The categorical agreement between disc diffusion and sprogse micro-dilution broth was 89.0%. Eight very serious errors were observed for staphylococci (four s. aureus and four strains of CoNS), including 3213, 3487, 3036, 5721, 7338, 0538, 0960 and 0908, with a rate of 53.3%; Another very serious error was observed in a strain of faecium E (3419) (Table 2).2. In the case of staphylococcus, the use of light and the measurement of the deepest edge of the exclusion zone would have reduced the very high error rate to 20.0%, four coNS strains (7338, 0538, 0960 and 0908) and an S. aureus strain (3036) resulted in reading in this area (with an average decrease in the diameter of the 4 mm zone) of the non-sensitive area. Four isolates of S. aureus produced non-sensitive results in new tests in reflected light; a fifth non-receptive isolate would have been detected with light. No major errors (i.e. poorly resistant results) were detected when imprecise light reads the diameters of staphylococcus isolates. Two E. faecium isolates produced minor errors.

The use of light did not improve the interpretation of enterococcal results. All systems were tested in parallel with the inocula made from the same subculture. All isolates for which there were differences between the results of the test method (i.e. sensitive, moderate or resistant) and the results of the reference method for micro-dilution broth were again tested in parallel by the micro-dilution of the broth and the method in question; However, only the initial results were used in error calculations. If two or more systems did not agree with the broth reference result, all systems were retested in parallel to determine the reproducibility of the results. In a categorical agreement, very large errors were defined as being sensitive to the outcome of the test method and the results of the reference method being resistant, larger errors were identified than those for which the result of the test method was resistant and where the result of the reference method was fragile, and minor errors are defined as those for which one of the two methods reported a result in as an intermediate product and the other reported the result as vulnerable or resistant. Very high error rates were calculated using the 15 non-receptive isolates as denominators for staphylococci and the 15 resistant isolates as denominators for enterococci. For larger error rate calculations, the denominators were 35 for staphylococcus and 33 for enterococci.

For smaller error rate calculations, the total number of organisms tested was used as a denominator, including two E`s.