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Antimicrobial susceptibility of Streptococcus suis isolates
P L Turgeon1, R Higgins, M Gottschalk
1Hopital Saint-Luc, Montréal, Qc, Canada.
Abstract:
The antimicrobial activities of penicillin (PEN), ampicillin (AMP), cephalothin (CT), trimethoprim-sulphamethoxazole (TMP-SMX), streptomycin (STM), and gentamicin (GM) against 122 representative strains of Streptococcus suis, were compared by the agar dilution procedure. The current US National Committee for Clinical Laboratory Standards (NCCLS) breakpoints for non-enterococcal streptococci were used for PEN, AMP, CT, and TMP-SMX. Overall, 50% of strains were not fully susceptible to PEN, whereas these percentages for AMP and CT were 9% and 6% respectively. One strain was resistant to TMP-SMX. High-level GM resistance could not be detected, but more than 46% of strains were highly resistant to STM (MIC > 2000 mg l-1). This high percentage of resistance to STM precludes the use of this aminoglycoside-penicillin combination as empiric therapy in severe S. suis infections. These results should prompt microbiology laboratories to carry out antimicrobial susceptibility tests on a routine basis on S. suis isolates.
Insights
Penicillin resistance is high in Streptococcus suis strains, with over 46% showing high-level streptomycin resistance. Routine antimicrobial susceptibility testing for S. suis is recommended.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Streptococcus suis is an important pathogen causing significant morbidity and mortality.
- Understanding antimicrobial susceptibility patterns is crucial for effective treatment strategies.
Purpose of the Study:
- To evaluate the in vitro antimicrobial activities of commonly used antibiotics against Streptococcus suis.
- To determine the prevalence of resistance to penicillin, ampicillin, cephalothin, trimethoprim-sulphamethoxazole, streptomycin, and gentamicin.
Main Methods:
- Agar dilution procedure was used to test 122 representative strains of Streptococcus suis.
- Antimicrobial susceptibility was assessed using current NCCLS breakpoints for non-enterococcal streptococci.
Main Results:
- 50% of S. suis strains were not fully susceptible to penicillin.
- Ampicillin and cephalothin resistance were observed in 9% and 6% of strains, respectively.
- High-level streptomycin resistance exceeded 46%, precluding its use in combination therapy for severe infections.
Conclusions:
- Significant penicillin and streptomycin resistance in S. suis necessitates careful antibiotic selection.
- Routine antimicrobial susceptibility testing for S. suis isolates is strongly recommended for guiding clinical decisions.