GENETIC-ANALYSIS OF A CLINICAL ISOLATE OF HUMAN CYTOMEGALOVIRUS EXHIBITING RESISTANCE AGAINST BOTH GANCICLOVIR AND CIDOFOVIR

Both ganciclovir-sensitive and -resistant human cytomegaloviruses (HCM V) were isolated from a patient with aplastic anemia complicated with CMV retinitis and encephalitis. Ganciclovir-resistant clinical isolate , 93-1R, also showed cross-resistance against (s)-1-(3-hydroxy-2-phosp honylmethoxypropyl) cytosine (cidofovir). Molecular analysis of plaque -cloned strains revealed that a single nucleotide substitution at 2160 (C to T) resulted in amino acid substitution at codon 501 from leucin e to phenylalanine in the DNA polymerase gene. This mutation at codon 501 was easily identified by means of AluI digestion of the selected P CR product. The same mutation existed in the DNA fragment amplified fr om the patient's brain, suggesting that cross-resistant mutant 93-1R c aused encephalitis. Furthermore, ganciclovir-resistant 93-1R-3 replica ted much faster and was released more efficiently into the culture med ium than ganciclovir-sensitive 91-7S-1.