Improved detection of viruses by electron microscopy after direct ultracentrifuge preparation of specimens

Abstract

We have adapted the Beckman Airfuge air turbine ultracentrifuge and the new EM-90 particle-counting rotor to improve detection by electron microscopy of viruses in clinical specimens. Samples were clarified by centrifugation, pelleted in the EM-90 rotor directly to Formvar-coated copper grids, and strained with 1.5% sodium phosphotungstate. Virus counts and endpoint titrations of serial dilutions of partially purified preparations of poliovirus, SA11 rotavirus, herpes simplex virus, and vaccinia virus showed an increase of ca. 1.5 log10 to 3.0 log10 over the virus titers of unconcentrated preparations of the same material. An increased yield of 14% more positive specimens for rotavirus was obtained after preparation of clinical samples by direct ultracentrifugation versus a method without virus concentration (82 versus 72). A prospective study showed that detection of adenoviruses, herpesviruses, and enteroviruses increased when specimens were prepared by direct ultracentrifugation. Direct ultracentrifugation with the EM-90 rotor in the Airfuge ultracentrifuge is a rapid concentration method which enhances the rate and yield of virus detection from clinical specimens by electron microscopy and is easily adaptable to a diagnostic virology laboratory.