Biofilm formation by otopathogenic strains of Pseudomonas aeruginosa is not consistently inhibited by ethylenediaminetetraacetic acid.

Hypothesis: Biofilm formation in otopathogenic of Pseudomonas aeruginosa (OPPA) strains is inhibited by ethylenediaminetetraacetic acid (EDTA).

Background: EDTA, a widely used chelating agent, has been shown to inhibit biofilm formation in a number of bacteria. Because EDTA may be a well-tolerated reagent to inhibit biofilm formation in cases of suppurative otitis media, we asked if it might be effective in all OPPA strains isolated from chronically infected cholesteatomas.

Methods: OPPA strains were isolated from patients with infected cholesteatomas. These strains were grown into log phase then were placed in minimal media with varying concentrations of EDTA and incubated for varying periods. Biofilm production was measured colorimetrically by staining with crystal violet.

Results: Without added EDTA, most otopathogenic PA exhibited a distinct, but varying, time course of biofilm formation and dissolution with peak production at 12 to 18 hours. Addition of 1 mM EDTA resulted in a delay in the time to peak biofilm formation for most strains, although the amount of biofilm was not decreased. In contrast, some strains showed greater biofilm production with 1 mM EDTA compared with the untreated bacteria. Addition of 10 mM EDTA resulted in a similar effect. Some strains increased biofilm production over controls. Moreover, EDTA inhibited planktonic growth of all OPPA strains at the concentrations studied.

Conclusion: Our hypothesis was disproven: EDTA tends to delay biofilm development, although it consistently inhibits planktonic growth. Because EDTA does not cause suppression of biofilm production in all isolates of OPPA, usefulness as an antimicrobial is questioned.