Susceptibility testing of macrolide and lincosamide antibiotics according to DIN guidelines. Deutsches Institut für Normung.

The in-vitro activity of azithromycin, clarithromycin, erythromycin, josamycin, midekamycin, roxithromycin and clindamycin against 674 Gram-negative and Gram-positive clinical isolates, including methicillin-resistant Staphylococcus aureus, was determined by agar dilution, microdilution and agar diffusion with Mueller-Hinton medium according to the Deutsches Institut für Normung (DIN) 58940 guidelines. The results obtained by regression analysis and the error-rate-bounded method of Metzler-DeHaan indicate that common interpretative criteria (breakpoints) for test discs may be assigned to susceptible/resistant Gram-positive strains for all antibiotics tested. The following tentative DIN values are suggested for 15 microg macrolide discs: for susceptible Gram-positive and Gram-negative strains, an inhibition zone diameter (IZD) of > or = 26 mm at a corresponding MIC of < or = 2 mg/L; for resistant Gram-positive strains, an IZD of < or = 21 mm; for resistant Gram-negative strains, an IZD of < or = 19 mm at a corresponding MIC of > or = 8 mg/L. For Haemophilus influenzae only, breakpoints for azithromycin are suggested with IZDs of > or = 21 mm for susceptible and < or = 18 mm for resistant.

[Susceptibility testing of yeasts against fluconazole: proposal for a standardized agar diffusion method with 25 microgram fluconazole paper discs]. / Empfindlichkeitsprüfung von Hefen gegenüber Fluconazol: Vorschlag für eine standardisierte Agardiffusions-Methode mit 25-microgram-Fluconazol-Testblättchen.

This paper gives a proposal for a standardised agar diffusion susceptibility testing method with 25 micrograms fluconazole discs. The methodology compiles the results of several years of work to develop a reliable and reproducible routine-method for the microbiology laboratory. In this proposal, in addition, the critics and experiences of a collaborative study for susceptibility testing of fluconazole with 21 laboratories from Germany and Austria are included.

[Susceptibility testing of yeasts against fluconazole: comparison of the Etest method with microdilution and agar dilution]. / Empfindlichkeitsprüfung von Hefen gegenüber Fluconazol: Vergleich der Etest-Methode mit der Mikrodilution und der Agardilution.

In bacteriology, the Etest has a broad field of application in bacteriology and is recently available for the antimycotics fluconazole and itraconazole. By means of the presence of gradient concentrations of the active substance on the carrier material, it is possible to obtain reproducible MICs of the antimycotic substances. The results of susceptibility testing of 326 clinical yeast isolates with the Etest were compared to those MICs obtained by microdilution and agar dilution. A 100% concordance of the MIC markers (mode-, MIC50- and MIC90-value, standard deviation of the mean log2-MIC-dilution steps) was given when compared by a +/- 1 MIC-dilution step range with microdilution and by +/- 2 MIC-dilution steps with agar dilution; species dependent all strains were within 2 x standard deviation of the individual MIC-mean of the species. By comparison of the individual MIC-values maximum differences of +/- 6 MIC-dilution steps were obtained, where 70% of all results were within +/- 2 MIC-dilution steps, and more than 92% of all strains were within +/- 3 MIC-dilution steps. The Pearson's correlation coefficients show a good agreement of the Etest with microdilution (r = 0.92) resp., agar dilution (r = 0.88) demonstrate, however, clearly insufficient correlations (r < 0.65) to the reference methods, for species with difficult to read Etest inhibition zones (e.g., Candida glabrata, Candida krusei, Candida parapsilosis). The differences between the proposed test methods recommended by the NCCLS and the working group "Clinical Mycology" of the German Speaking Mycological Society (AG-KMYK) are tabled.

An evaluation of seven methods of testing in vitro susceptibility of clinical yeast isolates to fluconazole.

Four commercially available in vitro test systems (Candifast, E-test, Mycototal and spiral-gradient end point method), agar diffusion with 25-micrograms fluconazole paper test discs and 15-micrograms test tablets and agar dilution were compared with the microbroth dilution method for fluconazole susceptibility testing of 145 clinical isolates. In addition, the culture media provided or recommended by the manufacturers of the test systems were compared with high-resolution (HR) antifungal test medium. With all currently available culture media, growth problems (inhibition or delayed growth of the clinical isolates) occurred with solid or semisolid media. With minor improvements, HR medium demonstrated the most reproducible and comparable results (supplementation with asparagine and deletion of sodium hydrogen carbonate). The best correlation with microdilution was obtained by the agar dilution method (> 95% concordance) followed by the spiral-gradient end point method (85%), Candifast (83%), Mycototal (81%) and the E-test (78%). Regression analysis demonstrated good correlation between agar diffusion and micro-/agar dilution (r > 0.9).

[Comparison of seven methods of in vitro susceptibility testing of clinical yeast isolates against fluconazole]. / Ein Vergleich von sieben Methoden zur In-vitro-Empfindlichkeitsprüfung von klinischen Hefe-Isolaten gegenüber Fluconazol.

Four commercially available in vitro test systems (Candifast, E-test, Mycototal, Spiral-Gradient Endpoint Method), agardiffusion with 25 micrograms fluconazole paper test discs and 15 micrograms test tablets, and agardilution were compared to the microbroth dilution method by fluconazole susceptibility testing of 145 clinical isolates. In addition, the culture media provided or recommended by the manufacturers of the test systems were compared to the high resolution (HR) antifungal test medium. With all currently available culture media growth problems (inhibition or delayed growth of the clinical isolates) occurred with solid or semi-solid media. With minor improvements, HR medium demonstrated the most reproducible and comparable results (supplementation with asparagine and deletion of sodium hydrogen carbonate). Best correlation to microdilution was obtained by the agardilution method > (95% concordance) followed by the spiral gradient endpoint method (85%), Candifast (83%), Mycototal (81%) and the E-test (78%). Regression analysis demonstrated good correlation between agardiffusion and micro-/agardilution(r > 0.9).