Gram Staining of Bacteria from Environmental Sources

Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - The University of Arizona
Demonstrating Author: Luisa Ikner

The spectrum of research in environmental microbiology is broad in scope and application potential. Whether the work is bench-scale with known bacterial isolates, or in the field collecting soil or water samples containing unknown bacterial isolates, the ability to quickly and visually discern culturable populations of interest remains of great import to environmental microbiologists even today with the abundance of molecular techniques available for use. This video will demonstrate one such technique, known as Gram staining.

1. Sample Collection

Collect soil sample and transport to the laboratory for microbial analysis.
In the lab, weigh a 10 g sample using an analytical balance.
Dilute the sample 1:10 into 95 mL of phosphate-buffered saline (10 parts soil is equivalent to 5 parts aqueous liquid), and vortex to mix (Figure 2, Step 1).
Perform subsequent 1:10 dilutions up to at least 10^-5 g soil per mL, and spread-plate selected dilutions in replicates of two or three onto

The Gram stain is used in the many sub-fields of both environmental and clinical microbiology. Water quality scientists may use the Gram stain as a confirmatory tool for the detection of fecal bacteria in water samples. Bacterial isolates from soils are Gram stained in order to further characterize culturable soil communities. For environmental microbiologists, Gram stain aids in the categorization of bacterial populations according to cell wall structure. This, in turn, provides information about the general ability of

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