Genotypic and phenotypic relationships between clinical and environmental isolates of Stenotrophomonas maltophilia

Abstract

While the gram-negative bacterium Stenotrophomonas maltophilia is used in biotechnology (e.g., for biological control of plant pathogens and for bioremediation), the number of S. maltophilia diseases in humans has dramatically increased in recent years. A total of 40 S. maltophilia isolates from clinical and environmental sources (plant associated and water) was investigated to determine the intraspecies diversity of the group and to determine whether or not the strains could be grouped based on the source of isolation. The isolates were investigated by phenotypic profiling (enzymatic and metabolic activity and antibiotic resistance patterns) and by molecular methods such as temperature-gradient gel electrophoresis of the 16S rRNA gene fragment, PCR fingerprinting with BOX primers, and pulsed-field gel electrophoresis (PFGE) after digestion with DraI. Results of the various methods revealed high intraspecies diversity. PFGE was the most discriminatory method for typing S. maltophilia when compared to the other molecular methods. The environmental strains of S. maltophilia were highly resistant to antibiotics, and the resistance profile pattern of the strains was not dependent on their source of isolation. Computer-assisted cluster analysis of the phenotypic and genotypic features did not reveal any clustering patterns for either clinical or environmental isolates.

FIG. 1

Percentages of clinical and environmental isolates resistant to antibiotics. AZL, azlocillin; PIP, piperacillin; TZP, piperacillin-tazobactam; TIM, ticarcillin-clavulanic acid; CFS, cefsoludin; CAZ, ceftazidime; GEN, gentamicin; TOB, tobramycin; AMK, amikacin; DOX, doxycycline; OFX, ofloxacin; CIP, ciprofloxacin; IPM, imipenem; ATM, aztreonam; SXT, trimethoprim-sulfamethoxazole (co-trimoxazole); CHL, chloramphenicol; KAN, kanamycin; ERY, erythromycin; TET, tetracycline.

FIG. 2

TGGE profiles of S. maltophilia strains. Lane 1, c5; lane 2, c2; lane 3, e10; lane 4, e16; lane 5, c13; lane 6, c10; lane 7, c15; lane 8, c17; lane 9, c12; lane 10, c20; lane 11, e19; lane 12, e3; lane 13, e8; lane 14, c9; lane 15, c2; lane 16, e15; lane 17, c11; lane 18, c8; lane 19, c7; lane 20, e5; lane 21, c4; lane 22, e12; lane 23, c14; lane 24, e7; lane 25, e17; lane 26, c6; lane 27, standard; lane 28, c10; lane 29, e13; lane 30, e18; lane 31, e1; lane 32, e9; lane 33, e4; lane 34, c16; lane 35, e6; lane 36, c1; lane 37, c19; lane 38, t20; lane 39, e11; lane 40, c3; lane 41, c18; lanes S, standard. A, Clostridium pasteurianum; B, Erwinia carotovora; C, Agrobacterium tumefaciens; D, Pseudomonas fluorescens; E, Pantoea agglomerans; F, Nocardia asteroides; G, Rhizobium leguminosarum; H, Actinomadura malachitica; I, Kineosporia aurantiaca; J, Nocardiopsis atra; K, Actinoplanes philippinensis.

FIG. 3

BOX-PCR profiles of S. maltophilia strains including statistical analysis and dendrogram showing the genetic relationship between strains.

FIG. 4

Examples of genomic DNA macrorestriction profiles of S. maltophilia produced by PFGE after DraI digestion. Lane 1, c12; lane 2, c1; lane 3, c7; lane 4, c17; lane 5, c5; lane 6, e1; lane 7, e2; lane 8, lambda ladder marker (size range, 225 to 1,900 kb); lane 9, e9; lane 10, e10; lane 11, t20; lane 12, e18; lane 13, e5.