ORIGINAL RESEARCH article
Front. Vet. Sci.
Sec. Veterinary Infectious Diseases
Volume 12 - 2025 | doi: 10.3389/fvets.2025.1613185
Analysis of pathogenic bacteria and antimicrobial residues in bovine waste milk on dairy farms in southern Chile
Provisionally accepted
Fernando Ulloa1,2
Martina Penati3
Miguel Hernández-Agudelo1,2
Carlos Rodrigo Tejeda2
Pamela Nicole Steuer2
Maria Filippa Addis3Armin Mella4
Nivia Canales4Juan Pablo Soto5
Miguel Salgado6,7*- 1Escuela de Graduados, Facultad de Ciencias Veterinarias, Universidad Austral de Chile, Valdivia, Los Lagos, Chile
- 2Instituto de Medicina Preventiva Veterinaria, Facultad de Ciencias Veterinarias, Universidad Austral de Chile, Valdivia, Chile
- 3Department of Veterinary Medicine and Animal Sciences, Faculty of Veterinary Medicine, University of Milan, Milan, Lombardy, Italy
- 4Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile., Valdivia, Chile
- 5Prolesur Los Lagos, Los Lagos, Chile
- 6Austral University of Chile, Valdivia, Chile
- 7Laboratorio de Enfermedades Infecciosas, Instituto de Medicina Preventiva Veterinaria, Facultad de Ciencias Veterinarias, Universidad Austral de Chile, Valdivia, Chile
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Waste milk (WM), a byproduct of dairy production, is often used as a cost-effective calf feed, but it can contain pathogens and antimicrobial residues, which pose health risks. This study examined the microbiological quality and the presence of antimicrobial residues in WM from 36 dairy farms in southern Chile. In a cross-sectional study, WM samples were collected and farm management data was gathered through a questionnaire. The samples were analysed for total bacterial load, coliforms, staphylococci, streptococci/streptococci-like organisms (SSLO), Salmonella spp., Mycobacterium avium subsp. paratuberculosis (MAP), Mycobacterium bovis, Mycoplasma spp., Prototheca spp., methicillin-resistant Staphylococcus aureus (MRSA), and extended-spectrum β-lactamase (ESBL)producing E. coli. Antimicrobial residues were detected using a commercial test. A high average bacterial load (7.63 × 10⁶ CFU/mL) and significant levels of staphylococci, SSLO, and coliform were found. In addition, S. aureus (33.3%), MAP (11.1%), and Salmonella spp. (2.8%) were detected. ESBL-E. coli was found on five farms, with blaCTX-M being the predominant gene. Antimicrobial residues, mainly beta-lactams, were present in 55.6% of samples. These results show that WM in this region frequently contains pathogens, antimicrobial residues, and resistant bacteria. Current farm practices, such as feeding untreated WM to calves, may contribute to the spread of antimicrobial resistance and compromise calf health.
Keywords: antimicrobial resistance, Calves, calf disease, grazing, ESBL
Received: 16 Apr 2025; Accepted: 27 Jun 2025.
Copyright: © 2025 Ulloa, Penati, Hernández-Agudelo, Tejeda, Steuer, Addis, Mella, Canales, Soto and Salgado. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Miguel Salgado, Austral University of Chile, Valdivia, Chile
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