title: Detection of penicillin resistance in Streptococcus pneumoniae by diffusion tests.
abstract: Four different diffusion tests used to detect penicillin resistance in Streptococcus pneumoniae were evaluated for 34 penicillin-susceptible pneumococci (MIC < 0.1 microgram/ml), 35 intermediate pencillin-resistant (MIC 0.1-1.0 microgram/ml) and 23 penicillin-resistant strains (MIC > 2 micrograms/ml). The 1 microgram oxacillin disk from AB Biodisk, the 1 microgram oxacillin Neo-Sensitabs from Rosco, the 5 micrograms penicillin Low Neo-Sensitabs and the penicillin E test were tested on Mueller-Hinton blood agar, PDM Antibiotic Sensitivity Medium II supplemented with blood, and Danish Blood Agar. MICs obtained by the agar dilution method were used as reference. The 1 microgram oxacillin AB Biodisk was able to separate all the penicillin-susceptible pneumococci correctly from those with reduced penicillin susceptibility (MIC > or = 0.1 microgram/ml), whereas use of the 1 microgram oxacillin Neo-Sensitabs resulted in high frequencies (14-29%) of intermediate penicillin-resistant strains interpreted as penicillin susceptible. The 5 micrograms penicillin Low Neo-Sensitabs proved completely useless for detecting penicillin resistance in pneumococci. High rates of agreement (82-93%) were found between the penicillin E test and the reference MIC determination method on all the tested media.
authors.affiliation: Department of Research and Development in Microbiology, Statens Serum Institut, Copenhagen, Denmark.
authors.forename: R L
authors.initials: RL
authors.lastname: Poulsen
authors.forename: J D
authors.initials: JD
authors.lastname: Knudsen
authors.forename: M B
authors.initials: MB
authors.lastname: Petersen
authors.forename: K
authors.initials: K
authors.lastname: Fuursted
authors.forename: F
authors.initials: F
authors.lastname: Espersen
authors.forename: N
authors.initials: N
authors.lastname: Frimodt-Møller
mesh_terms: D004058:Diffusion; D008826:Microbial Sensitivity Tests / Q000379:methods*; D010403:Penicillin Resistance; D013296:Streptococcus pneumoniae / Q000187:drug effects*