Mónica Chávez

Comparison of Etest with Modified Broth Microdilution Method for Testing Susceptibility of Aspergillus spp. to Voriconazole

ABSTRACT We compared the Etest with a broth microdilution method, performed according to a modified National Committee for Clinical Laboratory Standards guideline (M38-A), for determining the in vitro susceptibility of 77 isolates of Aspergillus spp. (26 A. fumigatus, 21 A. flavus, 10 A. terreus, 9 A. niger, 5 A. nidulellus, 4 A. glaucus, and 2 A. flavipes isolates). Overall, there was 92.2% agreement between both methods when Etest MICs were read at 24 h and 83.1% agreement when both methods were read at 48 h. When Etest MICs were read at 24 h, the agreement was >90% for all species tested except for A. fumigatus (84.6%). When Etest MICs were read at 48 h, the agreement ranged from 50 to 100%. The poorest agreement was seen with A. glaucus (50%) and A. fumigatus (65%). Where a discrepancy was observed between Etest and the reference method, the Etest MIC was generally higher. The Etest appears to be a suitable alternative procedure for testing the susceptibility of Aspergillus spp. to voriconazole.

Evaluation of the new API candida system for identification of the most clinically important yeast species

The API Candida system (bioMérieux) a new yeast identification system, was evaluated for its reliability in identifying 198 clinical yeast isolates in comparison with the API 20C system (bioMérieux) that was used as reference standard. The API Candida system correctly identified 91.4% and 71.7% of the isolates, with and without additional tests, respectively. The API Candida system identified 96.3% of common isolates studied, and 66.6% of uncommon isolates. We think that API Candida system is an easy and good yeast identification system and it could be used in a routine clinical microbiology laboratory.

Comparison of the Sensititre YeastOne Colorimetric Microdilution Panel and the NCCLS Broth Microdilution Method for Antifungal Susceptibility Testing against Candida Species

We evaluated the commercially prepared Sensititre YeastOne colorimetric antifungal panel to determine the susceptibility of 170 Candida spp isolates to amphotericin B, fluconazole, itraconazole, and flucytosine. The NCCLS reference microdilution method (M27-A document) was used as reference method. The YeastOne panel was performed according to the manufacturer’s instructions. For the colorimetric method, MICs were determined at 24 h of incubation. MICs for the NCCLS reference method were read at 48 h of incubation. The overall agreement within ±2 dilutions by both methods was calculated against the four antifungal agents. This agreement was 92.9, 68.2, 77.6 and 80% for amphotericin B, fluconazole, itraconazole, and flucytosine, respectively. Thirteen isolates (7.6%) showed very major discrepancies for fluconazole and 12 (7%) for itraconazole. We found that the reading of MIC with the YeastOne panel was somewhat easier than the reading of reference MIC, although the determination of endpoint was sometimes difficult, especially for azoles, because the trailing effect appeared in a high percentage of isolates.

Evaluation of the New VITEK 2 System for Determination of the Susceptibility of Clinical Isolates of Streptococcus pneumoniae

Background: The VITEK® 2 is a new version of the automated system for organism identification and susceptibility testing. One of the differences between this system and its predecessor, VITEK, is the ability to perform rapid susceptibility testing of Streptococcus pneumoniae. This study compares the results of susceptibility testing of S. pneumoniae using the VITEK 2 system and a commercial microbroth dilution method, Sensititre. Methods: A group of 214 clinical isolates of S. pneumoniae were selected to include isolates with previously documented penicillin resistance. The antimicrobial agents tested were benzylpenicillin, cefotaxime, erythromycin, trimethoprim/sulfamethoxazole, tetracycline, chloramphenicol, imipenem and vancomycin. Results: The best agreement was achieved with vancomycin (100%), erythromycin (95.8%) and tetracycline (95.8%). The lowest level of agreement was found with benzylpenicillin (88.6%) and cefotaxime (90.1%). We observed rates of 12.3 and 15.7% for minor errors with penicillin and cefotaxime, respectively, and 1 very major error for cefotaxime. Conclusion: The VITEK 2 allows rapid determination of the antimicrobial susceptibility of S. pneumoniae and demonstrated a good degree of agreement with the Sensititre method for most of the antimicrobials tested.