Isolation of nuc mutant isolates of Staphylococcus aureus from bovine clinical mastitis

Area of Science:

• Veterinary Microbiology
• Bacterial Genetics

Background:

• Bovine mastitis is a significant concern in dairy farming.
• Staphylococcus aureus is a common causative agent of bovine mastitis.
• The nuclease (nuc) gene is often used as a target for PCR-based diagnostics of S. aureus.

Purpose of the Study:

• To investigate the occurrence and characteristics of Staphylococcus aureus isolates with mutations in the nuclease (nuc) gene from bovine mastitis cases.
• To assess the potential impact of these mutations on the reliability of diagnostic PCR tests.

Main Methods:

• Isolation and characterization of S. aureus from bovine mastitis cases.
• Genetic analysis of the nuclease (nuc) gene, including sequencing for mutations.
• Molecular typing using spa typing and multiple-locus variable-number tandem-repeat fingerprinting (MLVF).
• Comparison of isolates with and without nuc mutations.

Main Results:

• S. aureus isolates with a 42 base pair duplication in the nuc gene were identified in Polish dairy herds.
• These nuc-mutated isolates belonged to sequence type 97 (ST97) and clonal complex 97 (CC97).
• Isolates with the nuc mutation exhibited different spa types and MLVF subtypes compared to non-mutated isolates from the same herd.

Conclusions:

• The presence of nuc-mutated S. aureus strains in bovine mastitis cases can potentially lead to false-negative results in diagnostic PCR assays targeting the nuc gene.
• This finding highlights the importance of considering genetic variations in bacterial pathogens when developing and implementing diagnostic tools.