Abstract

Mastitis is a major economic problem in dairy herds, as it might decrease fertility, and negatively affect milk quality and milk yield. Out of over 150 bacterial species responsible for the udder inflammation, Escherichia coli is one of the most notable. This study aimed to assess antimicrobial susceptibility, resistance to dipping agents and biofilm formation of 150 E. coli strains isolated from milk of cows with subclinical and clinical mastitis. The strains came from three dairy herds located in Northern and Central Poland. The statistical analyses were performed with post-hoc Bonferroni test and chi-square test (including Yates correction). The data with a p value of <0.05 were considered significant. We found that the tested strains were mostly sensitive to antimicrobials and dipping agents. It was shown that 37.33% and 4.67% of strains were resistant and moderately resistant to at least one antimicrobial agent, respectively. No extended-spectrum beta-lactamases (ESBL)-producing E. coli were detected. The majority of strains did not possess the ability to form biofilm or formed a weak biofilm. The strong biofilm formers were found only among strains derived from cows with subclinical mastitis. The lowest bacteria number was noted for subclinical mastitis cows’ strains, after stabilization with iodine (3.77 log CFU × cm−2) and chlorhexidine (3.96 log CFU × cm−2) treatment. In the present study, no statistically significant differences in susceptibility to antibiotics and the ability to form biofilm were found among the strains isolated from cows with subclinical and clinical mastitis. Despite this, infections in dairy herds should be monitored. Limiting the spread of bacteria and characterizing the most common etiological factors would allow proper treatment.

Highlights

  • Bovine mastitis (BM) is one of the most important diseases in the dairy industry

  • Milk samples were examined for visible abnormalities and screened using the California mastitis test (CMT; scored 1 to 5 corresponding to no reaction, trace, mild reaction, moderate reaction, and strong reaction, respectively)

  • Cows either with or without positive results in CMT and any clinical symptoms of other illness such as lameness or injuries were selected as cows with subclinical mastitis

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Summary

Introduction

Bovine mastitis (BM) is one of the most important diseases in the dairy industry. Mastitis is an inflammation of the mammary gland causing chemical, physical, microbiological changes, and an increase in the number of somatic cells in the milk [1]. Two types of bovine mastitis are distinguished, i.e., clinical and subclinical. The clinical form contributes to pathological changes in the mammary tissue and physical, chemical, and usually bacteriological changes in the milk [2]. The subclinical form of mastitis is 15–40 times more prevalent and no obvious signs in the milk and udder are observed [3]. On-farm screening tests are used traditionally, such as somatic cell count (SCC), California mastitis test, and the Surf field mastitis test [4,5].

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