Fimbriae and adherence of Stenotrophomonas maltophilia to epithelial cells and to abiotic surfaces.

Stenotrophomonas maltophilia is an emerging nosocomial bacterial pathogen associated with several infectious diseases and opportunistic infections, especially in immunocompromised patients. These bacteria adhere avidly to medical implants and catheters forming a biofilm that confers natural protection against host immune defences and different antimicrobial agents. The nature of the bacterial surface factors involved in biofilm formation on inert surfaces and in adherence of S. maltophilia to epithelial cells is largely unknown. In this study, we identified and characterized fimbrial structures produced by S. maltophilia grown at 37 degrees C. The S. maltophilia fimbriae 1 (SMF-1) are composed of a 17 kDa fimbrin subunit which shares significant similarities with the N-terminal amino acid sequences of several fimbrial adhesins (G, F17, K99 and 20K) found in Escherichia coli pathogenic strains and the CupA fimbriae of Pseudomonas aeruginosa. All of the clinical S. maltophilia isolates tested produced the 17 kDa fimbrin. Antibodies raised against SMF-1 fimbriae inhibited the agglutination of animal erythrocytes, adherence to HEp-2 cells and biofilm formation by S. maltophilia. High resolution electron microscopy provided evidence of the presence of fimbriae acting as bridges between bacteria adhering to inert surfaces or to cultured epithelial cells. This is the first characterization of fimbriae in this genus. We provide compelling data suggesting that the SMF-1 fimbriae are involved in haemagglutination, biofilm formation and adherence to cultured mammalian cells.

Characterization of flagella produced by clinical strains of Stenotrophomonas maltophilia.

Stenotrophomonas maltophilia is an emerging nosocomial pathogen associated with opportunistic infections in patients with cystic fibrosis, cancer, and HIV. Adherence of this organism to abiotic surfaces such as medical implants and catheters represents a major risk for hospitalized patients. The adhesive surface factors involved in adherence of these bacteria are largely unknown, and their flagella have not yet been characterized biochemically and antigenically. We purified and characterized the flagella produced by S. maltophilia clinical strains. The flagella filaments are composed of a 38-kDa subunit, SM(FliC), and analysis of its N-terminal amino acid sequence showed considerable sequence identity to the flagellins of Serratia marcescens (78.6%), Escherichia coli, Proteus mirabilis, Shigella sonnei (71.4%), and Pseudomonas aeruginosa (57.2%). Ultrastructural analysis by scanning electron microscopy of bacteria adhering to plastic showed flagellalike structures within the bacterial clusters, suggesting that flagella are produced as the bacteria spread on the abiotic surface.