Acyclovir resistance in herpes simplex virus isolates from keratitis cases: an analysis from a developing country.

Seven herpes simplex type-1 (HSV-1) isolates from herpes simplex keratitis (HSK) cases clinically resistant to acyclovir (ACV) were analyzed for the mechanism of ACV resistance in them. The purpose of the study was to focus the attention of ophthalmologists on the frequency of occurrence of ACV resistance in HSK and to characterize such a phenomenon. We employed in-vitro plaque reduction assay, thymidine kinase assay, polymerase chain reaction, single-strand confirmation polymorphism analysis and sequencing to detect any mutation(s) in thymidine kinase gene in this analytical study. Four of the seven HSV-1 isolates proved ACV resistant by plaque reduction assay and three of them showed reduced thymidine kinase activity. Altered mobility pattern indicative of mutation within 335 base pair PCR product bracketing the suggested homopolymer mutational hotspot (7 Guanosine) was detected in 2 of these 3 isolates. DNA sequencing showed a deletion at nucleotide position 336 from the tk gene transcription start in both the isolates. This mutation has generated the first TGA stop codon 27 nucleotides downstream in the tk open reading frame. Our study also suggests the need of clinical/molecular surveillance of ACV resistance in HSV types in a given geographic location for better management of HSV infections.