Effects of sublethal concentrations of antimicrobial agents on the hemagglutination, adhesion, and ultrastructure of pyelonephritogenic Escherichia coli strains.

The effects of trimethoprim, sulfadiazine, sulfamethoxazole, and sulfathiazole on the hemagglutination and adhesion by three Escherichia coli strains were studied. The strains were isolated from the urine of patients with acute pyelonephritis and carried P antigen-recognizing fimbriae (P fimbriae). At antimicrobial concentrations of 12.5 to 50% of the minimal inhibitory concentration, the ability of the bacteria to agglutinate human erythrocytes and to adhere to human buccal cells was markedly reduced. This reduction corresponded to a decrease in the number of P fimbriae per cell, suggesting that the antimicrobial agents decreased adhesion and hemagglutination by interfering with the formation of fimbriae. No major changes were observed in the outer membrane protein pattern of trimethoprim-treated cells, whereas freeze-fracture electron micrographs showed deorganization of both the cytoplasmic and outer membranes in bacteria opposed to sublethal concentrations of trimethoprim.