Interactions between biofilm cells of Pseudomonas aeruginosa and levofloxacin were studied. P. aeruginosa incubated for 6 days with Teflon sheets formed a biofilm on its surface. Against the biofilm bacteria, levofloxacin at an MIC determined by the standard method for the strain was highly bactericidal whereas gentamicin, ceftazidime, and ciprofloxacin showed no significant killing activity. Levofloxacin, ciprofloxacin, and gentamicin, but not ceftazidime, exhibited killing activity against nongrowing cells of the strain incubated in phosphate buffer. In addition, levofloxacin, ciprofloxacin, and ceftazidime, but not gentamicin, showed the ability to penetrate an agar containing alginate. These findings may explain the efficacy of levofloxacin and the ineffectiveness of gentamicin and ceftazidime against biofilm bacteria; however, the cause of the ineffectiveness of ciprofloxacin still remains to be determined. In experimental pneumonia in guinea pigs, in which the biofilm mode of growth of the strain was observed in the lung, only levofloxacin exhibited substantial therapeutic efficacy. These findings suggest the significant role of levofloxacin in therapy of biofilm bacterium-associated infectious diseases.

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Slow radioactive ion beams have been produced with an overall efficiency of 4% by thermalizing energetic ions produced by a projectile fragment separator in a He-gas cell and guiding them to a vacuum vessel by dc and rf fields. Space charge was observed to have a limiting effect. Since the ionization of He atoms by energetic ions creates a region of high space charge, many thermalized ions of interest are pushed toward the walls of the gas cell. Such losses have been investigated for different incoming ion intensities.

This study established a rat model of foreign body-associated urinary tract infection. A spiral polyethylene tube (PT) was placed transurethrally into the bladder without surgical manipulation, followed by transurethral inoculation with Pseudomonas aeruginosa. The persistence of P. aeruginosa in the kidneys and bladder was significantly enhanced by placement of the PT, whereas the bacteria were eliminated rapidly from the urinary tract in the animals without the PT. Scanning electron microscopy revealed a thick biofilm on the surface of the PT from the early stage of infection. Histopathologically, acute pyelonephritis was followed by chronic renal inflammation as well as continuous and sporadic polymorphonuclear leukocyte accumulation and hemorrhage in the pelvis and adjacent tissues, suggesting continuous ascending introduction of the bacteria from the biofilm adhering to the PT. We believe our model simulates the pathophysiology of foreign body-associated urinary tract infection characterized by biofilm formation on the surface of a foreign body.Key words: Rat model, Pseudomonas aeruginosa, Urinary tract infection, Foreign body-associated UTI Urinary tract infections (UTI) associated with foreign bodies including urinary catheters and/or stents are some of the most common and problematic of hospitalacquired infections (3, 16). Typically, the biofilm mode of bacterial growth on the surface of the urinary catheter and adjacent mucosa accounts for the pathophysiology of foreign body-associated UTI (6-8). The role of bacterial biofilms on the surface of urinary catheters in UTI has been studied in rabbit models (5, 13). To determine the pathogenesis of foreign body-associated UTI in terms of its immunological and bacteriological aspects, numerous efforts have been made to establish rodent models of foreign body-associated UTI. These include models in which UTI was induced by placement of foreign bodies, such as glass beads (I), zinc rings (10, 12, 15), catheter segments (4), sutures (11), and polyurethane sponges, into the bladder (9). These models, however, have had few clinical parallels mainly because surgical manipulation to implant the foreign body into the bladder could not be avoided. Surgical incision of the bladder

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