Colony Counts on Strips of Agar in Tubes

SUMMARY: For viable counting, 0.1 ml. volumes of bacterial suspension were in-corporated in 1.5-2 ml. nutrient agar, which after mixing was allowed to solidify in an almost horizontal test-tube so as to produce a 3 4 in. agar strip. After incubation in the vertical position, the counts of the strips gave estimates of a bacterial population which did not differ significantly from that obtained from plates inoculated with 1 ml. quantities. The study of bacterial populations requires a simple method for determining the viable count. The method most often used is the plate count, but with a large number of plates this method becomes rather cumbersome and expensive in equipment, medium and laboratory labour. Modifications of the plating method have been suggested from time to time with a view to reducing the amount of materials and labour involved without impairing the accuracy of the count (Esmarch, 1886; Miles & Misra, 1938). In an endeavour to find a simple method by which colony counts might be made, inoculation of small quantities of agar in test-tubes was tried