A survey of multiple candidate probiotic bacteria reveals specificity in the ability to modify the effects of key wound pathogens.

We have evaluated the inhibitory effects of supernatants and lysates derived from several candidate probiotics, on the growth and biofilm formation of wound pathogens, and their ability to protect human primary epidermal keratinocytes from the toxic effects of pathogens. Supernatants (neutralized and non-neutralized) and lysates ( sonication) from GG, and Nissle 1917 were tested for their inhibitory effects against and . The supernatants of and GG reduced the growth of and additionally inhibited growth. However, neutralized supernatants did not inhibit growth and in some cases were stimulatory. Lysates of and inhibited while lysates inhibited and growth. Nissle 1917 lysates enhanced the growth of and . Biofilm formation by was reduced by lysates of and neutralized supernatants of all candidate probiotics. biofilm formation was reduced by Nissle supernatant but increased by and lysates. decreased the toxic effects of on keratinocytes while Nissle 1917 lysates protected keratinocytes from toxicity. In conclusion, lactobacilli and Nissle lysates confer inhibitory effects on pathogenic growth independently of acidification and may beneficially alter the outcome of interactions between host cell-pathogen in a species-specific manner.IMPORTANCEOne of the attributes of probiotics is their ability to inhibit pathogens. For this reason, many lactobacilli have been investigated for their effects as potential topical therapeutics against skin pathogens. However, this field is in its infancy. Even though probiotics are known to be safe when taken orally, the potential safety concerns when applied to potentially compromised skin are unknown. For this reason, we believe that extracts of probiotics will offer advantages over the use of live bacteria. In this study, we have surveyed five candidate probiotics, when used as extracts, in terms of their effects against common wound pathogens. Our data demonstrate that some probiotic extracts promote the growth of pathogens and highlight the need for careful selection of species and strains when probiotics are to be used topically.