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Updated: May 9, 2025
Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus
Published on: September 5, 2013
Phylogenomic associations among methicillin-resistant Staphylococcus aureus isolates derived from pets, dairies, and
Margaret Krueger1, Shayla Bajric1, Sandra Godden2
1Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA.
Abstract:
Methicillin resistance in Staphylococcus aureus is conferred by the mobile genetic element, staphylococcal cassette chromosome mec (SCCmec). Methicillin-resistant Staphylococcus aureus (MRSA) can transmit among animals and humans, leading to persistence and back transmission events. The current study tested the hypothesis that companion animal and livestock-associated (LA) MRSA isolates share genomic similarity, suggesting shared ancestry with hospital-associated (HA) or community-associated (CA) MRSA. Eight S. aureus isolates from therapy dogs (n = 5) and bulk tank milk (n = 3) were genome sequenced, and 71,721 genome-wide single nucleotide polymorphism (SNP) locations were extracted and phylogenetically compared against methicillin-sensitive Staphylococcus aureus (MSSA) and MRSA genomes of isolates from a variety of species and time frames, available in the National Center for Biotechnology Information (NCBI) database. A maximum likelihood phylogenetic tree was constructed to define S. aureus lineages across isolates from animals and humans. Four isolates from companion animals and three bulk tank milk isolates clustered with human isolates, while one companion animal isolate clustered with genomes of MRSA isolated from swine. Four therapy dog isolates had CA-MRSA SCCmec types IVa, IVc, and V/VII, respectively, while one therapy dog and one bulk tank milk isolate shared SCCmec type (IIa) that is commonly seen in HA-MRSA. Two isolates from bulk tank milk were methicillin sensitive and did not carry mecA.
Importance:
Methicillin-resistant Staphylococcus aureus (MRSA) infections are a major medical concern, causing a range of conditions from skin infections and invasive disease to death. MRSA was discovered as a nosocomial infection; however, it has since been isolated in communities and animals worldwide. This research was significant because canine and bulk tank milk isolates were found to have genomic relatedness to human and domestic animal S. aureus isolates. This genetic relatedness implies either a parallel evolution within hosts converging to successful genotypes or real interspecies transmission events among animals and humans.
Insights
Genomic analysis reveals methicillin-resistant Staphylococcus aureus (MRSA) from companion animals and milk share ancestry with human MRSA strains. This suggests potential interspecies transmission events and shared evolution of MRSA.
Area of Science:
- Microbiology
- Genomics
- Veterinary Medicine
- Public Health
Background:
- Methicillin resistance in Staphylococcus aureus (MRSA) is a significant public health concern, with strains found in both humans and animals.
- The mobile genetic element staphylococcal cassette chromosome mec (SCCmec) confers methicillin resistance.
- MRSA transmission between humans and animals is a known phenomenon, complicating control efforts.
Purpose of the Study:
- To investigate the genomic similarity between MRSA isolates from companion animals and livestock with human-associated MRSA.
- To test the hypothesis that animal-associated MRSA shares common ancestry with hospital-associated (HA) and community-associated (CA) MRSA.
- To define Staphylococcus aureus lineages across animal and human isolates using phylogenetic analysis.
Main Methods:
- Genome sequencing of eight Staphylococcus aureus isolates from therapy dogs (n=5) and bulk tank milk (n=3).
- Extraction of 71,721 genome-wide single nucleotide polymorphism (SNP) locations.
- Phylogenetic comparison of extracted SNPs against a database of methicillin-sensitive (MSSA) and resistant (MRSA) S. aureus genomes from various hosts and time periods.
Main Results:
- Four companion animal and three bulk tank milk isolates clustered phylogenetically with human MRSA isolates.
- One companion animal isolate clustered with swine-associated MRSA.
- Therapy dog isolates exhibited CA-MRSA SCCmec types (IVa, IVc, V/VII); one dog and one milk isolate shared HA-MRSA-associated SCCmec type (IIa). Two milk isolates were methicillin-sensitive.
Conclusions:
- Companion animal and livestock-associated MRSA isolates demonstrate genomic relatedness to human MRSA strains, implying shared ancestry or interspecies transmission.
- The findings suggest potential for MRSA to circulate between animal populations and humans, necessitating One Health approaches.
- Understanding these transmission dynamics is crucial for developing effective strategies to control MRSA spread.
