Safety aspects of Lactobacillus plantarum strains isolated from Siahmazgi cheese

In order to use lactic acid bacteria as starter and non-starter cultures in fermentative products, their safety qualities should be evaluated. The objective of the present study was to evaluate safety characteristics including antibiotic sensitivity pattern, antimicrobial effect, H2O2 production, and biogenic amine production by Lactobacillus plantarum strains isolated from Siahmazgi cheese. Lactobacillus plantarum strains were unable to produce tyramine except for SD6 strain. All strains in the current study were able to produce histamine but unable to decarboxylate neither lysine nor omithine. Lactobacillus plantarum strains showed considerable antimicrobial activity against Salmonella typhimurium and Listeria monocytogenes. All L. plantarum strains showed stronger antimicrobial activity against S. typhimurium (3.5-42.55 mm) than L. monocytogenes (1.5-30.49 mm). The SC9 strain had the strongest inhibitory effect against both pathogens. After titering pH of the medium to approximately 6.5, no antimicrobial activity was noticed indicating that the antimicrobial activity of L. plantarum strains was contributed to their acid production and not to bacteriocin. All L. plantarum strains were capable of producing H2O2. SA32 and SD13 strains with 2.37 and 0.77 mmol/L were the strongest and the weakest strains regarding H2O2 production, respectively (P<0.05). All L. plantarum strains were sensitive to chloramphenicol, erythromycin, rifampicin, and tetracycline, yet resistant against vancomycin, and norfloxacin. Four patterns of antibiotic resistance were observed among L. plantarum strains. Only two strains of SC9 and SE4 were resistant against four antibiotics. L. plantarum strains naturally found in Siahmazgi cheese do not generally possess dangerous characteristics to be used in fermentative dairy products.