What Are Gram-Positive Rods?

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Gram-positive bacilli, also known as gram-positive rods, are one of the four most common types of bacteria. Bacilli are sometimes called rods because of their straight, stick-like shape. The other major types of bacteria are gram-negative bacilli, gram-positive cocci and gram-negative cocci. Bacteria are known as either gram-positive or gram-negative depending on the thickness of their cell walls.

J.M.C. Gram developed a method for distinguishing gram-postive and gram-negative bacteria.
J.M.C. Gram developed a method for distinguishing gram-postive and gram-negative bacteria.

How Gram-positive Bacteria Are Identified

Gram-positive rods and cocci have a thick cell wall that contains a substantial amount of peptidologlycan, which is made up of amino acids that form chains in cross-linked patterns. The resulting interlocking structure forms a strong cell wall. When gentian violet, a purple dye, touches gram-positive bacteria, the peptidologlycan in their cell walls retains the color and stains the bacteria. Gram-negative bacteria contain much less peptidologlycan in their cell walls and do not hold the color of the dye. The method for distinguishing the two bacteria types was developed by Danish scientist J.M.C. Gram, and it was named for him.

Gram-positive bacteria retain the purple color when stained with gentian violet.
Gram-positive bacteria retain the purple color when stained with gentian violet.

Common Infections Caused by Gram-positive Bacteria

Among the most common infections from gram-positive bacteria are Staphylococcus and Streptococcus. Staphylococcus sometimes affects the skin and can cause a rash or impetigo. Streptococcus is often the culprit with sore throats. Both are gram-positive cocci. Listeria and diphtheria are caused by gram-positive bacilli, as are the exceedingly dangerous botulism, tetanus and anthrax.

Gram-positive bacteria are responsible for several common infections, such as strep throat.
Gram-positive bacteria are responsible for several common infections, such as strep throat.

Antibiotics Used for Gram-positive Bacteria

Several classes of antibiotics are used for gram-positive bacterial infections. The best known is penicillin and its synthetic versions, amoxicillin and ampicillin. Tetracycline and doxycycline are also used, although increasing bacterial resistance has limited their usefulness. A third antibiotic class are the sulfonamides, also known as sulfa drugs. Doctors are prescribing this class of drugs less than previously, as many people are allergic to them, and bacterial resistance has grown.

Penicillins are often used to treat gram-positive bacterial infections.
Penicillins are often used to treat gram-positive bacterial infections.

Friendly Gram-positive Bacteria

Not all bacteria are harmful or cause infections. Several types of bacteria are actually beneficial and are used in food production and to help maintain gut health. Lactobacillus, a gram-positive rod, ferments yogurt and other foods and can contribute to a healthy intestinal tract. Bifidobacterium, another gram-positive bacillus, is also used in food fermentation and to treat diarrhea, ulcerative colitis and other intestinal problems. "Friendly" bacteria such as these are also known as probiotics.

Friendly bacteria, or probiotics, can help maintain intestinal tract health.
Friendly bacteria, or probiotics, can help maintain intestinal tract health.

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