Purpose: Are St. infantarius isolates able to survive in the human GIT, to compete with LAB and to present risk for consumption of contaminated milk?
Methods: Isolates K1-4 and K5-1, differentiated by RAPD-PCR have been investigated for their ability of aggregation to intestinal pathogens; de-conjugation of TCA, TDC, GCA and GDC; hydrophobicity; survival under conditions simulating the GIT; and resistance to antibiotics.
Results: Both St. infantarius showed good survival rates when exposed to simulating gastric and enteric conditions (86.9% and 69.9% for K1-4 and 25.9% and 68.6% for K1-5). Both St. infantarius were able to grow in presence of TDCA, TCA, GDCA or GCA, but did not show ability to de-conjugated bile-salts. St. infantarius K1-4 and K5-1 exhibited 25.4% and 89.9% hydrophobicity, and 67.9% and 23.0% auto-aggregation. St. infantarius K5-1 showed production of β-galactosidase, however, St. infantarius K1-4 was negative. The strain K1-4 showed resistance (MIC) to imepinem (0.5 µg/ml), vancomycin (2.0 µg/ml), ampicillin (0.25 µg/ml), clindamycin (4.0 µg/ml), tetracycline (0.25 µg/ml), erythromycin (0.25 µg/ml) and gentamicin (32 µg/ml). St. infantarius K5-1 presented similar resistance to antibiotics: imepinem (0.15 µg/ml), vancomycin (1.0 µg/ml), ampicillin (0.6 µg/ml), clindamycin (0.15 µg/ml), tetracycline (12 µg/ml), erythromycin (0.06 µg/ml) and gentamicin (32 µg/ml). High levels of co-aggregation with E. coli, L. monocytogenes, C. perfringens and Salmonella spp. have been recorded for both isolates.
Significance: According to the results, St. infantarius K5-1 present better potential to colonize and compete with GIT microflora compared to St. infantarius K1-4. Both strains presented resistance to the major groups of antibiotics. Milk contaminated with this two strains presenting a health risk since the studied St. infantarius strains presented good ability to survive to simulated GIT conditions and to be responsible for a chronicle GIT disorders.