the disinfection time in minutes at the lower temperature by the

Transcription

1 AN EXPERIMENTAL STUDY OF THE INFLUENCE OF TEMPERATURE ON THE BACTERICIDAL ACTIVITIES OF ALCOHOLS AND PHENOLS Senior Bacteriologist, Pathological Division, Bureau of Animal Industry, United State8 Department of Agriculture, Washington, D. C. Received for publication July 11, 1941 A study of the relation between concentration of disinfectants and the time required for disinfection was described in a previous paper.' A number of alcohols and phenols were used in that work, and from the experimental datav obtained the concentration exponent of each of these was calculated and reported. More recently a study has been made of the relation between temperature of disinfection and the time required for disinfection. Most of the alcohols and phenols previously used were also used in the recent work. From the results obtained the temperature coefficients of the alcohols and phenols used were calculated by dividing the disinfection time in minutes at the lower temperature by the disinfection time for the same concentration at the higher temperature. The temperature differenees were in all cases 10 C. In most instances the temperature coefficient was determined for each of a series of successive concentrations of the same disinfectant, and the average coefficient calculated for the series is considered the temperature coefficient of the particular disinfectant. The experimental procedure was si-ilar to that previously described except that the relative effectiveness of the same concentration at different temperatures was studied instead of, as formerly, the relative effectiveness of different concentrations at the same temperature. EXPERIMENTAL PROCEDUIRE Bactericidal efficiency was determined by the Rideal-Walker technique, modified as follows: Beef infusion broth adjusted to I An experimental study of the relation between concentration of disinfectants and time required for disinfection, F. W. Tilley, Jour. Bact., vol. 38, no. 5, November, 1939, pp

2 522 ph 7.0 was used instead of R-W standard broth; instead of a standardized dropping pipette, a 1-ml. pipette graduated into tenths was used to measure the 0.5 ml. of culture required for each disinfectant dilution; dilutions were made up in sterile Erlenmeyer flasks instead of in cylinders; fixed amounts of the stock solution of disinfectant were added to varying amounts of sterile distilled water, all measured with sterile standardized pipettes; the time of exposure was extended beyond 15 minutes, subcultures being made at 2.5-minute intervals from 2.5 to 30 minutes, at 5-minute intervals from 30 minutes to 80 minutes, and at 10-minute intervals beyond 80 minutes; Staphylococcus aureus was used as a test organism in addition to Eberthella typhosa; and tests were made at a number of different medication temperatures. In the more recent work, as in the previous work, stock solutions and subdilutions were made up on a weight basis. In spite of attempts to maintain constancy of conditions there were many variations in the results obtained with the same disinfectant in different experiments. However, by obtaining average results from a number of concentrations in each experiment and from a number of separate experiments, the effect of variations was minimized. As far as possible, parallel tests at two different temperatures were made on the same day, using for each test the same series of disinfectant concentrations. In each test the culture employed was exactly 24 hours old at the time when the test was begun. Results obtained in a representative experiment with phenol and S. aureus are shown in table 1, and the temperature coefficients obtained in a series of seven similar experiments are shown in table 2. The variations in results that occurred in different experiments are quite evident in table 2. However, the maximum deviations of average coefficients in individual experiments from the general series average of 5.0 were less than 20 per cent, and in three of the seven tests were less than 10 per cent. Temperature coefficients for a number of alcohols and phenols are shown in table 3. In general, it is evident that the effect of temperature on bactericidal activity varies with each disinfectant and each test organism. There are differences also with the same disinfectant and test organism at different temperature ranges.

3 INFLUENCE OF TEMPERATURE ON ALCOHOLS Provided temperature coefficients are calculated for a series of successive concentrations in individual experiments and provided there are a considerable number of duplicate experiments, the accuracy of the average results is sufficient to permit their use in calculating results at one temperature from results obtained at another. As an example, there are shown in table 4 calculated and observed results for phenol and S. aureus at 20 C. The cal- TABLE 1 Bactericidal efficiency of phenol againt Staphylococcus aureus at 100 and 200C. DILUTION DISINFECTION TInM TEMPER&TURE COIFFICIENTS minutes minutes Average 4.9 TABLE 2 Temperature coefficients with phenol and Staphylococcus aureus at 100 and 00C. DILUTIONS EXPERIMENT NUMBER AVERAGES Averages culated results at 20 C. are based upon the observed average results of 9 experiments at 10 C., and the observed results at 20 are averages of the results of 13 different experiments carried out at 20 C. In other instances where the amount of experimental data was sufficient to yield an adequate base for calculation, the correspondence between calculated and observed results was as close as that shown in table 4. Where there was less experimental material available, the correspondence was not so close.

4 524 There were greater variations in all instances where comparisons were made between results at very short exposures and those at very long exposures. Results obtained at extremes of exposure times are likely to be variable and inaccurate as compared with results obtained at intermediate exposures. This was noted es- DISINFECTANT TABLE 3 Temperature coefficients of phenols and alcohols TEST ORGANIM E. TYPEOSA TEST ORGANISM STAPH. AUREUS 100 to to to to to to to 500 Phenol Orthocresol Paracresol Resorcinol Orthobutylphenol Parabutylphenol Ethyl alcohol n-butyl alcohol TABLE 4 Observed and calculated disinfection time for phenol and Staphylococcus aureus at 5OC. Dilution OBSERVED AT 100 Time CArx!ULATED TIME AT 200* OBSERVED TIME AT 200 minutes minutes minuts *Calculated Observed Time at 100C. *Calculadtime timeat at (Tempp: Coef.) pecially in experiments with Eberthella typhosa and the two alcohols. With the alcohols, in many instances, results in individual experiments were obtained from a single disinfectant dilution at very short and very long exposures. Thus, the dilutions of the two alcohols which were effective against the test organism at 200C. in 5 minutes required at 100C. many hours' exposure. Such

5 INFLUENCE OF TEMPERATURE ON ALCOHOLS 525 results as were obtained were unreliable and erratic. On the other hand, when greater concentrations were used, each of the alcohols was effective at 10 C. but the disinfection time at 20 C. was too short to be determined by the technique employed. Temperature coefficients for the alcohols at 1O-20'C. are, therefore, not given. SUMMARY The bactericidal efficiencies of phenol, orthocresol, paracresol, orthobutylphenol, parabutylphenol, resorcinol, ethyl alcohol, and n-butyl alcohol against Staphylococcus aureus and Eberthella typhosa were determined by a modified Rideal-Walker technique. Parallel tests were made with each disinfectant and test organism at temperatures 10 C. apart, and temperature coefficients were calculated by dividing the disinfection time in minutes at the lower temperature by the disinfection time at the higher temperature. By averaging results from several concentrations in individual experiments and the results obtained in a considerable number of experiments, it was possible to obtain average temperature coefficients of sufficient accuracy to permit their use in calculating disinfection time at one temperature from results obtained at another. The experimental evidence presented indicates that the effect of temperature on bactericidal activity varies with each disinfectant and each test organism.