Probable phosphatidylethanolamine transferase Mcr-1 | |||||||
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Symbol | mcr1 | ||||||
UniProt | A0A0R6L508 | ||||||
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The mobilized colistin resistance (mcr) gene confers plasmid-mediated resistance to colistin, one of a number of last-resort antibiotics for treating Gram-negative infections. mcr-1, the original variant, is capable of horizontal transfer between different strains of a bacterial species. After discovery in November 2015 in E. coli (strain SHP45) from a pig in China it has been found in Escherichia coli , Salmonella enterica , Klebsiella pneumoniae , Enterobacter aerogenes , and Enterobacter cloacae . As of 2017 [update] , it has been detected in more than 30 countries on 5 continents in less than a year.
The "mobilized colistin resistance" (mcr-1) gene confers plasmid-mediated resistance to colistin, a polymyxin and one of a number of last-resort antibiotics for treating infections. [1] [2] The gene is found in no less than ten species of the Enterobacteriaceae: Escherichia coli , Salmonella , Klebsiella pneumoniae , Enterobacter aerogenes , Enterobacter cloacae , Cronobacter sakazakii , Shigella sonnei , Kluyvera species, Citrobacter species, and Raoultella ornithinolytica .[ citation needed ]
The mechanism of resistance of the MCR gene is a lipid A phosphoethanolamine transferase. The enzyme transfers a phosphoethanolamine residue to the lipid A present in the cell membrane of gram-negative bacteria. The altered lipid A has much lower affinity for colistin and related polymyxins resulting in reduced activity of the antimicrobial. This type of resistance is known as target modification. [3] Although the same mechanism has been observed before with enzymes like eptA, [4] mcr-1 is the first polymyxin resistance gene known to be capable of horizontal transfer between different strains of a bacterial species. [1]
mcr-1 also provides resistance to host antimicrobial peptides. Bacteria carrying the gene were better at killing infected caterpillars. [5]
The gene was first discovered in E. coli (strain SHP45) from a pig in China April 2011 and published in November 2015. [6] [7] It was identified by independent researchers in human samples from Malaysia, China, [1] England, [8] [9] Scotland, [10] and the United States. [11]
In April 2016, a 49-year-old woman sought medical care at a Pennsylvania clinic for UTI symptoms. PCR of an E. coli isolate cultured from her urine revealed the mcr-1 gene for the first time in the United States, [12] and the CDC sent an alert to health care facilities. In the following twelve months, four additional people were reported to have infections with mcr-1 carrying bacteria. [13]
As of February 2017 [update] mcr-1 has been detected in more than 30 countries on 5 continents in less than a year, [14] and it appears to be spreading in hospitals in China. [15] The prevalence in five Chinese provinces between April 2011 and November 2014 was 15% in raw meat samples and 21% in food animals during 2011–14, and 1% in people hospitalized with infection. [1]
Using genetic analysis, researchers believe that they have shown that the origins of the gene were on a Chinese pig farm where colistin was routinely used. [16] [17]
Given the importance of mcr-1 in enabling bacteria to acquire polymyxin resistance, MCR-1 (the protein that is encoded by mcr-1) is a current inhibition target for the development of new antibiotics. [18] For example, ethylenediaminetetraacetic acid (EDTA), a metal-chelating agent and common food additive, was shown to inhibit MCR-1 as it is a zinc-dependent enzyme. [3] Substrate analogues, such as ethanolamine and glucose, were also shown to inhibit MCR-1. [19] The use of a combined antibiotics regime has shown to be able to overcome the resistance that is caused by mcr-1, and the mechanism of action may be directly or indirectly targeting the MCR-1 protein. [20]
As of April 2021 [update] , ten mobilized colistin resistance genes termed mcr-1 through mcr-10 have been identified. They are homologous to each other, and work in similar ways. [21] The mcr-2 gene is a rare variant of mcr-1 and is found only in Belgium. The less-related mcr-3, mcr-4, and mcr-5 were identified in E. coli and Salmonella. [22]
On the phylogenic tree, the various clusters of mcr genes are scattered between immobile resistance genes of the same type, suggesting a history of multiple transfer to plasmids. [23] [24] [19] [25]
Beta-lactamases (β-lactamases) are enzymes produced by bacteria that provide multi-resistance to beta-lactam antibiotics such as penicillins, cephalosporins, cephamycins, monobactams and carbapenems (ertapenem), although carbapenems are relatively resistant to beta-lactamase. Beta-lactamase provides antibiotic resistance by breaking the antibiotics' structure. These antibiotics all have a common element in their molecular structure: a four-atom ring known as a beta-lactam (β-lactam) ring. Through hydrolysis, the enzyme lactamase breaks the β-lactam ring open, deactivating the molecule's antibacterial properties.
Klebsiella pneumoniae is a Gram-negative, non-motile, encapsulated, lactose-fermenting, facultative anaerobic, rod-shaped bacterium. It appears as a mucoid lactose fermenter on MacConkey agar.
Polymyxins are antibiotics. Polymyxins B and E are used in the treatment of Gram-negative bacterial infections. They work mostly by breaking up the bacterial cell membrane. They are part of a broader class of molecules called nonribosomal peptides.
Colistin, also known as polymyxin E, is an antibiotic medication used as a last-resort treatment for multidrug-resistant Gram-negative infections including pneumonia. These may involve bacteria such as Pseudomonas aeruginosa, Klebsiella pneumoniae, or Acinetobacter. It comes in two forms: colistimethate sodium can be injected into a vein, injected into a muscle, or inhaled, and colistin sulfate is mainly applied to the skin or taken by mouth. Colistimethate sodium is a prodrug; it is produced by the reaction of colistin with formaldehyde and sodium bisulfite, which leads to the addition of a sulfomethyl group to the primary amines of colistin. Colistimethate sodium is less toxic than colistin when administered parenterally. In aqueous solutions it undergoes hydrolysis to form a complex mixture of partially sulfomethylated derivatives, as well as colistin. Resistance to colistin began to appear as of 2015.
Multiple drug resistance (MDR), multidrug resistance or multiresistance is antimicrobial resistance shown by a species of microorganism to at least one antimicrobial drug in three or more antimicrobial categories. Antimicrobial categories are classifications of antimicrobial agents based on their mode of action and specific to target organisms. The MDR types most threatening to public health are MDR bacteria that resist multiple antibiotics; other types include MDR viruses, parasites.
An efflux pump is an active transporter in cells that moves out unwanted material. Efflux pumps are an important component in bacteria in their ability to remove antibiotics. The efflux could also be the movement of heavy metals, organic pollutants, plant-produced compounds, quorum sensing signals, bacterial metabolites and neurotransmitters. All microorganisms, with a few exceptions, have highly conserved DNA sequences in their genome that encode efflux pumps. Efflux pumps actively move substances out of a microorganism, in a process known as active efflux, which is a vital part of xenobiotic metabolism. This active efflux mechanism is responsible for various types of resistance to bacterial pathogens within bacterial species - the most concerning being antibiotic resistance because microorganisms can have adapted efflux pumps to divert toxins out of the cytoplasm and into extracellular media.
Acinetobacter baumannii is a typically short, almost round, rod-shaped (coccobacillus) Gram-negative bacterium. It is named after the bacteriologist Paul Baumann. It can be an opportunistic pathogen in humans, affecting people with compromised immune systems, and is becoming increasingly important as a hospital-derived (nosocomial) infection. While other species of the genus Acinetobacter are often found in soil samples, it is almost exclusively isolated from hospital environments. Although occasionally it has been found in environmental soil and water samples, its natural habitat is still not known.
Fosfomycin, sold under the brand name Monurol among others, is an antibiotic primarily used to treat lower urinary tract infections. It is not indicated for kidney infections. Occasionally it is used for prostate infections. It is generally taken by mouth.
An origin of transfer (oriT) is a short sequence ranging from 40-500 base pairs in length that is necessary for the transfer of DNA from a gram-negative bacterial donor to recipient during bacterial conjugation. The transfer of DNA is a critical component for antimicrobial resistance within bacterial cells and the oriT structure and mechanism within plasmid DNA is complementary to its function in bacterial conjugation. The first oriT to be identified and cloned was on the RK2 (IncP) conjugative plasmid, which was done by Guiney and Helinski in 1979.
Polypeptide antibiotics are a chemically diverse class of anti-infective and antitumor antibiotics containing non-protein polypeptide chains. Examples of this class include actinomycin, bacitracin, colistin, and polymyxin B. Actinomycin-D has found use in cancer chemotherapy. Most other polypeptide antibiotics are too toxic for systemic administration, but can safely be administered topically to the skin as an antiseptic for shallow cuts and abrasions.
NDM-1 is an enzyme that makes bacteria resistant to a broad range of beta-lactam antibiotics. These include the antibiotics of the carbapenem family, which are a mainstay for the treatment of antibiotic-resistant bacterial infections. The gene for NDM-1 is one member of a large gene family that encodes beta-lactamase enzymes called carbapenemases. Bacteria that produce carbapenemases are often referred to in the news media as "superbugs" because infections caused by them are difficult to treat. Such bacteria are usually sensitive only to polymyxins and tigecycline.
Plasmid-mediated resistance is the transfer of antibiotic resistance genes which are carried on plasmids. Plasmids possess mechanisms that ensure their independent replication as well as those that regulate their replication number and guarantee stable inheritance during cell division. By the conjugation process, they can stimulate lateral transfer between bacteria from various genera and kingdoms. Numerous plasmids contain addiction-inducing systems that are typically based on toxin-antitoxin factors and capable of killing daughter cells that don't inherit the plasmid during cell division. Plasmids often carry multiple antibiotic resistance genes, contributing to the spread of multidrug-resistance (MDR). Antibiotic resistance mediated by MDR plasmids severely limits the treatment options for the infections caused by Gram-negative bacteria, especially family Enterobacteriaceae. The global spread of MDR plasmids has been enhanced by selective pressure from antimicrobial medications used in medical facilities and when raising animals for food.
Carbapenem-resistant Enterobacteriaceae (CRE) or carbapenemase-producing Enterobacteriaceae (CPE) are Gram-negative bacteria that are resistant to the carbapenem class of antibiotics, considered the drugs of last resort for such infections. They are resistant because they produce an enzyme called a carbapenemase that disables the drug molecule. The resistance can vary from moderate to severe. Enterobacteriaceae are common commensals and infectious agents. Experts fear CRE as the new "superbug". The bacteria can kill up to half of patients who get bloodstream infections. Tom Frieden, former head of the Centers for Disease Control and Prevention has referred to CRE as "nightmare bacteria". Examples of enzymes found in certain types of CRE are KPC and NDM. KPC and NDM are enzymes that break down carbapenems and make them ineffective. Both of these enzymes, as well as the enzyme VIM have also been reported in Pseudomonas.
Antibiotic use in livestock is the use of antibiotics for any purpose in the husbandry of livestock, which includes treatment when ill (therapeutic), treatment of a group of animals when at least one is diagnosed with clinical infection (metaphylaxis), and preventative treatment (prophylaxis). Antibiotics are an important tool to treat animal as well as human disease, safeguard animal health and welfare, and support food safety. However, used irresponsibly, this may lead to antibiotic resistance which may impact human, animal and environmental health.
Kluyvera is a Gram negative, facultatively anaerobic bacterial and motile genus from the family of Enterobacteriaceae which have peritrichous flagella. Kluyvera occur in water, soil and sewage. Kluyvera bacteria can cause opportunistic infections in immunocompromised patients.
Escherichia virus CC31, formerly known as Enterobacter virus CC31, is a dsDNA bacteriophage of the subfamily Tevenvirinae responsible for infecting the bacteria family of Enterobacteriaceae. It is one of two discovered viruses of the genus Karamvirus, diverging away from the previously discovered T4virus, as a clonal complex (CC). CC31 was first isolated from Escherichia coli B strain S/6/4 and is primarily associated with Escherichia, even though is named after Enterobacter.
François Balloux is the director of the UCL Genetics Institute, and a professor of computational biology at University College London.
Lipid A phosphoethanolamine transferase is an enzyme that modifies Lipid A by linkage to a phosphoethanolamine moiety. Doing so at some positions reduces the affinity to colistin and related polymyxins, resulting in reduced activity of the antimicrobial. This type of resistance is known as target modification. This type of enzyme is of special medical note, as it offers resistance to a last-resort antibiotic. The modifications also provide cross-resistance to host immunity factors, specifically antimicrobial peptides and lysozyme. EC 2.7.8.43 catalyzes one of the following three reactions:
Timothy Rutland Walsh is a professor working at the University of Oxford. He is a specialist in antimicrobial resistance. Walsh is the Oxford Institute of Antimicrobial Research (IOI) Director of Biology. His work at IOI involves developing new antibiotics to use in animals, to replace use of human antibiotics. His IOI work also involves screening many chemicals to find new antimicrobials that overcome or impede antimicrobial resistance. Also he is involved in documenting the large scale effects of antibiotic resistance in low to middle income countries, such as China, Pakistan Bangladesh, Brazil and several African countries.