Drug resistant superbugs are expected to overwhelm the healthcare system, reverse a century’s worth of medical progress and claim more lives than cancer by 2050 unless efforts are accelerated to stop antibiotic resistant bacteria in their tracks.
While most studies to address the problem are focusing on the development of new drugs, a series of elegant studies in France has taken an unusual angle – analyzing the types of surfaces that can harbor drug resistant bacteria in healthcare settings.
Surfaces can serve as fomites, which refers to objects or materials likely to harbor infectious organisms, allowing them to promote the spread of pathogens when touched or used.
Scientists have long known that environmental surfaces are a potential reservoir for healthcare-associated infections. So the hunt has been underway in France to find a material with potent antimicrobial activity.
In the journal Antibiotics, Muhammad Tanveer Munir and colleagues at Ecole Supérieur du Bois in Nantes, located in northwestern France near the Atlantic coast, worked with collaborators from elsewhere in the region to take a fresh approach to potential materials in the healthcare environment.
They have discovered what may at first blush seem the most unlikely surface for healthcare settings – oak. Although his institution is aimed at studying wood, it is not designed to promote wood as a product for hospitals.
Wood is an old-school material and seems almost unthinkable for surfaces in a modern healthcare facility. It’s porous, and has nooks and crannies where bacterial colonies hypothetically might flourish.
Moreover, it just isn’t as sleek as stainless steel. But scientific research is proving otherwise.
“That is exactly the first perception – the porosity and organic nature of wood would somehow help the bacteria survive,” Munir told Medical Xpress.
Munir and his team compared oak to aluminum, polycarbonate and stainless steel surfaces and found that when four of the most notorious causes of drug-resistant bacterial infections were placed on these surfaces, oak fared best in thwarting pathogenic growth.
The finding was stunning – because oak would seem to be the least likely surface. Indeed, to most well-read armchair biologists the choice of oak as a material in hospitals would seem not only counterintuitive, but almost difficult to imagine as a surface for hospital bedrails, table tops, trays and other common items used in healthcare facilities.
But the research dramatically proved otherwise. Oak didn’t promote bacterial growth, it did the opposite – it inhibited it.
For example, the four bacterial species whose survival was studied in the research included Acinetobacter baumannii, Enterococcus faecalis, Klebsiella pneumoniae, and Staphylococcus aureus. Each species was analyzed on oak versus the three other materials.
“This investigation is a ‘One Health approach’ in collaboration with laboratories of multiple institutes including two public hospitals … and a veterinary school,” Munir said.
One-health approaches recognize the interconnection among people, animals, plants, and their shared environment.
“The multidisciplinary team of this project includes veterinarians, microbiologists, pharmacists, biologists, medical doctors, chemists, engineers and social scientists,” he added.
Millions of bacterial cells were deposited on each material, Munir explained, and their survival was measured on day 0, 1, 2, 6, 7 and 15 of the experiments.
Analyses were performed in triplicate for each material. When it came to oak surfaces, the team found the bacterial count decreased rapidly on transversal- and tangential-cut oak.
“Wood from a tree can be cut in various directions, the most commonly known are the tangential and transversal directions,” Munir explained.
“These two directions have a different cellular arrangement and their microscopic anatomy is different.
“For example, most of the fibers in wood run longitudinally in a tree, and when it is cut transversally, more cells would be exposed showing higher porosity, while the tangential – longitudinal – cut wood will have lower porosity.”
However, results of the research revealed no overall difference between transversal and tangential oak regarding a capacity to inhibit bacterial growth. Yet the question remains: Why would oak thwart antibiotic resistant bacteria?
“The tested bacteria are not the natural flora found on wood,” he explained.
“The wood material is hygroscopic, which means its fibers can absorb moisture and make it unavailable to these microbes, thus limiting their growth or killing them by a desiccation effect.
“The other mechanism is the chemical effect. The trees have a chemical defense mechanism against microbes in form of extractives – chemical compounds. These compounds are present even in dead wood material and have antimicrobial activities.
“We used untreated oak wood in this study because we have previously observed antimicrobial activities of this wood, and our objective was to study the natural antimicrobial potential of wood material.”
The French research arrives in the midst of a global coronavirus pandemic, which is overshadowing all other infectious diseases.
But in late November, Dr. Tedros Adhanom Ghebreyesus, director general of the World Health Organization, declared antimicrobial resistance as worrisome as the coronavirus pandemic.
“Antimicrobial resistance may not seem as urgent as a pandemic but it is just as dangerous,” he said.
While most of the world is riveted on the growing number of infections caused by SARS-CoV-2, which have exceeded 63 million worldwide, the drug resistance crisis threatens to reverse a century of medical progress, Ghebreyesus told a WHO news conference.
An estimated 700,000 people die annually of infections directly linked antimicrobial resistant organisms, according to WHO’s estimates, which also includes deaths attributed to a range of resistant microbes, such as fungi.
The agency additionally predicts drug resistance will likely soar uncontrollably to become the globe’s leading cause of death by 2050 unless measures are undertaken now to rein in drug resistant infections.
Munir, meanwhile, concludes that considering oak surfaces in hospitals might help lower the burden of drug resistant infections. “Bacteria responsible for healthcare-associated infections may survive for days to months on the commonly used hospital surface materials.”
Although wood unfairly is perceived as an unhygienic material “our research showed that the four most common bacteria responsible for healthcare-associated infections survive least on this material compared to other inanimate surfaces.”
Wood is an organic material and a renewable resource of nature. It is an eco-friendly material as compared to glass, plastic, and metals that cause environmental disorders i.e., pollution or health hazards . It is also an important constituent of nature-based themes aimed to improve the psychological well-being of inhabitants .
Untreated wood surfaces are traditionally used for food preparation, cutting, fermentation, and packaging . Wood and wood products are also used as flooring and beddings in animal husbandry practices where they contribute to improvement in the health and welfare of animals [4,5].
Meanwhile, the safety of wood material in hygienically significant places is questioned, owing to its porosity and hygroscopic nature. However, studies have shown that some commonly used wood speices have antimicrobial activities [6,7,8] and can be looked on as a safe material for indoor uses in hygienically significant places [2,9] and as food contact surfaces [3,10,11].
Therefore, the antimicrobial properties of this material are investigated either to validate its safety as a hygienic surface or for the discovery and identification of the active antimicrobial compounds present in it [9,12,13,14,15,16].
Various diagnostic methods are used to determine the antimicrobial properties of wood to evaluate the safety of this material via screening tests and/or quantify the presence of any active compounds [6,16]. Moreover, such tests can help identify the factors affecting the antimicrobial behavior of wood such as the nature of the microbes (type and resistance), the wood characteristics and variability (age, location, part, and treatment) and the environment (humidity, moisture, and temperature) [7,8,10].
In addition, such methods can also be used to evaluate the efficacy of disinfectants and treatments used to increase the antimicrobial effectiveness of surfaces [17,18,19,20].
In general, antimicrobial properties of wood are studied via extractive-based methods, where compounds are extracted using solvents (S1 in Supplementary Materials) and then subjected to conventional antimicrobial testing methods such as agar diffusion and broth dilution [8,12,21,22].
Meanwhile, the direct methods such as surface contact test, microbe recovery protocols (S2 in Supplementary Materials), and bioluminescence assay can assess the surface contamination of wood [23,24,25]. However, to our knowledge, there are no specific standard methods available for wood material to directly determine its antimicrobial potential or surface contamination.
Further, mass spectrometry and chromatography help in the identification and characterization of active compounds [16,26,27]. Each method has its own benefits and disadvantages regarding its suitability for the handler.
Few reviews exist on the subject of testing the antimicrobial potential of different materials [28,29,30,31]. It is believed that this is the first review of the suitability of these methods for wood and hygienically important microbes, particularly those that can be responsible for infections in the healthcare setting, and among them those being multiresistant to antibiotics.
Therefore, this article aims to describe the available antimicrobial assays, their suitability to wood material in different forms, along with their advantages and disadvantages regarding utilization.
This information is intended to serve as a guideline for researchers and field experts regarding the application of suitable methods in wood science, microbiology, hygiene, and the discovery of novel antimicrobial agents.
Results and discussion
A total of 57 articles were obtained to identify the methods of antimicrobial testing of wood material (Table 1). Further studies were added to describe the prospective methods (i.e., autobiography) of studying the antimicrobial properties of different compounds in the form of extractives.
Summary of publications selected for full-text review.
|Material||Microorganism||Objective of the Study||Methods||Main Findings||Reference|
|Oak and pine||Staphylococcus aureus, Salmonella enteritidis||Survival of pathogens on wooden surfaces in healthcare facilities||Swabbing, planning, and plate count||Wood surfaces showed antimicrobial properties|||
|Oak wood||Isolates of S. aureus||Oak in hospitals, the worst enemy of Staphylococcus aureus||Direct disc diffusion method||The method was efficient to show the antimicrobial properties of wood|||
|Pine and spruce wood-associated polyphenols||Salmonella, Listeria monocytogenes, S. epidermidis, S. aureus, Candida tropicalis, Saccharomyces cerevisiae||The antimicrobial effects of wood-associated polyphenols on food pathogens and spoilage organisms||Microbial cell wall permeability and membrane damage||Several stilbenes showed antimicrobial activities against food pathogens and spoilage organisms|||
|Populus lasiocarpa, P. tomentosa||N/A||Characteristics of antibacterial molecular activities in poplar wood extractives||GC/MS||The molecules were identified that are known to have antimicrobial properties|||
|Abies alba, Q. rubra, European oak, Fagus sylvatica||S.aureus, E. coli,|
P. aeruginosa, E. faecalis
|Direct screening method to assess antimicrobial behavior of untreated wood||Direct disc diffusion method||The method was efficient to show the antimicrobial properties of wood|||
|Larch (Larix decidua Mill.) and Pine (Pinus sylvestris L.)||Bacillus subtilis, S. aureus, Enterococccus faecium, Pseudomonas aeruginosa||Testing the antimicrobial activities of different wood and their parts against different bacteria||Direct disc diffusion, paper disc diffusion||Antimicrobial activities depended upon the type of wood, part of tree, and type of bacteria|||
|Spruce wood (P. abies), glass, polypropylene||L. monocytogenes||An assessment of bacterial transfer from wooden ripening shelves to cheeses||Food contact with surface||Wooden shelves had the lowest transfer rate of bacteria compared to other surfaces|||
|Wood and other cutting boards||S. Enteritidis||Transfer of bacteria to food after cleaning the surfaces||Swabbing and|
|Efficacy of cleaning methods was tested|||
|Spruce wood shelves||L. monocytogenes||Survival of bacteria after the cleaning and sanitation of cheese preparation boards||Surface contact/blot planning and blending||Bacteria could not be cleaned by brushing and rubbing|||
|Wood and other archeological objects||Variety of microbes||Isolation, characterization, and treatment of microbial agents responsible for the deterioration of archaeological objects||Swabbing||All samples were contaminated with various types of surface degrading microbes|||
|P. sylvestris, Picea abies||E.coli||Effect of extractives and thermal modification on antibacterial properties||Plate count method||Thermal treatments and extraction influence on the antimicrobial properties of wood|||
|P. sylvestris, P. abies||S. aureus, E. faecalis, E. coli, Streptococcus pneumoniae||Antibacterial properties of wooden extracts||Direct (extractive) agar diffusion method||Extractive showed antimicrobial properties|||
|Oak and Douglas fir wood||Wood degrading microbes||Interaction of bacteria and fungi on wooden surfaces||Scanning electron microscopy and plate contact test||Environmental factors’ influence on the microbial interaction on wooden surfaces|||
|Melamine, vinyl chloride, stainless steel, wood, and acrylonitrilebutadiene styrene||Total microbial count||ATP bioluminescence values are significantly different depending upon the material surface properties of the sampling location in hospitals||ATP bioluminescence, SEM, agar stamp/blotting||ATP and colony-forming unit (CFU) were different for wooden surfaces|||
|Wood and plastic||Foodborne bacteria||Analysis of microbial community and food-borne bacteria on restaurant cutting boards||Pyrosequencing||Distribution of 32 genera was identified||[32,33]|
|Wood, plastic, vinyl, quarry clay tile||L. monocytogenes||Efficacy of sonicating swabs to recover microbes from surfaces||Sonicating swab compared to cotton, sponge, and foam swab||Sonicating swabs recovered significantly higher number of microbes|||
|Contact surfaces including wood||Erwinia herbicola||Evaluation of two surface sampling methods for microbial detection on materials by culture and qPCR||Sponge and swabbing used for sample collection and tested by qPCR and plate count||qPCR is more sensitive than culturing, and swabbing was more efficient than sponge|||
|Pterocarpus spp. and poplar wood||White and brown rot fungus||Evaluation of antimicrobial activity of ethanol and aqueous extracts||Wood mass loss calculation and gas chromatography-mass spectrometry||The wood extracts provided protection against degradation owing to antimicrobial properties|||
|Wood and bamboo cutting boards||Vibrio parahaemolyticus||Efficacy of disinfectant to clean the cutting boards||Stirring method for microbial recovery||More microbes were recovered from plastic as compared to wood and bamboo|||
|Wood cutting board and other surfaces||Methicillin-resistant Staphylococcus aureus (MRSA)||Microbial survival on five environmental surfaces||Swabbing||Survival and recovery of microbes depends upon the type of surfaces and moisture conditions|||
|Calabrian and Sicilian|
chestnut, cedar, cherry, ash, walnut, black pine, poplar
|Salmonella, Listeria, E.cli, S. aureus, Lactic acid bacteria (LAB)||Formation and characterization of early bacterial biofilms on different wood typologies||SEM for biofilm observation and paper disc method to determine antimicrobial activities||LAB represent efficient barriers to the adhesion of the main dairy, pathogens, probably due to their acidity and bacteriocin generation|||
|Rubber wood cutting boards, plastic, glass||E. coli, S. aureus||Effectiveness of domestic antibacterial products in decontaminating food contact surfaces||Agar overlay method for microbial recovery||This method gave good results for testing the cleanability of surfaces|||
|Pine and plastic||E. coli, P. aeruginosa, S. aureus, L. monocytogenes||Efficacy of electrolyzed water to inactivate different bacteria on cutting boards||Swabbing||Treatment was efficient for reducing microbial contamination|||
|Poplar wood||E.coli||Confocal spectral microscopy—An innovative tool for the tracking of pathogen agents on contaminated wooden surfaces||Confocal spectral laser microscopy||The microbes could be located for their distribution by this method|||
|Melia azedarach wood||Agrobacterium tumefaciens, Dickeya solani, Erwinia amylovora, P. cichorii, Serratia pylumthica, Fusarium culmorum, Rhizoctonia solani||Wood preservation potential of extracts||Direct diffusion method||Antimicrobial properties were observed using the disc diffusion method|||
|Wooden toothpicks||Variety of microbes||Determination of microbial contamination of wood||Wet preparation techniques, concentration techniques, culture, biochemical tests||Wooden samples were found contaminated with a wide range of microorganisms|||
|Eucalyptus globulus wood||B. subtilis, S. aureus, S. epidermis, E. coli, C. krusei, P. aeruginosa C. parapsilosis, C. glabrata, C. albicans, Saccharomyces cerevisiae||Extraction of bioactive compounds from biomass of forest management and wood processing||Well diffusion method||Antimicrobial compounds were identified|||
|Spruce wood||L. monocytogenes, L. innocua||Comparison of methods for the detection of listeria on porous surfaces||Sponge swabbing||Porosity influences the recovery of microbes|||
|Rubber wood and plastic||L. monocytogenes||Transmission of bacteria from raw chicken meat to cooked chicken meat through cutting boards||Rinsing with normal saline to remove bacteria and meat contact to study transmission||Surfaces play role in transmission of bacteria|||
|Cork wood||S. aureus and E. coli||Evaluation of antimicrobial properties of cork||Agar dilution method||Cork has antimicrobial properties|||
|Wood of P. heldreichii Christ. var. leucodermis||S. aureus, S.epidermidis, E. coli, Enterobacter cloacae, Klebsiella pneumoniae, P. aeruginosa, C. albicans, C. tropicalis, C. glabrata||Chemical composition and biological activity of the essential oil from pine wood||GC and GC/MS and Agar dilution method||Antimicrobial activities of pine wood were identified and characterized|||
|Hardwood, carpets, vinyl and porcelain tiles||S. aureus, Aspergillus niger||Microbial survival on floor materials||Bulk rinsate, agar plate contact, vacuum suction||Microbial survival depends on the recovery method and surface type in hospitals (vet and human) and office buildings|||
|Spruce fir boards (P. abies)||L. monocytogenes, L. innocua||Sanitizing wooden boards used for cheese maturation by means of a steam-mediated heating process||Planning and cotton swabbing and then stomacher||Both recovery methods showed identical results|||
|Pine, poplar, spruce||E. coli,|
L. monocytogenes, P. expansum
|Comparative study of 3 methods for recovering microorganisms from wooden surfaces in the food industry||Planning, grinding and brushing||Humidity, type of wood and microbe, and recovery method influenced the recovery rates|||
|Sapwood and heartwood of the larch||K. pneumoniae,MRSA||Antimicrobial properties of wood against hygienic microbes||Blotting and vibration||Microbial quantities decreased after contact with wood|||
|Quercus baloot||C. albicans||Evaluation of anticandidal potential of wood||Thin-layer chromatography, contact bioautography, disc diffusion method, broth microdilution||Chemical constituents were identified and antimicrobial activities were reported|||
|Maple and Beech||Aerobic mesophilic|
microorganisms Enterobacteriaceae, Pseudomonas spp.
|Hygienic aspects of using wooden and plastic cutting boards||Swabbing||Survival of microbes on different cutting boards before and after cleaning|||
|Pine, larch, spruce, beech, maple, poplar, oak, polyethylene||E.coli, E. faecium||Studying the survival of pathogenic organisms in contact with wood material||PCR and culture-based recovery methods||Wood material has antimicrobial properties||[56,57]|
|Maple wood, steel, ceramic and carpet||Enterobacter aerogenes||Longer contact times increase cross-contamination of Enterobacter aerogenes from surfaces to food||Vortex for microbial recovery plate count method for enumeration||Contact time, food, and surface type all|
had highly significant effects on the log percent transfer of bacteria
|Poplar||E. coli, P. expansum||Assessment of Penicillium expansum and Escherichia coli transfer from poplar crates to apples||Grinding/blending||There is a low transmission of microbes from wood to food (apple) as compared to glass and plastic|||
|Wood, stainless steel, Formica, polypropylene||Salmonella Typhimurium||Recovery and transfer of Salmonella Typhimurium from four different domestic food contact surfaces||Swabbing (vortexting), contact pressing (635 g) and food contact||Number of microbes recovered and their transfer from wood to food was lowest compared to other surfaces|||
|Poplar||B. cereus spores, E. coli cells||Behavior of bacteria on poplar wood crates by impedance measurements||Direct contact (wood in broth)||Microbes in contact with wood present in broth showed decrease in CFU|||
|Poplar and pine||Total microbial counts, S. aureus||Hygienic properties exhibited by single-use wood and plastic packaging on the microbial stability for fish||Vortexing to recover microbes and enumerated by the TEMPO® system||Microbes decreased fastest on wood|||
|Leucaena leucocephala||Trichoderma viride, Fusarium subglutinans, A. niger||Antimicrobial properties of wood treated with natural extracts||GC-MS, direct diffusion method||Antifungal properties were observed|||
|P. abies, Larix decidua||P. funiculosum, P. ochrochloron, A. niger, C.albicans, A. flavus, A. ochraceus, E.coli, S. aureus, Micrococcus flavus, B. cereus, L. monocytogenes, P. aeruginosa, Pectobacterium atrosepticum, Pec. carotovorum, Dickeya solani||Antimicrobial properties of bark and wood extracts||GC-MS, microdilution method||The extracts showed antimicrobial properties, minimum inhibitory concentration (MIC) was determined|||
|Quercus incana||S.aureus, Micrococcus luteus, B. subtilis, E. coli, Ps. pickettii, Shigella flexneri, A. niger, A flavus||Identification, isolation, and characterization of novel antimicrobial compounds||Disc diffusion method, well diffusion method||Two new compounds were identified with their antimicrobial properties|||
|Q. suber, Q. macrocarpa, Q. montana, Q. griffithii, Q. serrata||B. subtilis, S. pneumonia, E. coli, S. aureus, A. niger, Penicillium spp., Fusarium oxysporum||Antimicrobial characterization combining spectrophotometric analysis of different oak species||Paper disc diffusion method and UV spectrophotometric analysis||Antimicrobial properties and active compounds were identified|||
|Rubber wood||Campylobacter jejuni||Transfer of Campylobacter jejuni from raw to cooked chicken via wood and plastic cutting boards||Rinsing with normal saline and then counting CFU by combined most-probable-number (MPN)-PCR||Transfer during uncooked/cooked meat chopping on unscored and scored cutting boards|||
|Heartwood of Scots pine (P. sylvestris)||L. monocytogenes, E. coli||Pine heartwood and glass surfaces: easy method to test the fate of bacterial contamination||Plate count and broth turbidity test||Wood does not allow the survival of microbes|||
|P. sylvestris and P. abies||MRSA, E.coli O157:H7||Microbial survival on extractive-treated glass cylinders was studied||Vortexting and plate count method||Extractive showed antimicrobial properties|||
|P. sylvestris and P. abies||S. aureus, E. coli, S. pneumoniae, S. enterica Typhimurium||Antimicrobial properties of volatile organic compounds (VOCs) of wood||Glass chamber and plate count method||VOCs reduced the microbial survival|||
|30 species of trees||B. cereus, S. aureus, L. monocytogenes, Lactobacillus plantarum, E. coli, Salmonella infantis, P. fluorescens, C albicans, Saccharomyces cerevisiae, A. fumigatus, Penicillium brevicompactum||Antimicrobial and cytotoxic knotwood extracts and related pure compounds and their effects on food-associated microorganisms||Broth dilution and agar well dilution methods||Antimicrobial properties were observed|||
|Beech wood (F. sylvatica L.)||Gloeophyllum trabeum, Trametes versicolor||Phenolic extractives of wound-associated wood of beech and their fungicidal effect||Spectrophotometrically analyzed and a paper disc screening test||Wood wounds have defensive chemicals to counter fungal invasion|||
|Hard maple and plastic cutting boards||E. coli||Bacterial retention and cleanability of cutting boards with commercial food-service maintenance practices||Wet sponge swabbing||Microbial recovery was 0.25% and 0.1% from plastic and wood respectively in dry conditions and was similar in wet conditions|
According to the literature findings, it was possible to categorize the methods into two broad groups based on form of test material used e.g., solid wood or extractives. Furthermore, they were subclassified into different groups according to the methodology, as shown in Figure 2.
reference link : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7277147/
More information: Ju-Chi Chen, et al. Survival of Bacterial Strains on Wood (Quercus petraea) Compared to Polycarbonate, Aluminum and Stainless Steel, Antibiotics (2020) DOI: 10.3390/antibiotics9110804