Biological Sciences
Bactericidal Antibiotics
Bactericidal antibiotics are a class of antibiotics that have the ability to kill bacteria. Unlike bacteriostatic antibiotics, which only inhibit the growth and reproduction of bacteria, bactericidal antibiotics directly target and destroy bacterial cells. This makes them particularly effective in treating severe bacterial infections and in situations where a rapid reduction in bacterial population is necessary.
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8 Key excerpts on "Bactericidal Antibiotics"
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- 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.
- 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.
eBook - PDF- Varaprasad Bobbarala(Author)
- 2012(Publication Date)
- IntechOpen(Publisher)
11 Bacteriostatic Agents Marzieh Rezaei 1 , Majid Komijani 1 and Seyed Morteza Javadirad 2 1 Department of Biology, Faculty of Science, Nour Danesh Institute of Higher Education, Hafez St., Meymeh, Isfahan, 2 Genetic Division, Biology Department, Faculty of Sciences, University of Isfahan, Isfahan, 1,2 Iran 1. Introduction In this chapter we begin to study the effect of the antibacterial agents used for control of microbial growth There are some essential related terms for studying the antibacterial agents that are mentioned as in following: a. Biocide : A widespread chemical or physical agent which inactivates microorganisms. b. Bacteriostatic : property of a specific biocide agent which is able to bacterial multiplication. c. Bactericida l: A specific term referring to the property by which a biocide is able to kill bacteria. d. Disinfectants : Products or biocides used to reduce only the number of viable microorganisms on the inanimate objects e. Septic : Characterized by the presence of pathogenic microbes in living tissue. f. Antisepti c: A biocide or product that inhibits the growth of microorganisms in or on living tissue. g. Aseptic : Free of or using methods to keep free of, microorganisms. h. Antibiotics : Naturally occurring or synthetic organic compounds which inhibit or destroy selective bacteria, generally at low concentrations. i. Sterilization : is defined as the process where all the living microorganisms, including bacterial spores are killed. Sterilization can be achieved by physical, chemical and physiochemical means. j. Asepsis is the employment of techniques (such as usage of gloves, air filters, uv rays etc) to achieve microbe-free environment. Large numbers of antibacterial agents are of clinical interest. The mechanisms by which compounds with antibacterial activity inhibit growth or cause bacterial death are varied and depend on the affected targets.
eBook - PDF- Firdos Alam Khan(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
The word antibiotic was first coined by Selman Waksman in 1942 to describe any substance produced by bacteria that retards the growth of other microorganisms. However, this original definition does not include naturally occurring substances that kill bacteria. With rapid advances in the field of medicinal chemistry, most antibiotics are basically semisynthetic in nature are derived from original compounds found in nature, for example, beta-lactams, which include the penicillins, produced by fungi in the genus Penicillium . Interestingly, some antibiotics are still produced and iso-lated from living bacteria, such as aminoglycosides, and others have been created through purely synthetic means such as sulfonamides, oxazolidinones, and quinolones. In addi-tion, antibiotic drugs can be classified into natural, semisynthetic, and synthetic based on their effects on the microorganisms (Tables 3.1 and 3.2). 3.5.1.1 Classification of antibiotics Antibiotic drugs can also be divided into two types: those that kill bacteria, known as bactericidal agents, and those that only impair bacterial growth, known as bacteriostatic agents. Furthermore, antibiotics are commonly classified based on their chemical structure and mechanism of action on the bacteria. It has been shown that most of the antibiotics generally target bacterial functions or growth. Antibiotics (penicillin and cephalosporins) that target the bacterial cell wall or cell membrane are usually bactericidal in nature and 66 Biotechnology in medical sciences antibiotics (aminoglycosides, macrolides, and tetracycline) that target protein synthesis are usually bacteriostatic in nature. Interestingly, there is a further categorization of anti-biotics based on their target specificity; for example, antibiotics will work differently for both Gram-negative and Gram-positive bacteria, respectively. There are broad-spectrum antibiotics known to affect a wide range of bacteria.
eBook - PDF- Mannfred A. Hollinger(Author)
- 2007(Publication Date)
- CRC Press(Publisher)
For example, the drug may (1) inhibit a reaction vital only to the microbe and not the host. The target reaction may, in fact, have no counterpart in the host. For example, penicillin inhibits the cross-linking of microbial peptidoglycan and thereby 168 Introduction to Pharmacology prevents microbial cell wall synthesis. Animal cells have membranes of a different composition; (2) inhibit a reaction that yields a product vital to both microbe and host. However, the host has an alternative mechanism of obtaining the substance. For example, sulfa drugs inhibit intracellular folic acid synthesis by microbes. Human cells can utilize preformed folic acid and are not susceptible to this antimetabolic effect; (3) undergo biochemical activation to a toxic form in the microbe. For example, acyclovir is used to treat herpes infections. In order to be active, it must undergo triple phosphorylation before it is able to inhibit herpes virus DNA polymerase; (4) selectively accumulate in the microbe because of a more active cell membrane transport mechanism. For example, quinine accumulates more readily in the malarial plasmodium cell than in the host cell; and (5) has a higher afnity for a critical site of action in the microbe. For example, chloramphenicol binds to a fragment of the 70S ribosome of bacterial cells thereby inhibiting synthesis of bacterial proteins. The drug has a much lower afnity for human ribosomes that are 80S. Antibiotics can be either bactericidal or bacteriostatic. That is, they can either kill the pathogen directly or arrest its replication until the body’s immune system can be mobilized. Generally, bactericidal drugs are more desirable, especially in the immunocompromised patient. However, when a microbe is killed by a cidal drug and immediately cleared from the body, the antigenic stimulus is greatly reduced. In some cases, it is so reduced that no immune response is triggered.
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)
155 chapter nine Bacteriocin A natural alternative to synthetic antibacterial antibiotics S. Latha and Dharumadurai Dhanasekaran 9.1 Introduction Antimicrobials are unarguably one of the most important medical discoveries of the twentieth century and function as a vital medicine for the treatment of bacterial infec-tions in both humans and animals. Moreover, they have played a major role in the growth and development of food-producing animals (poultry, goat, sheep, beef, and dairy cattle) mainly by improving their efficiency in growth rate, feed utilization, mortality reduction, etc. However, the continuous use of antibiotics led to the emergence of microbial resis-tance, dissemination of resistant bacteria, and resistance genes to pathogenic bacteria in both humans and animals. A major issue is that antimicrobial resistance (AMR) not only occurs among disease-causing organisms but has also become an issue for other resident organisms in the host. In addition, consumers are also becoming increasingly concerned about the accumulation of drug residues in meat products of food animals (Thacker, 2013). Contents 9.1 Introduction ........................................................................................................................ 155 9.2 Bacteriocins: A class of antimicrobial peptides ............................................................. 156 9.3 Bacteriocins versus conventional antibiotics ................................................................. 157 9.4 Classification of bacteriocins ............................................................................................ 158 9.4.1 Bacteriocins from gram-negative bacteria ......................................................... 158 9.4.2 Bacteriocins from gram-positive bacteria .......................................................... 161 9.4.2.1 Lactic acid bacterial bacteriocin ............................................................
eBook - PDFRevenge of the Microbes
How Bacterial Resistance is Undermining the Antibiotic Miracle
- Brenda A. Wilson, Brian T. Ho(Authors)
- 2023(Publication Date)
- ASM Press(Publisher)
50 • Revenge of the Microbes but rather their specificity for bacteria. By specifically targeting and disrupting key features and processes found exclusively in bacteria, antibiotics are able to inhibit or even destroy bacterial cells without killing the host. Consequently, the very best and safest antibiotics are those that have only bacterial targets and therefore do not cause any toxicity to our cells. What are some of these differences that can be targeted by antibiotics? Bacteria are prokaryotes. By definition, this means that unlike eukaryotic cells like ours, bacterial cells do not have an internal membrane-encased compartment, called a nucleus, that confines the genetic material (DNA) and the cell’s replication machinery. However, there are many other cellular differences. A basic drawing of a bacterial cell is depicted in Fig. 5.1. Bacterial cells are surrounded by a plasma membrane that with the aid of the outer cell wall holds the cellular contents inside as a gelatinous mixture of substances, called a cytoplasm. The cytoplasm contains all of the cell’s genetic material as well as most of the proteins and small molecules needed to carry out basic cellular processes, such as DNA replication, transcrip- tion (producing messenger RNA molecules called mRNA from the DNA tem- plate), translation (producing proteins from mRNA), and metabolism (producing energy from nutrients).
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