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Pediatric Infectious Disease Journal:
doi: 10.1097/INF.0b013e31827c9796
Brief Reports

Group A Streptococcus Colonies From a Single Throat Swab Can Have Heterogeneous Antimicrobial Susceptibility Patterns

Vandevoorde, Aurélie MD*†; Ascenzo, Sabrina Bsc*; Deyi, Veronique Yvette Miendje MD, PhD; Mascart, Georges MD, PhD; Mansbach, Anne-Laure MD; Landsberg, Marguerite MD§; Dreze, Pierre BSc*; Steer, Andrew C. MD, PhD; Van Melderen, Laurence PhD*; Smeesters, Pierre R. MD, PhD*‖

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This study describes for the first time heterogeneity of antibiotic resistance profiles among group A Streptococcus isolates originating from a single throat swab in patients with acute pharyngitis. For each throat swab, 10 group A Streptococcus colonies were randomly selected from the primary plate and subcultured to a secondary plate. These isolates were characterized by various phenotypic and genotypic methods. Our results demonstrated that differing antibiotic resistance profiles were present in 19% of pediatric patients with acute pharyngitis before antimicrobial treatment. This heterogeneity likely resulted from horizontal gene transfer among streptococcal isolates sharing the same genetic background. As only a minority of colonies displayed antibiotic resistance among these heterogeneous samples, a classical diagnostic antibiogram would have classified them in most instances as “susceptible,” although therapeutic failure could be caused by the proliferation of resistant strains after initiation of antibiotic treatment.

© 2013 Lippincott Williams & Wilkins, Inc.


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