chemical and lactic acid in killing bacterial Isotretinoin pathogens associated with the human vagina, urinary tract or intestine by two hydrogen peroxide-producing strains: enteric L. johnsonii NCC933 (Pridmore et al., 2008) and vaginal Lactobacillus gasseri KS120.1 (Atassi et al., 2006b). The human bacterial pathogens we used were Gardnerella vaginalis strain DSM 4944, uropathogenic E. coli (UPEC) strain CFT073 (UPEC CFT073) and Salmonella enterica serovar Typhimurium strain SL1344 (S. typhimurium SL1344). Gardnerella vaginalis is a heavily pilated, gram-negative bacterium (Boustouller et al., 1987) that produces cytolysin (Cauci et al., 1993) and attaches to epithelial cells (Scott et al., 1987). It is of particular importance in the etiology of bacterial vaginosis (Mikamo et al., 2000; Aroutcheva et al., 2001a). Strain CFT073 is the prototype UPEC strain involved in inducing recurrent UTI (Johnson & Russo, 2005). It displays various virulence factors (Marrs et al., 2005) such as toxins, and type 1 pili that help to form an intracellular reservoir of the pathogen by invading uroepithelial cells (Mysorekar & Hultgren, 2006), as well as flagella that enables them to ascend to the upper urinary tract and to disseminate throughout the host (Lane et al., 2007).