Air–liquid interface biofilm formation by psychrotrophic pseudomonads recovered from spoilt meat

The ability to colonise the surface of liquids has obvious advantages for bacteria and biofilm formation at the meniscus and air–liquid (A–L) interface is common amongst environmental pseudomonads. Bacteria from this genus also colonise raw meat and in this work the ability of these to produce biofilms was assessed. Sixty isolates were recovered from vacuum-packed venison, phenotypically characterised and shown by hierarchical cluster analysis to represent a diverse collection of psychrotrophic spoilt venison-associated pseudomonads. Of these, 12 % were found to produce biofilms limited to the meniscus region of the microcosm walls, 31 % produced attached biofilms with significant extensions across the A–L interface and 45 % produced unattached ‘floating’ biofilms. A combined statistical analysis of growth, biofilm strength and attachment levels revealed that growth affected strength but not attachment, and that there was a significant relationship between attachment and strength. Some environmental pseudomonads are known to utilise cellulose as a biofilm matrix component and here 28 % of the SVP isolates were found to express cellulose by epifluorescent microscopy. This survey suggests that biofilm formation may be more common in psychrotrophic meat-associated isolates than amongst the wider pseudomonad community from which spoilage bacteria might be recruited. This may reflect a selective advantage of bacterial aggregations such as biofilms in environments subject to high levels of physical disturbance. Aggregations may be more resistant to competition and dehydration stress than individual bacteria, whilst fragments of these aggregations may prove more effective in the colonisation of new habitats.