In recent years, preservation of native microbial flora of different geographical regions of the world and their use has been of interest to the food industry. In Iran, the effort to discover, eva‎luate and introduce new native strains to the food industry is special. Due to the sensitive nature of the use of bacteria in food production, especially those with the non-food origin, their safety assessment is considered one of the basic requirements of introducing new spices into the food industry. Other problems of dairy industry is the occurrence of phage attack and as a result the destruction of starter cultures. One of the most effective ways to prevent this is the selection of phage-resistant starter strains. In this regard, in this study, two bacterial strains of Enterococcus faecium and Lactobacillus delbrueckii subsp. bulgaricus, which has a favorable technological efficiency in the production of soft cheese in previous studies. The signs of safty and resistance to phage were investigated. This study is carried out in a separate sections. At The first part, these two strains were assayed from the point of view of antibiotic resistance with Disc Diffusion method according to the protocols of the Institute of Clinical Standards and Laboratory (CLSI). Then the results of resistance or sensitivity levels of the strains were compared with the standard tables. In the second part of the research, the sensitivity or resistance status of these two strains to the phages collected from dairy factories in Isfahan city was investigated by spot test. For this purpose, samples were taken from the industrial wastewater of 7 factories on 3 different days and then, using the filtration method, phages were separated from its bacteria. In order to the phages enrichment, the testing bacteria were inoculated in solution containing the phages over night, so that if the specific phage of these two strains is present in the sample, it will propagate. Then, by performing the filtration process, the bacterial part was separated from the phage part, and the spot test was performed by pouring the phage solution on the lawn culture of each strain. In the third part, the presence of pathogenic traits in Enterococcus faecium, such as cytolysin activity, gelatinase activity, were investigated with phenotypic tests. The results of the antibiotic resistance test indicated that Enterococcus faecium has the highest resistance to kanamycin, clindamycin and erythromycin and showed 50% sensitivity to gentamicin and streptomycin, while it was quite sensitive tochloramphenicol, tetracycline, vancomycin and ampicillin. The results of the spot test to eva‎luate the phage resistance of the strains revealed that none of the phages were able to lyse the tested strains out of 21 samples. In the third part, it was observed that Enterococcus faecium is not capable of hemolysis of blood and production of gelatinase. According to the results of the tests, the desired Enterococcus faecium did not have some of the most important enterococcal pathogenic features and is was sensitive to the most important clinical antibiotics. Also, the results showed that Enterococcus faecium and Lactobacillus delbrueckii subsp. bulgaricus are resistant to the phages of dairy factories. Although the use of new strains in the food industry requires further studies, the two strains in question, in addition to satisfactory technological properties, also showed favorable safety status and significant phage resistance. Therefore, they can be considered as potential starter strains of cheese and probiotics for introduction in the food industry.

صبيحه سليمانيان زاد , علي نصيرپور

مريم فنائي كهراني , اميرحسين مهدوي