The most distinctive bacteriologic features of the genus Klebsiella are the absence of motility and the presence of a polysaccharide capsule. This gives colonies a glistening, mucoid character and forms the basis of a serotyping system. Over 70 capsular types have been defined, including some that cross-react with those of other encapsulated pathogens, such as Streptococcus pneumoniae and Haemophilus influenzae. Limited studies suggest that the capsule interferes with complement activation in a way similar to the other encap-sulated pathogens. Several types of pili are also present on the surface and probably aid in adherence to respiratory and urinary epithelium.
K. pneumoniae, the most common species, is able to cause classic lobar pneumonia, acharacteristic of other encapsulated bacteria. Most Klebsiella pneumonias are indistin-guishable from those produced by other members of the Enterobacteriaceae. Of all the Enterobacteriaceae, Klebsiella species are now among the most resistant to antimicrobics.
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