Correlation between use of antibiotics and prevalence of resistant strains of coagulase-positive staphylococci (S. aureus) in dairy farms in Apulia (Southern Italy)

The spread of multidrug-resistant bacteria is a concerning problem worldwide. This preliminary study investigated the correlation between antibiotic consumption and the antimicrobial resistance trends of coagulase-positive Staphylococci (S. aureus) in raw milk from 154 dairy farms located in two provinces of the Apulia region in Southern Italy: Bari and Taranto.
Data concerning antibiotic consumption expressed in DDDAit (Defined Daily Dose Animal for Italy) were extracted from the VETINFO portal. Data on antibiotic resistance (percentage of antibiotic-intermediate or -resistant isolates) were obtained from raw milk analysis performed at the laboratory of the Istituto Zooprofilattico Sperimentale di Puglia e Basilicata, Putignano (BA).
The data collected suggest a strong correlation between the quantities of some antibiotics used (i.e. penicillins, aminoglycosides, cephalosporins, macrolides, lincosamides, fluoroquinolones and third-generation cephalosporins) and the prevalence of Staphylococcus aureus strains resistant to the molecules used (i.e. oxacillin, ampicillin, penicillin, amoxicillin/clavulanic acid, rifampicin, kanamycin, gentamicin, cefazolin, erythromycin, pirlimycin, enrofloxacin and ceftiofur). These data are in agreement with a previous study by Parisi et al. (2016) and may indicate a possible positive correlation between the use of antibiotics and the development of antibiotic resistance. This study, although preliminary, must be interpreted in the broader context of safeguarding public health: the presence of antimicrobial-resistant bacteria in dairy products, particularly those produced from raw milk, poses a potential risk of infection and/or colonization for humans, with limited treatment options and complications in treatment outcome. The overall data present a discrete indicator of antibiotic use and resistance patterns in Apulian dairy farms. A continued review of databases and a more rigorous use of antimicrobials therefore appear critical to minimizing the risk of the emergence of resistant organisms.