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Phenotypic and molecular characterization of multidrug-resistant mastitis causing pathogens in dairy cattle

Maya Mathew1, Athulya B2, Sandhya C3

  • 1School of Biosciences, Mahatma Gandhi University, Kottayam, India.

International Journal of Environmental Health Research
|October 20, 2025
PubMed

Insights

Antibiotic-resistant bacteria, including multidrug-resistant (MDR) Staphylococcus, were isolated from cow milk. These resistant dairy bacteria pose a public health risk, necessitating careful antimicrobial use and preventative strategies.

Area of Science:

  • Veterinary Microbiology
  • Antimicrobial Resistance
  • Food Safety

Background:

  • Mastitis is a significant concern in dairy herds, impacting animal health and milk production.
  • The rise of antibiotic resistance in bacteria associated with livestock presents a potential public health threat.
  • Understanding the prevalence and characteristics of resistant mastitogens is crucial for effective control.

Purpose of the Study:

  • To isolate and identify antibiotic-resistant bacterial species from bovine mastitis milk samples.
  • To characterize the multidrug-resistant (MDR) strains, including their resistance genes and biofilm-forming capabilities.
  • To assess the public health implications of resistant dairy bacteria.

Main Methods:

  • Milk samples were screened for mastitis using the California mastitis test.
  • Bacterial isolates were identified using the Vitek® 2 automated system.
  • Phenotypic and genotypic screening identified multidrug-resistant strains and antibiotic resistance genes (e.g., mecA, blaZ, gyrA, gyrB).
  • Biofilm formation was assessed using a tissue culture plate assay.

Main Results:

  • 57% of tested milk samples were positive for mastitis.
  • 167 bacterial strains were isolated, with 14 identified as multidrug-resistant (MDR).
  • MDR strains included Staphylococcus spp., Enterobacter spp., Morganella spp., and Elizabethkingia spp.
  • Staphylococcus strains exhibited the highest resistance; 8% of mastitis isolates were MDR.
  • Commonly detected antibiotic resistance genes were gyrA (50%), gyrB (59%), blaZ (43%), and mecA (21%).
  • 11 MDR bacteria were identified as strong biofilm formers.

Conclusions:

  • The study identified multidrug-resistant bacteria, particularly Staphylococcus spp., in cow milk associated with mastitis.
  • The presence of antibiotic resistance genes and biofilm formation in these isolates highlights their potential for persistence and transmission.
  • These findings underscore a public health risk, emphasizing the need for prophylactic measures and responsible antimicrobial stewardship in dairy farming to prevent zoonotic spread.
Keywords:
AMREnterobacter sppMastitisStaphylococcus sppbiofilm

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