Biological Sciences
Types of Antibiotics
Antibiotics are classified into several types based on their mechanism of action and chemical structure. Common types include penicillins, cephalosporins, tetracyclines, macrolides, fluoroquinolones, and sulfonamides. Each type targets specific bacterial functions, such as cell wall synthesis or protein production, and may have varying spectra of activity against different types of bacteria.
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10 Key excerpts on "Types of Antibiotics"
- Varaprasad Bobbarala(Author)
- 2015(Publication Date)
- IntechOpen(Publisher)
◦ the broad-spectrum drug affects a wide range of disease-causing bacteria, including both Gram-positive and Gram-negative bacteria ◦ the narrow-spectrum antibacterial drug, which acts against specific families of bacteria. For example, ampicillin is a widely used broad-spectrum antibiotic. For a better understanding of the different types of antimicrobial drugs, Figure 2 displays the main classes of these substances and their applications. Figure 2. Classification of antimicrobial drugs and their applications Antibiotics act by inhibiting the basic life-sustaining processes in the microorganism. In order to minimize toxicity, the targets of antibiotics must be selective. However, all antibiotics are toxic to some degree. Selective toxicity should be focused on harming the bacteria, not the host. Selection of the appropriate antibiotic depends on the following parameters: • Knowledge of organism’s natural resistance • Pharmacological properties of the antibiotic toxicity, binding, distribution, absorption achievable levels in blood, urine • Previous experience with same species • Nature of patients underlying pathology • Patient’s immune status Concepts, Compounds and the Alternatives of Antibacterials 6 Evaluation of susceptibility focuses mainly on the interaction of antimicrobial agents, the organisms, and their resistance mechanisms. The resistance to antimicrobial drugs is based on several mechanisms, including the following: • Microbes may generate drug-metabolizing enzymes (such as penicillinase) • Microbes may cease active uptake of certain drugs • Microbial drug receptors may suffer change resulting in reduced antibiotic binding and action • Microbes may produce compounds that antagonize drug actions Susceptibility tests are essentially artificial measurements that include in vitro response, approximate range of effective inhibitory action and reflect possible error equivalent to one tube dilution.
eBook - PDF- Ranjith N. Kumavath(Author)
- 2017(Publication Date)
- IntechOpen(Publisher)
It is aimed that this approach will be equally helpful for researchers, clinicians, and academicians. 2. Classification Infectious diseases are the major causes of human sickness and death. To overcome such health care issues, antibiotics proved to be promising agents ever since they were introduced in the 1940s. Antibacterials, which are a subclass of antibiotics, have been classified earlier in several ways; however, to make it more easily understandable, we can classify antibacterial agents into five groups: type of action, source, spectrum of activity, chemical structure, and function [1 ]. 2.1. Classification based on type of action Generally, antibacterials can be classified on the basis of type of action: bacteriostatic and bactericidal. Antibacterials, which destroy bacteria by targeting the cell wall or cell membrane of the bacteria, are termed bactericidal and those that slow or inhibit the growth of bacteria are referred to as bacteriostatic. Actually, the inhibition phenomenon of bacteriostatic agents involves inhibition of protein synthesis or some bacterial metabolic pathways. As bacterio‐ static agents just prevent the growth of the pathogenic bacteria, sometimes it is difficult to mark a clear boundary between bacteriostatic and bactericidal, especially when high concen‐ trations of some bacteriostatic agents are used then they may work as bactericidal [2 ]. Some prominent examples of bacteriostatic and bactericidal antibacterials along with their mode of action are presented in Table 1 . Antibacterial Agents 2 2.2. Classification based on source of antibacterial agents Antibacterials are the subclass of antibiotics, which can be naturally obtained from fungal sources, semi‐synthetic members which are chemically altered natural product and or syn‐ thetic. Cephalosporins, cefamycins, benzylpenicillin, and gentamicin are well‐known exam‐ ples of natural antibiotics/antibacterials.
eBook - PDFAntimicrobials
Synthetic and Natural Compounds
- Dharumadurai Dhanasekaran, Nooruddin Thajuddin, A. Panneerselvam, Dharumadurai Dhanasekaran, Nooruddin Thajuddin, A. Panneerselvam(Authors)
- 2015(Publication Date)
- CRC Press(Publisher)
They also classified as broad-spectrum and narrow-spectrum antibiotics as they possess inhibitory action on several pathogenic microorganisms as well as single pathogens, respectively. 7.3.1 Antibacterial compounds The emergence of multidrug-resistant bacteria is a phenomenon of concern to the clini-cian and the pharmaceutical industry, as it is the major cause of failure in the treatment of infectious diseases. The most common resistance mechanism of pathogenic bacteria to the antibiotics, namely, aminoglycoside, beta-lactam (penicillins and cephalosporins), and chloramphenicol types, involves the enzyme inactivation of the antibiotic by hydrolysis or by formation of inactive derivatives. Such resistance determinants most probably were acquired by pathogenic bacteria from a pool of resistance genes in other microbial genera, including antibiotic-producing organisms. Certain antibiotics produced by actinobacteria have a high activity upon bacteria and fungi. Some antibiotics are used by the geneticists to select a mutant bacteria. Others are used by the biochemists as specific inhibitors of metabolic reaction, such as chloramphenicol (inhibition of protein synthesis), antimycin A (inhibition of cytochrome oxidase), and actinomycin (activity upon nucleic acids). Among the various uses, the treatment of various infectious diseases of human and animals is the remarkable role of antibiotics (Waksman, 1943). 7.3.2 Antifungal compounds Antifungal compounds have been overshadowed by antibacterials in research interest and applications due to the greater impact of bacterial infections on health. Resistance to antibacterial drugs and the resultant clinical impact are of widespread concern regarding public health (Parks and Casey, 1996). However, resistance by pathogenic fungal infections to drug treatment has become more common in the past two decades. Certain antibiotics produced by actinobacteria have a high activity upon fungi.
- Carlos F. Amabile-Cuevas(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
This definition would therefore include all drugs, of natural or synthetic origin, used against bacte-ria; and would exclude compounds used against viruses, fungi, protozoans or other microorganisms, as well as non-selective biocides, such as disinfectants and antiseptics. 1.1.1 Origin and mechanism of action of main antibiotic classes Although it is not within the purview of this book to enlist and review the origin and mechanism of action of each class of antibiotics, having an overview included could be helpful for the reader not well versed into this mainly pharmacological area. It may be important to point out that a sort of unifying mechanism of action of bactericidal antibiotics, through a common pathway of generating reactive oxygen species, recently proposed (Kohanski et al., 2007), was first shown to be inconsistent with physiological evidence (Mahoney and Silhavy, 2013), and then most likely to be based on a labo-ratory artifact (Renggli et al., 2013). It is also important to emphasize that these are the mechanisms of bacteriostatic or bactericidal effects of high, clinically-attainable concentrations of antibiotics; as will be discussed below, this could very well be a human-made situation, with natural antibiotics actually exerting other physiological roles at much lower concentrations. The following paragraphs enlist some relevant information about each antibiotic class, with those that include mostly natural prod-ucts first. For additional information on the chemistry, pharmacology and clinical uses of each drug, two comprehensive texts can be useful: Bryskier A. (ed.) Antimicrobial agents, antibacterials and antifungals ; ASM Press, Washington DC, 2005; and Grayson M.L. et al. (eds.) Kucers’ The use of antibiotics , 6th ed; Hodder Arnold, London, 2010.
- Richard Schwalbe, Lynn Steele-Moore, Avery C. Goodwin(Authors)
- 2007(Publication Date)
- CRC Press(Publisher)
7 2 Antimicrobial Classifications: Drugs for Bugs Cassandra B. Calderón and Beulah Perdue Sabundayo CONTENTS 2.1 Introduction .............................................................................................................................. 9 2.2 Antibiotics ................................................................................................................................ 9 2.2.1 Penicillins ..................................................................................................................... 9 2.2.1.1 Background ................................................................................................... 9 2.2.1.2 Mechanism of Action .................................................................................. 12 2.2.2.3 Chemical Structure ...................................................................................... 12 2.2.2.4 Mechanisms of Resistance .......................................................................... 12 2.2.2.5 Classi fi cation ............................................................................................... 12 2.2.2.6 Antimicrobial Activity and Therapeutic Uses ............................................ 12 2.2.2.7 Adverse Effect Pro fi le ................................................................................. 14 2.2.3 Cephalosporins ........................................................................................................... 14 2.2.3.1 Background ................................................................................................. 14 2.2.3.2 Mechanism of Action .................................................................................. 14 2.2.3.3 Chemical Structure ...................................................................................... 14 2.2.3.4 Mechanisms of Resistance ..........................................................................
eBook - PDFFundamentals of Pharmacology
For Nursing and Healthcare Students
- Ian Peate, Barry Hill, Ian Peate, Barry Hill(Authors)
- 2021(Publication Date)
- Wiley-Blackwell(Publisher)
The goal of antibacterial therapy is to reduce bacteria (infection causing) to a point at where the body’s immune system can effectively deal with the microorganisms (Xiu and Datta, 2019). These drugs have certain properties: bactericidal, that is, they directly kill the bacteria; for example, peni-cillin and aminoglycosides; or, bacteriostatic, that is, they inhibit bacterial growth and rely on the body’s immune system to kill the bacteria; for example, tetracycline; or a combination of both properties; for example, aminoglycosides (Barber and Robertson, 2020; Ashelford, Raynsford and Taylor, 2016). The combination of bacteriostatic and bactericidal properties in certain drugs is due to the dosage and serum level concentration of the drug as well as outside influences and the health of the person. Narrow therapeutic index drugs, such as aminoglycosides, rely on the moni-toring of the serum concentration as this determines whether they lie within therapeutic range; the aim is to prevent underdosing or drug toxicity (Burchum and Rosenthal, 2019). As this chapter focuses on antibacterial agents, an understanding of bacteria cell structure and the various mechanisms of antibacterial action need to be considered. Antibacterials Chapter 9 155 Bacteria Bacteria are invisible to the naked eye, existing inside or outside organisms and they can live inde-pendent from a host (Barber and Robertson, 2020) (see Figure 9.1). Bacteria are single-cell microor-ganisms (prokaryotic) that have no nucleus but contain DNA (Ashelford, Raynsford and Taylor, 2016). They use their enzymes and ribosomes to manufacture proteins that allow their growth and reproduction to occur. Each bacterial type has a different shape: bacilli are rod-shaped, cocci are round-shaped and spirochetes are spiral/corkscrew-shaped (Barber and Robertson, 2020). Table 9.1 Classifications of antimicrobials with examples.
eBook - PDF- N T Crosby(Author)
- 1991(Publication Date)
- Woodhead Publishing(Publisher)
BASIDIOMYCETES AND ASCOMYCETES LICHENS AND ALGAE 23 82 49 37 12 71 53 9 Korzybski el al. (1978). 86 Antibiotics [Ch. 4 broad to be much use for analytical chemists, since the majority of substances are derived from the genus Aclinomycetes. Furthermore, some compounds can be produced by different and unrelated genera. Equally, the same genus may produce more than one antibiotic. The activity spectrum is of prime importance to clinicians, and classifications based on biological properties are widely encountered. Antimicrobials are often described as being effective against Gram-positive or Gram-negative organisms, or against both. This refers to a classification of bacteria based on the organism's response when stained with a purple dye. The organism either retains or releases the dye on subsequent washings, so that Gram-positive organisms show up blue under the microscope whilst Gram-negative organisms appear red. Other classifications are based on differences in the mode of action of the active ingredient. Antibiotics are thought to function by interference in the synthesis and development of parts of the bacterial cell. They may prevent the formation of nucleic acids, or the synthesis of protein. Alternatively, they can attach themselves to the cell wall or cell membrane and prevent essential cross-linking of the structure or promote the ingress of ions, thus destabilizing the whole structure and eventually causing complete rupture. However, the mechanism of action of some antibiotics is not yet fully understood and it is possible that some compounds can act in more than one mode. Hence a classification based on chemical structure is increasingly becoming more popular, now that the molecular formulae of more and more compounds have been eluci-dated. For the analytical chemist, a classification based on chemical structure is clearly the most appropriate. 4.2.1 Chemical classification of antibiotics Antibiotics used in animal husbandry can be divided into the
- Arti Gupta, RAM PRASAD, Arti Gupta, RAM PRASAD(Authors)
- 2023(Publication Date)
- CRC Press(Publisher)
However, during the early 1900s, most of the global population suffered from common ailments, namely cold and flu, owing to the paucity of antimicrobial agents. The substances that inhibit the growth and development of microorganisms such as bacteria, viruses, protozoa and fungi are called antimicrobials (Burnett-Boothroyd and McCarthy 2011). The term antibiotic, on the other hand, originates from antibiosis which means ‘against life’. Earlier, the use of this term was confined to the natural chemical ingredients produced by microbes that were either lethal (bactericidal) or inhibitory (bacteriostatic) to other related microorganisms (such as algae, bacteria and fungi) but now they also include chemically-synthesized compounds (Aminov and Mackie, 2007 ; Amnirov, 2009). Till now, ~250 Types of Antibiotics have been noted for use in humans and animals where they have been shown to affect the biosynthesis of components of cell wall, protein synthesis machinery, folic acid synthesis, metabolism and genetic element of the organisms (Figure 4.1 ; Kummerer, 2003 ; Singh et al., 2021). The prime source for antimicrobials/antibiotics includes algae, bacteria, fungi and plants (Hayashi et al., 2014; Inamuddin et al. 2021). With advances in therapeutics, the multitude of antibiotics usage and lack of surveillance gathered crucial setbacks, of which acquired resistance is the prominent one. Bacterial resistance can be categorized into multidrug-resistant (MDR), pan drug-resistant (PDR) and extreme drug-resistant (XDR) (Magiorakos et al., 2012). MDR bacteria have become an alarming concern owing to their steadily growing resistance to last drug resorts such as vancomycin and colistin
- Robert L. Bill(Author)
- 2016(Publication Date)
- Mosby(Publisher)
10Antimicrobials
Chapter OutlineTypes of Antimicrobials ,213Goals of Antimicrobial Therapy ,213Susceptibility, Resistance, Intermediate, and Breakpoints, 214Resistance of Microorganisms to Antimicrobial Therapy ,215How Does Bacterial Resistance Occur?, 216Selective Pressure, Resistance, and Clinical Disease, 216Resistance and Drug Residues, 217Classification of Antimicrobials by Their Mechanism of Action ,218Classes of Antimicrobials ,219Penicillins, 219Cephalosporins, 223Aminoglycosides, 224Fluoroquinolones or Quinolones, 228Tetracyclines, 230Sulfonamides and Potentiated Sulfonamides, 232Other Antimicrobials Used in Veterinary Medicine ,234Lincosamides, 234Macrolides, 234Metronidazole, 235Chloramphenicol and Florfenicol, 236Rifampin, 236Bacitracin, 236Antifungals ,237Amphotericin B, 237Azoles: The Imidazole Derivatives, 237Griseofulvin, 238Terbinafine, 240Nystatin, 240ObjectivesAfter studying this chapter, the veterinary technician should be able to:• Describe the meaning of characterizing terms that describe antimicrobials: -cidal, -static, concentration-dependent, time dependent, etc.• Explain in detail how resistance develops and emerges from bacterial populations, why this is of concern to human health, and what can be done to reduce the emergence of resistant bacteria.• Describe the basic mechanism of action, key characteristics of the drug group, and the clinically significant disadvantages or adverse reactions for each of the key veterinary drugs described.• Explain the role bacterial antibiotics play in treating heartworm disease and controlling protozoa like coccidia and giardia.• Explain how kidney damage can be avoided when using aminoglycosides.• Identify what drugs are best to use to treat intracellular bacteria like Rickettsia, Chlamydia, and Mycoplasma
eBook - PDF- Stuart Hogg(Author)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
17.1 ANTIBIOTICS 425 Table 17.2 Some commonly used antibiotic classes Mode of inhibition Representatives Inhibitors of cell wall synthesis Penicillins, cephalosporins Disrupters of cell membranes Polymixins, polyenes Inhibitors of protein synthesis Streptomycin, tetracyclines Inhibitors of nucleic acid synthesis Rifamycins host human or animal cells unaffected (Table 17.2). The most commonly used antibiotics exert their effect by one of the following methods: I. Inhibition of cell wall synthesis II. Disruption of cell membranes III. Interference with protein synthesis IV. Interference with nucleic acid synthesis Those antibiotics belonging to groups I and III are better able to discrimi- nate between prokaryotic and eukaryotic cells, and consequently show more selective toxicity and a higher therapeutic index. 17.1.3 I: Inhibitors of cell wall synthesis Antibiotics may either kill their bacterial target, or merely prevent them from proliferating; they are said to be bactericidal or bacte- riostatic, respectively. It is possible for an antibiotic to be bactericidal towards one organism and bacte- riostatic towards another, or to be bactericidal at one dose and bacteriostatic at another. The main group that work in this way are the β-lactam antibiotics, so-called because they contain a β-lactam ring in their structure. Well- known members of this group are the penicillins and the cephalosporins. The β-lactams exert their effect by inhibiting cell wall synthesis in the target bacteria. You may recall from our discussion of bacterial cell wall structure in Chapter 3 that an important factor in the strengthening of the peptidoglycan component of the bacterial cell walls is the cross-linking of chains by transpeptidation. β-lactams disrupt this process by binding to the transpeptidase enzyme, 1 forming covalent bonds with a serine residue within the enzyme’s active site.
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