Enterococci in cheese – phenotypization and antibiotic resistance

Abstract

The material of investigation was consisted of samples of fresh and ripened cheeses made from raw and cooked milk subjected to rennet or acid coagulation. The primary isolation of enterococci was carried out on kanamycin-aesculine-azide agar at 37 °C and 42 °C during 24 hours. It was isolated totally 42 strains of enterococci. The examination of antibiotic resistance/sensitivity profiles was performed by applying disk-diffusion procedure on Muller-Hinton agar. The number of enterococci determined in cheese samples depended on applied technological process. In the samples of fresh, by rennet coagulated cheese made from raw and cooked milk the number of enterococci was ranged from 8.0×104 to 9.0×106 cfu g–1, and from 4.0×107 to 4.4×107 cfu g–1, respectively. In the case of ripened cheeses made from raw and cooked milk subjected to acid coagulation the number of enterococci was ranged from <102 to 5.0×104 cfu g–1 and from 2.5×104 to 1.5×105 cfu g–1, respectively. In the samples of fresh cheeses made from raw and cooked milk subjected to acid coagulation the number of enterococci was ranged from 2.4×105 to 2.12×107 cfu-g, and from 5×104 to 6×104 cfu g–1, respectively. The phenotypic identification of isolated enterococcal strains was performed according to the following biochemical-physiological characteristics: microscopic examination (cell morphology), catalase activity, growth in MRS broth at 10 °C and 45 °C, growth at pH 9.6, growth in broth containing 6.5% NaCl, growth in 0.1% methylen blue milk, resistance at 60 °C/15 and 30 minute, Voges/Proskauer reaction, fermentation of ribose. The isolated strains of enterococci were resistant to following antibiotics: penicillin (65.82%), tetracycline (62.02%), lincomycin (68.35%), gentamycin (27.84%), neomycin (31.64%), erythromycin (31.64%) and chloramphenicol (65.82%).