Imaging the propagation of viruses

The propagation of viruses in a growing plaque has been measured using a digital image acquisition and analysis system. Plaques of phage T7 incubated at 37 degrees C and illuminated against a dark field emerged as dark growing spots against a background of host bacteria. Images of the growth were acquired using a charge-coupled device (CCD) camera at 1-h intervals over 24 h. The first 10 h of plaque development coincided with rapid growth of the agar-immobilized Escherichia coli host, measured as a reduction in gray value. Following this period, the average radial velocity of plaque growth remained constant at 0.059 mm/h while the standard deviation about this velocity increased. These results suggest the suitability of the system for spatially resolving the dynamics of viral evolution during plaque growth. (c) 1996 John Wiley & Sons, Inc.