IMPAIRMENT OF THE MICROBICIDAL EFFICACY O F FORMALDEHYDE, GLUTARDIALDEHYDE, PERACETIC-ACID, CHLORAMINE-T (N-CHLORO-4-TOLUENESULPHONAMIDE), M-CRESOL, ETHANOL, AND BENZYLDIMETHYLDODECYLAMMONIUMBROMIDE BY BLOOD (MODEL EXPERIMENTS FOR CHEMICAL DISINFECTION OF INSTRUMENTS)

In a preceding paper (Zbl. Hyg. 191 [1991] 457-477) we reported on the dependence of the microbicidal efficacy of active agents of the disin fection of instruments on the amount of coagulated blood adhering to t he instruments. In the present investigation, we were interested in th e dependence of the microbicidal effects on the amount of blood in the solutions of the active agents. Test areas of 2 cm(2) were contaminat ed with 50 and 100 mu l coagulating blood, respectively, containing ce lls of Staphylococcus aureus as test germ. The solutions of the microb icidal agents were contaminated with heparinized blood up to a concent ration of 4% immediately before starting the disinfection and 24 hours before, respectively. After a period of action lasting 1 hour at 20 d egrees C, the relative number of test germs capable of multiplying (N/ N-0) was determined. The concentration of the microbicidal substances reducing the relative number of test germs capable to multiply to 10(- 4) served for estimating the dependence of the microbicidal efficacy o f the agents on the blood content of the solutions. The experimental r esults depended on the thickness of the layer of coagulated blood. The dependence of the efficacy of the microbicidal substances on the bloo d content of the solutions was the higher the thinner the blood layer was. At a thickness of the layer of the coagulated blood of 0.25 mm, a blood content of the solution of 4%, and applying it immediately afte r adding the blood, the concentration of glutardialdehyde had to be 1. 6 times that without blood to reach the same microbicidal efficacy. Wh en applying the solution 24 hours after adding the blood, the concentr ation of glutardialdehyde had to be 4.2 times that without blood. The quaternary ammonium compound reacted faster with the blood than did gl utardialdehyde; the respective factors were 2.6 and 4.5. The concentra tion factors of chloramine T were 3.3 and 3.8. Under the conditions of the test, peracetic acid exhibited small concentration factors: 1.3 a nd 1.6. The microbicidal efficacy of ethanol, formaldehyde and m-creso l soap solution was not or only slightly altered by the amount of bloo d in the solution of the microbicidal agent.