Assessment of antimicrobial resistance patterns in bovine mastitis pathogens and evaluation of alternative therapies in dairy herds

Project Abstract

This study investigates the current antimicrobial resistance (AMR) patterns among bovine mastitis pathogens and evaluates the efficacy of alternative therapies in dairy herds, with the aim of informing evidence-based treatment strategies and reducing antimicrobial use. A cross-sectional survey was conducted across multiple dairy farms, collecting milk samples from clinical and subclinical mastitis cases. Isolates were identified to species level using standard bacteriological methods and MALDI-TOF confirmation, followed by antimicrobial susceptibility testing (AST) using disk diffusion and broth microdilution in accordance with CLSI guidelines. Resistance profiles were analyzed against commonly used antimicrobials in veterinary practice, including beta-lactams, macrolides, tetracyclines, aminoglycosides, phenicols, and sulfonamides, to determine multidrug resistance (MDR) prevalence and patterns by pathogen and farm management practices. Concurrently, we evaluated the therapeutic potential of alternative strategies such as intramammary infusions of essential oils, bacteriophage therapy, probiotics, and non-antibiotic antiseptics, alongside optimized non-antibiotic management protocols (milking hygiene, teat canal sealing, and teat off management). In vitro assays assessed the bactericidal activity of selected alternatives against prevalent mastitis pathogens, while in vivo trials on a subset of herds examined clinical cure rates, bacteriological clearance, milk yield, and somatic cell counts, compared to conventional antibiotic regimens. Genotypic analyses, including PCR and whole-genome sequencing, identified resistance determinants (e.g., bla, tet, aadA, and mec genes) and virulence factors, enabling correlation between genotypes and phenotypes, and the detection of potential clonal spread across farms. Data synthesis employed multivariate logistic regression and network analysis to explore associations between AMR patterns and factors such as farm size, antibiotic stewardship practices, pasteurization methods, and housing systems. The study also conducted a cost-benefit evaluation of alternative therapies relative to standard antibiotic therapy, considering drug costs, labor, milk withdrawal periods, and production losses. Findings revealed a high prevalence of resistant isolates among Staphylococcus aureus, Streptococcus agalactiae, and Escherichia coli mastitis cases, with notable MDR clusters in farms lacking stringent withdrawal compliance and routine culture-based treatment. In vitro results demonstrated variable efficacy of essential oils and probiotics, with several formulations showing synergistic effects when combined with antiseptics. In vivo trials indicated that certain non-antibiotic strategies achieved comparable clinical cure rates to antibiotics in select cases, particularly when integrated into comprehensive udder health programs emphasizing milking hygiene and prompt therapy guided by culture and susceptibility results. The genotypic data highlighted diverse resistance determinants, including mecA-mediated resistance in staphylococci and plasmid-borne tet and sul genes, underscoring the need for rapid diagnostics to guide therapy. Overall, the research provides a robust evidence base for revising treatment guidelines, promoting targeted antimicrobial use, and integrating validated alternative therapies to mitigate AMR in bovine mastitis while safeguarding milk safety and farm profitability. Recommendations include routine bacteriological cultuur, antimicrobial stewardship training for farm personnel, adoption of non-antibiotic adjuncts with demonstrated efficacy, and policy support for stewardship programs.

Project Overview

What This Project Is About

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A plain-language overview of the topic and what the project investigates.

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The Problem It Addresses

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What problem or gap this project tackles and why it matters to the field or society.

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Objectives of the Project

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1. Identify common bacteria that cause bovine mastitis.
2. Test how these bacteria respond to typical antibiotics.
3. Explore non-antibiotic alternatives for treatment and prevention.
4. Compare resistance patterns across different farms or regions.
5. Suggest practical guidelines for better herd health management.

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What You Will Do Step by Step

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1) Learn basics about bovine mastitis and why antibiotic resistance happens. 2) Collect milk samples from cows with mastitis. 3) Identify the bacteria in samples using simple lab tests. 4) Check which antibiotics the bacteria are resistant to. 5) Review alternative therapies like clean housing, teat care, and non-antibiotic options. 6) Analyze results to see patterns of resistance and effectiveness. 7) Write up findings with practical farm recommendations. 8) Reflect on limitations and future research needs.

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Expected Outcome

Clear understanding of resistance patterns in mastitis pathogens and practical guidance on alternatives to antibiotics for treatment and prevention.