Comparison of five media for detection of extended-spectrum Beta-lactamase by use of the wasp instrument for automated specimen processing.

Overall, 2,337 rectal screening samples (RSSs) were seeded by using the Wasp instrument for automated microbiological processing with five media for detection of extended-spectrum β-lactamase (ESBL): CHROMagar, ChromID, Brilliance, BD Drigalski, and HEGP media. Of 354 RSSs harboring ESBL-producing isolates, 89.3% were found to be positive on all media. Sensitivity and specificity ranged from 95.5 to 98.3% and from 57.9 to 72.3%, respectively. No medium was perfectly ESBL selective, and non-ESBL-producing strains were mainly Enterobacteriaceae overproducing AmpC β-lactamase and nonfermenting Gram-negative bacilli, mostly Pseudomonas aeruginosa.