Abstract
An antibiotic is an agent that either kills or inhibits the growth of a
microorganism. The term antibiotic was first used in 1942 by Selman Waksman and his
collaborators in journal articles to describe any substance produced by a
microorganism that is antagonistic to the growth of other microorganisms in high
dilution. This definition excluded substances that kill bacteria but that are not
produced by microorganisms (such as gastric juices and hydrogen peroxide). It also
excluded synthetic antibacterial compounds such as the sulfonamides. Many
antibacterial compounds are relatively small molecules with a molecular weight of
less than 2000 atomic mass units.
With advances in medicinal chemistry, most modern antibacterial are semi synthetic
modifications of various natural compounds. These include, for example, the beta-
lactam antibiotics, which include the penicillin (produced by fungi in the genus
Penicillium), the cephalosporin, and the carbapenems. Compounds that are still
isolated from living organisms are the amino glycosides, whereas other
antibacterial—for example, the sulfonamides, the quinolones, and the oxazolidinones
—are produced solely by chemical synthesis.
In accordance with this, many antibacterial compounds are classified on the basis
of chemical/biosynthetic origin into natural, semi synthetic, and synthetic.
Another classification system is based on biological activity; in this
classification, antibacterial are divided into two broad groups according to their
biological effect on microorganisms: Bactericidal agents kill bacteria, and
bacteriostatic agents slow down or stall bacterial growth.
What is Antibiotic Resistance?
Antibiotic resistance is a form of drug resistance whereby some (or, less commonly,
all) sub-populations of a microorganism, usually a bacterial species, are able to
survive after exposure to one or more antibiotics; pathogens resistant to multiple
antibiotics are considered multidrug resistant(MDR) or, more colloquially,
superbugs.
Antibiotic resistance is a serious and growing phenomenon in contemporary medicine
and has emerged as one of the pre-eminent public health concerns of the 21st
century, in particular as it pertains to pathogenic organisms (the term is
especially relevant to organisms that cause disease in humans). A World Health
Organization report released April 30, 2014 states, "this serious threat is no
longer a prediction for the future, it is happening right now in every region of
the world and has the potential to affect anyone, of any age, in any country.
Antibiotic resistance–when bacteria change so antibiotics no longer work in people
who need them to treat infections–is now a major threat to public health."
In the simplest cases, drug-resistant organisms may have acquired resistance to
first-line antibiotics, thereby necessitating the use of second-line agents.
Typically, a first-line agent is selected on the basis of several factors including
safety, availability, and cost; a second-line agent is usually broader in spectrum,
has a less favorable risk-benefit profile, and is more expensive or, in dire
circumstances, may be locally unavailable. In the case of some MDR pathogens,
resistance to second- and even third-line antibiotics is, thus, sequentially
acquired, a case quintessentially illustrated by Staphylococcus aureus in some
nosocomial settings. Some pathogens, such as Pseudomonas aeruginosa, also possess a
high level of intrinsic resistance.
It may take the form of a spontaneous or induced genetic mutation, or the
acquisition of resistance genes from other bacterial species by horizontal gene
transfer via conjugation, transduction, or transformation. Many antibiotic
