Antibiotic Resistance Profile of Yogurt Bacteria Exposed to Various Stress Conditions

This study aims to reveal the differences that may occur in the susceptibilities of 2 yogurt bacteria strains, S. thermophilus and L. delbrueckii subsp. bulgaricus, to antibiotics under 2 different durations and 3 different stress conditions. The study also introduces new approaches to reduce potential issues in milk containing antibiotics in the fermented milk industry. To this end, the bacteria were exposed to 2 different low-pressure, low-temperature, and magnetic field activities under 2 different durations. The research concluded that as the severity of the applied stress conditions and application period increase, the antibiotic susceptibility of the bacteria decreases, and resistance to certain antibiotics develops (p < 0.05). In the conclusion of the 3 different stress applications, it was found that the bacteria had the highest resistance to antibiotics in the magnetic field applications. In these 3 different stress applications, S. thermophilus showed the highest resistance to lincomycin, cephalexin, and streptomycin; L. delbrueckii subsp. bulgaricus developed resistance to streptomycin, erythromycin, and chloramphenicol. Of the 2 yogurt bacteria, L. delbrueckii subsp. bulgaricus developed a resistance to more antibiotics than S. thermophilus after the stress applications; the developed resistance was also more substantial than that of S. thermophilus.