Enterococci in cheese – phenotypization and antibiotic resistance | Enterokoki v sirih – fenotopizacija in rezistenca proti antibiotikom

English. 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%).

Slovenian. V raziskavi smo proučevali vzorce svežih in zorenih sirov, izdelanih iz surovega ali toplotno obdelanega mleka s potopkom encimske ali kislinske koagulacije. Začetno izolacijo enterokokov smo opravili na kanamicin-eskulin-azidnem agarju pri temperaturi 37 °C in 42 °C in 24-urni inkubaciji. Izolirali smo 42 sevov enterokokov. Za ugotavljanje rezistence oziroma občutljivosti izoliranih sevov proti antibiotikom smo uporabili difuzni test z diski, na Muller-Huntonovem agarju. Število enterokokov, ki so jih ugotovili v vzorcih sirov, je bilo odvisno od tehnološkega postopka izdelave sira. V svežih sirih, narejenih z encimsko koagulacijo surovega in toplotno obdelanega mleka, se je število enterokokov gibalo med 8,0×104 in 9,0×106 cfu g–1 ter 4,0×107 in 4,4×107 cfu g–1. Pri zorenih sirih, narejenih s kislinsko koagulacijo, se je število enterokovov gibalo od < 102–5,0×104 cfu g–1 v sirih iz surovega mleka in od 2,5×104 do 1,5×105 cfu g–1 v sirih iz toplotno obdelanega mleka. Sveži siri, narejeni s kislinsko koagulacijo surovega in toplotno obdelanega mleka so vsebovali med 2,4×105 in 2,12×107 cfu g–1, ter med 5×104 in 6×104 cfu g–1. Fenotipsko smo izolirane seve opisali na osnovi morfologije celic, katalaznega testa, rasti pri 10 °C in 45 °C, rasti v mleku z 0,1 % metilenskega modrila in pri pH 9,6, rasti v bujonu s 6,5 % NaCl, rezistence ob izpostavitvi temperaturi 60 °C za 15 in 30 minut, Voges-Proskauerjeve reakcije in fermentacije riboze. Izolirani sevi enterokokov so bili v 65,82 % primerov odporni proti penicilinu, 62,02 % sevov je bilo odpornih proti tetraciklinu, 68,35 % proti linkomicinu in 27,84 % proti gentamicinu. Odpornost proti neomicinu je bila prisotna pri 31,64 % proučevanih sevov, proti eritromicinu pri 31,64 % in proti kloramfenikolu pri 65,82 % sevov.