A SIMPLIFIED TECHNIQUE FOR DETERMINING THE SENSITIVITY OF CYTOMEGALOVIRUS STRAINS TO GANCICLOVIR

A technique for determining the susceptibility to ganciclovir of cytom egalovirus (CMV) strains isolated in clinical samples is described. Th e inoculum was composed of a partially infected suspension of cells fr om a young positive culture (< 10 days), usually the first passage of the primary culture. The appropriate dilution of the cell suspension t o provide a suitable inoculum was based on a previous study of five st rains grown in different dilutions which provided a countable number o f plaques and avoided titration of each of the isolated strains. Fifty -three strains were studied at three different dilutions. Five from pa tients on maintenance ganciclovir therapy with poor clinical response had a 50% inhibitory dose (ID50) between 21.46 and 13.35 mu M and the remainder an ID50 between 2.31 and 10.5 mu M, comparable to results ob tained by other authors using susceptibility techniques with a sonicat ed inoculum. Three of these strains were studied by both methods using sonicated inoculum and cell suspension inoculum. The mean lime which elapsed between seeding the specimen and obtaining sensitivity was 39. 00 and 27.66 days, respectively. The technique reduces significantly t he time involved since relatively young cultures can be studied and pr evious titration is not required.