Gram Lab Gram Staining Lab

The Gram staining of bacteria is one of the most important tests in identifying specific bacterial strains, and is usually the first test performed when medical or research laboratories need to identify an unknown bacteria (Xu, 1997; AACC, 2011). Named for the inventor of the technique, Hans Christian Gram, Gram staining first came into use in Gram's own Danish medical and research practice in 1882, and became very widely known and used after the details of the technique were published in 1884 (Xu, 1997). Though some adjustments can be made to the original technique without losing effectiveness, the basic process of Gram staining has remained unchanged for over a century, and is as effective and essential a test today as it was in the latter half of the nineteenth century (Xu, 1997).

Simply put, the Gram staining test often (though not always) allows the researcher to determine the broad class of bacteria that an unknown species belongs to by using dyes and washes that are absorbed and retained differently by different bacteria (AACC, 2011). Crystal violet dye is the standard dye used in the first step of Gram stain...

Those bacteria that retain the dye and thus take on a crystal violet hue are called Gram positive, while those bacteria that do not retain the dye (and are usually stained with another dye to provide better contrast in subsequent steps of the test are Gram negative (AACC, 2011; Xu, 1997).
Steps in Gram Testing

The first step of Gram stain testing, after properly preparing a slide with a smear of bacterial culture, is to add crystal violet stain to the slide containing the culture smear in order to allow Gram positive bacteria to absorb the dye (Xu, 1997). The dye only needs to set for ten seconds to up to a minute, though it can be even more immediate for very thinly prepared slides (Xu, 1997). After the staining, washing away the excess dye with a thin and gentle stream of water (taking care not to wash off the sample itself) is necessary, and the sample is then saturated in an iodine solution and rinsed again, this time in order to bring out the…