Escherichia coli is a member of the family Enterobacteriaceae, which includes gram-negative, facultatively anaerobic rod-shaped bacteria (possessing both a fermentative and respiratory metabolism) and which do not produce the enzyme oxidase.

(E. coli) The gram-negative bacterium Escherichia coli is the most numerous aerobic commensal inhabitant of the large intestine.

Gram-variable organisms are those that cannot be grouped as either negative or positive. The appearance of organisms that stain gram-positive or -negative means that the smear contains organisms. These organisms may be pathogenic or nonpathogenic. Further identification is required to interpret the results.

E. coli stains Gram-negative because its cell wall is composed of a thin peptidoglycan layer and an outer membrane. During the staining process, E. coli picks up the color of the counterstain safranin and stains pink.

E coli is a gram-negative bacillus that grows well on commonly used media. It is lactose-fermenting and beta-hemolytic on blood agar. Most E coli strains are nonpigmented. The image below shows Escherichia coli on Gram staining.

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Basic Microbiology. Escherichia coli are typically Gram-negative, rod shaped (2.0–6.0 μm in length and 1.1–1.5 μm wide bacilli) bacteria with rounded ends. The actual shape of these bacteria does, however, vary from spherical (cocci) cells through to elongated or filamentous rods.

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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 bacteria can cause many serious infections, such as pneumonia, peritonitis (inflammation of the membrane that lines the abdominal cavity), urinary tract infections, bloodstream infections, wound or surgical site infections, and meningitis.

The proteobacteria are a major phylum of gram-negative bacteria, including Escherichia coli (E. coli), Salmonella, Shigella, and other Enterobacteriaceae, Pseudomonas, Moraxella, Helicobacter, Stenotrophomonas, Bdellovibrio, acetic acid bacteria, Legionella etc.

Gram positive bacteria have a thick peptidoglycan layer and no outer lipid membrane whilst Gram negative bacteria have a thin peptidoglycan layer and have an outer lipid membrane.

Gram-positive bacteria cause tremendous problems and are the focus of many eradication efforts, but meanwhile, Gram-negative bacteria have been developing dangerous resistance and are therefore classified by the CDC as a more serious threat.

Gram-positive bacteria don’t have this feature. Because of this difference, gram-negative bacteria are harder to kill. This means gram-positive and gram-negative bacteria require different treatments. Though gram-negative bacteria are harder to destroy, gram-positive bacteria can still cause problems.

If bacteria are present, this test can also help your doctor learn if the bacteria are gram negative or gram positive. The difference between gram-negative and gram-positive bacteria can affect their recommended treatment plan. Gram stains can be performed on various types of specimens, including: blood.

Fourth-generation cephalosporins such as cefepime, extended-spectrum β-lactamase inhibitor penicillins (piperacillin/tazobactam, ticarcillin/clavulanate) and most importantly the carbapenems (imipenem/cilastatin, meropenem, ertapenem) provide important tools in killing Gram-negative infections.

The two categories cause different types of infections: Gram-positive infections include methicillin-resistant Staphylococcus aureus (MRSA), strep infections, and toxic shock. Gram-negative infections include salmonella, pneumonia, urinary tract infections, and gonorrhea.

Fungi (in the form of yeasts or molds) can also be initially recognized with the Gram stain, but viruses cannot be seen with a Gram stain. Though Gram stains are useful as initial tests for detecting and identifying general types of bacteria or fungi, results are usually considered preliminary.

Any alteration in the outer membrane by Gram-negative bacteria like changing the hydrophobic properties or mutations in porins and other factors, can create resistance. Gram-positive bacteria lack this important layer, which makes Gram-negative bacteria more resistant to antibiotics than Gram-positive ones [5,6,7].

Gram-positive cocci: Staphylococcus aureus is a gram-positive, catalase-positive, coagulase-positive cocci in clusters. S. aureus can cause inflammatory diseases, including skin infections, pneumonia, endocarditis, septic arthritis, osteomyelitis, and abscesses.