Introduction
The Gram staining technique, devised by the Danish scientist Hans Christian Gram in 1884 (Amazon.com: Microbiology: An introduction: 9780134720388: Tortora, … 2019), has stood as a foundational pillar in microbiology, facilitating the categorization of bacteria into two primary groups: Gram-negative and Gram-positive bacterias. The differential staining of the cell wall found in the bacterial species is another technique used to classify and identify bacteria as it provides sufficient information on the physical and structural characteristics found in the bacteria. Different dye behaviors between Gram-negative and Gram-positive bacteria reflect fundamental, cell-wall-related, morphological differences, influencing bacterial pathogenesis, antibiotic susceptibility, and clinical opting on infectious diseases.
Differences between Gram-negative bacteria and Gram-positive bacteria
| Difference | Gram-negative bacteria | Gram-positive bacteria |
| Their cell wall comprises a thin peptidoglycan layer and an outer membrane outside the peptidoglycan layer. | Their cell wall has a thick peptidoglycan layer. | |
| They have an outer membrane. | They lack an outer membrane. | |
| Lipopolysaccharide (LPS), lipoproteins and phospholipids in outer membrane | Lipopolysaccharide (LPS) is not present | |
| Teichoic acids absent | They have Teichoic acids in two classes: Lipoteichoic acid and Wall teichoic acid. | |
| Stain color after Gram staining: Pink or red
After Gram staining, Gram-negative bacteria look pink or red under the microscope because they have a thinner peptidoglycan layer on their cell wall, allowing the CV-1 complex to be washed through the thin peptidoglycan by the alcohol wash. Gram-negative cells will remain colorless unless stained with a counterstain— (Safranin), after which they appear pink or red. |
Stain color after Gram staining: Purple or blue
Following Gram staining, the CV-I complex remains purple or blue in Gram-positive bacteria. The peptidoglycan polymer in their cell wall is thicker, preventing the alcohol wash from disrupting the complex. Hence, Gram-positive cells retain purple or blue, giving them a distinct appearance under the microscope. |
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| They are less susceptible to Beta-lactams such as cephalosporins and penicillin. Their resistance is due to the outer membrane resistance layer since the beta-lactams cannot go through the lipopolysaccharide layer. | They are more susceptible to beta-lactams such as penicillin and cephalosporins. | |
| Susceptibility to lysozyme: More sensitive | Less susceptible because of the thicker peptidoglycan layer | |
| The presence of porins in the outer membrane | Absence of porins. | |
| Susceptibility to detergents: More resistant | Less resistant | |
| Resistance to some antibiotics like polymyxins | More vulnerable to certain antibiotics | |
| Production of endotoxins | Absence of endotoxin production | |
| Forming biofilms is easier. | Biofilms are less likely to form. | |
| Susceptibility to Gram-negative specific medications like tetracycline | Susceptibility to Gram-positive specific medications like vancomycin | |
| The presence of Braun’s lipoprotein in the outer membrane | The absence of Braun’s lipoprotein | |
| Complex outer membrane structure | Simple outer membrane structure | |
| Existence of periplasmic space | Absence of periplasmic space | |
| Susceptibility to environmental stressors: More tolerant | Less tolerant to environmental stressors. | |
| Resistance to complement-mediated killing | More susceptible to complement-mediated killing | |
| Multiple layers in the cell envelope | Fewer layers in the cell envelope | |
| Different lipid composition in the outer membrane | Uniform lipid composition |
In conclusion, the Gram staining technique offers an effective tool for not only the differentiation between the Gram-negative and the Gram-positive but also the identification of the bacteria. Such distinctions are, however, important for designing customized therapies that can help treat bacterial infections; to estimate this gap, healthcare workers need to highlight these differences and administer personalized treatments, thus improving the performance in the fight against infectious diseases without killing the beneficial microbiota.
Reference
Amazon.com: Microbiology: An introduction: 9780134720388: Tortora, … (n.d.). https://www.amazon.com/Microbiology-Introduction-Books-Carte-13th/dp/0134720385
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