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)
“When one of us dies of cancer, loses her mind, or commits suicide, we must not blame her for her inability to survive an ongoing political mechanism bent on the destruction of that human being. Sanity remains defined simply by the ability to cope with insane conditions.”
—Ana Castillo (b. 1953)
“I am not sure but I should betake myself in extremities to the liberal divinities of Greece, rather than to my country’s God. Jehovah, though with us he has acquired new attributes, is more absolute and unapproachable, but hardly more divine, than Jove. He is not so much of a gentleman, not so gracious and catholic, he does not exert so intimate and genial an influence on nature, as many a god of the Greeks.”
—Henry David Thoreau (1817–1862)
“It was not seen that woman’s place was in the home until she began to go out of it; the statement was a reply to an unspoken challenge, it was attempted resistance to irresistible change.”
—Rose Wilder Lane (1886–1965)