Unprocessed milk as a source of multidrug-resistant Staphylococcus aureus strains

Abstract

Staphylococcus aureus is the most relevant pathogen of animal mastitis and milk-related intoxications. Its presence in directly sold milk is rather not to be expected if strict udder health management and regular microbiological control of raw milk are performed. In this one-year survey, we present the results of monthly microbiological testing of milk from vending machines in Croatia for S. aureus and its multi-drug resistance. Staphylococcus aureus was detected in 27.58% of the samples. Among 60 tested isolates from 10 farmers, a total of 41 isolates were resistant to at least one antimicrobial agent (68.33%). A Multiple Antibiotic Resistance (MAR) index of 0.2 or higher had 48.8% of the resistant isolates, which is considered a high-risk potential for the spread of antimicrobial resistance. The majority of the isolates were resistant to penicillin and ampicillin followed by ciprofloxacin, ceftazidime, and kanamycin. The results impose the need for improving the control measures in the raw milk distribution chain focused on MAR risk reduction.