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Trends in the resistance to antimicrobial agents of Streptococcus suis isolates from Denmark and Sweden
F M Aarestrup1, S R Rasmussen, K Artursson
1Danish Veterinary Laboratory, Copenhagen, Denmark. faa@svs.dk
Abstract:
This study was conducted to determine the MIC values of historical and contemporary Streptoccocus suis (serotypes 2 and 7) from Denmark and S. suis (serotype 2) from Sweden. A total of 52 isolates originating from 1967 through 1981 and 156 isolates from 1992 through 1997 in Denmark and 13 isolates from Sweden were examined for their MICs against 20 different antimicrobial agents. Most antimicrobials were active against most isolates. A frequent occurrence of resistance to sulphamethoxazole was observed, with most resistance among historic isolates of serotype 7 and least resistance among isolates from Sweden. A large number of the isolates was resistant to macrolides. However, all historic serotype 2 isolates from Denmark were susceptible, whereas 20.4% of the contemporary isolates were resistant. Among serotype 7 isolates 23.3% of the historic isolates were resistant to macrolides, whereas resistance was found in 44.8% of the contemporary isolates. All isolates from Sweden were susceptible to macrolides. Time-associated frequency of resistance to tetracycline was also found. Only a single historic isolate of serotype 2 was resistant to tetracycline, whereas 43.9% of the contemporary serotype 2 isolates and 15.5% of the contemporary serotype 7 isolates were resistant. Only one (7.7%) of the isolates from Sweden was resistant. The differences in resistance between historic and contemporary isolates from Denmark were statistically significant. This study demonstrated a significant serotype-associated difference in the susceptibility to macrolides and tetracycline and demonstrated that an increase in resistance among S. suis isolates has taken place during the last 15 years to the two most commonly used antimicrobial agents (tylosin and tetracycline) in pig production in Denmark.
Insights
Antimicrobial resistance in Streptococcus suis has increased over 15 years, particularly macrolide and tetracycline resistance in Danish isolates. Swedish isolates showed less resistance.
Area of Science:
- Veterinary Microbiology
- Antimicrobial Resistance
- Bacterial Pathogenesis
Background:
- Streptococcus suis is a significant swine pathogen.
- Monitoring antimicrobial susceptibility is crucial for effective disease management.
- Historical and contemporary data provide insights into resistance trends.
Purpose of the Study:
- To determine minimum inhibitory concentration (MIC) values for historical and contemporary Streptococcus suis isolates.
- To compare antimicrobial resistance patterns between different serotypes and geographic origins (Denmark and Sweden).
- To assess temporal trends in antimicrobial resistance in S. suis.
Main Methods:
- MIC testing of 52 historical (1967-1981) and 156 contemporary (1992-1997) Danish S. suis isolates (serotypes 2 and 7), and 13 Swedish S. suis isolates (serotype 2).
- Testing against 20 different antimicrobial agents.
- Statistical analysis to compare resistance frequencies.
Main Results:
- Increased resistance to macrolides and tetracycline was observed in contemporary Danish S. suis isolates compared to historical ones.
- Serotype 7 isolates showed higher macrolide resistance than serotype 2.
- Swedish isolates exhibited lower resistance to macrolides and tetracycline compared to Danish isolates.
- Significant temporal increases in resistance to tylosin and tetracycline were noted in Danish pig production.
Conclusions:
- A significant increase in macrolide and tetracycline resistance has occurred in Danish S. suis isolates over the past 15 years.
- Resistance patterns differ significantly between serotypes and geographic locations.
- These findings highlight the need for ongoing surveillance of antimicrobial resistance in S. suis.