Antibiotics: An Overview
Antibiotic, which is derived from the Greek words, anti ( for “against”) and bios (for “life”), is a chemical substance produced by a microorganism that either kills or inhibits the growth of other microorganisms. The term is used to characterize any drug, whether found in nature or produced by chemical synthesis, used to treat or prevent bacterial infections.
The terms antibiotic and antibacterial are often used synonymously. However, not all antibacterial agents are antibiotics, but all antibiotics are antibacterial. Antibacterial agents can be metabolic compounds of microbes such as antibiotics, physical agents like radiation, heat, or chemicals like alcohols, Iodine, and Chlorine.
Antibiotics belong to the broader group of antimicrobial drugs used to treat and prevent infectious diseases caused by all types of pathogenic microbes in addition to bacteria, such as viruses, fungi, parasites, and protozoa. Antibiotics are only to be used to treat bacterial infections. Antibiotics are either bactericidal (meaning they kill bacteria) or they are bacteriostatic, meaning they slow the growth of bacteria. They are useless against viral infections, fungal infections, or parasitic infections.
The discovery of the antibiotic penicillin in 1928 by Alexander Fleming, was hailed as one of the most important scientific achievements of the 20th century. Since then, over 100 types of antibiotics have been discovered and put to use in fighting bacterial infections.
In order for an antibiotic to be useful in treating an infection, the drug must selectively target a bacterium without harming human cells. The term “mechanism of action” describes how an antibiotic works in the body. More precisely, it describes what cellular functions in the bacteria the antibiotic “targets.” Many of the cellular functions targeted by antibiotics are either absent or different in human cells. However, since there is some overlap of cellular function, some antibiotics have been found to be useful as antineoplastic agents.
Different types of antibiotics have different mechanisms of action, due to their chemical structure. When antibiotics are classified by their mechanism of action, they are generally divided into several different groups. While each group is composed of multiple drugs, each drug is unique in some way.
The first group is: cell wall synthesis inhibitors. Two different subgroups of antibiotics inhibit or interfere with cell wall synthesis: the first subgroup includes the Beta-lactam antibiotics such as penicillins, cephalosporins, monobactams, and carbapenems; the second subgroup is made of the glycopeptide antibiotics, which includes vancomycin, teicoplanin, telavancin, and bleomycin.
Next, you have protein synthesis inhibitors. This is a diverse group of antibiotics that all affect protein synthesis at the ribosomal level. Remember, ribosomes are cell structures that make protein. Bacterial ribosomes are composed of two subunits, 30S and 50S. Antibiotics that inhibit the 30S subunit include Aminoglycosides (such as gentamicin) and Tetracyclines. Antibiotics that target the 50S subunit include Macrolides, Clindamycin and Linezolid.
The next group is known for disrupting cell membrane function. Cell membranes are important barriers that separate the interior of cells from the outside environment. The cell membrane helps regulate the intra- and extracellular flow of substances. Any disruption or damage to this structure could result in leakage of proteins essential for the cell’s survival. Examples of antibiotics in this group include: polymyxin and gramicidin.
The next group of antibiotics inhibit DNA or RNA synthesis. Antibiotics in this group inhibit nucleic acid metabolism by binding to nucleic acid or interacting with enzymes necessary for nucleic acid synthesis. There are two major classes of antibiotics that inhibit nucleic acid synthesis: rifamycin, which binds to the bacterial DNA-dependent RNA polymerase, the enzyme responsible for transcription of DNA into RNA; and quinolones (such as ciprofloxacin) and fluoroquinolones (such as norfloxacin) which inhibit bacterial replication by blocking their DNA replication pathway.
The final group is made of bacterial metabolism inhibitors. Antibiotics that target specific metabolic pathways cause a decrease in essential cell components or synthesis of nonfunctional analogues of normal metabolites. An antimetabolite is a chemical that inhibits the use of a metabolite, a chemical that is part of normal metabolism. An antimetabolite can have toxic effects on cells, such as halting cell growth or cell division. For example, sulfa antibiotics disrupt the production of a specific enzyme critical for the synthesis of folic acid, which bacteria use to synthesize proteins.
The goal of antibiotic therapy is to ensure a favorable therapeutic result by destroying or sufficiently inhibiting further growth of the microorganism by selecting an antibiotic that the target bacterium is sensitive to and is least likely to cause side effects, an adverse drug event, or an allergic reaction.
Factors to consider in the selection of an antibiotic include:
- Sensitivity pattern of the bacteria
- Severity of infection
- The location of the infection
- The patient’s age, the presence of comorbidities, immunological status; renal and liver function; as well as genetic factors; history of allergies and whether or not they are pregnant or breastfeeding.
Antibiotics should only be prescribed to treat bacterial infections that could infect others unless treated, are unlikely to resolve without treatment, or carry a high risk of complications.
Antibiotics may also be used prophylactically for people who are more vulnerable to the harmful effects of infection.
The benefits of antibiotics in the treatment and prevention of bacterial diseases cannot be overstated. Antibiotics save lives; but they do have risks associated with their use.
These risks include:
- Adverse effects, ranging from mild reactions, such as nausea, loss of appetite, vomiting, or diarrhea; to serious life-altering reactions like Steven-Johnson Syndrome, anaphylaxis, neurotoxicity, and hepatic or renal failure.
- There is also the risk of adverse interactions with other drugs; including anticoagulants, anticonvulsants, birth control pills, aspirin, and statins.
- The overgrowth of other microorganisms can also occur, for example: vaginal yeast infections or C-difficile infections.
- And there is the risk of the emergence of antibiotic-resistant bacteria, such as Methicillin-resistant Staphylococcus aureus (MRSA); Vancomycin-resistant Enterococcus (VRE); and multi-drug-resistant Mycobacterium tuberculosis.
Antibiotics are among the most frequently prescribed medications and given in almost all patient populations. Nurses in every setting need to understand the basic principles of antibiotic therapy, monitor patients for both their response to therapy or the development of adverse effects, and provide thorough patient and family education to ensure their understanding of the drug therapy.
Ok, let’s review by going over a few questions:
1. Antibiotics that kill bacteria are:
If you chose the answer c, you’re correct! “Bactericidal” means that it kills bacteria.
Antibiotics should only be prescribed:
- Prophylactically for people who are more vulnerable to the harmful effects of viral infections.
- If an infestation is unlikely to resolve without treatment
- If the bacterial infection is associated with a high risk of complications
- Whenever there is a risk of overgrowth of another microorganism.
If you chose the answer c, you’re correct! Antibiotics should only be prescribed to treat bacterial infections that could infect others unless treated; are unlikely to resolve without treatment; carry a high risk of complications. Antibiotics can also be used prophylactically for people who are more vulnerable to the harmful effects of a bacterial infection.
Based on their mechanism of action on bacteria, antibiotics can be divided into all of the following groups except:
- Cell Wall Synthesis Inhibitors
- DNA Synthesis Inhibitors
- Bacterial Growth Inhibitors
- Bacterial Metabolism Inhibitors
- Protein Synthesis Inhibitors
If you chose the answer c, Bacterial Growth Inhibitors, you’re correct! Antibiotics are divided into the following groups based on their mechanism of action: DNA Synthesis Inhibitors; Bacterial Metabolism Inhibitors; Protein Synthesis Inhibitors; Cell Wall Synthesis Inhibitors, as well as Disruption of Cell Membrane Function which was not listed as a choice.
Thank you for watching, and happy studying!