Cephalexin: interpretation of sensitivity disc testing in veterinary practice

A regression study using 30 micrograms cephalexin sensitivity discs with bacterial strains isolated from veterinary sources is described. Techniques suitable for use in veterinary investigation laboratories were used and critical zone sizes calculated from a linear regression analysis. Zone sizes of less than or equal to 18 mm, 19 to 20 mm and greater than or equal to 21 mm were found to be suitable to categorise strains as resistant, intermediate or sensitive, respectively. Experience in the use of these recommended critical zone sizes in clinical practice will be necessary before firm recommendations can be made.