Facilitating quality control of the antimicrobial susceptibility test.

Standard reference strains of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were suspended in sterile deionized water and tested daily via disk agar diffusion for their antimicrobial susceptibilities. Inocula of E. coli and P. aeruginosa yielded acceptable results for up to 32 days; however, results on S. aureus were unacceptable due to loss of viability of the organism in water. E. coli and P. aeruginosa inocula, in water, can be used daily for quality control of the disk gear diffusion test.