Antibiotics for Gram Negative Bacteria Infections

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What is Gram Negative Bacteria?

A gram negative bacteria is a bacteria which does not retain the violet stain during the gram staining procedure. It is different from a gram positive bacteria, which does retain the violet stain. Another difference between gram negative and gram positive bacteria is that gram negative bacteria feature a protective outer membrane.

Most of the bacteria in the gastrointestinal tract are gram negative. Some examples of gram negative bacteria include E-coli and Salmonella. Several diseases are caused by gram negative bacteria, including venereal diseases and bacterial meningitis. Cholera and the bubonic plague are also caused by gram negative bacteria.

There are several antibiotics for treating gram negative bacterial infections, including levofloxacin, moxifloxacin, ampicillin, chloramphenicol, streptomycin, and nalidixic acid.


Levofloxacin is a fluoroquinolone antibiotic which is effective against gram negative bacteria and gram positive bacteria. It works by inhibiting an enzyme responsible for separating DNA during replication. A side effect of the drug is tendinitis and possible tendon rupture. The elderly are more at risk for this, but all ages are at a higher risk for rupturing the Achilles tendon.


There are several more fluoroquinolone antibiotics for gram negative bacteria, including moxifloxacin. It prevents cell division by preventing enzymes from separating DNA. In addition to tendinitis and tendon rupture, moxifloxacin can cause peripheral neuropathy. This involves numbness and pain in the hands and feet. It can also produce tingling or burning sensations.


Ampicillin is a beta-lactam antibiotic that is effective against gram negative bacteria. It works by disrupting the synthesis of proteins required for the membrane of the bacteria. Some of the side effects of ampicillin include nausea, vomiting, and loss of appetite. It can also affect the normal bacteria in the gastrointestinal tract, leading to inflammation.


Chloramphenicol is produced from the bacteria Streptomyces venezuelae. It attacks gram negative bacteria by interrupting protein synthesis. This prevents the bacteria from producing the proteins it needs. A potential side effect of this antibiotic is aplastic anemia, which is a condition in which the bone marrow does not produce enough new cells for the body.


Streptomycin is an aminoglycoside that is produced from the bacteria Spectromyces griseus. It works by binding to the ribosomes in gram negative or gram positive bacteria. This prevents the bacteria from producing proteins. This antibiotic is effective at treating tuberculosis. A side effect of this antibiotic is kidney damage and deafness.

Nalidixic Acid

Nalidixic Acid is a chemotherapy drug which is effective against gram negative bacteria. It works by inhibiting DNA replication through enzyme inhibition. It is often used to treat urinary tract infections. A common side effect of nalidixic acid is skin rash.


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3. “Ampicillin and Bacteria.” Newton Ask a Scientist.

4. “Common Antibiotics.” Think Quest.