Zentralblatt fur Bakteriologie, Parasitenkunde, Infektionskrankheiten und Hygiene. Erste Abteilung Originale. Reihe B: Hygiene, praventive Medizin最新文献

Bacteria which have been treated by a disinfectant may be partially damaged so that they will be able to survive and to multiply only if all environmental factors are kept as optimal as possible. Otherwise no growth at all is obtained and the disinfectant solution will be wrongly considered as active. Therefore the technique of the post-medication recovery of surviving microorganisms is a matter of great importance. Since our aim is to elaborate a quantitative test, the counting technique using pour or streak plates is investigated here. In contrast to the results of viable counts of normally cultivated P. aeruginosa (Tables 1 and 2), the colony counts of phenol-treated bacteria gain higher figures when the spread plate method is used instead of the pour plate technique (Table 3). - Out of nine solid media examined (Table 4), four culture media are considered to be superior to the others (Table 5). They are Davis Agar, the Nutrient Agar of the German pharmacopoeia, the Nutrient Agar proposed by the APHA, and Tryptone Soy bean peptone Agar. Further investigation on the influence of the recovery medium is needed since there is stated that significant differences are obtained when three preparations of the same formulation are compared (Table 6). Finally the author observed that the volume of the culture medium affects the survival rate (Table 8). The recovery of disinfectant-treated bacteria is found to be very complex; further research on this domain should be encouraged.

A matter of special concern in disinfectant testing is the preparation of the bacterial suspension that shall be exposed to the action of the disinfectant. In the present paper attention is drawn to three details of the testing method being determinative for the resistivity of the test organism and for the degree of standardization of the test results. - In the first place the influence of the nutrient medium used in the cultivation of the test organism has been investigated. Sixteen culture media (Table 1) have been compared. The resistance of Pseudomonas aeruginosa to phenol depends on the formulation of the preparatory medium: significantly more bacteria survive if the test organism is grown on the nutrient agar following the German pharmacopoeia (Table 2). Further the author has investigated the effect of the temperature and the length of the initial culture incubation period (Tables 3 and 4). Here also the differences among temperatures (37, 32 and 22 degrees C) or incubation periods (48, 24 and 18 h) are statistically significant. The highest numbers of survivors are found when the initial culture is incubated at 37 degrees C and for 48 h. Whereas the resistance of the test culture is determined by these three factors, the variability of the test results is not. The coefficients of variation calculated for the different initial culture media, the three incubation temperatures or the three incubation periods show no differences among these test conditions.

The preceding test results appear to favour the impression method used for the testing of surface disinfection procedures. Further investigations were concerned with the selection of a suitable germ carrier. The high recovery rate of the bacteria and the invariably uniform quality of the germ carrier are the decisive criteria. Since a dependence on the type of germ was also to be expected, we checked Staph. aureus, Str. faecalis, E. coli, Kl. pneumoniae and P. aeruginosa for their behaviour on PVC, varnished wooden surfaces, V 2A, rough and smooth glass, resopal, ceramic tiles with dull and glazing finish as well as on plywood. The germ carriers were contaminated quantitatively, dried, sprayed with distilled water to stimulate disinfection and examined after they were allowed to react for a period of 6 hours. A set of 10 germ carriers was examined simultaneously with 10 Rodac impressions. The data were checked by variance analytical methods and evaluated on the mean (or median) values. It was found that while the initial germ number was kept equal OP tiles and V 2A steel produced the highest germ yield. Plywood proved largely unsuitable. Among the test germs, E. coli and Kl. pneumoniae had the lowest adhesion; it was inferior to that of staphylococci and pseudomonads. However, for these 4 germ types 3 impressions per germ carrier suffice for a reliable assessment based on computations. The yield amounts to more than 90 per cent. 94 per cent of the Streptococci were also recovered with 3 impressions, but the absolute germ quantity was low. The use of this type of germ can be recommended only with reservation.

Based on the findings obtained from the previous experiments (information I-VI), a proposal is made for the examination of surface disinfection procedures under conditions roughly resembling those prevailing in practice. This test allows the action of the disinfectant to be calculated, while making due allowance for the natural rate of kill. The results of three tests with a liminally effective disinfectant concentration extensively agreed with each other. This permits the conclusion that the method has reached optimal standardization.