Potravinarstvo (Oct 2016)
Selected technological properties and antibiotic resistance of enterococci isolated from milk
Abstract
The aim of this work was to determine counts of enterococci in raw cow milk, to isolate and identify them, to determinate their antibiotic resistance, ability of lactose fermentation, proteolytic and lipolytic activity in different conditions of cultivation. Counts of enterococci were determined after 48 ±2 h cultivation on Slanetz-Bartley agar at 37 ±1 °C. The counts of enterococci in raw cow milk fluctuated from 1.80 x 102 to 1.77 x 103 CFU.mL-1 with average value 7.25 x 102 CFU.mL-1. Species identifications of enterococci isolates were performed using commercial EN-COCCUS test and confirmed by PCR. Majority of tested isolates (85.7%) was included to species E. faecalis. Antibiotic resistance was tested on Mueller-Hinton agar using following antimicrobial discs: vancomycin (VA) 30 µg.disc-1, gentamicin (CN) 120 µg.disc-1, erythromycin (E) 15 µg.disc-1, tetracycline (TE) 30 µg.disc-1, ampicillin (AMP) 10 µg.disc-1, teicoplanin (TEC) 30 µg.disc-1. From 13 isolates of enterococci, 1 strain was resistant to vancomycin, 1 strain to tetracycline and 1 to ampicillin, but higher prevalence of intermediate resistance of isolates was determined to tetracycline (5 strains). Ability of lactose fermentation was monitored by change of titratable acidity in UHT milk after 0, 18, 24, 40 and 48 h of cultivation at temperature 25, 30 and 37 °C. The tested strains of enterococci exhibit low milk acidifying ability. Production of proteolytic enzymes was evaluated after cultivation at temperature 7, 25 and 30 °C after 10 days on nutrient agar no. 2 with sterile skim milk (10% w/v) with pH 6.0 and 6.5. Proteolytic activity of tested enterococci strains varied depending on tested temperature and pH. Lipolytic activity was determined similarly like proteolytic activity but on tributyrin agar base with tributyrin (1% w/v). Lipolytic activity of isolated enterococci was very low. The tested strains produced halos with zone in range from 7 to 15 mm regardless of pH, cultivation time and temperature. Some of isolated and tested enterococci strains have shown suitable technological properties, but they have exhibited resistance to antibiotic.
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