Use of the Gram stain in microbiology

Abstract

The Gram stain differentiates bacteria into two fundamental varieties of cells. Bacteria that retain the initial crystal violet stain (purple) are said to be "gram-positive," whereas those that are decolorized and stain red with carbol fuchsin (or safranin) are said to be "gram-negative." This staining response is based on the chemical and structural makeup of the cell walls of both varieties of bacteria. Gram-positives have a thick, relatively impermeable wall that resists decolorization and is composed of peptidoglycan and secondary polymers. Gram-negatives have a thin peptidoglycan layer plus an overlying lipid-protein bilayer known as the outer membrane, which can be disrupted by decolorization. Some bacteria have walls of intermediate structure and, although they are officially classified as gram-positives because of their linage, they stain in a variable manner. One prokaryote domain, the Archaea, have such variability of wall structure that the Gram stain is not a useful differentiating tool.

Intestinal parasitic and candida infection associated with HIV infection in Cameroon

“…Fecal smears were then stained following the Safranin and Kinyoun method, a modified acid-fast stain technique, to detect oocysts [11]. Third, stools were cultured on Sabouraud's dextrose agar and subsequently subjected to Gram stain for identification of Candida species colonies [12].…”

High-Resolution Visualization ofPseudomonas aeruginosaPAO1 Biofilms by Freeze-Substitution Transmission Electron Microscopy

“…The structural attributes of biofilms have been difficult to study by traditional light microscopic methods (9); these communities are thick (and randomly scatter light), are difficult to image via stains (such as the Gram reaction [6]), and are challenging for phase-contrast microscopy. Confocal scanning laser microscopy has been the preferred method of microscopy because many fluorescent probes are now available and because optical sections can be readily rendered into three-dimensional images with suitable software (43).…”

Decoding Complex Soil Microbial Communities through New Age "Omics"

“…The study of microbes predates to 1600 AD, when Leeuwenhoek described his oral organisms in 1676 [20], which was followed by Robert Koch who designed nutrient media using potato slices or gelatin to isolate bacteria and count them [21]. Later, with the advancement in microscopy and staining techniques like Gram, Ziehl-Neelsen and Schaeffer and Fulton, the identification and characterization of microbes was significantly improved [21,22].…”