E-TEST AS AN ALTERNATIVE TO CONVENTIONAL MIC DETERMINATION FOR SURVEILLANCE OF DRUG-RESISTANT STREPTOCOCCUS-PNEUMONIAE

A commercial E test was compared with the standard agar dilution metho d for the determination of minimum inhibitory concentration (MIC) of p enicillin, erythromycin, chloramphenicol and cefotaxime for 36 strains of Streptococcus pneumoniae from patients with invasive diseases. Add itional strains were tested for MIC values for penicillin (6), erythro mycin (14) and cefotaxime (13) for a better statistical evaluation, Be sides, 5 reference standards with predetermined MIC values obtained fr om WHO pneumococcal reference center at Copenhagen, Denmark were teste d for penicillin and erythromycin, for quality assessment using both a gar dilution as well as E test methods, An overall agreement within +/ - 2 dilutions was noted for 97 per cent of the strains tested for all the antimicrobials, A high degree of correlation was noted for erythro mycin (r = 1), penicillin (r = 0.99), chloramphenicol (r = 0.95) and c efotaxime (r = 0.9). In MIC determination of a single antimicrobial fo r diagnostic purpose, E test was found to be more cost effective than conventional agar dilution method, E test was simple to perform, easy to interpret and a valid method for MIC determination of antimicrobial s for S. pneumoniae in our center.