Colistin Case Study

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Q1A: What is the mechanism of action of colistin? Colistin is an antibiotic that works best against Gram-negative bacteria. It works by binding to LPSs (lipopolysaccrides) and phospholipids in the outer cell membrane of the bacteria. This, in turn, disrupts the outer cell membrane by displacing cations and leaking the intracellular contents, combining it with outer cellular contents, causing the bacteria to be unable to differentiate the bacteria’s intra and outer cellular contents from one another. This ultimately leads to the bacteria’s death.
Q1B: What infections are treated with colistin? Colistin is used to treat infections caused by gram-negative or MDRO (Multidrug-Resistant Organisms). Occasionally, professionals will choose to avoid
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Afterwards, with the use of Glimmer 3.02 and BLAST, gene prediction and annotation were completed with another plasmid, pHN122-1, as a reference. To confirm the role of the gene that caused polymyxin resistance and contained mcr-1, the gene and its sequence were place into a cloning vector pUC18 that yielded pUC18-mcr-1. With this yield and electroporation, it was used to transform an E.coli strain, revealing its ability to confer colistin resistance.
Q3D: By what mechanism do the authors propose that the mcr-1 gene confers colistin resistance, and what evidence do they use to support this assertion?
The protein sequence of mcr-1 showed its similarity to the polymyxin-producing bacterium, Paenibacillus spp., which showed the possibility of gene transfer occurring. The mcr-1 gene enables protection from polymyxin. The mechanism that the authors proposed on how the mcr-1 gene confers colistin resistance is that mcr-1 causes a modification in lipid A, present in the lipopolysaccharides of most bacteria, which leads to lessened polymyxin affinity. The lipid A has phosphoethanolamine added to it, which in turn, inhibits the bacteria from any attachment.
Q3E: What is the origin of the mcr-1 gene, and what evidence do the authors use to support this
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Veterinarians and food companies are constantly using colistin in their operations which provides mcr-1 to be a more preferable trait and resistance to have. This, in turn, will cause more plasmids to be transferred around due to the need for survivability. MCR-1 has also proven to be quite stable in multiple types of E.coli strains, making it likely that it will remain a significant aspect of the strains. Along with the fact that the mcr-1 numbers are increasing and it’s showing that it has high stability, it is also transferrable to E.coli strains that are pathogenic to humans. Colistin is a significant polymyxin that had been working well against E.coli strains. However, if the effectiveness is reduced, there would be a great loss of methods to counter these types of strains. Also, since there is capability of it being transferred to other strains, there is a rising concern that it will also transfer to other human

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