Isolation of biofilm producing microorganisms isolated from urinary indwelling catheter in geriatric hospitalized patients

Introduction: In nature, bacterial cells can exist in two different states: individual (planktonic) cells, or biofilm. In biofilms, bacterial cells are adherent to a surface and contained in an extracellular matrix mainly composed of polysaccharides and proteins.The cells in biofilms differ from planktonic counterparts for a different pattern of gene expression and increased resistance to antibiotics.This means that biofilms in hospital can cause persistent infections, due to the immunocompromised state of the patient and from a previous infection or exposure to the antibiotic. The aim of our work was to: 1) to assess the presence of microorganisms in institutionalized geriatric patients carrying indwelling catheter 2) assess the ability of gram-negative microorganisms to produce biofilm. Methods: 150 samples from urine of patients with indwelling urinary catheter hospitalized at ASP Pio Albergo Trivulzio were studied. Adhesion of bacteria was tested using LB medium diluted 1:4 and staining the biofilm cells with crystal violet. Results: 120 samples (80%) tested positive for the presence of microorganisms; in 96 samples only one microrganism was detected, while 24 were contaminated with 2 or more bacterial species. 88% of isolates testing positive to a single species consisted of Gram negative microorganisms: E. coli (48%), P. mirabilis (16%), P. aeruginosa (13%), K. pneumoniae (5%), P. stuartii (2%), C. freundii (1%), E. aerogenes (1%), E. cloacae (1%), K. oxytica (1%), M. morganii (1%).Adhesion assays show that all strains of P. aeruginosa, K. pneumoniae, K. oxytoca, E. cloacae and C. freundii isolates produced biofilm. In contrast, strains of E. aerogenes and M. morganii did not produce any biofilm. 26% of E. coli strains were able to produce biofilm, as well as 93% of P. mirabilis and 50% of P. stuartii.Overall, 55% of Gram negative microrganisms isolated were capable of producing biofilms. Conclusion: The use of a nutritionally poor medium (LB diluted 1:4) and a synthetic substrate define an experimental model in vitro that plays in a relatively faithful to what may occur in vivo. The fact that biofilms are known to be more tolerant to antibiotics and the high proportion of biofilm-forming bacteria isolated from patients carrying indwelling underlines the need for novel antimicrobial agents with higher potency on bacterial biofilms than the ones currently used in therapy.