Skip to main content

How Major Antibiotics Work and Facts About Arylomycins

Linda Crampton is an experienced teacher with a first-class honors degree in biology. She writes about the scientific basis of disease.

This is a gram-positive bacterial cell. Some bacteria have a spherical or spiral shape.

This is a gram-positive bacterial cell. Some bacteria have a spherical or spiral shape.

Antibiotics and Disease Treatment

Antibiotics are vital chemicals that destroy the bacteria that make us sick. The methods of action of five major categories of antibiotics are described below. The drugs in the categories are commonly prescribed to treat disease. Unfortunately, some of them are losing their effectiveness.

Antibiotic resistance in bacteria is a serious problem at the moment and is becoming worse. Some diseases are much harder to treat than they were in the past. Discoveries of new and potentially important antibiotics are always exciting. One group of chemicals that may provide us with effective drugs to fight bacteria is the arylomycins.

This article discusses:

  • beta-lactams
  • macrolides
  • quinolones
  • tetracyclines
  • aminoglycosides
  • arylomycins

The first five classes of antibiotics listed above are in common use. The last one isn't used yet but may be in the future.

Why Don't Antibiotics Harm Our Cells?

Our body is made of cells. Antibiotics are able to harm bacterial cells but not ours. The explanation for this observation is that there are some important differences between the cells of bacteria and those of humans. Antibiotics attack a feature that our cells don’t possess or that is slightly different in us.

The action of current antibiotics depends on one of the following differences between bacteria and humans. Bacterial cells are covered by cell walls while ours aren't. The structure of the cell membrane in bacteria and humans is different. There are also differences in the structures or molecules used to make proteins or copy DNA.

The choice of antibiotic depends on a variety of factors. One is whether the drug is a narrow-spectrum antibiotic (one that affects a narrow range of bacteria) or a broad-spectrum medication that is effective against a wide range of bacteria. Other factors that are considered are how effective the drugs are at treating a particular disease and their potential side effects. Gram-positive bacteria sometimes require a different treatment from gram-negative ones.

Cell wall of a gram-positive bacterium

Cell wall of a gram-positive bacterium

Gram Staining

Gram staining distinguishes gram-positive cells from gram-negative ones. Gram-positive cells look purple after the staining procedure and gram-negative ones look pink. The different results reflect differences in structure. The staining system was created by a Danish bacteriologist named Hans Christian Gram (1853–1938). Some publications capitalize the word "Gram" when describing the staining system for this reason.

A gram-positive cell is covered by a cell membrane, which is in turn covered by a thick cell wall made of peptidoglycan. Gram-negative cells have a thinner cell wall and a membrane on both sides of it.

Gram staining is of medical as well as scientific interest. Some antibiotics work on gram-positive bacteria but not gram-negative ones, or vice versa. Others work on both types of bacteria but may be more effective at killing one type than the other. It's important to note that an antibiotic for gram-positive microbes (or gram-negative ones) may not work for every species or strain of bacteria in the group.


Beta-lactam or β-lactam antibiotics are broad-spectrum medications. They work against gram-positive and gram-negative bacteria but are generally more effective against the first type.

The beta-lactam group includes penicillin, ampicillin, and amoxicillin. Penicillin is a natural antibiotic made by a mold, which is a type of fungus. Most antibiotics were discovered in fungi or bacteria, which produce the chemicals to destroy the organisms that can harm them. The chemicals are normally produced and released in a process that doesn't harm the individual that makes them. Ampicillin and amoxicillin are semi-synthetic drugs derived from penicillin. Cephalosporins and carbapenems are also beta-lactam antibiotics.

The benefit of beta-lactam antibiotics is related to the fact that bacteria have a cell wall around their cell or plasma membrane while our cells don’t. The peptidoglycan wall is a relatively thick and strong layer that protects the bacterial cell. The cell membrane performs vital functions but is much thinner than the wall.

Peptidoglycan contains chains of alternating NAG (N-acetylglucosamine or N-acetyl glucosamine) and NAM (N-acetylmuramic acid) molecules, as shown in the illustration above. Short cross-links made of amino acids connect the chains and give strength to the wall. One of the steps in the formation of the cross-links is controlled by penicillin-binding proteins (PBPs). Beta-lactam antibiotics bind to PBPs and prevent them from doing their job. The cross-links are unable to form and the weakened cell wall breaks. The bacterium dies, often as a result of fluid entering the cell and causing it to burst.


Like many antibiotics, macrolides are natural chemicals that have given rise to semi-synthetic versions. Erythromycin is a common macrolide. It's made by a bacterium once named Streptomyces erythraeus. The bacterium is currently known as Saccharopolyspora erythraea.

Macrolides are effective against most gram-positive and some gram-negative bacteria. They inhibit protein synthesis in the bacteria, which kills the microbes. Proteins are a vital component of cell structure and function.

The process of protein synthesis can be summarized as follows.

  • DNA contains chemical instructions for making proteins. The instructions are copied into messenger RNA or mRNA molecules, a process known as transcription.
  • The mRNA goes to cell structures called ribosomes. The proteins are made on the surface of these structures.
  • Transfer RNA or tRNA molecules bring amino acids to the ribosomes and "read" the instructions in the mRNA.
  • The amino acids join in the correct order to make each of the required proteins. The process of building a protein molecule on the surface of a ribosome is known as translation.

Macrolides bind to the surface of bacterial ribsomes, stopping the process of protein synthesis. Ribosomes contain two subunits. In bacteria, these are known as the 50s subunit and the 30s subunit. The second subunit is smaller than the first one. (The s stands for Svedberg unit.) Macrolides bind to the 50s subunit. Our ribosomes consist of a 60s and a 40s subunit.


Quinolones are found in various places in nature, but the ones used as medicines are generally synthetic. Most quinolones contain fluorine and are known as fluoroquinolones. Ciprofloxacin is a common example of a fluoroquinolone. Quinolone antibiotics are effective against both gram-positive and gram-negative bacteria.

A bacterial cell divides to make two cells in a process called binary fission. Before the division starts, the DNA molecule in the cell replicates, or makes a copy of itself. This enables each of the cells produced by fission to have an identical copy of the molecule.

A DNA molecule consists of two strands wound around each other to form a double helix. The helix unwinds in one section after another in order for replication to occur. DNA gyrase is a bacterial enzyme that helps to relieve strains in the DNA helix as it unwinds. The strains develop in areas that become "supercoiled" as the DNA helix unravels.

Quinolone antibiotics kill bacteria by inhibiting DNA gyrase. This stops DNA from replicating and prevents cell division. In some bacteria, quinolones inhibit an enzyme called topoisomerase IV instead of DNA. This enzyme plays a role in relaxing DNA supercoils and can't do its job if it's inhibited.

Possible Side Effects of Fluoroquinolone Use

Quinolones have been widely prescribed because they can be very helpful. Like all medications, they can cause side effects. These effects may be mild, but unfortunately some people experience major problems after using the drugs. Scientists are now paying attention to this situation and are investigating the effects of the medications.

There is enough evidence of potential harm from fluoroquinolones for the FDA (Food and Drug Administration) to issue a warning about the use of the antibiotics. The FDA is a United States government organization. The organization says that the drugs can cause "disabling side effects involving tendons, muscles, joints, nerves and the central nervous system. These side effects can occur hours to weeks after exposure to fluoroquinolones and may potentially be permanent". The document containing the warning is listed in the "References" section below.

Despite the FDA's warning, the organization says that in some serious illnesses the benefits of fluoroquinolones outweigh the risks. It also says that the drugs should still be used to treat certain conditions for which no other effective treatment is available.

Fluoroquinolones have risks and benefits that should be considered very carefully. It’s important that both health care providers and patients are aware of both the risks and benefits of fluoroquinolones and make an informed decision about their use.

— Edward Cox, M.D., Food and Drug Administration

Tetracyclines and Aminoglycosides

Facts About Tetracyclines

The first tetracyclines were obtained from soil bacteria in the genus Streptomyces. As is the case with most antibiotics, semi-synthetic forms are now produced. Tetracycline is the name of a specific antibiotic in the tetracyclines category. It's sold under various brand names, including Sumycin. It's most notable side effect is that it can cause permanent staining of the teeth in young children.

Tetracyclines are broad-spectrum antibiotics characterized by four rings in their molecular structure. They kill gram-positive and gram-negative bacteria that are aerobic (ones that require oxygen in order to grow). They are much less successful at destroying anaerobic bacteria. Like macrolides, they join to the bacterial ribosome and inhibit protein synthesis. Unlike macrolides, they bind to the 30s subunit of the ribosomes.

Facts About Aminoglycosides

Aminoglycosides are narrow-spectrum antibiotics. They affect aerobic, gram-negative bacteria and some anaerobic gram-positive bacteria in the class Bacilli. Streptomycin is an example of an aminoglycoside. It's produced by a bacterium named Streptomyces griseus. Like tetracyclines, aminoglycosides harm bacteria by binding to the 30s subunit of the ribosome and thereby inhibit protein synthesis.

Unfortunately, aminoglycosides sometimes cause harmful side effects. They can be toxic to the kidney and the inner ear. They cause sensorineural hearing loss and tinnitus in some patients.

The ability of a bacterium to survive in the presence of antibiotics is known as antibiotic resistance. Arylomycins could be useful in hindering antibiotic resistance because they attack bacteria in a different way from current antibiotics.

Development of Antibiotic Resistance

Many antibiotics are not as helpful as they once were due to the development of antibiotic resistance. The process happens because bacteria obtain genes from other bacteria or experience changes in their own collection of genes over time.

Individual bacteria that have obtained or developed a helpful gene variant survive when exposed to an antibiotic. They pass a copy of the beneficial variant to their offspring during reproduction. Individuals without the variant will be killed by the antibiotic. As this process repeats, the population will gradually become resistant to the drug.

Unfortunately, scientists expect bacteria to develop resistance to any antibiotic given enough time. We have the ability to slow this process down by using antibiotics only when necessary and by using them correctly when they are prescribed. This would give us more time to find new drugs. A new antibiotic group that might be helpful in the fight against bacteria is the arylomycin one.

The white circles in the dishes above contain antibiotics. The clear areas represent regions where the bacterial culture has been killed by antibiotics. Bacteria that are able to grow around the white circles are resistant to the antibiotics.


Arylomycins fight gram-negative bacteria. Though there are exceptions, gram-negative bacteria are often more dangerous for us. The chemicals are of interest because they kill bacteria by a different method from other antibiotics that are used medicinally.

Most of our current antibiotics destroy bacteria by interfering with the cell wall, the cell membrane, or protein synthesis. A few affect the structure or function of DNA or interfere with folic acid synthesis. (Folic acid is a form of vitamin B.) Arylomycins work by a different mechanism. They inhibit a bacterial enzyme called bacterial type 1 signal peptidase. Since we haven't used arylomycins as antibiotics yet, many bacteria may still be susceptible to their effects.

In their natural form, arylomycins kill a narrow range of gram-negative bacteria and aren't very powerful. Researchers have recently created an artificial version known as G0775, which seems to be both more effective and to have a broader spectrum of activity. The discovery is exciting. No new antibiotic for gram-negative bacteria has been approved in over fifty years in the United States.

Outer layers of a gram-negative bacterium

Outer layers of a gram-negative bacterium

Inhibition of Signal Peptidases

Signal peptidases are enzymes that remove an extension from proteins called the signal peptide. The removal of this extension activates the proteins. If signal peptidases are inhibited, the relevant proteins aren't activated and can't carry out their functions, which are essential for the life of bacterial cells. As a result, the cells die.

In gram-positive cells, the signal peptidase enzyme is located near the surface of the cell membrane. In gram-negative cells, it's located near the surface of the inner membrane. In either case, if we could administer a chemical that inactivates the signal peptidases, we could kill bacteria. G0775 may be a suitable chemical.

Drugs designed to attack gram-negative cells have to travel through the outer membrane and the peptidoglycan layer (or the cell wall) in order to reach the inner membrane. This is one reason why it's often hard to create effective antibiotics for the cells. G0775 is able to penetrate the outer layers of the cell and reach the signal peptidase, however.

One problem with G0775 is that the drug has been tested in isolated cells and mice but not (as far as I know) in humans. The good news is that it has destroyed a range of bacteria, including gram-negative, gram-positive, and multidrug resistant bacteria.

Antibiotic Benefits and Problems

The actions of arylomycins aren't as well understood as those of many other antibiotics. Another problem is that a concern about toxicity needs to be investigated. The arylomycin molecule has some structural features that remind certain researchers of molecules that are toxic to the kidneys. They need to find out whether the similarity is unimportant or something to worry about.

Some additional candidates for new antibiotics have been found. It takes time to prove that a drug is both helpful and safe for humans. Hopefully, new candidates will continue to appear and tests will show that both optimized arylomycin and other potentially helpful chemicals are safe for us.


This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2018 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on March 21, 2020:

Thank you for the interesting comment, Peggy. Resistance to antibiotics is certainly becoming a major problem. I hope some good solutions are found soon.

Peggy Woods from Houston, Texas on March 21, 2020:

Antibiotic resistance is becoming a huge problem. People are partially to blame by not finishing the prescribed dosage when they are given prescriptions. Of course, the bacteria are also morphing over time. It is a complex problem. Hopefully, new lines of defense will soon emerge over time that are effective and safe for human consumption. Nothing is static when it comes to medicine.

Linda Crampton (author) from British Columbia, Canada on August 14, 2019:

It's sad that fluoroquinolone antibiotics have caused problems. We need help to fight harmful bacteria, but whatever method is used, it must be safe for us. I appreciate your comment.

RTalloni on August 14, 2019:

Thanks for this look at antibiotics. G0775 is an exciting discovery. We have much to be thankful for in modern medical advances. The suffering caused by fluoroquinolone drugs is something I am familiar with so I'm always interested in learning more about antibiotics in case of future need. That it took doctors so long to pay attention to what patients were experiencing due to fluoroquinolone drugs has so many ramifications, resulting in a serious lack of trust, that one can only hope that the lessons will not be dismissed in future research.

Linda Crampton (author) from British Columbia, Canada on September 29, 2018:

Thank you for such a kind comment, Devika. I appreciate it very much.

DDE on September 29, 2018:

I think all your hubs are beneficial to someone in some way. The research you time taken to make your hubs perfect and appealing to readers is just amazing!

Linda Crampton (author) from British Columbia, Canada on September 23, 2018:

Hi, Adrienne. Thanks for the visit. It is an important and scary topic. We badly need new antibiotics.

Adrienne Farricelli on September 23, 2018:

Linda, this is a very important topic. It is very scary to think about antibiotic resistance. The inventor of penicillin, Alexander Fleming predicted this many years ago.

Linda Crampton (author) from British Columbia, Canada on September 19, 2018:

Thanks for the suggestion, Manatita.

manatita44 from london on September 19, 2018:

I forgot to say that it may be worth developing an Index like your name sake Linda L. Some of your work are very beneficial and time-lasting.

Linda Crampton (author) from British Columbia, Canada on September 19, 2018:

I appreciate your comment, as always, Manatita. Thank you for sharing the information. We need to explore new ways to treat disease as antibiotics become less effective.

manatita44 from london on September 19, 2018:

A very thorough and educational piece. This one, like some of your others, are very much my field. Researchers have been waging war on antibiotics for some time, simply because antibiotics are waging or have began to wage war on us.

American nuturopaths, like Dr Morse and Grundy (Grundy is actually unusual, as he is a Consultant Surgeon) have been waging their own wars by the use of pre and probiotics, increasing their efficacy with time. Grundy has a book called the Plant Paradox, you may like it.

There does seem to be scope for hope, but you will know that this is an ever-changing environment and so much can happen. Thank you so much!!

Linda Crampton (author) from British Columbia, Canada on September 18, 2018:

Hi, Prashanth. Thanks for the comment. I have read about some interesting research in mice that is related to what you’ve said. The researchers found that the immune system of the mice was less effective after the administration of the antibiotic. Other research suggests that when antibiotics kill good bacteria in the gut they indirectly harm the host. I’ve also read that some antibiotics may affect mitochondrial function. It’s been suggested that this is because mitochondria are believed to have once been bacteria. It’s a fascinating idea biologically, but the situation is worrying. We need safe and effective antibiotics.

Prashanth Lakshmana from BENGALURU, INDIA on September 17, 2018:

A great article, Linda. These are some really interesting facts about these drugs. A lot of antibiotics these days do interfere with some bodily functions to achieve their purpose. In the process, they also do reduce the capacity of the body to strengthen its own immunity, which is a major concern as many bacteria are becoming resistant to these drugs.

Linda Crampton (author) from British Columbia, Canada on September 17, 2018:

Your alternate treatment is interesting, Jackie. Thanks for sharing the information.

Jackie Lynnley from the beautiful south on September 17, 2018:

Very interesting. I try my best to stay away from antibiotics just in case I seriously need it one day. (Which I did need a very different one for RMSF from tick bite.)

I use garlic oil and oregano oil capsules as a replacement and they do seem to work well for me.

Linda Crampton (author) from British Columbia, Canada on September 17, 2018:

That sounds like an unpleasant side effect of antibiotic use, Bede. I hope potentially helpful antibiotics are tested well to determine safety and side effects and then released for public use soon after that. We need new medications to treat diseases.

Bede from Minnesota on September 17, 2018:

Hi Linda, I was unaware of how exactly antibiotics work, or are supposed to work. Thanks for explaining the process well. It will be interesting to see if G0775 works on humans. If so, let’s hope the FDA doesn’t delay its introduction on the market. It’s quite a tricky science to know which antibiotics to use and avoiding side effects. I had to take some antibiotics a few years ago but they caused my liver enzymes to elevate.

Linda Crampton (author) from British Columbia, Canada on September 17, 2018:

Thanks for the visit and the comment, Heidi. Antibiotic resistance is an urgent issue. I hope the situation is improved soon.

Heidi Thorne from Chicago Area on September 17, 2018:

This is such an urgent issue for the healthcare field! I do hope that some alternatives are found soon. Thanks for the thorough review of how these medicines work!

Linda Crampton (author) from British Columbia, Canada on September 17, 2018:

Hi, Mary. I appreciate the useful discoveries made by researchers. There is so much to investigate in nature and science.

Linda Crampton (author) from British Columbia, Canada on September 17, 2018:

Thank you, Eman. I appreciate your kind comment.

Mary Norton from Ontario, Canada on September 17, 2018:

This is a very comprehensivE. I never knew there are different kinds of antibiotics and that they are discovering more. I hope they are successful in this research. We benefit now from the results of many research and I really respect the ones who do these.

Eman Abdallah Kamel from Egypt on September 17, 2018:

I always benefit from your writing, Linda. Very educational. Thank you very much for this useful article.

Linda Crampton (author) from British Columbia, Canada on September 17, 2018:

Thank you very much, Kyokusiima Diana.

Kyokusiima Diana from Kampala-Uganda on September 17, 2018:

So benefical.I did not know about it. Thanks for the information

Linda Crampton (author) from British Columbia, Canada on September 17, 2018:

Thanks, Bill. I always appreciate your visits.

Linda Crampton (author) from British Columbia, Canada on September 17, 2018:

I'm sorry about your experience, Flourish. Antibiotics can be very important, as in your situation. I hope we find some new and effective ones in the near future.

Linda Crampton (author) from British Columbia, Canada on September 17, 2018:

Thank you for sharing your experience, Pamela. I think your comment about many people failing to read about the possible side effects of a medicine is very accurate. It's important to read the pamphlet that accompanies a packaged medicine.

Linda Crampton (author) from British Columbia, Canada on September 17, 2018:

Thanks for the visit and the interesting comment, Alan. Science and scientists have made some wonderful contributions to our lives.

Bill Holland from Olympia, WA on September 17, 2018:

Fascinating as always, Linda! Thanks for filling in the gaps of my education.

FlourishAnyway from USA on September 17, 2018:

I appreciated your description of the different types of antibiotics in particular.

My former doctor was so stingy with antibiotics that I had to switch providers. As someone with an autoimmune condition, an infection that gets out of hand can cause permanent degradation in my physical ability, from mobility to other aspects of daily living. I wish there was better guidance for doctors in deciding whether something is viral or bacterial. Mine would always say an illness must be viral then I’d go back a week later sicker than ever and demand the antibiotics I should have had originally.

Pamela Oglesby from Sunny Florida on September 17, 2018:

Antibiotic resistance has been a concern for such a long time, and I guess this trend will continue to worsen. I saw this situation quite often as a nurse when an antibiotic wouldn't work.

I think there is a price to be paid (side effects) with any medication. I have found this out in my own situation.

Your list of the various types of antibiotics certainly gave me a better understanding of how these antibiotics work, and it was so thorough. I think many people (me included) take a medication without reading the side effects on the enclosed information. I think this article is a great reminder of how important it is to have some understanding about the function of antibiotics.

jonnycomelately on September 17, 2018:

Fascinating account and well-written, thank you. Much of it is beyond my comprehension but there is more for me to admire: that is the great learning, research and dedication to scientific advancement. Individuals give their brilliant minds to coming up with hypothesis, inquiry, experiment, recording, presentation and publication. This is human endeavour at its greatest.

Whether we will thereby populate the world with humans to the point of explosion, who knows? I doubt it. There will always be something to stop us or at least to slow our advancement.