The Calibrated Dichotomous Sensitivity (CDS) test is a disc diffusion method calibrated using agar dilution. The method is maintained by the CDS Reference Laboratory at St George Hospital, Australia.
The CDS reference laboratory is responsible for supporting users as well as upkeep of the method. Before any new antimicrobial agent can be included in the manual it is necessary to confirm that there is a correlation between zone size and minimal inhibitory concentration (MIC).
Ceftolozane-tazobactam is a novel antimicrobial agent with activity against Pseudomonas aeruginosa (including drug-resistant strains) and other common Gram-negative pathogens (including most extended-spectrum-β lactamase [ESBL]-producing Enterobacteriaceae strains).
A selection of current and historical strains of Enterobacteriaceae and Pseudomonas species were tested against ceftolozane in the presence of 4 mg/L tazobactam to establish the breakpoint and determine whether a uniform zone size could be applied for use with the CDS disc diffusion test.