Abstract
The study aimed to evaluate the safety and probiotic properties of selected Lactobacillus strains, which are intended to be fed to monogastric animals. The Lactobacillus spp. appeared to be safe since they did not degrade mucus and did not exhibit β-haemolysis. Moreover, the survival of Caco-2 cells in the presence of metabolites of the selected strains was high, which also indicated their safety. The analysed strains showed moderate or strong antagonistic activity against Salmonella spp., Listeria monocytogenes, Campylobacter jejuni and Campylobacter coli, which was tested with the usage of the agar slab method. Furthermore, the strains showed high survivability in an acidic environment and the presence of bile salts (~90%). High resistivity or moderate susceptibility to antibiotics was also observed, as a result of the disc diffusion method. The strains were mostly moderately hydrophilic (hydrophobicity: 10.43–41.14%); nevertheless, their auto-aggregation capability exceeded 50% and their co-aggregation with pathogens varied between 12.12 and 85.45%. The ability of the selected strains to adhere to Caco-2 cells was also analysed; they were found to be moderately adhesive (85.09–95.05%) and able to hinder pathogens attaching to the cells (up to 62.58%). The analysed strains exhibit probiotic properties, such as high survivability and adherence to epithelial cells; therefore, they are suitable for administration to monogastric animals. Since the overuse of antibiotic growth promoters in livestock leads to the spread of antibiotic-resistant pathogens and accumulation of chemotherapeutic residues in food of animal origin, it is of vital importance to introduce alternative feed additives.
Highlights
The Lactobacillus genus consists of Gram-positive, nonspore-forming and facultatively anaerobic or microaerophilic rod-shaped bacteria which belong to the Lactobacillales order and constitute one of the lactic-acid-producing bacteria genera (LABs) [1]
Based on the fact that no visible discoloured halos around the colonies were observed, it was found that selected Lactobacillus strains cannot degrade mucin
Metabolites produced by most of the analysed strains, except Lact. reuteri ŁOCK 1092, showed weak or no cytotoxic potential towards Caco-2 cells when the Bacterial Culture Supernatants (BCS) was used in concentrations of 5% and 10% (v/v), the effect was comparable to that of the control
Summary
The Lactobacillus genus consists of Gram-positive, nonspore-forming and facultatively anaerobic or microaerophilic rod-shaped bacteria which belong to the Lactobacillales order and constitute one of the lactic-acid-producing bacteria genera (LABs) [1]. LABs are comprised of over 200 species and subspecies of Lactobacillus sp., as well as Lactococcus sp., Streptococcus sp., Enterococcus sp., etc., which can be used as probiotics [2,3,4]. Live microorganisms that can contribute to the improvement of host health, when administered in the proper amounts, are called probiotics [5, 6]. Prior to their in vivo administration, the beneficial functionality and safety of the isolated microorganisms must be assessed [7]. The human gastrointestinal tract (GIT) is considered a safe environment to isolate potentially probiotic microorganisms. Novel probiotics are isolated from various natural sources, such as plants, soil, animals’ GITs and dairy products [9]
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