Effect of disinfection on number and stainability of gram-positive bacteria

Evidence provided by the Brown and Brenn stain for the presence of bacteria in fixed tissue sections depends on the ability to demonstrate them by staining. Previously, in a model experiment, it has been shown that demineralizing agents reduce the number of blue-staining Gram-positive bacteria (Wijnbergen & Van Mullem 1987). In the present study the influence of a structure-destroying disinfectant, a structure-preserving disinfectant or heat disinfection on number and stainability was investigated using S. faecalis suspensions. Numbers were determined using a haemocytometer, and percentages of blue-staining organisms were ascertained from smears. Immediately after disinfection the relative number of Gram-positive staining bacteria was reduced by a factor of three for chlorhexidine, almost two for alcoformol, and was slightly reduced by heat. After 4 days of storage the reduction factors were 90, 4, and 2, respectively. After 14 days of storage the reduction factors were infinite, 30 and 5, respectively. These results were explained on the basis of the rate of cell wall destruction evoked by the respective agents.