Gram Positive And Gram Negative Difference Pdf

gram positive and gram negative difference pdf

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Retain crystal violet dye and stain blue or purple.

Differences between Gram Positive and Gram Negative Bacteria

Most bacteria are classified into two broad categories: Gram positive and Gram negative. These categories are based on their cell wall composition and reaction to the Gram stain test. The Gram staining method, developed by Hans Christian Gram , identifies bacteria based upon the reaction of their cell walls to certain dyes and chemicals.

The differences between Gram positive and Gram negative bacteria are primarily related to their cell wall composition. Gram positive bacteria have cell walls composed mostly of a substance unique to bacteria known as peptidoglycan , or murein. These bacteria stain purple after Gram staining. Gram negative bacteria have cell walls with only a thin layer of peptidoglycan and an outer membrane with a lipopolysaccharide component not found in Gram positive bacteria. Gram negative bacteria stain red or pink after Gram staining.

The cell walls of Gram positive bacteria differ structurally from the cell walls of Gram negative bacteria. The primary component of bacterial cell walls is peptidoglycan.

Peptidoglycan is a macromolecule composed of sugars and amino acids that are assembled structurally like woven material. These molecules are crosslinked together by short peptides which help give peptidoglycan strength and structure.

Peptidoglycan provides protection for bacteria and defines their shape. The Gram positive cell wall has several layers of peptidoglycan. The thick layers of peptidoglycan help to support the cell membrane and provide a place of attachment for other molecules. The thick layers also enable Gram positive bacteria to retain most of the crystal violet dye during Gram staining causing them to appear purple.

Gram positive cell walls also contain chains of teichoic acid that extend from the plasma membrane through the peptidoglycan cell wall. These sugar-containing polymers assist in maintaining cell shape and play a role in proper cell division. Teichoic acid helps some Gram positive bacteria to infect cells and cause disease.

Some Gram positive bacteria have an additional component, mycolic acid , in their cell walls. Mycolic acids produce a waxy outer layer that provides additional protection for mycobacteria, such as Mycobacterium tuberculosis. Gram positive bacteria with mycolic acid are also called acid-fast bacteria because they require a special staining method, known as acid-fast staining, for microscope observation.

Pathogenic Gram positive bacteria cause disease by the secretion of toxic proteins known as exotoxins. Exotoxins are synthesized within the prokaryotic cell and released into the exterior of the cell. They are specific to certain bacterial stains and can cause serious damage to body organs and tissues. Some Gram negative bacteria also produce exotoxins. Gram positive cocci refer to Gram positive bacteria that are spherically shaped.

Two genera of Gram positive cocci noted for their role as human pathogens are Staphylococcus and Streptococcus. Staphylococcus are spherical in shape and their cells appear in clusters after they divide.

Streptococcus cells appear as long chains of cells after division. Examples of Gram positive cocci that colonize the skin include Staphylococcus epidermidis , Staphylococcus aureus , and Streptococcus pyogenes.

While all three are part of the normal human microbiota , they can cause disease under certain conditions. Staphylococcus epidermidis form thick biofilms and can cause infections associated with implanted medical devices. Like Gram positive bacteria, the Gram negative bacterial cell wall is composed of peptidoglycan. However, the peptidoglycan is a single thin layer compared to the thick layers in Gram positive cells. This thin layer does not retain the initial crystal violet dye but picks up the pink color of the counterstain during Gram staining.

The cell wall structure of Gram negative bacteria is more complex than that of Gram positive bacteria. Located between the plasma membrane and the thin peptidoglycan layer is a gel-like matrix called periplasmic space. Unlike in Gram positive bacteria, Gram negative bacteria have an outer membrane layer that is external to the peptidoglycan cell wall.

Membrane proteins, murein lipoproteins, attach the outer membrane to the cell wall. Another unique characteristic of Gram negative bacteria is the presence of lipopolysaccharide LPS molecules on the outer membrane. LPS is a large glycolipid complex that protects bacteria from harmful substances in their environment. It is also a bacterial toxin endotoxin that can cause inflammation and septic shock in humans if it enters the blood.

The lipid A component attaches the LPS to the outer membrane. Attached to the lipid A is the core polyssaccharide. It is located between the lipid A component and the O antigen. The O antigen component is attached to the core polyssaccharide and differs between bacterial species.

It can be used to identify specific strains of harmful bacteria. Gram negative cocci refer to Gram negative bacteria that are spherically shaped. Bacteria of the genus Neisseria are examples of Gram negative cocci that cause disease in humans.

Neisseria meningitidis is diplococcus, meaning that its spherical cells remain in pairs after cell division. Neisseria meningitidis causes bacterial meningitis and can also cause septicemia and shock.

Another diplococcus bacterium, N. Gram negative coccobacillus bacteria have bacterial shapes that are in between spherical and rod shaped. Bacteria of the genus Haemophilus and Acinetobacter are coccobacilli that cause serious infections. Haemophilus influenzae can cause meningitis, sinus infections, and pneumonia. Khatoon, Zohra, et al. Adamik, Barbara, et al. Coureuil, M. Bernhard, Sara, et al. Oikonomou, Katerina, et al.

Share Flipboard Email. Table of Contents Expand. Gram Positive Bacteria. Gram Positive Cocci. Gram Negative Bacteria. Gram Negative Cocci. Regina Bailey. Biology Expert. Regina Bailey is a board-certified registered nurse, science writer and educator. Updated February 06, View Article Sources. Cite this Article Format. Bailey, Regina. Gram Positive vs. What Are Prokaryotic Cells? Structure, Function, and Definition. ThoughtCo uses cookies to provide you with a great user experience.

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In clinical microbiology, phenotypic typing schemes particularly Gram staining are some of the most common and effective techniques for bacteria identification. Discovered in , Gram stain technique has proven to be one of the most useful phenotypic classification systems through which bacteria can be identified based on their staining properties and general morphology. Using this technique, bacteria are classified as either Gram positive or Gram negative. Bacteria are single-celled prokaryotes ubiquitous in nature. As such, they can be found in different types of environments ranging from aquatic to the hot rocks of the Mojave Desert.

We've updated our Privacy Policy to make it clearer how we use your personal data. We use cookies to provide you with a better experience, read our Cookie Policy. Bacterial species, and even specific strains can be differentiated using a number of molecular techniques such as PCR, quantitative PCR, genome sequencing and mass spectrometry. But even without getting into the molecular nitty gritty, there are phenotypic differences between groups of bacteria that can be used to differentiate them. This includes characteristics like their shape bacilli vs cocci for example , growth in particular nutrients and preference for high or low oxygen environments. Depending on the characteristic being studied, bacterial species may be broken down into broad groups, but taken together this information can narrow the possible identities greatly. One such useful classification — if a bacterium is Gram positive or Gram negative - is based on the structure of bacterial cell walls.


What is the gram-negative bacteria and its cell wall structure? ‐ What are the main differences between gram positive and gram negative bacteria?


Gram Positive Bacteria

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Most bacteria are classified into two broad categories: Gram positive and Gram negative. These categories are based on their cell wall composition and reaction to the Gram stain test.

Gram Positive vs. Gram Negative Bacteria

Gram-negative bacteria are a significant cause of infections acquired in both hospital and community settings, resulting in a high mortality rate worldwide. Currently, a Gram-negative infection is diagnosed by symptom evaluation and is treated with empiric antibiotics which target both Gram-negative and Gram-positive bacteria. A rapid and simple diagnostic method would enable immediate and targeted treatment, while dramatically reducing antibiotic overuse. Herein, we introduce a method utilizing a fluorescent derivative of colistin COL-FL , that can directly label the Gram-negative cell wall of live bacteria and universally detect the targets within 10 min. By using the COL-FL assay, we achieved the differential labeling of various Gram-negative pathogens related to hospital-acquired infections, which could be subsequently detected via spectrofluorometry and microscopy.

Gram-negative bacteria are classified by the color they turn after a chemical process called Gram staining is used on them. Gram-negative bacteria stain red when this process is used. Other bacteria stain blue. They are called gram-positive bacteria. Gram-negative and gram-positive bacteria stain differently because their cell walls are different. They also cause different types of infections, and different types of antibiotics are effective against them. Gram-negative bacteria are enclosed in a protective capsule.

Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the gram-staining method of bacterial differentiation. Gram-negative bacteria are found everywhere, in virtually all environments on Earth that support life. The gram-negative bacteria include the model organism Escherichia coli , as well as many pathogenic bacteria , such as Pseudomonas aeruginosa , Chlamydia trachomatis , and Yersinia pestis. They are an important medical challenge, as their outer membrane protects them from many antibiotics including penicillin ; detergents that would normally damage the peptidoglycans of the inner cell membrane; and lysozyme , an antimicrobial enzyme produced by animals that forms part of the innate immune system. Additionally, the outer leaflet of this membrane comprises a complex lipopolysaccharide LPS whose lipid A component can cause a toxic reaction when these bacteria are lysed by immune cells. This toxic reaction can include fever, an increased respiratory rate, and low blood pressure—a life-threatening condition known as septic shock. Several classes of antibiotics have been designed to target gram-negative bacteria, including aminopenicillins, ureidopenicillins, cephalosporins, beta-lactam-betalactamase inhibitor combinations e.


Differences between Gram Positive and Gram Negative Bacteria S.N.; Characteristics; Gram Positive; Gram Negative entire page on the screen, but you can save the table to Drive in landscape as a PDF and it looks great.


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Gram-negative bacteria

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Gram Positive Bacteria: The thickness of the cell wall in gram positive bacteria is around 20 80 nm. Gram Negative.

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