Low-voltage electric-discharge biolistic device.

dilution is limited primarily in its sensitivity. However, this is of concern only if very small numbers of organisms are suspected in a particular specimen, because the lower limits of detection for a 10-μL aliquot of undiluted material would be approximately 100 cfu/mL. There exists the possibility of crossing of paths as the plates are tilted. We experienced this problem only: (i) on media that were either excessively dry or had gross irregularities on their surfaces or (ii) when more than 6 samples were placed on a single 100× 15-mm plate. Use of media with a smooth surface and adequate spacing of samples minimizes erroneous track migration and mixing. Since detergents are often used for tissue homogenization (i.e., phagocytosis assays), we tested samples containing 10% (vol/vol) Triton X-100 and observed no interference with proper track formation (data not shown). In conclusion, bacterial enumeration by track dilution should prove a simple and reproducible tool, applicable to any number of experimental systems including bacterial growth kinetic studies and time-kill determinations. Although not specifically tested in this study, track dilution may prove useful for rapid enumeration of yeasts as well.