[The activity of formaldehyde, glutardialdehyde, peracetic acid, chloramine T (N-chlor-4-toluolsulfonamide), m-cresol, ethanol and benzyldimethyldodecylammonium bromide against bacteria which are found in coagulated blood. (Model studies for chemical disinfection of instruments].

The experiments were performed using frosted glass as carrier with its surface being contaminated with whole blood containing Staphylococcus aureus as test organism. At the time of sampling, a heparin preparation was added to the blood to prevent premature coagulation. After addition of the staphylococci, coagulation was initiated by means of a heparin antagonist. 10, 25, 50, 100, and 150 microliters, respectively, of the blood were homogeneously spread on rectangular test areas of 10 x 20 mm. After the blood had coagulated, each of the test objects was placed in 15 ml of the solution (20 degrees C) containing the active ingredient tested for 60 min. After that, the test objects were removed from the disinfectant and, in order to inactivate any adhering active components, treated with a neutralizing solution of suitable composition. The number of viable germs (colony-forming units) was determined quantitatively. The blood samples were ground together with quartz sand. Aliquots of the diluted suspensions were mixed with molten agar medium. The plates then were incubated at 37 degrees C over a period of 14 days. The relative number of viable germs (N/No) per test object was calculated from the number of colonies. Plotting of the microbicidal effects obtained (log N/No] versus the concentration of the active substance (see Figs. 1-3) yielded curves differing in some characteristics as e.g. curvature, slope of the lower curve section (log N/No). less than -3), concentration range according to the layer thickness of the contamination. To visualize the reduction of the efficacy of the respective disinfectants caused by blood, the concentrations of active components were determined which are necessary to achieve a microbicidal effect of log (N/No) = -4. These concentrations were plotted versus the amounts of blood per test area (Fig. 4). The resulting curve for formaldehyde was slightly U-shaped. With a raising amount of blood, the concentration required slightly decreased in the beginning and increased again from an amount of ca. 100 microliter blood per test area. For all other active substances, the required concentration of these substances increased with the amount of blood used. The curve obtained for ethanol exhibited the lowest slope. The slope of the curves increased in the following order: ethanol, m-cresol, peracetic acid, chloramine T, glutardialdehyde, benzyldimethyldodecylammoniumbromide. The curves for chloramine T and glutardialdehyde nearly paralleled each other.(ABSTRACT TRUNCATED AT 400 WORDS)