Beneficial effects of a strain of Lactobacillus paracasei subsp. paracasei in Staphylococcus aureus-induced intestinal and colonic injury.

Objectives: The aim of this study was to investigate the in vitro and in vivo anti-staphylococcal activity of a lactic acid bacterial strain and its effect on the intestinal histological damage caused by Staphylococcus aureus infection.

Methods: Lactobacillus paracasei subsp. paracasei was isolated in our laboratory from breastfed newborn feces and identified phenotypically and genotypically. The strain was analyzed by spot-on-lawn and well diffusion assays for the production of bacteriocins against five antibiotic-resistant S. aureus strains isolated from the feces of hospitalized patients with antibiotic-associated diarrhea. The anti-staphylococcal activity of this strain was evaluated in fermented milk and in vivo using holoxenic rabbits.

Results: The strain was able to produce a bacteriocin-like substance active against the staphylococcal strains. A reduction of 2 log in S. aureus cell numbers was registered in co-culture with L. paracasei in fermented milk. Administration of skimmed milk containing S. aureus (10(7) cells/ml) to healthy rabbits induced a persistent diarrheal state 5 days after the challenge. Dissection of the rabbits and consequent histological observations showed damage and an atrophy of the intestinal and colonic mucosae of the diarrheal rabbits; in contrast an arrest of the diarrhea concomitant with recovery of the intestinal villi and the colonic crypts was observed in the rabbits treated with L. paracasei-fermented milk. Furthermore, the diarrheal state persisted in spite of a decrease in the level of S. aureus cells in the feces of the rabbits receiving sterile milk; this was in contrast to the rabbits treated with L. paracasei-fermented milk, in which the decrease in the S. aureus fecal number was associated with the arrest of the diarrhea.

Conclusions: L. paracasei could act as a potential barrier to prevent S. aureus- associated injury and might exert its effect on the staphylococcal enterotoxins or their target.