[Comparative study of 3 methods for quantifying bacterial flora of the hands: membrane filtration, agar inclusion and...

We report a study comparing three methods of quantifying bacterial flora on hands: filtration on a 0.22 mu membrane, pour-plate method, and conventional plate culture. Forty samples were taken using Gaschen's bag method with 400 ml of buffer solution. The bacteria in each sample were then counted using each method in duplicate. By adjusting the size of the sample and the number of dilutions, a countable number of colonies was obtained with each method. Culture media, and incubation time and atmosphere were the same for all three methods. Results, expressed as the log 10 of the number of bacteria per hand for aerobic and facultative anaerobic organisms respectively were as follows: membrane filtration 5.65 +/- 0.72 and 6.02 +/- 0.62; pour-plate 5.81 +/- 0.68 and 5.83 +/- 0.62; surface culture 5.80 +/- 0.69 and 5.97 +/- 0.52. None of the differences were statistically significant. The three methods were then compared for manipulation time, cost, volume of sample required and ease of reading and subsequent speciation. Overall, the pour-plate method emerged as the best, especially if speciation is required.