Legally admissible amounts of antibiotics in milk affect the growth of lactic acid bacteria

Abstract

The antibiotic administration in dairy livestock is a current widespread practice. The purpose of the study was to evaluate whether milk from antibiotic-treated animals, following the application of the withdrawal time and fully complying with European requirements in relation to residue content, affected the development of lactic acid bacteria. Forty-five raw milk samples were collected after the withdrawal period and analysed to verify their compliance with the European maximum limits using four commercial screening tests. Lactobacillus delbrueckii subsp. bulgaricus growth and acidifying activity were delayed from 5 to 8 h in milk from cow treated with β-lactams and sulfonamides present in low concentration (cephalosporins < 15 μg/kg; penicillins < 8 μg/kg; sulfonamides < 10 μg/kg) and their effect persisted over time. No influences were detected in Streptococcus thermophilus and Lb. helveticus development. The use of antibiotics can hamper the starter performances, opening questions about the safety of dairy products and human health.