Direct antimicrobial susceptibility testing in bacteriuria

A method for diagnosis of bacteriuria using semiquantitative culture in combination with direct susceptibility testing is described. Susceptibility testing with the breakpoint method was performed by means of a multiple inoculation technique. A simple biochemical typing on solid media of lactose-fermenting Enterobacteriaceae strains and aesculin testing of Enterococcus strains were performed simultaneously. Staphylococcus and Streptococcus strains were tested for susceptibility using the conventional disc diffusion technique. The results of the direct susceptibility test and the disc diffusion test were compared in a study of 983 consecutively positive urine cultures: 6624 susceptibility tests from 882 specimens with one microorganism revealed complete agreement in 6343 cases (95.8%); the discrepant results were 15 very major errors (0.2%), 84 major errors (1.3%) and 182 minor errors (2.7%). The direct susceptibility test revealed 42 more cases of bacteriuria with enterococci in combination with Enterobacteriaceae strains compared to the conventional method. 59% of all positive urine cultures were completed, including the susceptibility test report, within 24 h after arriving at the laboratory. The diagnostic costs were approximately the same as for the conventional method.