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

1) Bacterial Genetics and Physiology Laboratory, Institut de Biologie et de Médecine Moléculaires, Faculté des Sciences, Université Libre de Bruxelles, Bruxelles, Belgium. 2) ENT Department, University Children's Hospital Reine Fabiola, Université Libre de Bruxelles, Bruxelles, Belgium. 3) Microbiology Department, Brugmann Hospital, Université Libre de Bruxelles, Bruxelles, Belgium. 4) Paediatric Department, University Children's Hospital Reine Fabiola, Université Libre de Bruxelles, Bruxelles, Belgium. 5) Centre for International Child Health, Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Melbourne, Australia. 6) Murdoch Children Research Institute, Melbourne, Australia.
The Pediatric Infectious Disease Journal (Impact Factor: 3.14). 12/2012; 32(3). DOI: 10.1097/INF.0b013e31827c9796
Source: PubMed

ABSTRACT This study describes for the first time heterogeneity of antibiotic resistance profiles among group A Streptococcus (GAS) isolates originating from a single throat swab in patients with acute pharyngitis. For each throat swab, ten GAS 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 amongst 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.

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