Confocal spectral microscopy, a non-destructive approach to follow contamination and biofilm formation of mCherry Staphylococcus aureus on solid surfaces

Abstract

Methods to test the safety of wood material for hygienically sensitive places are indirect, destructive and limited to incomplete microbial recovery via swabbing, brushing and elution-based techniques. Therefore, we chose mCherry Staphylococcus aureus as a model bacterium for solid and porous surface contamination. Confocal spectral laser microscope (CSLM) was employed to characterize and use the autofluorescence of Sessile oak (Quercus petraea), Douglas fir (Pseudotsuga menziesii) and poplar (Populus euramericana alba L.) wood discs cut into transversal (RT) and tangential (LT) planes. The red fluorescent area occupied by bacteria was differentiated from that of wood, which represented the bacterial quantification, survival and bio-distribution on surfaces from one hour to one week after inoculation. More bacteria were present near the surface on LT face wood as compared to RT and they persisted throughout the study period. Furthermore, this innovative methodology identified that S. aureus formed a dense biofilm on melamine but not on oak wood in similar inoculation and growth conditions. Conclusively, the endogenous fluorescence of materials and the model bacterium permitted direct quantification of surface contamination by using CSLM and it is a promising tool for hygienic safety evaluation.

The survival of multi-drug resistant bacteria on raw Douglas fir material

“…In fact, we can make the hypothesis of low levels of these extracts in the wood samples tested here, which would impact the antibacterial properties. Another studies show the antibacterial properties of oak compared to other materials, including stainless steel, on four bacteria, two of which were identical to those used in our study 8 and a significantly greater decrease in Staphylococcus aureus colonisation over time on Douglas fir compared to oak and poplar 9 . So, it can be said the antibacterial properties of wood are timber-specific (Douglas fir, oak versus maritime pine), showing that the antibacterial action of certain species is not only due to the mechanical properties of the wood, but also to its molecular composition, its pH level, as several studies have shown 5 , 27 .…”

“…Douglas fir with an antibacterial coating showed no difference in bacterial survival compared to other materials, the coating can moderate the chemical and physical antibacterial activities of wood by affecting its surface structure, it can be said that this contributes to its lower effectiveness compared to raw Douglas fir versus stainless steel. In fact, several studies 9 , 28 , 29 show that the porosity of wood has an influence on its antibacterial properties, in particular by trapping bacteria deep down in an unsuitable environment for their survival. Similarly, Douglas fir shows a significant reduction in bacterial survival compared to pumice, a very porous material, which supports the fact that porosity plays a role in the antibacterial properties of wood, but is not the only one.…”

“…Then, a study of Chen et al has shown an effect of oak on the survival of bacteria classically responsible for HAIs ( Acinetobacter baumannii , Enterococcus faecalis , Klebsiella pneumoniae , Staphylococcus aureus ) compared to aluminium, polycarbonate and stainless steel 8 . Munir et al proved wood to be less exposed to the development of S. aureus bacterial biofilm than other materials such as melamine 9 . However, some studies also highlight that this antibacterial effect of raw wood material can vary according to the wood species.…”

“…Indeed, some results suggest that Douglas fir has greater antibacterial properties than other wood species. Furthermore, the effect of wood treatment on this properties, such as varnishing or disinfection, has not been evaluated 9 .…”