Antimicrobial Agents in the Treatment of Infectious Disease (2023)

Antimicrobial Agents in the Treatment of Infectious Disease
(page 3)
(This chapter has 6 pages)© Kenneth Todar, PhD

Antimicrobial Agents Used in the TreatmentofInfectious Disease
Examination of the foregoing table reveals that there are ahandfulof fundamental ways that antibacterial antibiotics work as therapeuticagents. Recall that the target of an antibiotic should be unique to thebacterium and not found, or not accessible to the antibiotic, in thepatient. These are the most important targets in bacteria that havebeen exploited so far.

1. Attack bacterial cell wall synthesis. Bacteria have murein in theircell walls, not found in the host, and murein (peptidoglycan) isessential to the viability of the bacterium.

2. Interfere with protein synthesis. Attack is almost always ate thelevel of translation using 70S ribosomes in the translation machinery.70S cytoplasmic ribosomes are absent in eucaryotes.

3. Interference with nucleic acid synthesis (RNA and DNA), whichexploits differences between RNA polymerases and DNA replicationstrategies in bacteria and eucaryotes.

4. Inhibition of an essential metabolic pathway that exists in thebacterium but does not exist in the host. This is usually brought aboutthrough the use of competitive chemical analogs for bacterial enzymaticreactions.

5. Membrane inhibition or disruption doesn't work too well because ofthe similarities between eucaryotic and bacterial membranes. However,the outer membrane of Gram-negative bacteria is a reasonable point ofattack and some membrane inhibitors are included in the discussionbelow.

(Video) Antibiotic Classes in 7 minutes!!

Cell wall synthesis inhibitors

Cell wall synthesis inhibitors generally inhibit some step in thesynthesis of bacterial peptidoglycan. They exert theirselective toxicity against bacteria because humans cells lack cellwalls.

Beta lactam antibiotics. Chemically, these antibioticscontain a4-membered beta lactam ring. They are the products of two genera offungi, Penicillium and Cephalosporium, and arecorrespondingly represented by the penicillins and cephalosporins.

Antimicrobial Agents in the Treatment of Infectious Disease (1)
Chemical structures of somebeta-lactam antibiotics. Clockwise: penicillin, cephalosporin,monobactam, carbapenem. Note the characteristic structure of the betalactam ring.

The beta lactam antibiotics are stereochemically related toD-alanyl-D-alanine, which is a substrate for the last step inpeptidoglycan synthesis, the final cross-linking between betweenpeptide side chains. Penicillins bind toand inhibit the carboxypeptidase and transpeptidase enzymes that arerequired for this step in peptidoglycan biosynthesis. Beta lactamantibiotics are bactericidal and require that cells beactively growing in order to exert their toxicity.

Different beta lactams differ in their spectrum of activity andtheir effecton Gram-negative rods, as well as their toxicity, stability in thehumanbody, rate of clearance from blood, whether they can be taken orally,abilityto cross the blood-brain barrier, and susceptibility to bacterialbeta-lactamases.

Natural penicillins, such as penicillin G or penicillinV (benzyl penicillin), are produced by fermentation of Penicilliumchrysogenum.They are effective against streptococci, gonococci andstaphylococci, except where resistance has developed. They areconsidered narrow spectrum since they are not effective againstGram-negative rods.

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Antimicrobial Agents in the Treatment of Infectious Disease (2)

PenicillinG(Benzylpenicillin) is typically given by parenteral administrationbecause it is unstable in the acid of the stomach. However, thisachieves higher tissue concentrations than orally-administeredpenicillins and this increases its antibacterial potential."PenG" may be used in treatment of bacterial endocarditis, gonorrhea,syphilis, meningitis, and pneumonia.

Semisynthetic penicillins first appeared in 1959. A moldproduces the main part of the molecule (6-aminopenicillanic acid),whichcan be modified chemically by the addition of side chains. Many ofthese compounds have been developed to have distinct benefits oradvantages over penicillin G, such as increased spectrum of activity(effectiveness against Gram-negative rods), resistance topenicillinase, effectiveness when administered orally, etc.; amoxicillinand ampicillin have broadened spectra against Gram-negativebacteriaand are effective orally; methicillin ispenicillinase-resistant.

Antimicrobial Agents in the Treatment of Infectious Disease (3)

The semisynthetic beta-lactam, amoxicillin. Amoxicillin is usually thedrug of choice within the class because it is better absorbed followingoral administration than other beta-lactam antibiotics. It issusceptible to degradation by bacterial beta-lactamase enzymes so itmay be given with calvulanic acid (below) to decrease itssusceptibility. It is used against a wide range of Gram-positivebacteria, including Streptococcuspyogenes, penicillin-sensitiveStreptococcus pneumoniae, non beta-lactamase producing strainsof Staphylococcus aureus and Enterococcus faecalis. SusceptibleGram-negative organisms include non beta-lactamase producing strains ofHaemophilus influenzae, Neisseriagonorrhoeae and N.meningitidis.

Clavulanic acid
is a chemical sometimes added to asemisynthetic penicillin preparation. Thus, amoxicillin plusclavulanate is clavamox or augmentin. The clavulanateis not an antimicrobial agent. It inhibits beta lactamase enzymes andhas given extended life to penicillinase-sensitive beta lactams.

Antimicrobial Agents in the Treatment of Infectious Disease (4)
The structure of calvulanicacid. Clavulanic acid is not an antibiotic. It is a beta-lactamaseinhibitor sometimes combined with semisynthetic beta lactam antibioticsto overcome resistance in bacteria that produce beta-lactamase enzymes,which otherwise inactivate the antibiotic. Most commonly it is combinedwith amoxicillin (above) as Augmentin (trade name) or the veterinarypreparation, clavamox.

Although nontoxic, penicillins occasionally cause death whenadministered to persons who are allergic to them. In the U.S. there are300 - 500 deaths annually due to penicillin allergy. In allergicindividuals the beta lactam molecule attaches to a serum protein andinitiates an IgE-mediated inflammatory response.

Cephalosporins are beta lactam antibiotics with a similarmode of action to penicillins. They are produced by species ofCephalosporium molds. The havea low toxicity and a somewhat broader spectrumthan natural penicillins. They are often used as penicillinsubstitutes against Gram-negative bacteria and in surgicalprophylaxis. They are subject to degradation by some bacterialbeta-lactamases, but they tend to be resistant to beta-lactamases from S.aureus.

Antimicrobial Agents in the Treatment of Infectious Disease (5)
The core structure ofcephalosporin. Substituent groups added at position Xon the six-membered ringgenerates variants of the antibiotic.

Two other classes of beta lactams are the carbapenems and monobactams.The latter are particularly useful for the treatment of allergicindividuals. A person who becomes allergic to penicillin usuallybecomes allergic to the cephalosporins and the carbapenems as well.Such individuals can still be treated with the monobactams, which arestructurally different so as not to induce allergy.

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Antimicrobial Agents in the Treatment of Infectious Disease (6)

Aztreonam is a synthetic monocyclic beta lactam antibiotic (amonobactam) originally isolated from the bacterium Chromobacterium violaceum. Itis not useful against Gram-positive bacteria but it has strong activityagainst a wide range of susceptible Gram-negative bacteria, including Pseudomonas aeruginosa, E. coli,Haemophilus and Klebsiella.

is a polypeptide antibiotic produced by Bacillusspecies. It prevents cell wall growth by inhibiting the release ofthe muropeptide subunits of peptidoglycan from the lipid carriermolecule that carries thesubunit to the outside of the membrane. Teichoic acid synthesis, whichrequiresthe same carrier, is also inhibited. Bacitracin has a high toxicitywhichprecludes its systemic use. It is present in many topical antibioticpreparations,and since it is not absorbed by the gut, it is given to "sterilize" thebowelprior to surgery.

Antimicrobial Agents in the Treatment of Infectious Disease (7)
Bacitracin is a polypeptide antibiotic produced by the licheniformisgroup of Bacillus subtilis var.Tracy. It is effective used topically, primarily against Gram-positivebacteria. It is used in ointment or cream form for topical treatment ofa variety of localized skin and eye infections, as well as for theprevention of wound infections. A popular brand name Neosporin,containsbacitracin, neomycin and polymyxin B.

Cycloserine inhibits the early stages of murein synthesiswhere D-alanyl-D-alanine is added to the growing peptide side chain.The antibiotic resembles D-alanine in spatial structure, and itcompetitively inhibits the racemase reaction that converts L-alanine toD-alanine and the synthetase reaction that joins two D-alaninemolecules. The affinity of cycloserine for these enzymes is about ahundred times greater than that of D-alanine. Cycloserine entersbacterial cells by means of an active transport system for glycine andcan reach a relatively high intracellular concentration. Thisconcentrating effect, along with its high affinity for susceptibleenzymes, enables cycloserine to function as a very effectiveantimicrobial agent. However, it is fairly toxic and has limited use asa secondary drug for tuberculosis.

Antimicrobial Agents in the Treatment of Infectious Disease (8)

Cycloserine is an oral broad spectrumantibiotic effective against tuberculosis,by inhibiting cell wall synthesis of TB bacilli at the early stagesofpeptidoglycan synthesis. For the treatment against tuberculosis, it isclassified as a second line drug.

Glycopeptides, such as the antibiotic vancomycin,inhibit both transglycosylation and transpeptidationreactions during peptidoglycan assembly. They bind to the muropeptidesubunit as it is transferred out of the cell cytoplasm and inhibitsubsequent polymerization reactions. Vancomycin is not effectiveagainst Gram-negative bacteria because it cannot penetrate their outermembrane. However, it has become important in clinical usage fortreatment of infections by strains of Staphylococcus aureusthat are resistant to virtually all other antibiotics (MRSA).

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Antimicrobial Agents in the Treatment of Infectious Disease (9)

Vancomycinis a glycopeptide antibiotic used in the prophylaxis and treatment ofinfections caused by Gram-positive bacteria. It has traditionally beenreserved as a drug of "last resort",used only after treatment with other antibiotics had failed, althoughthe emergence of vancomycin-resistant organisms means that it isincreasingly being displaced from this role by linezolid and thecarbapenems.

Cell membrane inhibitors

These antibiotics disorganize the structure or inhibit the functionof bacterial membranes. The integrity of the cytoplasmic and outermembranes is vital to bacteria, and compounds that disorganize themembranes rapidly kill the cells. However, due to the similarities inphospholipids in eubacterial and eucaryotic membranes, this action israrely specific enough to permit these compounds to be usedsystemically. The only antibacterial antibiotics of clinical importancethat act by this mechanism are the polymyxins, producedby Bacillus polymyxa. Polymyxin is effective mainly againstGram-negativebacteria and is usually limited to topical usage. Polymyxins bind tomembrane phospholipids and thereby interfere with membrane function.Polymyxin is occasionally given for urinary tract infections caused by Pseudomonasstrains that are gentamicin, carbenicillin and tobramycin resistant.The balance between effectiveness and damage to the kidney and otherorgansis dangerously close, and the drug should only be given under closesupervision in the hospital.

Antimicrobial Agents in the Treatment of Infectious Disease (10)
PolymyxinB.Polymyxins are cationic detergent antibiotics, with a general structureof a cyclic peptide with a long hydrophobic tail. They disrupt thestructure of the bacterial cell membrane by interacting with itsphospholipids. Polymyxins have a bactericidal effect on Gram-negativebacilli, especially on Pseudomonas and coliform bacteria. Polymyxinantibiotics are highly neurotoxic and nephrotoxic, and very poorlyabsorbed from the gastrointestinal tract. Polymyxins also haveantifungal activity.

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What are antimicrobial agents used in the treatment of infections? ›

Infections and diseases may be caused by different types of organisms like bacteria, fungi, and viruses, etc., in humans and animals. The drug used to prevent the pathogenicity of microorganisms is called an antimicrobial agent. Examples: Antibiotics, antiseptics, and disinfectants.

What are the 3 types of antimicrobials? ›

There are three types of public health antimicrobials: sterilizers, disinfectants, and sanitizers.

What is an antimicrobial drug used in the treatment and prevention of bacterial infections? ›

Antibiotics are used to treat or prevent some types of bacterial infection. They kill bacteria or prevent them from reproducing and spreading. Antibiotics aren't effective against viral infections. This includes the common cold, flu, most coughs and sore throats.

What are examples of antimicrobials? ›

What are examples of antimicrobials?
  • Penicillin (an antibiotic).
  • Valacyclovir (an antiviral agent).
  • Fluconazole (an antifungal medication).
  • Praziquantel (an antiparasite medication).
Apr 27, 2021

What are the types of antimicrobial agents? ›

Antimicrobial agents are classified into several categories, i.e. inhibitors for bacterial cell wall such as beta-lactam drugs, fosfomycin, and vancomycin; inhibitors for protein biosynthesis such as tetracyclibnes, macrolides, aminoglycoside antibiotics; inhibitors for DNA synthesis such as 4-quinolones; inhibitors ...

What are the two most common antimicrobial agents? ›

Gentamicin and tobramycin are used most commonly and are the primary agents used to treat infections caused by gram-negative rods, most notably Pseudomonas species. Although most antibiotics that inhibit protein synthesis are bacteriostatic, the aminoglycosides are frequently bactericidal.

What is the most common antimicrobial agent? ›

Ethyl alcohol, n-propanol and isopropyl alcohol are the most commonly used antimicrobial agents. Methanol is also a disinfecting agent but is not generally used as it is highly poisonous. Escherichia coli, Salmonella, and Staphylococcus aureus are a few bacteria whose growth can be inhibited by alcohols.

What are the five main classes of antimicrobial drugs? ›

The antibacterial agents can be classified into five major groups, i.e. type of action, source, spectrum of activity, chemical structure, and function.

What was the first antimicrobial drug used to treat disease? ›

The first antimicrobial agent in the world was salvarsan, a remedy for syphilis that was synthe- sized by Ehrlich in 1910. In 1935, sulfonamides were developed by Domagk and other researchers. These drugs were synthetic compounds and had limitations in terms of safety and efficacy.

What are antimicrobial drugs? ›

SilverSure™ microfiber cloths are treated with SILVADUR™ antimicrobial to inhibit the growth of microorganisms in fabric. Cloths feel and look new longer by inhibiting odor-causing bacteria and fungi.

What is are the four 4 targets of antimicrobial agents? ›

Therefore, according to its mechanism of action, the targets of antibacterial drugs include cell membrane, cell wall, protein synthesis, nucleic acid synthesis, and biological metabolic compound synthesis.

What are the 4 main infectious agents? ›

Infectious agents are organisms that are capable of producing infection or infectious disease. They include bacteria, fungi, viruses, and parasites.

What is the difference between antibiotics and antimicrobial agents? ›

Antimicrobials refer to a group of agents that share the common aim of reducing the possibility of infection and sepsis. Antibiotics are often derived from moulds or are made synthetically and are absorbed into the body with the aim of killing bacteria (bactericidal) or preventing their multiplication (bacteriostatic).

What are the 6 infectious agents? ›

A brief review of the general characteristics of each of these agents and examples of some diseases they cause follows.
  • Bacteria. ...
  • Viruses. ...
  • Fungi. ...
  • Protozoa. ...
  • Helminths. ...
  • Prions.

Is Penicillin an antimicrobial drug? ›

Penicillins are a group of antibacterial drugs that attack a wide range of bacteria. They were the first drugs of this type that doctors used.

What are the 7 main types of antibiotics? ›

Classes of antibiotics include the following:
  • Aminoglycosides. ...
  • Carbapenems. ...
  • Cephalosporins. ...
  • Fluoroquinolones. ...
  • Glycopeptides and lipoglycopeptides. ...
  • Macrolides.

What was the first antibiotic used in the clinical treatment of bacterial infections? ›

The first antibiotic, salvarsan, was deployed in 1910. In just over 100 years antibiotics have drastically changed modern medicine and extended the average human lifespan by 23 years.

What is the oldest antimicrobial agent? ›

Dawn of the modern era

Pyocyanase was probably the first antibiotic to be used to treat human infections. Rudolf Emmerich (1856–1914) and Oscar Löw (1844–1941) discovered that the green bacteria isolated from injured patients' bandages inhibited the growth of other microbes.

Was penicillin the first antimicrobial drug? ›

This phenomenon has long been known; it may explain why the ancient Egyptians had the practice of applying a poultice of moldy bread to infected wounds. But it was not until 1928 that penicillin, the first true antibiotic, was discovered by Alexander Fleming, Professor of Bacteriology at St. Mary's Hospital in London.

What type of drug product is an antimicrobial? ›

Antimicrobial drugs include all drugs that work against a variety of microorganisms, such as bacteria, viruses, fungi, and parasites. An antibiotic drug is effective against bacteria. All antibiotics are antimicrobials, but not all antimicrobials are antibiotics.

Which of the following are antimicrobial drugs? ›

Antibiotics, antiseptics and disinfectants are antimicrobial drugs.

What are the 5 modes of action of antimicrobial agents? ›

Basis of Antimicrobial Action

Various antimicrobial agents act by interfering with (1) cell wall synthesis, (2) plasma membrane integrity, (3) nucleic acid synthesis, (4) ribosomal function, and (5) folate synthesis.

What are the 5 characteristics of an ideal antimicrobial agents? ›

An ideal antimicrobic: - soluble in body fluids, - selectively toxic, - nonallergenic, - reasonable half life (maintained at a constant therapeutic concentration) - unlikely to elicit resistance, - has a long shelf life, - reasonably priced.

What are the 4 major action modes of antimicrobial drugs? ›

Most antimicrobials fall into one of four main categories, based on their site of activity. These include inhibition of cell wall synthesis, protein synthesis, nucleic acid synthesis, or dis- ruption of cell membrane integrity.

What is the best antimicrobial agent? ›

Penicillin is most effective against gram-positive bacteria, as their cell walls are mostly peptidoglycan, rather than gram-negative bacteria who also have a lipopolysaccharide and protein layer.


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