Bacterial adhesion to stainless steel is reduced by aqueous fish extract coatings

Abstract

Microbial adhesion and biofilm formation on surfaces pose major problems and risks to human health. One way to circumvent this problem is to coat surfaces (in this report stainless steel) with a non-toxic fish extract that generates an abiotic surface with less bacterial attachment than uncoated surfaces or surfaces coated with, for example, tryptone soy broth. The bacteria grow well in the fish extract; hence a general bacteriocidal effect is not the reason for the antifouling effect. Bacterial attachment was quantified by different methods including (a) direct fluorescence microscopy, (b) removal by ultrasound and subsequent quantification of the adhered bacteria, and (c) regrowth of the adhered bacteria measured by indirect conductometry. Surprisingly, the bacterial counts on surfaces coated with aqueous fish extract were 10–100 times lower than on surfaces coated with laboratory broths when surfaces were submerged in bacterial suspensions. The effect was seen forPseudomonas fluorescensAH2,Pseudomonas aeruginosaPAO1,Escherichia coliMG1655,Vibrio anguillarum90-11-287 andAeromonas salmonicidaJno 3175/88. It lasted for at least 7 days. Atomic force microscopy showed that steel surfaces conditioned with fish extract were covered by a thin layer of spherical, nanosized particles. Chemical analysis of the surfaces coated with adsorbed fish extract using X-ray photoelectron spectroscopy revealed that the layer was proteinaceous and had a thickness less than 2 nm. Numerous protein bands/peaks were also detected by sodium dodecyl sulphate–polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry techniques. We conclude that coating the stainless steel surface with fish extract results in a thin protein layer that reduces bacterial adhesion significantly.

Blocking of Bacterial Biofilm Formation by a Fish Protein Coating

“…The influence of protein conformational changes cannot, however, be excluded. The coating has also previously been shown to increase the wettability of the surfaces, suggesting a reduction in surface hydrophobicity (5). These characteristics suggest that the biofilm-reducing activity of the coating is probably linked to changes in electrostatic repulsion and surface hydrophobicity, as also suggested previously for other proteins (42).…”

“…During the preconditioning of various materials with the aqueous fish muscle extract, a significant antiadhesive proteinaceous conditioning film is formed (5,43). This coating layer was previously found to consist primarily of ␣-like tropomyosins (43).…”

“…The aqueous fish muscle extracts were prepared as described previously (5,12). Briefly, pieces of cod fillet were cooked for 5 min in 0.5 liter of water per kg of fillet, and the aqueous solution was passed through a strainer and recooked.…”

“…This conditioning layer may in turn influence the extent of bacterial adhesion (1,23). Recently, we have found that the preconditioning of inert materials with an aqueous extract of fish muscle proteins (FMPs) can significantly reduce bacterial attachment to these surfaces (5,43). Based on this finding, we have tested the biofilm-reducing activity of this nontoxic coating against a range of urinary tract infectious (UTI) E. coli and Klebsiella strains.…”

Marine Bacteria from Danish Coastal Waters Show Antifouling Activity against the Marine Fouling Bacterium Pseudoalteromonas sp. Strain S91 and Zoospores of the Green Alga Ulva australis Independent of Bacteriocidal Activity

“…We quantified bacteria on the steel coupons with removal by sonication, followed by plate count on marine agar with and without streptomycin. We have previously demonstrated in pure cultures that the bacterial numbers determined by sonication removal and subsequent plating agrees well with numbers determined by the direct staining of attached bacteria (3). In situ quantification by staining with different probes followed by fluorescence microscopy also could have been used but would require strain-specific probes and that the number of bacteria on the surface was quantifiable by microscopy.…”