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Clindamycin resistance among erythromycin-resistant Streptococcus pneumoniae
R N Jones1, M G Cormican, A Wanger
1Department of Pathology, University of Iowa College of Medicine, Iowa City 52242, USA.
Diagnostic Microbiology and Infectious Disease
|August 1, 1996
Summary
Testing susceptibility medium impacts clindamycin resistance detection in Streptococcus pneumoniae. Routine testing, including induction, is crucial for macrolide-lincosamide-streptogramin (MLS) drugs.
Area of Science:
- Microbiology
- Antimicrobial Resistance
- Clinical Pharmacy
Background:
- Increasing penicillin resistance in Streptococcus pneumoniae necessitates alternative therapies.
- Clindamycin is a potential oral treatment for pneumococcal otitis media.
Purpose of the Study:
- To evaluate in vitro clindamycin susceptibility in erythromycin-resistant S. pneumoniae strains.
- To determine the influence of susceptibility testing media on MLS resistance expression.
Main Methods:
- Etest methodology used for in vitro susceptibility testing.
- Tested 59 erythromycin-resistant S. pneumoniae strains against clindamycin, penicillin, trimethoprim-sulfamethoxazole, and rifampin.
- Compared Mueller-Hinton (MH) and IsoSensitest (Iso) blood agar media.
Main Results:
- Constitutive clindamycin resistance observed in 37% of isolates on Iso vs. 22% on MH agar.
- Nine strains showed inducible clindamycin resistance only on MH agar.
- High resistance rates to penicillin (83%) and trimethoprim-sulfamethoxazole (85%-89%) were noted.
Conclusions:
- Susceptibility testing medium significantly affects the detection of constitutive and inducible MLS resistance in S. pneumoniae.
- The assumption of cross-resistance between erythromycin and clindamycin may not always hold true.
- Routine susceptibility testing, including induction methods when using MH agar, is recommended for MLS drugs.