Effects of yeast probiotic formulation on viability, revival and protection against infection with Salmonella enterica ssp. enterica serovar Typhimurium in mice.

AIMS: To compare the effects of five yeast probiotic formulations on viability, revival and washout kinetic in the digestive tract of mice, and the protection against an experimental infection with Salmonella enterica serovar Typhimurium. METHODS AND RESULTS: The number of viable cells in five commercial probiotic products codified as A, B, C and D (Saccharomyces boulardii- lyophilized) and E (Saccharomyces cerevisiae- aqueous suspension) was determined, as well as revival and washout kinetic in mouse intestine. Protective capacity was evaluated by survival rate and histopathology of liver and intestine of mice treated with each product and then challenged with Salm. Typhimurium. CONCLUSIONS: Product A contained the highest number of viable cells and, fed to mice, gave the highest counts of viable yeasts and the longest persistence in faeces. Probably as a consequence, the highest survival and protection of intestinal and hepatic tissues were observed when product A was used for mouse treatment. Product E showed low counts in the formulation and was not recovered from mouse intestine. SIGNIFICANCE AND IMPACT OF THE STUDY: Formulation (lyophilization or aqueous suspension) is an important factor for revival and survival of a probiotic product in vivo and consequently for its protective properties.

Phenotypic changes in a laboratory-derived ertapenem-resistant Escherichia coli strain.

The aim of this study was to identify phenotypic changes in a laboratory-derived strain of ertapenem-resistant Escherichia coli (Ec-ERT) when compared to its susceptible parent strain (Ec-WT). In both strains, we assessed both the effects of ertapenem via time-kill curves and the occurrence of cross resistance with other beta-lactams. The strains were compared based on growth pattern, biochemical-physiological profile and changes in the subproteome using 2D-DIGE followed by MALDI-TOF/TOF MS. To assess virulence, we employed a murine model of intraperitoneal infection in which we investigated the invasiveness of both strains. Growth persistence of the laboratory-derived resistant strain was observed via the time-kill curve assay, but cross resistance was not observed for other beta-lactams. We also observed a slower growth rate and changes in the biochemical and physiological characteristics of the drug-resistant bacteria. In the resistant strain, a total of 51 protein spots were increased in abundance relative to the wild-type strain, including an outer membrane protein A, which is related to bacterial virulence. The mouse infection assay showed a higher invasiveness of the Ec-ERT strain in relation to the Ec-WT strain. In conclusion, the alterations driven by ertapenem in E. coli reinforce the idea that antimicrobial agents may interfere in several aspects of bacterial cell biology, with possible implications for host-bacteria interactions.