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ANTIBIOTICS

Introduction:
Antibiotics or antibacterials are a type of antimicrobial used in the treatment and
prevention of bacterial infection
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Several antibiotics are also effective against fungi and protozoans, and some are toxic to
humans and animals
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Sometimes the term antibiotic is used to refer to any substance used against microbes,
synonymous to antimicrobial
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, but not as medicine
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History:
In 1929, Alexander Fleming identified penicillin, the first chemical compound with
antibiotic properties
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He observed
that the presence of the mold killed or prevented the growth of the bacteria
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Their effectiveness and easy access led to overuse, especially in live-stock raising,
prompting bacteria to develop resistance
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The era of antibacterial chemotherapy began with the discovery of arsphenamine, first
synthesized by Alfred Bertheim and Paul Ehrlich in 1907, used to treat syphilis
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All classes of
antibiotics in use today were first discovered prior to the mid 1980s
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g
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• Immunomodulation
2) Prevention:
• Surgical wound
• Dental antibiotic prophylaxis
• Conditions of neutropenia, e
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Cancer-related
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Most target bacterial functions or growth
processes
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Example: Penicillins, Cephalosporins,
Rifamycins and Sulfonamides
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Example: Macrolides,
Lincosamides and Tetracyclins
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"Narrow-spectrum"
antibacterial antibiotics target specific types of bacteria, such as Gramnegative or Gram-positive bacteria, whereas broad-spectrum antibiotics affect a wide
range of bacteria
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These are called semisynthetic antibiotics
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• Synthetic: Which are produced solely by chemical synthesis
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• Natural: Compounds those are still isolated from living organisms
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Side-Effects:
Antibiotics are screened for any negative effects on humans or other mammals before
approval for clinical use, and are usually considered safe and most are well-tolerated
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Side-effects range from mild to very serious depending on the antibiotics used, the
microbial organisms targeted, and the individual patient
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Common side-effects include diarrhea,
resulting from disruption of the species composition in the intestinal flora
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Emergence of resistance often reflects evolutionary processes that take place during
antibiotic therapy
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Under certain conditions, it may result in preferential growth of resistant bacteria,
while growth of susceptible bacteria is inhibited by the drug
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The survival of bacteria often results from an inheritable resistance,
but the growth of resistance to antibacterials also occurs through horizontal gene
transfer
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Antibacterial resistance may impose a biological cost, thereby reducing fitness of
resistant strains, which can limit the spread of antibacterial-resistant bacteria, for
example, in the absence of antibacterial compounds
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Several molecular mechanisms of antibacterial resistance exist
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For example, an
antibiotic target may be absent from the bacterial genome
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Antibacterial-producing bacteria have evolved resistance mechanisms that have
been shown to be similar to, and may have been transferred to, antibacterial-resistant
strains
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For instance, antibacterial resistance genes can be
exchanged between different bacterial strains or species via plasmids that carry these
resistance genes
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Cross-resistance to several antibacterials may also
occur when a resistance mechanism encoded by a single gene conveys resistance to
more than one antibacterial compound
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For
example, emergent bacterial strains causing tuberculosis (TB) that are resistant to
previously effective antibacterial treatments pose many therapeutic challenges
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Misuse:
Inappropriate antibiotic treatment and overuse of antibiotics have contributed to the
emergence of antibiotic-resistant bacteria
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Many antibiotics are frequently prescribed to treat symptoms or diseases
that do not respond to antibiotics or that are likely to resolve without treatment
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The
overuse of antibiotics, like penicillin and erythromycin, has been associated with
emerging antibiotic resistance since the 1950s
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Common forms of antibiotic misuse include excessive use of prophylactic antibiotics in
travellers and failure of medical professionals to prescribe the correct dosage of
antibiotics on the basis of the patient's weight and history of prior use
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Several organizations concerned with antimicrobial resistance are lobbying to eliminate
the unnecessary use of antibiotics
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Alternatives:
The increase in bacterial strains that are resistant to conventional antibacterial
therapies has prompted the development of bacterial disease treatment strategies that
are alternatives to conventional antibacterials
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For example, some
resistance-modifying agents may inhibit multidrug resistance mechanisms, such as drug
efflux from the cell, thus increasing the susceptibility of bacteria to an antibacterial
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Vaccination either excites
or reinforces the immune competence of a host to ward off infection, leading to the
activation of macrophages, the production of antibodies, inflammation, and other classic
immune reactions
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Vaccines made from attenuated whole cells or lysates have
been replaced largely by less reactogenic, cell-free vaccines consisting of purified
components, including capsular polysaccharides and their conjugates, to protein
carriers, as well as inactivated toxins (toxoids) and proteins
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Bacteriophages, also known simply as phages, are precisely bacterial
viruses that infect bacteria by disrupting pathogenic bacterium lytic cycles
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One of the worries about using phages to fight
pathogens is that the phages will infect "good" bacteria, or the bacteria that are
important in the everyday function of human beings
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