Gram staining

Gram staining

Gram staining is a fundamental and widely used microbiological technique that differentiates bacteria into two major groups—Gram-positive and Gram-negative—based on the structural and chemical properties of their cell walls. Developed by Danish bacteriologist Hans Christian Gram in 1884, this staining method remains a cornerstone in bacterial identification, guiding clinical diagnosis and treatment decisions as well as research and environmental microbiology.

Principle of Gram Staining

The core principle of Gram staining lies in the differential retention of the primary dye, crystal violet, by bacterial cell walls during a solvent-based decolorization step. Gram-positive bacteria possess a thick, multilayered peptidoglycan cell wall (approximately 50–90% of the cell envelope), which traps the crystal violet-iodine complex and resists decolorization, causing these cells to appear purple or blue under the microscope. In contrast, Gram-negative bacteria have a thinner peptidoglycan layer (about 10% of the cell envelope) surrounded by an outer membrane rich in lipids. The alcohol or acetone-based decolorizer dissolves this lipid outer membrane and washes out the crystal violet-iodine complex, rendering Gram-negative bacteria colorless until counterstained with a secondary dye such as safranin or basic fuchsin, which stains them pink or red.

Clinical and Microbiological Significance

Gram staining is typically the first diagnostic test performed on clinical specimens such as blood, sputum, cerebrospinal fluid, and wound exudates. It provides rapid, preliminary information about the bacterial morphology (cocci, bacilli, or spirilla) and Gram reaction, which helps guide empirical antibiotic therapy and infection control measures. 

Beyond clinical diagnostics, Gram staining aids in bacterial classification and research, environmental monitoring, and quality control in food and pharmaceutical industries.

The Gram stain remains an indispensable microbiological technique due to its simplicity, speed, and diagnostic value. By exploiting differences in bacterial cell wall architecture, it enables rapid differentiation of bacteria into Gram-positive and Gram-negative groups, facilitating early clinical decision-making and advancing microbiological research.

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orb1566760-8x5ml
Discontinued
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21770020-1
 100mL 
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 250mL 
21770020-3
 500mL 
27100-01
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25036-1
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PL.4961
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