Pili-mediated Agglutination of Serratia marcescens in Human Urine

Most strains of S. marcescens isolated from clinical materials formed large aggligates in human urine. This phenomenon was specifically observed on S. marcescens but not on the other gram-negative bacilli such as E. coli, K. pneumoniae, P. aeruginosa, P. maltophilia, P. vulgaris and P. mirabilis. Among 24 strains of S. marcescens isolated 15 strains showed agglutination in human urine. Nine strains were nonagglutinating strain. Electron microscopic observation of these strains revealed that the agglutinating strains had numerous pili on their surface but none of pili were observed on nonagglutinating strains. The diameter of the pili was 30 A. It showed more flexible profile than that of the haemagglutinating strain of E. coli. The role of the pili in urinary tract infection is still remained to be elucidated.