A method for assaying biofilm capacity on polyurethane-coated slides

Isolates of coagulase-negative Staphylococci (CNS) were examined for their ability to form biofilms on polyurethane-coated slides. These slides provided a smooth plastic coating simulating polymeric plastic surfaces of medical grade catheter tubing. Slides were placed into plastic conical tubes containing tryptic soy broth inoculated with 10(6) bacteria per mL. The tubes were then incubated at 37 degrees for 48 hours. After incubation, 1 of the slides was stained with a fluorescent acridine orange stain and the other with a safranin stain. The incubation tubes were also stained with safranin. Forty-eight percent of the 65 CNS isolates were found to form a biofilm using acridine orange staining. Forty percent of the 65 CNS isolates were found to form a biofilm using the safranin stain on slides, whereas only 34% were found to adhere on sides of plastic tubes. Increased sensitivity of the fluorescent stain was probably due to enhanced visualization of smaller numbers of bacteria on the plastic. This method using fluorescent stained plastic-coated slides was easier to visualize and interpret than the tube method.