An antimicrobial is an agent that kills microorganisms or prevents their growth. The medicines are grouped according to the microorganisms they act against. Antibiotics are used against bacteria, and antifungals are used against fungi. They are also be classified according to function. If they destroy microbes, they are microbicidal, ones which prevent growth are biostatic.
What is an Antimicrobial (Discovery and History)?
2000 years ago, ancient Egyptians and the Greeks used plant extracts to fight infection. Pasteur and Joubert observed antagonism between bacteria, in the 1800’s and speculated the use in medicine. Pasteur’s detailed work in fermentation led to the classification of anaerobic and aerobic bacteria. Lister incorporated beneficial antiseptic methods, such as sterilising surgical tools, from this early information.
Deaths through surgery were significantly reduced following these antiseptic techniques. In 1928, Fleming returned from holiday and discovered that a Petri dish filled with Staphylococcus was separated into colonies due to Penicillium rubens. In 1942, Florey, Chain, and Abraham used Fleming’s work to extract penicillin for medicinal uses earning them the 1945 Nobel Prize in Medicine.
Examples of antimicrobial – chemical
Antibacterials are used to treat bacterial infections and antibiotics are classified as beta-lactams, macrolides, quinolones, tetracyclines or aminoglycosides. Their antimicrobial spectra identify them via pharmacodynamics, and chemical composition.
The discovery and use of antibacterials has reduced mortality from bacterial infections remarkably. Application of nitroglycerine drugs between 1945 and the 70’s, when a number of structurally diverse and highly effective agents were discovered. In parallel, there has been an overwhelming increase in antimicrobial resistance to fungi, parasites and some viruses.
The overuse of antibacterials over time has led to a catalysed rise of highly resistant pathogens, leading to the search for alternative variations effective against pathogenic bacteria. Combatting this, can be via the application of metagenomics to identify bioactive compounds, produced by currently unknown and uncultured microorganisms.
Antimicrobial resistance (AMR) is a global health threat and requires action to achieve the Sustainable Development Goals (SDGs). The World Health Organisation (WHO) has declared that AMR is one of the top 10 global public health threats. There is a huge cost of AMR to the economy. Prolonged illness leads to longer hospital stays, more expensive medicines and ultimately, financial consequences.
Investment into the research of new antimicrobial medicines and vaccines, aiming at carbapenem-resistant Enterobacteriaceae and Acinetobacter baumannii. The launch of the Antimicrobial Resistance Multi Partner Trust Fund (AMR MPTF), AMR Action Fund are positive steps.
Antifungals prevent further growth of fungi and in medicine they are used as a treatment for infections such as ringworm and thrush. They exploit differences between mammalian and fungal cells. Fungal and human cells are similar at the molecular level, making it more difficult to find a target for an antifungal drug to attack that does not also exist in the host organism.
Antifungals can also be utilised to control indoor mould. Another antifungal solution is a mix of hydrogen peroxide and a thin surface coating that neutralises the mould. Paints are also produced with an antifungal agent for use in high humidity areas like bathrooms.
Antiviral drugs are a class of medication used specifically for viral infections. Many antiviral drugs are designed to treat infections by retroviruses, including HIV. Important antiretroviral drugs, include the class of protease inhibitors. Viral hepatitis is caused by five unrelated hepatotropic viruses (A-E) and may be treated with antiviral drugs.
Antiparasitics treat infectious diseases like leishmaniasis, caused by parasites like nematodes, cestodes and trematodes. Antiparasitic medications include metronidazole, iodoquinol and albendazole.
Broad-spectrum therapeutics are active against multiple classes of pathogens. Azithromycin is the only broad-spectrum therapeutic.
Antimicrobial mouthwash – disadvantages
There are many species of microorganisms in the oral biofilm. Commensal microbes have clear benefits for the host. A publication in Free Radical Biology and Medicine, has rationalised the impact of antibiotic mouthwashes. Researchers studied the consequences of reduced nitrite-producing oral bacteria, post exercise. Acute physical exercise will induce post exercise hypotension, which contributes to a lower blood pressure.
The study monitored 23 humans, after treadmill workouts. Blood and salivary nitrite levels were measured. Participants in the research received either antimicrobial mouthwash or a null sample. Subjects not receiving antimicrobial mouthwash, showed a reduced systolic blood pressure. The authors concluded that nitrite synthesis by oral bacteria promotes lowered blood pressure and elevated oxygenation in the muscles. By contrast, destruction of oral bacteria may nullify the lower blood pressure, resulting from exercise.
A wide range of chemical compounds are used as antimicrobials. Organic acids and their salts are used widely in food products, e.g. lactic acid, citric acid, acetic acid, either as ingredients or as disinfectants.
Copper-alloy surfaces have natural intrinsic antimicrobial properties and can kill microorganisms such as E. coli and Staphylococcus. Other heavy metal cations such as Hg2+ and Pb2+ have antimicrobial activities.
Traditional herbalists used plants to treat infectious disease. Certain plant products can inhibit the growth of pathogenic microorganisms. Some of these agents appear to have structures and modes of action that are distinct from those of antibiotics.
Essential oils are claimed to possess antimicrobial activity, with the oils of bay, cinnamon, clove and thyme, the most potent with respect to bacterial pathogens. Active constituents include terpenoids and secondary metabolites. Barriers to increased usage in mainstream medicine include poor regulatory oversight and quality control.
Antimicrobial pesticides are used in order to control growth of microbes through disinfection, sanitation, industrial processes or systems, surfaces, water, or other chemical substances from contamination, fouling, or deterioration caused by bacteria, viruses, fungi, protozoa, or algae.
Although antimicrobial stewardship originated within human healthcare, it is increasingly applied to animal health too. The overuse of antibiotics has drastically contributed to resistance. Published in Antibiotic Resistance Threats in the United States, 2019. It is estimated that over 2.5 million antibiotic-resistant infections occur in the US annually.
Antibiotic stewardship programs can lead to better patient outcomes. Antibiotic Stewardship Programs (ASPs) help clinicians minimise negative effects by improving antibiotic prescribing. Hospital stewardship can increase infection cure rates. They can also decrease the rate of treatment failures, C.Difficile infections, resistance and the cost and length of the hospital stay.
In 2014, CDC called on all hospitals to uptake stewardship programs. The following year, The US National Action Plan for Combating Antibiotic Resistant Bacteria set targets of Core Elements in all hospitals.
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