A small worksheet on Antibiotics

A small work sheet for antibiotics. For AS Level, and Only A* Pupils at GCSE.

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Testing the susceptibility of Staphylococcus aureus to antibiotics by the KirbyBauer disk
diffusion method. Antibiotics diffuse out from antibioticcontaining disks and inhibit growth of S.
aureus resulting in a zone of inhibition.
In modern usage, an antibiotic is a chemotherapeutic agent with activity against microorganisms
such as bacteria, fungi or protozoa.[1]
The term "antibiotic" (from the Ancient Greek language ­ anti, "against" and ­ bios,
"life") was coined by Selman Waksman in 1942 to describe any substance produced by a
microorganism that is antagonistic to the growth of other microorganisms in high dilution. This
original definition excluded naturally occurring substances, such as gastric juice and hydrogen
peroxide (they kill microorganisms but are not produced by microorganisms), and also
excluded synthetic compounds such as the sulfonamides (which are antimicrobial agents). Many
antibiotics are relatively small molecules with a molecular weight less than 2000 Da.
With advances in medicinal chemistry, most antibiotics are now modified chemically from
original compounds found in nature, as is the case with betalactams (which include the
penicillins, produced by fungi in the genus Penicillium, the cephalosporins, and the
carbapenems). Some antibiotics are still produced and isolated from living organisms, such as
the aminoglycosides in addition, many more have been created through purely synthetic means,
such as the quinolones.
Unlike many previous treatments for infections, which often consisted of administering chemical
compounds such as strychnine and arsenic, with high toxicity also against mammals, most
antibiotics from microbes have fewer sideeffects, and high effective target activity. Most
antibacterial antibiotics do not have activity against viruses, fungi, or other microbes.
Antibacterial antibiotics can be categorized based on their target specificity: "narrowspectrum"
antibiotics target particular types of bacteria, such as Gramnegative or Grampositive bacteria,
while broadspectrum antibiotics affect a wide range of bacteria.
The environment of individual antibiotics varies with the location of the infection, the ability of the
antibiotic to reach the infection site, and the ability of the microbe to inactivate or excrete the

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Some antibacterial antibiotics destroy bacteria (bactericidal), whereas others prevent
bacteria from multiplying (bacteriostatic).
Oral antibiotics are simply ingested, while intravenous antibiotics are used in more serious cases,
such as deepseated systemic infections. Antibiotics may also sometimes be administered
topically, as with eye drops or ointments.
In the last few years three new classes of antibiotics have been brought into clinical use. This
follows a 40year hiatus in discovering new classes of antibiotic compounds.…read more

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Points of attack on bacteria by antibiotics
At the highest level, antibiotics can be classified as either bactericidal or bacteriostatic.
Bactericidals kill bacteria directly where bacteriostatics prevent cell division. However, these
classifications are based on laboratory behavior in practice, both of these are capable of ending
a bacterial infection.[2] The bactericidal activity of antibiotics may be growth phase dependent
and in most but not all cases action of many bactericidal antibiotics requires ongoing cell activity
and cell division for the drugs' killing activity.…read more

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One of the more common side effects is
diarrhea, sometimes caused by the anaerobic bacterium Clostridium difficile, which results
from the antibiotic disrupting the normal balance of the intestinal flora,[8] Such overgrowth of
pathogenic bacteria may be alleviated by ingesting probiotics during a course of
antibiotics.[citation needed]. An antibioticinduced disruption of the population of the bacteria
normally present as constituents of the normal vaginal flora may also occur, and may lead to
overgrowth of yeast species of the genus Candida in the vulvovaginal area.…read more

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Microbiology (ASM), American Public Health Association (APHA) and the American Medical
Association (AMA)) have called for restrictions on antibiotic use in food animal production and
an end to all nontherapeutic uses.[citation needed] However, delays in regulatory and legislative
actions to limit the use of antibiotics are common, and may include resistance to these changes
by industries using or selling antibiotics, as well as time spent on research to establish causal
links between antibiotic use and emergence of untreatable bacterial diseases. Two federal bills
(S.…read more

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These plasmids can
carry different genes with diverse resistance mechanisms to unrelated antibiotics but because
they are located on the same plasmid multiple antibiotic resistance to more than one antibiotic is
transferred.[31] Alternatively, crossresistance to other antibiotics within the bacteria results when
the same resistance mechanism is responsible for resistance to more than one antibiotic is
selected for.[31]
Resistance modifying agents
One solution to combat resistance currently being researched is the development of
pharmaceutical compounds that would revert multiple antibiotic resistance.…read more

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Bacteriocins are also a growing alternative to the classic smallmolecule antibiotics [34]. Different
classes of bacteriocins have different potential as therapeutic agents. Small molecule
bacteriocins (microcins, for example, and lantibiotics) may be similar to the classic antibiotics
colicinlike bacteriocins are more likely to be narrowspectrum, demanding new molecular
diagnostics prior to therapy but also not raising the spectre of resistance to the same degree.…read more


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