Probiotic properties and antibiotic susceptibility assessment of Streptococcus thermophilus isolates

Abstract

Abstract Background Streptococcus thermophilus were considered one of probiotic bacterial strain; found in milk, cheese, and yogurt, that providing health benefits to humans. Due to their probiotic potentiality, S. thermophilus can be very helpful in replacing chemicals preservatives. This study came out to investigate the probiotic activity of ten S. thermophilus isolates obtained from raw cow milk in eastern Morocco against multidrug-resistant bacteria (MDR) bacteria: Staphylococcus aureus (ATCC 29213), Escherichia coli (ATCC: 25922 and 35218). Besides their antioxidant potential, bile salts tolerance as well as their antibiotic susceptibility, were evaluated Result The results showed remarkable in vitro inhibitory ability of the studied S. thermophilus isolates against the tested multidrug-resistant bacteria, as reported for S. thermophilus CFS and supernatant against Staphylococcus aureus (ATCC29213), confirming their potential as antibacterial agents. The mixtures of NaOH, catalase and proteinase K showed no inhibition zones against all tested multidrug-resistant bacteria; suggesting the main antibacterial effect of all isolates based on acids, hydrogen peroxide and/or proteins. For the antioxidant activity, the DPPH inhibition values varied between 18.97% and 44.44%, for the bacterial isolate ST9 and ST5, respectively. Notably, S. thermophilus isolates were able to survive up to 6h of incubation with a concentration of 0.1% of bile salt at 37°C. Thus, ST5 could be considered as the most promising bacterial isolate in terms of antioxidant activity. All isolates of S. thermophilus exhibited sensibility to all tested antibiotics except for rifampicin and trimethoprim-sulfamethoxazole compared to the standards proposed by the European committee on antimicrobial susceptibility testing. Conclusions The tested isolates were exhibited excellent antibacterial and potential antioxidant activities. In addition to that, these isolates were reported to resist rifampicin and trimethoprim-sulfamethoxazole antibiotics. These findings presage the use of S. thermophilus isolates as good probiotics.