Variations in the gram staining results caused by air moisture.

Abstract

The exposure of heat-fixed bacterial smears to relative humidities of 0, 52 and 98%, following the iodine step in a dry Gram stain procedure, markedly influenced the rate of decolorization upon exposure to 95% ethyl alcohol. If a single decolorization time were used to give a proper Gram differentiation after exposure to 98% relative humidity, this decolorization time might not result in proper Gram differentiation following exposure to 0% relative humidity. Different organisms varied in the degree of their response to changes in humidity. Hence the “degree of Gram-positivity,” as compared with other organisms, differed with changes in relative humidity. When Neisseria catarrhalis was compared with strongly Gram-positive and Gram-negative organisms, it was always found to be in an intermediate position in its Gram characteristics regardless of the relative humidity used. Because of the intermediate position of this organism, its proper Gram differentiation would require a precise definition of both the de...