Experiences with the Coulter counter in bacteriology

Viable and killed suspensions of Staphylococcus aureus SM, Escherichia coli, and Serratia marcescens, as well as polystyrene spheres, 0.81 and 2.85 mu in diameter, were counted electronically with a model A Coulter Counter. Simultaneous counts by standard bacteriological methods and microscopy were done for purposes of control and comparison with the data from the Coulter Counter. Results indicated: (i) electrical characteristics of different bacterial populations are different; (ii) electronic counts were consistent for species used; (iii) live S. aureus exhibits a denser pattern of thick bright pulses on the cathode-ray tube than does live E. coli; (iv) killed bacteria resemble inert particles in pulse pattern; and (v) some viable bacteria do not react independently of current flow, as do inert particles and killed bacteria.