Figure 1.
Induction of planktonic mode of growth in pre-established biofilms formed by food pathogens using CDA.
(A) Biofilms were grown for 5 days in petri dishes in which the medium was replaced every 24 h. Dispersion induction was tested by replacing the growth medium with fresh medium containing three different concentrations of CDA (100, 310 or 620 nM) or just the carrier as a control and the cells were incubated for a further 1 h. Medium containing dispersed cells was then homogenized and cell density was determined by measuring the optical density. (B) After 5 days of biofilm growth in flow cell continuous cultures, the influent medium was switched from fresh medium in the test lines to three indicated concentrations of CDA and control lines were switched to new lines containing just the carrier. Effluent runoffs were then collected and cell density was determined by measuring the OD. Error bars indicate standard errors (n = 3) and mean values sharing at least one common lowercase letter shown above the bars are not significantly different (P-value <0.05).
Figure 2.
Effect of CDA combined antimicrobial treatments on eradication and killing of pre-established biofilms.
(A) After 120 h of growth on the surface of SS discs, biofilms were treated for 1 h with biocides alone or combined with 310 nM CDA; CFU plate counts were then performed to assess the viability of the bacteria. (B) The amount of biofilm remaining was determined by the absorbance at 590 nm of crystal violet after staining the 120 h different biofilms in a microtiter plate assay after treatment with tested concentrations of antibiotics alone (- CDA) or in combination with 310 nM CDA (+CDA) for 1 h. All readings are corrected to reflect 0% and 100% controls (blank well, 0%; biofilms without any treatments, 100%). Error bars indicate standard errors (n = 3) and mean values sharing at least one common lowercase letter shown above the bars are not significantly different (P-value <0.05).
Table 1.
MICs of tested microorganisms' planktonic cells to examined disinfectants and antibiotics.
Figure 3.
Effect of CDA combined disinfectant or antibiotic treatments on biofilms surface area.
Following dispersion of biofilms by CDA, cells remaining on the surface are easily killed and removed by various disinfectants (Epimax S and Percidine) or antibiotics (vancomycin; Van, ampicillin; Amp, ciprofloxacin; Cip) in biofilms grown in continuous culture flow cells. Pre-established biofilms were grown for 48 h without any treatment and then were treated with indicated concentrations of antimicrobials alone (- CDA) or combined with 310 nM CDA (+ CDA) for 1 h, stained with LIVE/DEAD staining and quantified (percent surface coverage) using digital image analysis. The bars show the levels of biofilm biomass after treatment with antimicrobials alone or combined with 310 nM CDA. Error bars indicate standard errors (n = 3) and mean values sharing at least one common lowercase letter shown above the bars are not significantly different (P-value <0.05).
Figure 4.
Effect of CDA combined antimicrobial treatments on killing of pre-established biofilms.
CDA treatment reverses biofilm formation in pre-established biofilms and cells remaining on the surface are easily removed and killed various disinfectants (Epimax S and Percidine) or antibiotics (vancomycin; Van, ampicillin; Amp, ciprofloxacin; Cip) in biofilms grown in continuous culture flow cells. Pre-established biofilms were grown for 48 h without any treatment, then were treated with indicated concentrations of antimicrobials alone (- CDA) or combined with 310 nM CDA (+CDA) for 1 h and stained with LIVE/DEAD staining to allow analysis using fluorescence microscopy. The images show microscopic pictures of the biofilms on the surface of cover slip after combinatorial treatments. Images are top-down views (x-y plane); scale bars: 50 µm. Results are representative of 3 separate experiments.