[Susceptibility testing with fosfomycin in an agar diffusion test on Mueller-Hinton agar]

A disc loading of 50 microgram fosfomycin + 50 microgram glucose-6-phosphate is recommended for disc susceptibility testing. Regression analyses for the correlation of the diameter of inhibition zones with the MIC result in the following equations. For Pseudomonas aeruginosa x = -0.15 y + 16.67 and for Enterobacteriacae plus gram-positive cocci x = -0.34 y + 19.55 (x = log2MIC + 9; y = diameter of inhibition zone in mm). The correlation coefficients are r = -0.9219 and -0.8627 respectively. The analysis yield the following zone diameter interpretive standards. For Pseudomonas aeruginosa less than 12 mm resistant, greater than or equal to 25 mm susceptible, and for Enterobacteriaceae plus gram-positive cocci less than 14 mm resistant, greater than or equal to 20 mm susceptible.