Plasmid profiles of Staphylococcus aureus causing bovine mastitis

Area of Science:

• Veterinary Microbiology
• Bacterial Genetics
• Animal Health

Background:

• Chronic bovine mastitis is a significant concern in dairy herds.
• Staphylococcus aureus is a primary pathogen associated with bovine mastitis.
• Understanding the genetic basis of Staphylococcus aureus in mastitis is crucial for control.

Purpose of the Study:

• To investigate the plasmid profiles of Staphylococcus aureus strains isolated from bovine mastitis.
• To determine the relationship between plasmid content and antibiotic resistance.
• To assess the potential role of plasmids in Staphylococcus aureus virulence and geographic spread.

Main Methods:

• Plasmid DNA extraction and profiling from 85 Staphylococcus aureus strains.
• Isolation of strains from 18 different dairy herds affected with chronic bovine mastitis.
• Analysis of plasmid patterns in relation to antibiotic resistance and geographic origin.

Main Results:

• Plasmid profiles of Staphylococcus aureus were highly heterogeneous across strains and farms.
• Strains lacking antibiotic resistance were often plasmid-free.
• Related plasmid patterns were observed among antibiotic-resistant strains (penicillin and streptomycin) from different farms, suggesting geographic dissemination.
• Variations in plasmid content were noted even within the same animal.

Conclusions:

• The presence of specific virulence plasmids in mastitis-causing Staphylococcus aureus is unlikely.
• Antibiotic resistance in Staphylococcus aureus associated with bovine mastitis may be linked to geographic spread of specific strains.
• Plasmid heterogeneity highlights the complex genetic landscape of Staphylococcus aureus in dairy herds.