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Antibiotic Resistance: Will existing antibiotics remain effective in the future?



What are Antibiotics?

What are Antimicrobials?


The thoughtless person playing with penicillin treatment is morally responsible for the death of the man who succumbs to infection with the penicillin-resistant organism. -- Sir Alexander Fleming (1945)

The discovery and subsequent manufacture of Penicillin led to the finding of an array of antibiotics that had varied biological actions and belonged to different chemical classes. Rather, with advances in molecular- and micro- biology, and various analytical techniques, numerous antimicrobial compounds have been identified and are synthesized for varied uses. From treating serious microbial infections, to preventing infections in surgical and cancer patients, to protecting individuals who are immunocompromised - the role of antimicrobials, more specifically antibiotics, have expanded over the years. Over the years, antibiotics usage have also been extended to veterinary medicine (consequentially in animal husbandry), poultry farming, aquaculture, and even in plant diseases.

Usage of Antibiotics
  • Antibiotics are used in clinical settings/hospitals for the eradication of certain diseases in humans. However, misuse, self-medication, and overuse of antibiotics also exist which may cause adverse reactions, recurrent issues, antibiotic resistance, and other prolonged health issues. [India is one of the world’s largest consumers of antibiotics, and inappropriate use is potentially widespread.]

  • Antibiotics are employed in livestock farming, where they are used for disease treatment of animals. However, they are also given in sub-therapeutic levels in concentrated animal feed for growth promotion, improved feed conversion efficiency, and for the prevention of diseases.

  • Antimicrobials/antibiotics are extensively used in the aquaculture industry. In many parts of the world, fish farming is integrated with poultry wastes, or with sewage or industrial wastewater, or with land agriculture, as manure and other agricultural residues are commonly employed in fish feed. Often antibiotics as prophylaxis are administered to the fishes to compensate for the unhygienic practices and overcrowding of fish (which act as stressors for fish). Antibiotics often reach fishes through livestock wastes in the case of integrated farming.

  • Antibiotics are used in plant agriculture to control certain bacterial diseases of high-value fruit, vegetable, and ornamental plants.

Most of the time, antibiotics used in livestock farming, aquaculture industries, agriculture, or even self medications are often administered in un-regulated doses and purchased over-the-counter.

Antibiotic Pathways in the Environment

Through the years, this heedless and rampant use of antibiotics has resulted in presence of unwanted concentration of antibiotics in different compartments of the environment (e.g. surface water, groundwater, drinking water, municipal sewage, soil, vegetables, sludge) which can be termed as antibiotic pollution. The sources through which the antibiotics enter the environment are diverse (as given below):

  • Wastewater from antibiotic manufacturing industries

At one wastewater plant in India, which is receiving waste from ~90 drug manufacturers, 45 kg (99 lbs.) of ciprofloxacin were released into the nearby river each day. As a comparison, the total daily consumption for the whole country of Sweden is 9 kg. [Ref.]
  • Improper disposal of unused or expired antibiotic medicines by discharging them in sewerage systems. Though the antibiotic contaminated wastewater is treated in wastewater treatment plants (WWTPs), conventional WWTPs cannot provide 100% removal of antibiotics. As such antibiotics remain present in the sludge as well as the effluent, the final products from the WWTPs. The sludge is often used as manure in agricultural lands which further passes on the antibiotics to the soil; the effluent is disposed of in surface waters thus contaminating water bodies. Irrigation of crops with this antibiotic-laden water can lead to agro-ecosystem contamination.

  • Antibiotics used for therapeutic and prophylactic uses in humans and animals enter the environment through urine and excreta. Depending on the class and dosage of the medication, often 40-90% of the administered antibiotic dose is excreted as the parent compound from urine or feces, eventually reaching the environment, contaminating soils, waters, plants, etc. The antibiotic contaminated manure generated from large-scale animal farming may further contaminate soils if applied to agricultural lands as fertilizer without proper treatment.

  • Antibiotic application in plants may eventually end up in the soil or percolate into underground water or join the surface wastewater stream thus contaminating them in the process.

  • Farmers may improperly dispose of their antibiotic containers by throwing them on bare ground, or refuse dumps, or open drains. Under varied environmental conditions, the adhering medication may be released into the environment further leading to contamination.

Antibiotic Resistance

These antibiotic residues, resulting from the indiscriminate use and squandering of antibiotics for purposes other than treatment of infections, have placed immense pressure on the microbial communities, leading to resistance to antibiotics; ergo, natural selection (natural fight for survival). Bacterial populations may also carry mutations due to normal genetic variations or develop advantageous mutations (in presence of antibiotics) transferred via plasmid exchange which renders the antibiotics ineffective against them.

Antibiotic Resistance (ABR) is a process in which a microorganism (in this case bacteria) evolves to become either more, or fully resistant to an antibiotic that could previously treat it effectively, and is a direct result of antibiotic use.

As a result of ABR, the infectious microorganisms no longer respond to medications (antibiotics) making infections difficult or impossible to treat thus increasing the risk of disease spread, severe illness and death.

Researches show that the antibiotics (intended for non-human use) have the same mode of actions or belong to the same general classes as those used for humans. Studies have also shown that many classes of bacteria residing in the gastrointestinal tracts of humans, as well as animals, have developed antibiotic resistance due to constant exposure to sublethal levels of these antibiotics via foods (meat, fish, egg, milk, vegetables), or animal-human/human-human contact pathways. Also, increased consumption of antibiotics may have been the cause of antibiotic resistance in humans, thus delaying the recovery, and increasing morbidity and mortality in many regions throughout the world.

According to WHO,

Antibiotics are becoming increasingly ineffective as drug resistance spreads globally leading to more difficult to treat infections and death. New antibacterials are urgently needed. However, if people do not change the way antibiotics are used now, these new antibiotics will suffer the same fate as the current ones and become ineffective.

According to WHO, high rates of ABR have been observed worldwide for antibiotics used to treat common bacterial infections like urinary tract infections, sepsis, sexually transmitted infections, and some forms of diarrhea.

For example, the rate of resistance to ciprofloxacin, an antibiotic commonly used to treat urinary tract infections, varied from 8.4% to 92.9% for Escherichia coli and from 4.1% to 79.4% for Klebsiella pneumoniae in countries reporting to the Global Antimicrobial Resistance and Use Surveillance System (GLASS).

We are running out of antibiotics/antimicrobials.

In 2019, the WHO identified 32 antibiotics in clinical development that addresses the WHO list of priority pathogens, of which only six were classified as innovative.


For a detailed list of existing antibiotics that have become resistant to microbes, you may refer to this WHO website.


What Dr. Fleming had predicted some 70+ years back is seemingly becoming true for the present generations and future.

While the discovery of antibiotics (like Penicillin) ushered in an era of incredible advances in medicine in the 20th century, it also created a setting for a more dangerous period for mankind where minor wounds may become untreatable with the existing medicines.

Antibiotic resistance is emerging as a major problem of global significance which demands judicious use of these drugs in every system. Novel antibiotics need to be developed by the pharmaceutical companies and also judiciously used so that we retain the capability of treating infectious diseases for the coming generations.











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