Characterization of bacterial biofilms formed on urinary catheters.

BACKGROUND: The formation of bacterial biofilms on urinary catheters is a leading cause of urinary tract infections in intensive care units. Cytobacteriological examination of urine from patients is often misleading, due to the formation of these biofilms. Therefore, characterizing these biofilms and identifying the bacterial species residing on the surface of catheters are of major importance.

METHODS: We studied the formation of biofilms on the inner surface of urinary catheters using microbiological culture techniques, with the direct contact of catheter pieces with blood agar. The bacterial species on the surface were characterized by scanning electron microscopy, and the kinetic profile of biofilm formation on a silicone substrate for an imipenem-resistant Acinetobacter baumannii bacterium was evaluated with a crystal violet staining assay.

RESULTS: The bacterial species that constituted these biofilms were identified as a variety of gram-negative bacilli, with a predominance of strains belonging to Pseudomonas aeruginosa. The other isolated strains belonged to A baumannii and Klebsiella ornithinolytica. Kinetic profiling of biofilm formation identified the transient behavior of A baumannii between its biofilm and planktonic state. This strain was highly resistant to all of the antibiotics tested except colistin. Scanning electron microscopy images showed that the identified isolated species formed a dense and interconnected network of cellular multilayers formed from either a single cell or from different species that were surrounded and enveloped by a protective matrix.

CONCLUSIONS: Microbiological analysis of the intraluminal surface of the catheter is required for true identification of the causative agents of catheter-associated urinary tract infections. This approach, combined with a routine cytobacteriological examination of urine, allows for the complete characterization of biofilm-associated species, and also may help prevent biofilm formation in such devices and help guide optimum antibiotic treatment.