title: Group A streptococcus colonies from a single throat swab can have heterogeneous antimicrobial susceptibility patterns.
abstract: 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.
authors.affiliation: Bacterial Genetics and Physiology Laboratory, Institut de Biologie et de Médecine Moléculaires, Faculté des Sciences, Belgium.
authors.forename: Aurélie
authors.initials: A
authors.lastname: Vandevoorde
authors.forename: Sabrina
authors.initials: S
authors.lastname: Ascenzo
authors.forename: Veronique Yvette
authors.initials: VY
authors.lastname: Miendje Deyi
authors.forename: Georges
authors.initials: G
authors.lastname: Mascart
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Mansbach
authors.forename: Marguerite
authors.initials: M
authors.lastname: Landsberg
authors.forename: Pierre
authors.initials: P
authors.lastname: Dreze
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Steer
authors.forename: Laurence
authors.initials: L
authors.lastname: Van Melderen
authors.forename: Pierre R
authors.initials: PR
authors.lastname: Smeesters
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D018740:Genetic Heterogeneity; D005838:Genotype; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D010612:Pharyngitis / Q000382:microbiology*; D010614:Pharynx / Q000382:microbiology*; D010641:Phenotype; D013290:Streptococcal Infections / Q000382:microbiology*; D013297:Streptococcus pyogenes / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*
chemical_list: D000900:Anti-Bacterial Agents