Fire Ant Venom Alkaloids Inhibit Biofilm Formation

Abstract

Biofilm formation on exposed surfaces is a serious issue for the food industry and medical health facilities. There are many proposed strategies to delay, reduce, or even eliminate biofilm formation on surfaces. The present study focuses on the applicability of fire ant venom alkaloids (aka 'solenopsins', from Solenopsis invicta) tested on polystyrene and stainless steel surfaces relative to the adhesion and biofilm-formation by the bacterium Pseudomonas fluorescens. Conditioning with solenopsins demonstrates significant reduction of bacterial adhesion. Inhibition rates were 62.7% on polystyrene and 59.0% on stainless steel surfaces. In addition, solenopsins drastically reduced cell populations already growing on conditioned surfaces. Contrary to assumptions by previous authors, solenopsins tested negative for amphipathic properties, thus understanding the mechanisms behind the observed effects still relies on further investigation.

Keywords: LTQ Orbitrap Hybrid Mass Spectrometer; industrial biotechnology; myrmecology; natural antibiotics; piperidine heterocyclic amines.

Figure 1

Diameters of inhibition zones resulting from the antimicrobial activity of solenopsins by the paper disk diffusion method. Points are raw data and vertical whiskers represent SD around the mean. Disks impregnated with different concentrations (μg/mL) of solenopsins were added to a confluent Pseudomonas fluorescens growth plate and incubated at 25 °C for 24 h. Treatments topped by same letters were statistically similar based on Dunn’s test at alpha = 0.05.

Figure 2

Inhibition of biofilm formation (as discounted % relative to control) by Pseudomonas fluorescens ATCC 13525 on surfaces of polystyrene and stainless steel 304 conditioned with solenopsin alkaloids at different concentrations. Points are raw data and vertical whiskers represent SD around the mean; ‘CTL’ stands for negative control and ‘poly’ for polystyrene. Treatments accompanied by same letters were statistically similar based on Dunn’s test at alpha = 0.05: no difference was observed between results with different surface materials.

Figure 3

Reduction of mature biofilm (as % discounted of controls) by Pseudomonas fluorescens ATCC 13525 on non-conditioned surfaces of polystyrene (red) and stainless steel 304 (blue) by solenopsin alkaloids at different concentrations. Points are raw data and vertical whiskers represent SD around the mean; ‘CTL’ stands for negative control and ‘poly’ for polystyrene. Concentration groups within the same surface treatment accompanied by the same letter did not differ significantly by Dunn’s test at alpha = 0.05 (polystyrene: lowercase on top; stainless steel: uppercase below).

Figure 4

Viability of cells (in log/mL) recovered from biofilm of Pseudomonas fluorescens ATCC 13525 formed on surfaces of polystyrene conditioned with extracted solenopsins. No viable cells were recovered from a conditioned stainless steel coupon. Points are raw data and vertical whiskers represent SD around the mean; ‘CTL’ is negative control, and concentration groups topped by the same letter did not differ significantly by Dunn’s test at alpha = 0.05.

Figure 5

Surface adhesion by Pseudomonas fluorescens ATCC 13525 on polystyrene (left-hand panels) and stainless steel (right-hand panels) coupons after 24 h of incubation, as shown by epifluorescence of viable cells: Top panels (A,B) are negative non-conditioned controls; panels (C,D) are surfaces conditioned with 1000 µg/mL solenopsin alkaloids.