Antimicrobial Susceptibility of Bacteria Isolated from Milk of Healthy and Drug-Treated Cow Udder

Cilj ovog rada bio je istražiti sastav mikroflore mlijeka krava te pojavnost otpornosti bakterija mlijeka na antimikrobne tvari s obzirom na zdravlje njihova vimena. Mlijeko je sterilno uzorkovano od krava koje nisu nikada pokazivale znakove mastitisa (n=17) te krava koje su bile terapirane i izliječene (n=19), a potjecale su s 4 različite farme. Normiranim mikrobiološkim metodama određivan je broj aerobnih mezofilnih bakterija, psihrofilnih bakterija, bakterija mliječne kiseline, stafilokoka, Escherichia coli, enterokoka, enterobakterija, Listeria spp. te sulfitreducirajućih klostridija, Testiranje osjetljivosti na antimikrobne lijekove provedeno je na ukupno 56 izolata enterokoka, 30 izolata Escherichia coli, 24 enterobakterija i 94 stafilokoka. Ovisno o bakterijskoj skupini ili vrsti u disk difuzijskom testu korišteni su diskovi ampicilina, rifampina, kloramfenikola, tetraciklina, eritromicina, nitrofurantoina, vankomicina, penicilina, linezolida, trimetoprima, cefoperazona, kanamicina, trimetoprim/sulfametoksazola, nalidiksične kiseline, ciprofloksacina, gentamicina, teicoplanina, sulfonamida, levofloksacina, klindamicina te amoksicilina s klavulanskom kiselinom. Statistički značajne razlike (p<0,05) s obzirom na podrijetlo uzoraka mlijeka utvrđene su u broju aerobnih mezofilnih bakterija i bakterija mliječne kiseline. Pojavnost višestruko otpornih izolata E. coli i stafilokoka bila je značajno veća (P<0.05) u mlijeku liječenih krava. Postotni odnos (liječene:zdrave krave) višestruko otpornih E. coli bio je 56,3:0, enterobakterija 57,14:30, te stafilokoka 56,5:4,8. Nije bilo značajne razlike (P>0.05) u pojavnosti rezistentnih enterokoka u mlijeku zdravih i liječenih krava (73,7 : 87.2 %). Visoka učestalost otpornosti na antimikrobne tvari enterokoka u mlijeku zdravih krava može biti posljedica kohabitacije životinja i križnog onečišćenja.The aim of this study was to determine the composition of cow milk microbiota and antimicrobial resistance of milk microbiota in relation to udder health. Milk was aseptically sampled from healthy cows without any signs of mastitis (n=17) and drug-treated cows with mastitis (n=19), originated from 4 farms. Total viable count, psychrophilic bacteria, lactic acid bacteria, staphylococci, Escherichia coli, enterococci, enterobacteria, Listeria spp. and sulphite-reducing clostridia were determined using standard cultured methods. Antimicrobial susceptibility testing was performed in 56 enterococci, 30 Escherichia coli, 24 enterobacteria and 94 staphylococci. Depending of bacterial group or species, the following antibiotic disks were used – ampicillin, rifampin, chloramphenicol, tetracycline, erythromycin, nitrofurantoin, vancomycin, penicillin, linezolid, trimethoprim, cefoperazone, kanamycin, nitrofurantoin, trimethoprim/sulfamethoxazole, nalidixic acid, ciprofloxacin, gentamicin, teicoplanin, sulfonamides, levofloxacin, klindamycin and amoxicillin/clavulanic acid. Statistically significant differences (P<0,05) considering the origin of milk samples were found in total viable count and lactic acid bacteria. occurrence of multiresistant E. coli and staphylococci was significantly higher (P<0.05) in milk of drug-treated cows. The percentage ratio (drug-treated: healthy udders) of multiresistant E. coli was 56.3:0, enterobacteria 57.14:30 and staphylococci 56.5: 4.8. There was no significant difference (P>0.05) between the prevalence of multiresistant enterococci in the milk of healthy cows and cows with cured mastitis (73.7: 87.2). High prevalence of resistance in enterococci isolated from milk samples of healthy cows could be result of animal cohabitation and crosscontamination. Keywords: milk, udder health, ant