Ten-Year Monitoring of Bovine Mastitis-Causing Bacteria in Northern Italy and Evaluation of Antimicrobial Resistance in Raw Milk

TL;DR

This study tracks bovine mastitis-causing bacteria and antibiotic resistance in raw milk in Northern Italy over ten years.

Contribution

The study provides updated data on bacterial prevalence and antimicrobial resistance trends in bovine mastitis over a decade.

Findings

Streptococcus uberis, Escherichia coli, and Enterococcus faecium increased in prevalence.

Prototheca, yeasts, Staphylococcus aureus, and Streptococcus agalactiae decreased in prevalence.

Antimicrobial resistance to trimethoprim increased, highlighting the need for targeted therapy.

Abstract

Bovine mastitis is a multifactorial disease defined by the inflammation of the udder in cattle. It can be caused by different factors, but contagious or environmental pathogens play a major role in the onset of this disease. The main treatment for this condition is the administration of antibiotics, either parenterally or via the intramammary route. The samples were processed by the National Reference Centre for Bovine Milk Quality (CRNQLB) and bacteriologically examined by the IZSLER Primary Production Department (BS, Italy) over the period from 2015 to 2024. Moreover, this study presents the minimum inhibitory concentrations (MICs) obtained from all the bacterial pathogens isolated in the last three years of the study (2022–2024). This study aimed to describe the main frequencies recorded during the decade, in order to provide an enumeration of pathogens circulating in the IZSLER jurisdiction and to estimate trends in antimicrobial resistance, highlighting increases or decreases in observed resistance levels. Results show an increased prevalence of Streptococcus uberis, Escherichia coli, and Enterococcus faecium, with a decrease in Prototheca, yeasts, Staphylococcus aureus, and Streptococcus agalactiae. The general increase in antimicrobial resistance to trimethoprim needs to be highlighted to express the need for a targeted therapy based on accurate diagnosis to limit the spread of resistance in dairy farms.

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