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 less than or equal to 8.0 micrograms of HR810 per ml). Tests and statistical methods to establish in vitro antimicrobial susceptibility test criteria favor tentative breakpoints of greater than or equal to 18 mm (less than or equal to 8.0 micrograms/ml) as susceptible and less than or equal to 14 mm (greater than or equal to 32 micrograms/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-micrograms HR810 disk diffusion test used during the clinical trials.