title: Factors that affect in vitro measurement of the susceptibility of herpes simplex virus to nucleoside analogues.
abstract: OBJECTIVE
  To identify factors that contribute to variability of HSV antiviral susceptibility breakpoints.
  
  
  METHODS
  Acyclovir and penciclovir IC(50)'s for 12 HSV clinical isolates were measured in two laboratories using plaque reduction assay (PRA), an enzyme immunoassay (EIA)-based antigen reduction, and DNA hybridization on Vero, A549, MRC-5, HEL299 and HELG monolayers. Pair-wise comparisons were performed to evaluate variables including testing laboratory, technique, monolayer, and antiviral. The proportion of false results was analyzed using a conventional susceptibility IC(50) breakpoint of 2 microg/ml.
  
  
  RESULTS
  Acyclovir-resistant HSV isolates were correctly identified by all methods. In contrast, there were 6-67% of susceptible isolates incorrectly characterized as drug-resistant. Variables associated with these errors included testing site, assay method, cell line and antiviral. A549, DNA hybridization, and penciclovir were associated with the highest IC(50)'s, whereas the PRA, EIA, and human fibroblast-monolayers provided the best differentiation between susceptible and resistant HSV isolates.
  
  
  CONCLUSIONS
  The current recommendations to use a single discriminating value to define HSV resistance to nucleoside analogues can be problematic. False results are influenced in various degrees by the laboratory method, tissue culture and antivirals.
authors.affiliation: Pediatric Infectious Diseases, University of Colorado Health Sciences Center, Denver, CO, United States. adriana.weinberg@uchsc.edu
authors.forename: Adriana
authors.initials: A
authors.lastname: Weinberg
authors.forename: Jeffry J
authors.initials: JJ
authors.lastname: Leary
authors.forename: Robert T
authors.initials: RT
authors.lastname: Sarisky
authors.forename: Myron J
authors.initials: MJ
authors.lastname: Levin
mesh_terms: D000212:Acyclovir / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology*; D018929:Cell Culture Techniques; D002522:Chlorocebus aethiops; D024882:Drug Resistance, Viral; D005347:Fibroblasts; D006147:Guanine; D018259:Herpesvirus 1, Human / Q000187:drug effects* / Q000302:isolation & purification; D018258:Herpesvirus 2, Human / Q000187:drug effects* / Q000302:isolation & purification; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods; D020128:Inhibitory Concentration 50; D009693:Nucleic Acid Hybridization; D014709:Vero Cells; D010948:Viral Plaque Assay / Q000379:methods
chemical_list: D000998:Antiviral Agents; C053539:penciclovir; D006147:Guanine; D000212:Acyclovir