Mechanism of Acquired Vancomycin Resistance
Six different types of vancomycin resistance are shown by enterococcus : Van-A, Van-B, Van-C, Van-D, Van-E and Van-F. Of these, only Van-A, Van-B and Van-C have been seen in general clinical practice, so far. The significance is that Van-A VRE is resistant to both vancomycin and teicoplanin, Van-B VRE is resistant to vancomycin but sensitive to teicoplanin, and Van-C is only partly resistant to vancomycin, and sensitive to teicoplanin. In the US, linezolid is commonly used to treat VRE, as teicoplanin is not available.
The mechanism of resistance to vancomycin found in enterococcus involves the alteration to the terminal amino acid residues of the NAM/NAG-peptide subunits, under normal conditions, D-alanyl-D-alanine, to which vancomycin binds. The D-alanyl-D-lactate variation results in the loss of one hydrogen-bonding interaction (four, as opposed to five for D-alanyl-D-alanine) being possible between vancomycin and the peptide. This loss of just one point of interaction results in a 1000-fold decrease in affinity. The D-alanyl-D-serine variation causes a six-fold loss of affinity between vancomycin and the peptide, likely due to steric hindrance.
Some VREs respond to the presence of vancomycin rather than just its effect on the cell wall.
Read more about this topic: Vancomycin-resistant Enterococcus
Famous quotes containing the words mechanism of, mechanism, acquired and/or resistance:
“Life is an offensive, directed against the repetitious mechanism of the Universe.”
—Alfred North Whitehead (1861–1947)
“I’ve never known a Philadelphian who wasn’t a downright “character;” possibly a defense mechanism resulting from the dullness of their native habitat.”
—Anita Loos (1888–1981)
“When I contemplate the accumulation of guilt and remorse which, like a garbage-can, I carry through life, and which is fed not only by the lightest action but by the most harmless pleasure, I feel Man to be of all living things the most biologically incompetent and ill-organized. Why has he acquired a seventy years’ life-span only to poison it incurably by the mere being of himself? Why has he thrown Conscience, like a dead rat, to putrefy in the well?”
—Cyril Connolly (1903–1974)
“Even the most subjected person has moments of rage and resentment so intense that they respond, they act against. There is an inner uprising that leads to rebellion, however short- lived. It may be only momentary but it takes place. That space within oneself where resistance is possible remains.”
—bell hooks (b. c. 1955)