The correlation of in-vitro susceptibility tests with in-vivo results of antibiotic treatment.

The reason why the results of the clinical response to therapy do not always correspond to antibiotic laboratory testing include errors in performance or interpretation of test results, imprecise definition of resistance and host factors which influence the outcome of treatment regardless of the antibiotic being used. These factors are reviewed. Cephalosporins and penicillins pose problems because the prime effects of enzymes in influencing the outcome of treatment are not always clear in standard tests for susceptibility. Inter-laboratory differences in interpretation of tests makes comparisons of tests between centres difficult and the use of reference strains for validation of testing is proposed.