THE EFFECT OF PROTAMINE ON THE MICROBICID E EFFICACY OF FORMALDEHYDE

Testing the ability of commercial compounds to provide an effective di sinfection of instruments requires test conditions that are close to r eality which includes the proper selection of the material used to con taminate the test objects. The adhesion of the material must be strong enough to keep it attached to the test object during and after insert ion into the disinfectant solution. Its characteristics should come as close as possible to those of the contaminations encountered in pract ice. The guideline for instrument disinfectants published by the Rober t Koch-Institute recommends the use of coagulated blood. Accordingly, heparinized sheep blood is mixed with the test germs, and protamin is added to initiate coagulation. In the present investigation we compare d this contamination procedure with a second one, in which coagulation was achieved by adding a CaCl2 solution to citrate blood. We also inc luded agarose as an almost inert contaminant in our experiments. The r esults showed that protamine is able to increase the microbicidal effi cacy of formaldehyde on staphylococci significantly. When these test g erms were embedded either in citrat blood or in agarose, it took about twice the disinfectant concentrations to achieve the same microbicida l effect as with protamine blood (Fig. 1). Remarkably, the results obt ained with citrate blood were the same as those with agarose, regardle ss of the differences in material between the two contaminants. It sho uld also be noted that the microbicidal effect of the formaldehyde pro ved to be almost independent from the amount of contaminant per test a rea, hence, from the thickness of the layer. When M. terrae was employ ed as test germ, the results obtained with protamine blood and citrate blood, respectively, as contaminants were identical (Fig. 2). The sam e was true for the other test germs investigated, except for E. faeciu m (Fig. 3). The addition of even very small amounts of protamine to th e embedding compound, agarose led to a substantially increased efficac y of the formaldehyde against staphylococci (Fig. 4). This effect was especially distinct in suspension (Fig. 5). Whenever the efficacy of f ormaldehyde-containing disinfectants is to be tested and evaluated, on e should be aware of this synergism between protamine and formaldehyde . In these cases, it is advised to employ other contaminating agents, such as coagulated blood prepared by addition of CaCl2 to citrate bloo d.