RESEARCH Figure 8. Ultrastructural analysis of Stenotrophomonas maltophilia adhering to plastic. (A) Scanning electron micrographs showing the tight adhesion of SMDP92 to the plastic surface. (B) Structures resem- bling flagella seem to be protruding and interconnecting bacteria (arrowheads) or connecting bacteria to the plastic (arrows). (C) In addi- tion to the flagellalike filaments (arrowheads), high-power magnification shows the presence of thin fibrillar structures connecting bacteria to the abiotic surface. Bars: A 10 µ m, B 1 µ m, C 2 µ m. S. maltophilia and P. aeruginosa was 57.2%, which is lower than that observed with enterobacterial flagellins. In spite of the similarity between SMFliC and these other flagellins, they are antigenically distinct since only antibodies against P. mira- bilis flagellin, FlaA and FlaB of P. aeruginosa reacted with SMFliC in immunoblots. We do not yet know the biological relevance of this finding, but based on these data, we can spec- ulate that the flagellin gene of S. maltophilia was probably modified through the evolution of the organism, yielding a FliC protein with different antigenic properties but similar bio- logical functions. Visualization by high-resolution scanning electron micros- copy of bacterial monolayers adhering to plastic showed flagellalike filaments connecting bacteria to each other and to the inert surface, suggesting that these structures are involved in adherence, along with other thin fibers, resembling pili. In P. aeruginosa, the flagella appear to act as structures that pro- mote the initial interaction of the bacteria with the abiotic sur- face during early stages of biofilm development, as demonstrated with flagella mutants that are unable to produce biofilm (18). While the definitive role for flagella in adherence by S. maltophilia needs to be supported by the use of defined motility-lacking and flagella-deficient constructs, the presence of flagella at late stages of adherence on bacteria adhering to the plastic suggests that flagella may play some role in this event. Much remains to be understood concerning the virulence mechanisms of S. maltophilia. The adherence of these bacteria to plastic may be important for the establishment of opportu- nistic infections in hospitalized and immunocompromised patients. Elucidating the surface factors that allow S. malto- philia to adhere to inert surfaces will contribute to the develop- ment of effective antimicrobial strategies for controlling these infections. Acknowledgments We thank Angelo Geraldo Gambarini and Izaura Nobuko Toma for N-terminal amino acid sequencing and Harry T. Mobley and Arora Shiwani for antisera against flagella of Proteus mirabilis and Pseudomonas aeruginosa, respectively. J.A. Girón thanks James B. Kaper for support during preparation of this manuscript and Richard L. Friedman for critical discussions. This study was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (98/15415-0). JAG received support from Conacyt Grant 32777-M. Dr. Garcia is a microbiologist working as a scientific researcher at Instituto Adolfo Lutz, São Paulo, Brazil. Her main interests are the virulence factors and molecular epidemiology of nonglucose-fer- menting Gram-negative bacilli isolated from the respiratory tract of patients with or without cystic fibrosis. References 1. Hugh R, Ryschenkow E. Pseudomonas maltophilia, an Alcaligenes-like species. J Gen Microbiol 1961;26:123–32. 2. Swings J, De Vos P, Van der Mooter M, Deley S. Transfer of Pseudomo- nas maltophilia HUGH 1981 to the genus Xanthomonas as Xanthomonas maltophilia (HUGH 1981). comb. nov. Int J Syst Bacteriol 1983;33:400– 13. 3. Palleroni NJ, Bradbury JF. Stenotrophomonas, a new bacterial genus for Xanthomonas maltophilia (Hugh, 1980) Swings et al. 1983. Int J Syst Bacteriol 1993;43:606–9. 4. Denton M, Kerr KG. Microbiological and clinical aspects of infection associated with Stenotrophomonas maltophilia. Clin Microbiol Rev 1998;11:57–80. 5. Marshall WF, Keating MR, Anhalt JP, Steckelberg JM. Xanthomonas maltophilia: an emerging nosocomial pathogen. Mayo Clin Proc 1989;64:1097–104. 6. Schock PE, Cunha BA. Pseudomonas maltophilia. Infect Control 1987;8:169–72. 7. Spencer RC. The emergence of epidemic, multiple-antibiotic-resistant Stenotrophomonas (Xanthomonas) maltophilia and Burkholderia (Pseudomonas) cepacia. J Hosp Infect 1995;30 (suppl.):453–64. 8. Robin T, Janda JM. Pseudo-, Xantho-, Stenotrophomonas: an emerging pathogen in search of genus. Clin Microbiol News 1996;18:9–16. 9. Fujita J, Yamadori I, Xu S, Hojo S, Negayama, K, Miyawaki H, et al. Clinical features of Stenotrophomonas maltophilia pneumonia in immu- nocompromised patients. Respir Med 1996;90:35–8. 10. Gopalakrishnan R, Hawley B, Czachor, JS, Markert RJ, Bernstein JM. Stenotrophomonas maltophilia infection and colonization in the intensive care units of two community hospitals: a study of 143 patients. Heart Lung 1999;28:134–41. 11. Julve R, Rovira E, Belda A, Prat J, Escoms R, Albert A, et al. Espectro clínico de la infección por Stenotrophomonas (Xanthomonas) malto- philia. An Med Interna 1998;15:476–80. 922 Emerging Infectious Diseases • Vol. 8, No. 9, September 2002