title: Population analysis of Escherichia coli isolates with discordant resistance levels by piperacillin-tazobactam broth microdilution and agar dilution testing.
abstract: Population analysis was performed for 42 Escherichia coli isolates to determine whether heterogeneity of resistance was a factor in piperacillin-tazobactam category differences between agar dilution and broth microdilution. Of 20 isolates discordant between methods, 80% were heterogeneous. Of 22 isolates in agreement, 59% were homogeneous. Heterogeneity and homogeneity rates for those in agreement were significantly different from those that were discordant (P value, 0.010). Heterogeneity of resistance expression appears to be an important factor in category differences observed between broth microdilution and agar dilution for piperacillin-tazobactam.
authors.affiliation: bioMérieux, Inc., R&D Microbiology, St. Louis, Missouri, USA.
authors.forename: Carole
authors.initials: C
authors.lastname: Shubert
authors.forename: Jen
authors.initials: J
authors.lastname: Slaughter
authors.forename: David
authors.initials: D
authors.lastname: Creely
authors.forename: Alex
authors.initials: A
authors.lastname: van Belkum
authors.forename: Jean Pierre
authors.initials: JP
authors.lastname: Gayral
authors.forename: William Michael
authors.initials: WM
authors.lastname: Dunne
authors.forename: Gilles
authors.initials: G
authors.lastname: Zambardi
authors.forename: Dee
authors.initials: D
authors.lastname: Shortridge
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects*; D008826:Microbial Sensitivity Tests / Q000379:methods; D010397:Penicillanic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D010878:Piperacillin / Q000494:pharmacology*; D000078142:Tazobactam
chemical_list: D000900:Anti-Bacterial Agents; D010397:Penicillanic Acid; D000078142:Tazobactam; D010878:Piperacillin