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Characterization of methicillin-resistant Staphylococcus aureus isolated from dogs in Korea
1Department of Internal Medicine, Veterinary Medical Teaching Hospital, College of Veterinary Medicine, Seoul National University, Shillim-dong Kwanak-gu Korea.
Abstract:
Twelve strains of the methicillin-resistant Staphylococcus aureus (MRSA) recovered from hospitalized dogs were analyzed for in vitro antimicrobial susceptibility and virulence, and were genetically characterized by pulsed-field gel electrophoresis (PFGE). Antibiotic susceptibility test showed that nearly all isolates were resistant to beta-lactam antibiotics tested and all the strains were fully susceptible to glycopeptides. There were no inhibitory activities among the aminoglycosides. The 50% lethal dose (LD50) was determined by intraperitoneal injection of cell suspensions and estimated by the Spearman-Kärber method. The mouse lethality of MRSA and methicillin-susceptible S. aureus (MSSA) was not significantly different in both normal and cyclophosphamide-treated mice (p>0.05), indicating that they were equally virulent. There was a great difference in the incidence of toxin production between the MRSA and MSSA group; 83.3% (10 of 12) of the MRSA and 14.3% (1 of 7) of the MSSA were toxin producers. The predominant types produced by MRSA was B. All the MRSA strains were capsular type 5 producers, while of 7 MSSA strains, four were type 5, one for type 8, and two were nontypeable. Based on the PFGE analysis, the 12 MRSA isolates generated 9 to 11 fragments in the size range of <48.5 to 630.5 kb, and yielded 6 different patterns. The results indicated that production of toxin and capsule type do not play a role in the pathogenicity to mouse and PFGE is a valuable tool for the characterization of MRSA. This report is the first such cases in the veterinary literature in Korea and may indicate the frequent emergence of MRSA in veterinary clinic hereafter.
Insights
This study analyzed methicillin-resistant Staphylococcus aureus (MRSA) in dogs, finding it resistant to beta-lactams but susceptible to glycopeptides. Virulence was similar to MSSA, but MRSA produced more toxins, suggesting potential for increased emergence in veterinary clinics.
Area of Science:
- Veterinary Microbiology
- Antimicrobial Resistance
- Molecular Epidemiology
Background:
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a growing threat in both human and animal health.
- Limited data exists on MRSA characteristics and virulence in veterinary settings, particularly in Korea.
Purpose of the Study:
- To characterize MRSA strains isolated from hospitalized dogs.
- To evaluate their in vitro antimicrobial susceptibility, virulence in mice, and genetic relatedness.
Main Methods:
- Antibiotic susceptibility testing using standard methods.
- Virulence assessment via median lethal dose (LD50) determination in mice.
- Genetic typing using pulsed-field gel electrophoresis (PFGE).
- Detection of toxin production and capsular typing.
Main Results:
- All MRSA isolates were resistant to beta-lactams and susceptible to glycopeptides; aminoglycosides showed no inhibitory activity.
- MRSA and methicillin-susceptible S. aureus (MSSA) exhibited similar mouse lethality, indicating comparable virulence.
- A significantly higher incidence of toxin production was observed in MRSA (83.3%) compared to MSSA (14.3%).
- PFGE analysis revealed 6 distinct patterns among the 12 MRSA isolates, highlighting genetic diversity.
Conclusions:
- Toxin production and capsule type do not appear to influence MRSA pathogenicity in mice.
- PFGE is an effective tool for characterizing MRSA isolates.
- This study represents the first report of MRSA in Korean veterinary literature, signaling its potential emergence in veterinary clinics.