title: Oxacillin disk diffusion testing for the prediction of penicillin resistance in Streptococcus pneumoniae.
abstract: Objective To 1) describe the correlation between the zones of inhibition in 1-µg oxacillin disk diffusion (ODD) tests and penicillin and ceftriaxone minimum inhibitory concentrations (MICs) of meningeal and non-meningeal strains of Streptococcus pneumoniae and 2) evaluate the usefulness of the ODD test as a predictor of susceptibility to penicillin in S. pneumoniae and as a quick and cost-effective method easily implemented in a routine clinical laboratory setting. Methods S. pneumoniae isolates from healthy nasopharyngeal carriers less than 2 years old, obtained in a multicentric cross-sectional study conducted in various Peruvian hospitals and health centers from 2007 to 2009, were analyzed. Using Clinical and Laboratory Standards Institute (CLSI) breakpoints, the correlation between the zones of inhibition of the ODD test and the MICs of penicillin and ceftriaxone was determined. Results Of the 571 S. pneumoniae isolates, 314 (55%) showed resistance to penicillin (MIC ≥ 0.12 µg/mL) and 124 (21.7%) showed resistance to ceftriaxone (MIC ≥ 1 µg/mL). Comparison of the ODD test zones of inhibition and the penicillin MICs, using the CLSI meningeal breakpoints, showed good correlation (Cohen's kappa coefficient = 0.8239). Conclusions There was good correlation between ODD zones of inhibition and penicillin meningeal breakpoints but weak correlation between the ODD results and non-meningeal breakpoints for both penicillin and ceftriaxone. Therefore, the ODD test appears to be a useful tool for predicting penicillin resistance in cases of meningeal strains of S. pneumoniae, particularly in low- and middle- income countries, where MIC determination is not routinely available.
authors.forename: Gertrudis
authors.initials: G
authors.lastname: Horna
authors.forename: María L
authors.initials: ML
authors.lastname: Molero
authors.forename: Liliana
authors.initials: L
authors.lastname: Benites
authors.forename: Sigri
authors.initials: S
authors.lastname: Roman
authors.forename: Luz
authors.initials: L
authors.lastname: Carbajal
authors.forename: Erik
authors.initials: E
authors.lastname: Mercado
authors.forename: María E
authors.initials: ME
authors.lastname: Castillo
authors.forename: Rito
authors.initials: R
authors.lastname: Zerpa
authors.forename: Eduardo
authors.initials: E
authors.lastname: Chaparro
authors.forename: Roger
authors.initials: R
authors.lastname: Hernandez
authors.forename: Wilda
authors.initials: W
authors.lastname: Silva
authors.forename: Francisco
authors.initials: F
authors.lastname: Campos
authors.forename: Andy
authors.initials: A
authors.lastname: Saenz
authors.forename: Isabel
authors.initials: I
authors.lastname: Reyes
authors.forename: Alex
authors.initials: A
authors.lastname: Villalobos
authors.forename: Theresa J
authors.initials: TJ
authors.lastname: Ochoa
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002443:Ceftriaxone / Q000494:pharmacology; D003430:Cross-Sectional Studies; D052978:Disk Diffusion Antimicrobial Tests / Q000379:methods*; D006801:Humans; D010068:Oxacillin / Q000494:pharmacology*; D010403:Penicillin Resistance; D010568:Peru; D013296:Streptococcus pneumoniae / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents; D002443:Ceftriaxone; D010068:Oxacillin