|MadSci Network: Microbiology|
Yes, using a Petroff-Hausser (PH) chamber would be an appropriate method to validate your cell counts. They look like a fancy microscope slide and work by placing a small amount of cell suspension (or cell dilution) onto a subdivided surface (the center of the microscope slide). This surface will look like graph paper under high magnification, with each etched square (or cell, like a honeycomb) representing a specific area and volume (example: one square = 0.01mm and 1 microliter).
The smallest squares will be visualized at 400-1000X magnification (I think) and will hold something like 0.1 microliters of your cell suspension. Now you simply count the number of bacterial cells per PH chamber cell and multiply to obtain cell#/ml. Check out this website for a nice summary (and figures) of this type of "direct microscope method" of cell ounting and to know how to calculate your total cell count from your measurements ( http://student.ccbcmd.edu/courses/bio141/labmanua/lab4/lab4.html). Here is a link to a journal article describing their use of a PH chamber ( http://www.ajtmh.org/cgi/content/full/73/5/962).
So, in brief, you just need one of these fancy microscope slides (the PH chamber) and you will easily be able to validate your optical density measurements!
All the best,
Try the links in the MadSci Library for more information on Microbiology.