Gram-Negative Bacteria in Indoor Environments
The designation of a bacterium as “Gram-negative” is based on the reaction of the organism in the Gram stain test. This test quickly classifies bacteria into two major groups based on the structure of their cell walls.
The cell walls of Gram-negative bacteria consist of an outer membrane and a thin peptidoglycan layer. This cell wall cannot retain the crystal violet (blue/purple), but is stained with the counterstain, sadarnin (red). This difference in cell wall structure translates into differences in how these two groups of organisms behave in the environment. Gram-negative organisms tend to be more vulnerable to drying due to their thinner cell wall, but less susceptible to cleaning agents as they possess an outer membrane that acts as a barrier to the uptake of sanitizers and disinfectants.
The concentrations of Gram-negative bacteria in indoor environments depend on a number of factors. These include the ventilation rate of the space, the presence of animals, and the presence of standing water or sewage.
In ISO-classified areas, the main source of Gram-negative microbial contamination is sink drains, refrigerator condensate pans, or other sources of standing water.
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