Effect of subinhibitory concentrations of cephalosporins on surface properties and siderophore production in iron-depleted Klebsiella pneumoniae.

Subinhibitory MICs (sub-MICs) of several cephalosporins significantly reduced the enterochelin production of Klebsiella pneumoniae 327 grown under iron-depleted conditions and also reduced capsule formation regardless of iron availability. The surface hydrophobicity of K. pneumoniae 327 increased significantly when the bacteria were grown in either iron-sufficient or iron-depleted media in the presence of sub-MICs of all the cephalosporins used in this study. Antisera raised against a non-encapsulated K. pneumoniae strain caused rapid agglutination of K. pneumoniae 327 grown in the presence of sub-MICs of the cephalosporins but no agglutination of the same strain grown in drug-free media. The results indicated that the cephalosporins reduced enterochelin production and also capsule formation to the extent that noncapsular surface antigens were exposed, with possible significant consequences in vivo.