Disk diffusion testing, quality control guidelines, and antimicrobial spectrum of HR810, a fourth-generation cephalosporin in clinical microbiology laboratories

Abstract

HR810 is a new, very broad-spectrum cephalosporin with significant activity against members of the family Enterobacteriaceae, pseudomonads, gram-positive cocci, and anaerobes that is generally greater than the third-generation cephalosporins (99.6% of 4,128 clinical facultative enteric isolates were inhibited by ≤8.0 μg of HR810 per ml). Tests and statistical methods to establish in vitro antimicrobial susceptibility test criteria favor tentative breakpoints of ≥18 mm (<8.0 μg/ml) as susceptible and ≤14 mm (>32 μg/ml) as resistant. This provides a 93.7 to 98.3% absolute interpretive accuracy. Several preliminary ranges for zone sizes obtained with quality control organisms are proposed for the 30 μg HR810 disk diffusion test used during the clinical trials.