∞ generated and posted on 2016.12.15 ∞

Selectively toxic chemical antibacterial, historically as produced by other microorganisms.

An Antibiotic is a drug that is harmful especially to bacteria, ideally not to other organisms (such as ourselves), and unquestionably not effective against viruses.

These other microorganisms include both fungi and other bacteria. More loosely, however, the concept of antibiotic has come to describe also synthetic chemical antibacterials that similarly are selectively toxic and consequently specific for only certain bacterial targets. Contrast disinfectants, which often are more generally acting germicides.

Note that not all bacteria are sensitive to every antibiotic and in fact antibiotics can be differentiated in terms of their spectra of activity, with some displaying broad spectrums of activity while others have spectra that are more narrow—just Gram-positive bacteria rather than both Gram-negative bacteria and Gram-positive bacteria, for example.

Figure legend: Just what is an antibiotic? Basically, it is a selectively toxic, chemotherapeutic, antibacterial, and, at least as traditionally defined, it is something that is naturally synthesized by microorganisms such as fungi and other bacteria.

The first antibiotic identified, penicillin, was discovered in 1928 by Alexander Fleming but was not available in substantial quantities until during and after World War II.

Though antibiotics have played an essential role in combating pathogenic bacteria, they are limited in their effectiveness by a combination of side effects if dosed at too high levels and the potential for bacteria to evolve resistance. Note that penicillin has the distinction of being unusually safe to use (allergic reactions aside), but displays a fairly narrow spectrum of activity and also has selected for a substantial amount of resistance among target bacteria.

From Cotter et al. (2013):

It could be argued that the identification and development of antibiotic therapy represents the most significant scientific achievement of the twentieth century in terms of an impact on human morbidity and mortality. Unfortunately, several problems have arisen that limit these initial benefits and cast doubt on how useful antibiotics will prove to be in the twenty-first century. Pathogens have emerged that are resistant to single, and subsequently multiple, antibiotics. Moreover, there is a shortage of new families of antibiotics that could potentially compensate for resistance to existing antibiotics, in part owing to the high costs and risks associated with developing and using such products Finally, it has become clear that the administration of broad-spectrum antibiotics can lead to 'collateral damage' to the human commensal microbiota, which has several key roles in host health. The potential association between the use of broad-spectrum antibiotics and the increasing incidence of atopic and autoimmune diseases is a particular cause for concern .

From Berleman and Kirby (2009):

The 21st century is likely to be defined by how our global society comes to terms with the reality of limited resources. One example of this is the use of antibiotics since their commercial introduction 80 years ago. The first century of antibiotic usage was marked by the assumption that there will always be another antibiotic available. Yet, as molecule after molecule loses its effectiveness in the wake of emerging multi-drug resistant pathogens, it becomes ever more clear that this approach is not likely to be sustainable over the next 80 years.

The following video provides a very basic introduction to antibiotics:

The following can be considered a standard definition of antibiotic, from Waksman, 1947 , though see as well the discussion of Bentley and Bennett :

An antibiotic is a chemical substance, produced by micro-organisms, which has the capacity to inhibit the growth of and even to destroy bacteria and other micro-organisms. The action of an antibiotic against micro-organisms is selective in nature, some organisms being affected and others not at all or only to a limited degree; each antibiotic is thus characterized by a specific antimicrobial spectrum. The selective action of an antibiotic is also manifested against microbial vs. host cells. Antibiotics vary greatly in their physical and chemical properties and in their toxicity to animals. Because of these characteristics, some antibiotics have remarkable chemotherapeutic potentialities and can be used for the control of various microbial infections in man and animals.

Note that an additional property cited in later Waksman publications is also "that antibiotics were effective in low concentrations, a change intended to exclude materials such as acids and alcohols."

Note, however, from Bentley and Bennett :

Do antibiotics have to be microbial products? Contemporary usage answers this question with a resounding " no." Current usage, by most workers in the field, is extremely inclusive with multicellular plants and animals both being accepted as legitimate sources of antibiotic materials. ¶ …Waksman's antibiotic was synonymous with "all antimicrobial substances of microbial origin." ¶ A difficulty not foreseen by Waksman, or the other early pioneers, was that almost all the clinically significant antibiotics isolated for most of a half century were active only against bacteria. Antifungal agents, antiprotozoal agents, and antiviral agents were-with few exceptions-too toxic for therapeutic use. Therefore, the clinical application of antibiotics was largely restricted to treatment of diseases caused by bacterial pathogens. Because these drugs were so efficacious, many lay people came to expect that they should be effective against all infectious disease. To correct this misconception, it became commonplace for health care workers to warn patients that antibiotics did not work against influenza, malaria, and other microbial diseases of nonbacteriological etiology. This practical advice has affected the vernacular and clinical meaning of antibiotic…