Abstract
In recent years there has been an increasing interest for application of natural products as antiinfectives and concerns about the safety of synthetic compounds have encouraged more detailed studies of natural resources. Two different strains of the nontoxic cyanobacterium Arthrospira from the United States and Egypt have been characterized by sequence analysis of the intergenic spacer region of the phycocyanin gene. Both cyanobacteria were identified as Arthrospira fusiformis by phylogenetic tree analysis. The antiherpetic activity of crude aqueous extracts from the US and the Egyptian A. fusiformis isolates was determined. Antiviral activity against herpes simplex virus of cold water extracts, hot water extracts and phosphate buffer extracts from the American and the Egyptian strains was assessed in plaque reduction assays and their mode of antiherpetic action was analysed. In virus suspension assays, all extracts of the American cyanobacterium and the phosphate buffer extract of the Egyptian cyanobacterium inhibited virus infectivity by >90% in a dose-dependent manner. Phosphate buffer extract and hot water extract of the US cyanobacterium demonstrated the highest antiviral activity at low extract concentrations with high selectivity indices of 7464 and 542, respectively. The mode of antiviral action has been determined by addition of cyanobacterial extracts separately at different time periods during the viral infection cycle. Two extracts of the US A. fusiformis strain clearly inhibited herpesvirus multiplication before and after virus infection of host cells. In contrast, extracts of the Egyptian A. fusiformis strain affected only free herpes simplex virus prior to infection of host cells by direct inactivation of virus particles. In this study different Arthrospira crude extracts showed a significant antiviral effect and might be applied in recurrent herpetic infections.