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Antibiotics: what are they and how do they work?
The US National Library of Medicine1 says that antibiotics - powerful medicines that fight bacterial infections - can save lives when used properly. Antibiotics either stop bacteria from reproducing or kill them. "Your body's natural defenses can usually take it from there."

Before bacteria can multiply and cause symptoms, the body's immune system can usually destroy them. We have special white blood cells that attack harmful bacteria. Even if symptoms do occur, our immune system can usually cope and fight off the infection. There are occasions, however, when it is all too much and some help is needed.....from antibiotics.

Alexander Fleming
Alexander Fleming discovered penicillin, the first natural antibiotic, in 1928.
The first antibiotic was penicillin. Such penicillin-related antibiotics as ampicillin, amoxicillin and benzylpenicilllin are widely used today to treat a variety of infections - these antibiotics have been around for a long time.

There are several different types of modern antibiotics and they are only available with a doctor's prescription in most countries.

Overusing antibiotics - There is concern worldwide that antibiotics are being overused. Antibiotic overuse is one of the factors that contributes towards the growing number of bacterial infections which are becoming resistant to antibacterial medications.
Antibiotics fight against bacterial infections, they are not anti-viral. Taking antibiotics knowingly for viral infections is likely a mistake. Some doctors just prescribe it because without doing couple of tests it is hard to tell whether or not the infection is viral or bacterial.
Antibiotics came as a boon to human civilization with invent of the Penicillin that saved a million lives. Antibiotics are chemotherapeutic agent that abolishes or retards growth of microbe, such as fungi, bacteria or protozoa. Classically an antibiotic is defined as a compound produced by one microorganism that inhibits the growth of another microorganism. This definition over the years has been elaborated to include synthetic and semi-synthetic agents. Although not synonymous antibiotics are also referred as antimicrobials or chemotherapeutics. As, for example, antimicrobials may be effective against viruses. The term ‘chemotherapeutical” is also known as anti-neoplastic drugs referred to compounds used for the treating disease like cancer. The term, ‘‘chemotherapeutical” may also refer to antibiotics in which case it is known as antibacterial chemotherapy. Currently there are nearly 250 different chemical entities registered for its application in medicine and veterinary medicine. The first antibiotic, Penicillin was of natural origin produced by fungi Penicillium, and streptomycin by bacteria Streptomyces. In recent times antibiotic such as sulfa drugs (e.g. sulfamethoxazole) are being synthesized chemically or by chemically modifying compounds of natural origin. Some antibiotics are relatively small molecules with molecular weight less than 1000 Da.

In contrast to the desired properties and affects the therapeutic application of antibiotics, are often disadvantageous for target and non-target organisms present in the environment

Although over the decades antibiotic have been used in large quantities, the existence of these substances in the environment has gained little notice. A more complex investigation of antibiotic substances has been undertaken only in recent years, so as to assess the environmental risks they may pose. It was found that the concentrations of antibiotics measured in hospital effluents, municipal sewage, surface and ground water, influents and effluents of STPs, are mostly in the same range, respectively.
Although an increasing number of investigations covering input, fate, occurrence and effect of antibiotics have been published over the last decades, but, despite the numerous studies performed there is still a lack of proper understanding and knowledge about the existence and effects of antibiotic agents in the aquatic environment. Therefore, extensive and thorough research is needed to explore certain significant issues and questions related to these substances that are still open and must be properly handled in the future for a better understanding of the risk associated and behavior of antibiotics in the environment. I hope this reply addresses the present state of knowledge relating to the occurrence and effects of antibiotics in the aquatic environment.
It is important not to become confused between bacteriophages, which are viruses that infect bacteria rather than eukaryotes, and the multiple types of viruses that directly infect eukaryotes including humans, and cause illnesses such as influenza, measles, chicken pox, AIDS and rubella. Antibiotics are antibacterial drugs that kill bacteria and are useless in terms of killing the types of viruses that directly infect humans; as another reply in this discussion thread points out this would require therapy with specific anti-viral medications or can be prevented by vaccinations such as the MMR against measles, mumps and rubella. However, they can be useful if the viral infection then leaves the patient susceptible to secondary bacterial infections, as mentioned by another poster.

Bacteriophages, which infect bacteria are found as part of our gastrointestinal microbiota, for example, as they infect the bacteria in our gut. These bacteriophages express antibiotic resistance genes which are thought to be protective in maintenance of gut health as they help protect the ‘good’ bacteria against the harmful effects of naturally occurring antibiotics. This expression of antibiotic-resistance genes has been a feature of bacteriophages since long before antibiotics were used therapeutically. For example, antibiotic-resistance genes have been identified in bacteriophages found in fossilised faecal samples dating from the 14th century; the presence of these bacteriophages in coprolites (fossilised faecal samples) is indicative that they would have been present in the gastrointestinal tract. Many of the bacteriophage sequences identified were related to phages that we know currently infect bacteria commonly identified in stools, including both harmless, helpful and pathogenic bacteria. They differ taxonomically from bacteriophages identified in modern faecal samples but functionally their role in antibiotic resistance has been conserved. This interesting study has been considered before in a news article on this website (

However, such bacteriophages with antibiotic resistance genes also infect pathogenic bacteria, which would contribute to their resistance to antibiotics, as well as these bacteria evolving their own direct antibiotic resistance mechanisms faster than scientists can develop new antibiotics. Over-prescription of antibiotics over time, for example in cases of viral infections, has contributed to the growing public health crisis of multidrug resistant ‘superbugs’. Multi-drug resistant bacteria, such as extended-spectrum β-lactamase (ESBL)–producing Enterobacteriaceae, third-generation cephalosporin-resistant (G3CR) Enterobacteriaceae and methicillin resistant Staphylococcus aureus are now a serious international public health threat. In response to the international nature of this threat, a joint programme initiative, namely the Joint Programme on Antimicrobial Resistance (JPIAMR), has been launched to aims to gather research funders from nineteen European countries, Canada and Israel, as well as having support from other countries ranging from Australia to South Africa (

Various research avenues are being explored in an effort to win the battle of antibiotic resistance, for example developing use of uncultured bacteria, which comprise approximately 99% of all bacterial species in external environments, as a source of antibiotics. An example of this was published last week in the journal Nature, in which a new antibiotic called teixobactin, derived from growth of uncultured bacteria, is described. Teixobactin inhibits bacterial cell wall synthesis and when tested on mutant Staphylococcus aureus or Mycobacterium tuberculosis strains, no resistant mutants were identified. This study is the subject of a recent news article on this website (


APPELT, S., FANCELLO, L., LE BAILLY, M., RAOULT, D., DRANCOURT, M. and DESNUES, C., 2014. Viruses in a 14th-century coprolite. Appl. Environ. Microbiol. (2014) doi:10.1128/AEM.03242-13

LING LL et al. A new antibiotic kills pathogens without detectable resistance. Nature (2015); doi:10.1038/nature14098

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Antibiotics: what are they and how do they work?00