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Polymyxin B sensitivity |
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Sensitivity to the antimicrobial agent polymyxin B has been used to differentiate the biotypes of V. cholerae O1. A 50-unit polymyxin B disk is used for this test, and known strains of classical and El Tor biotypes are used as controls. The El Tor
biotype is usually resistant to this concentration of polymyxin B and will not give a zone of inhibition. If there is any doubt about the result of this test, other biotyping tests should be performed or the isolate should be sent to a reference laboratory for confirmation. Classical strains are usually sensitive to polymyxin B
and will give a zone of inhibition. Because the zone size is not important, any zone is interpreted as a positive result.
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Microscopy:
Gram-negative, curved, non-spore-forming rods. |
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