Abstract
BackgroundOne of the working mechanisms of probiotic bacteria is their ability to compete with pathogens. To define the probiotic properties of seven Lactic Acid Bacteria (LAB) strains, we tested them for survival in simulated gastro-intestinal conditions, antimicrobial activities, co-aggregative abilities, and interferences studies against five human intestinal pathogens (Salmonella enteritidis ATCC 13076, Listeria monocytogenes ATCC 7644, Escherichia coli O157: H7 ATCC 35150, Cronobacter sakazakii ATCC 29544 and Campylobacter jejuni ATCC 33291).ResultsThe LAB strains were able to survive the stomach simulated conditions, and varied in their abilities to survive the small intestinal-simulated conditions. The strains showed antibiotic susceptibility profiles with values equal or below the breakpoints set by the European Food and Safety Authority. The LAB cell-free cultures supernatants showed antimicrobial activities, with inhibition zones ranging from 10.0 to 17.2 mm. All the LAB strains showed moderate auto-aggregation abilities while the greatest co-aggregation abilities were observed for Bifidobacterium bifidum W23, Lactobacillus plantarum W21 and Lactobacillus rhamnosus W71. The individual LAB strains showed strain-specific abilities to reduce the invasion of intestinal pathogens in an interference model with Caco-2 cells. Increased invasion inhibition was found when different combinations of LAB strains were used in the interference tests.ConclusionThe LAB strains examined in this study may protect the intestinal epithelium through a series of barriers (antimicrobial activity, co-aggregation with pathogens, adherence) and interference mechanisms. Consequently, these LAB strains may be considered candidates for prophylactic use to prevent intestinal infections.
Highlights
One of the working mechanisms of probiotic bacteria is their ability to compete with pathogens
L. acidophilus W37, L. rhamnosus W71, and L. salivarius W24 were unable to survive in this in vitro GI model, while L. casei W56 and L. lactis W58 showed a reduction of 3 log CFU/ml, and L. plantarum W21 of 1.5 log CFU/ml
The minimal inhibitory concentrations of nine different antibiotics for the seven Lactic Acid Bacteria (LAB) strains are summarized in Table 1; all values are equal or below the breakpoints set by the European Food and Safety Authority
Summary
One of the working mechanisms of probiotic bacteria is their ability to compete with pathogens. To define the probiotic properties of seven Lactic Acid Bacteria (LAB) strains, we tested them for survival in simulated gastro-intestinal conditions, antimicrobial activities, co-aggregative abilities, and interferences studies against five human intestinal pathogens (Salmonella enteritidis ATCC 13076, Listeria monocytogenes ATCC 7644, Escherichia coli O157: H7 ATCC 35150, Cronobacter sakazakii ATCC 29544 and Campylobacter jejuni ATCC 33291). Food spoilage-inducing bacterial pathogens such as Escherichia coli O157: H7 (EHEC), Salmonella, Listeria monocytogenes, and Campylobacter cause numerous illnesses and deaths, and huge economical loss [2]. The mechanisms underlying the activity of LAB strains against bacterial pathogens appear to be multifactorial and include the production of hydrogen peroxide, lactic acid, bacteriocin-like molecules, stimulation of the immune system, and modulation of intestinal microbiota [9,10,11]. Micro-organisms with the ability to co-aggregate with other bacteria, such as pathogens, may have an advantage over the non-coaggregating bacteria that are removed from the intestinal gut [15]
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