Stenotrophomonas maltophilia is one of the most prevalent opportunistic bacteria causing nosocomial infections. It has become problematic because most of the isolates are resistant to multiple antibiotics, and therefore, development of phage therapy has attracted strong attention. In this study, eight S. maltophilia phages were isolated from clinical samples including patient specimens, catheter-related devices, and wastewater. These phages can be divided into four distinct groups based on host range and digestibility of the phage DNAs with different restriction endonucleases. One of them, designated SMA5, was further characterized. Electron microscopy showed it resembled Myoviridae, with an isometric head (90 nm in diameter), a tail (90 nm long), a baseplate (25 nm wide), and short tail fibers. The SMA5 double-stranded DNA, refractory to digestion by most restriction enzymes, was tested and estimated to be 250 kb by pulsed-field gel electrophoresis. This genome size is second to that of the largest phage, KZ of Pseudomonas aeruginosa. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, 25 virion proteins were visualized. N-terminal sequencing of four of them suggested that each of them might have had its N terminus cleaved off. Among the 87 S. maltophilia strains collected in this study, only 61 were susceptible to SMA5, indicating that more phages are needed toward a phage therapy strategy. Since literature search yielded no information about S. maltophilia phages, SMA5 appears to be the first reported.Stenotrophomonas maltophilia, previously known as Xanthomonas maltophilia (37) and Pseudomonas maltophilia (22), is an aerobic, gram-negative bacillus widespread in a variety of environments. It has been found in the environment as a growth-promoting agent in the rhizospheres of plants, as well as in soil, water, sediment, sewage, frozen foods, and some other habitats (3,8,14,20,23,25). More importantly, S. maltophilia is increasingly prevalent in hospitals as an opportunistic human pathogen causing nosocomial infections in immunocompromised individuals and involved in postoperative infections, the infections of urinary tracts and respiratory tracts, and other disease syndromes (15,20,34,40). This organism was reported to be the second most frequently isolated nosocomial bacterium after Pseudomonas aeruginosa, and its infections have a growing clinical importance (43). The prevalence of S. maltophilia in Taiwan has also been increasing. For example, among the 6,092 bacterial strains isolated from the nosocomial infections of respiratory tracts in Taichung Veterans Hospital of Taiwan in the year 2003, 451 strains (7.4%) were identified as S. maltophilia. This bacterium ranked fifth among 86 causative bacterial species, after P. aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, and Staphylococcus aureus (Clinical Microbiology Report, Taichung Veterans Hospital, Taichung, Taiwan, 2004). Furthermore, most of these isolates were resistant to multiple antibiotics, including imipenem (H.-C. Chang ...

BackgroundStenotrophomonas maltophilia is a ubiquitous Gram-negative bacterium previously named as Xanthomonas maltophilia. This organism is an important nosocomial pathogen associated with infections in immunocompromised patients. Clinical isolates of S. maltophilia are mostly resistant to multiple antibiotics and treatment of its infections is becoming problematic. Several virulent bacteriophages, but not temperate phage, of S. maltophilia have been characterized.ResultsIn this study, a temperate myophage of S. maltophilia (Smp131) was isolated and characterized. Sequence analysis showed that its genome is 33,525-bp long with 47 open reading frames (ORFs). Its similarity to P2-like phages and prophages in S. maltophilia and several Xanthomonas pathovars includes genomic organization, arrangement of several operons, and possession of a slippery sequence T7G for translational frameshifting in tail assembly genes. Smp131 encodes a tyrosine family integrase that shares low degrees of similarity with those of other phages and a lysin belonging to family 19 chitinase that is observed in plants and some bacteria, although not in phages. tRNA are the preferred sites for host integration of Smp131 and the related phages: tRNA-Thr for Smp131 and prophage of S. maltophilia K279a; tRNA-Lys for prophages of X. campestris pv. campestris ATCC33913, X. oryzae pv. oryzae strains MAFF311018, and KACC10331; and tRNA-Asn for prophage of X. oryzae pv. oryzae PXO99A and remnant of X. axonopodis pv. citri 306. Regions flanking the prophages are varied highly in nucleotide sequence and rich in transposase genes, suggesting that frequent insertion/excision had occurred.ConclusionsPrevalence of closely related prophages in Stenotrophomonas and Xanthomonads may have contributed to the diversity of these closely related species owing to possible horizontal gene transfer mediated by the phages.