Impact of different hand-drying methods on surrounding environment: aerosolization of virus and bacteria, and transfer to surfaces.

BACKGROUND: In recent years, hand drying has been highlighted as a key step in appropriate hand hygiene, as moisture on hands can increase the transfer of micro-organisms from hands to surfaces and vice versa. AIM: To understand bacterial and viral aerosolization following hand drying, and study the transfer of micro-organisms from hands to surfaces after drying using different methods. METHODS: Groups of five volunteers had their hands pre-washed with soap, rinsed and dried, then inoculated with a concentrated mixture of Pseudomonas fluorescens and MS2 bacteriophage. Volunteers entered an empty washroom, one at a time, and rinsed their hands with water or washed their hands with soap prior to drying with a jet dryer or paper towels. Each volunteer applied one hand successively to various surfaces, while their other hand was sampled using the glove juice method. Both residual bacteria and viruses were quantified from the washroom air, surface swabs and hand samples. FINDINGS: P. fluorescens and MS2 bacteriophages were rarely aerosolized while drying hands for any of the drying methods studied. Results also showed limited, and similar, transfer of both micro-organisms studied on to surfaces for all drying methods. CONCLUSION: The use of jet dryers or paper towels produces low levels of aerosolization when drying hands in a washroom. Similarly, all drying methods result in low transfer to surfaces. While the coronavirus disease 2019 pandemic raised concerns regarding public washrooms, this study shows that all methods tested are hygienic solutions for dry washed hands.

Evaluating the environmental microbiota across four National Health Service hospitals within England.

Hospital surfaces contaminated with microbial soiling, such as dry surface biofilms (DSBs), can act as a reservoir for pathogenic micro-organisms, and inhibit their detection and removal during routine cleaning. Studies have recognized that such increases in bioburden can hinder the impact of disinfectants and mask the detection of potential pathogens. Cleanliness within healthcare settings is often determined through routine culture-based analysis, whereby surfaces that exhibit >2.5 colony-forming units (CFU) per cm2 pose a risk to patient health; therefore, any underestimation could have detrimental effects. This study quantified microbial growth on high-touch surfaces in four hospitals in England over 19 months. This was achieved using environmental swabs to sample a variety of surfaces within close proximity of the patient, and plating these on to non-specific low nutrient detection agar. The presence of DSBs on surfaces physically removed from the environment was confirmed using real-time imaging through episcopic differential interference contrast microscopy combined with epifluorescence. Approximately two-thirds of surfaces tested exceeded the limit for cleanliness (median 2230 CFU/cm2), whilst 83% of surfaces imaged with BacLight LIVE/DEAD staining confirmed traces of biofilm. Differences in infection control methods, such as choice of surface disinfectants and cleaning personnel, were not reflected in the microbial variation observed and resulting risk to patients. This highlights a potential limitation in the effectiveness of the current standards for all hospital cleaning, and further development using representative clinical data is required to overcome this limitation.

Modelling vaporised hydrogen peroxide efficacy against mono-species biofilms.

This pilot study investigates a novel approach towards efficacy testing of antimicrobial cleaning agents; focusing primarily on hydrogen peroxide vapour (HPV). Contaminated surfaces are recognised modes of pathogen transmission within healthcare environments and increase the risk of pathogen acquisition in newly admitted patients. Studies have shown these pathogens can survive on surfaces for extended periods of time in spite of cleaning. This resilience is characteristic of biofilm formation and recent publications have identified their presence in hospitals. In this study, biofilm models comprised of multidrug-resistant organisms (MDROs) were generated using a drip flow reactor and exposed to HPV decontamination. The MDROs included Acinetobacter baumannii, Enterococcus faecalis, Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus. Upon exposure, samples were periodically removed and enumerated to generate kill curves for each species. Consequently revealing any inherent resistances; such as catalase-producing organisms which expressed reduced susceptibility. Epifluorescence microscopy revealed an abundance of viable and non-viable microcolonies before and after decontamination, respectively. Greater than 6-Log10 reduction was achieved within a 100 minutes exposure time. This pilot study puts forward a potential methodology for testing antimicrobial agents against biofilms and supports the efficacy of HPV.

Influence of copper surfaces on biofilm formation by Legionella pneumophila in potable water.

Legionella pneumophila is a waterborne pathogen that can cause Legionnaires' disease, a fatal pneumonia, or Pontiac fever, a mild form of disease. Copper is an antimicrobial material used for thousands of years. Its incorporation in several surface materials to control the transmission of pathogens has been gaining importance in the past decade. In this work, the ability of copper to control the survival of L. pneumophila in biofilms was studied. For that, the incorporation of L. pneumophila in polymicrobial drinking water biofilms formed on copper, PVC and PEX, and L. pneumophila mono-species biofilms formed on copper and uPVC were studied by comparing cultivable and total numbers (quantified by peptide nucleic acid (PNA) hybridisation). L. pneumophila was never recovered by culture from heterotrophic biofilms; however, PNA-positive numbers were slightly higher in biofilms formed on copper (5.9 × 10(5) cells cm(-2)) than on PVC (2.8 × 10(5) cells cm(-2)) and PEX (1.7 × 10(5) cells cm(-2)). L. pneumophila mono-species biofilms grown on copper gave 6.9 × 10(5) cells cm(-2) for PNA-positive cells and 4.8 × 10(5) CFU cm(-2) for cultivable numbers, showing that copper is not directly effective in killing L. pneumophila. Therefore previous published studies showing inactivation of L. pneumophila by copper surfaces in potable water polymicrobial species biofilms must be carefully interpreted.

Effect of chlorine on incorporation of Helicobacter pylori into drinking water biofilms.

The use of a specific peptide nucleic acid (PNA) probe demonstrated that Helicobacter pylori persisted inside biofilms exposed to low concentrations of chlorine (0.2 and 1.2 mg liter(-1)) for at least 26 days, although no culturable cells were recovered. Coupled with data obtained using viability stains in pure culture, this result suggests that H. pylori can survive chlorination but remain undetectable by culture methods, which can be effectively replaced by PNA hybridization.

Comparison between standard culture and peptide nucleic acid 16S rRNA hybridization quantification to study the influence of physico-chemical parameters on Legionella pneumophila survival in drinking water biofilms.

Legionella pneumophila is a waterborne pathogen that is mainly transmitted by the inhalation of contaminated aerosols. In this article, the influence of several physico-chemical parameters relating to the supply of potable water was studied using a L. pneumophila peptide nucleic acid (PNA) specific probe to quantify total L. pneumophila in addition to standard culture methods. A two-stage chemostat was used to form the heterotrophic biofilms, with biofilm generating vessels fed with naturally occurring L. pneumophila. The substratum was the commonly used potable water pipe material, uPVC. It proved impossible to recover cultivable L. pneumophila due to overgrowth by other microorganisms and/or the loss of cultivability of this pathogen. Nevertheless, results obtained for total L. pneumophila cells in biofilms using a specific PNA probe showed that for the two temperatures studied (15 and 20 degrees C), there were no significant differences when shear stress was increased. However, when a source of carbon was added there was a significant increase in numbers at 20 degrees C. A comparison of the two temperatures showed that at 15 degrees C, the total cell numbers for L. pneumophila were generally higher compared with the total microbial flora, suggesting that lower temperatures support the inclusion of L. pneumophila in drinking water biofilms. The work reported in this article suggests that standard culture methods are not accurate for the evaluation of water quality in terms of L. pneumophila. This raises public health concerns since culture methods are still considered to be the gold standard for assessing the presence of this opportunistic pathogen in water.

Validation of SYTO 9/propidium iodide uptake for rapid detection of viable but noncultivable Legionella pneumophila.

Legionella pneumophila is an ubiquitous environmental microorganism that can cause Legionnaires' disease or Pontiac fever. As a waterborne pathogen, it has been found to be resistant to chlorine disinfection and survive in drinking water systems, leading to potential outbreaks of waterborne disease. In this work, the effect of different concentrations of free chlorine was studied (0.2, 0.7, and 1.2 mg l(-1)), the cultivability of cells assessed by standard culture techniques (buffered charcoal yeast extract agar plates) and viability using the SYTO 9/propidium iodide fluorochrome uptake assay (LIVE/DEAD BacLight). Results demonstrate that L. pneumophila loses cultivability after exposure for 30 min to 0.7 mg l(-1) of free chlorine and in 10 min when the concentration is increased to 1.2 mg l(-1). However, the viability of the cells was only slightly affected even after 30 min exposure to the highest concentration of chlorine; good correlation was obtained between the rapid SYTO 9/propidium iodide fluorochrome uptake assay and a longer cocultivation with Acanthamoeba polyphaga assay, confirming that these cells could still recover their cultivability. These results raise new concerns about the assessment of drinking water disinfection efficiency and indicate the necessity of further developing new validated rapid methods, such as the SYTO 9/propidium iodide uptake assay, to assess viable but noncultivable L. pneumophila cells in the environment.

Persistence of Helicobacter pylori in heterotrophic drinking-water biofilms.

Although the route of transmission of Helicobacter pylori remains unknown, drinking water has been considered a possible transmission vector. It has been shown previously that, in water, biofilms are a protective niche for several pathogens, protecting them from stressful conditions, such as low carbon concentration, shear stress, and less-than-optimal temperatures. In this work, the influence of these three parameters on the persistence and cultivability of H. pylori in drinking-water biofilms was studied. Autochthonous biofilm consortia were formed in a two-stage chemostat system and then inoculated with the pathogen. Total numbers of H. pylori cells were determined by microscopy using a specific H. pylori 16S rRNA peptide nucleic acid probe, whereas cultivable cells were assessed by standard plating onto selective H. pylori medium. Cultivable H. pylori could not be detected at any time point, but the ability of H. pylori cells to incorporate, undergo morphological transformations, persist, and even agglomerate in biofilms for at least 31 days without a noticeable decrease in the total cell number (on average, the concentration was between 1.54 x 10(6) and 2.25 x 10(6) cells cm(-2)) or in the intracellular rRNA content may indicate that the loss of cultivability was due to entry into a viable but noncultivable state. Unlike previous results obtained for pure-culture H. pylori biofilms, shear stress did not negatively influence the numbers of H. pylori cells attached, suggesting that the autochthonous aquatic bacteria have an important role in retaining this pathogen in the sessile state, possibly by providing suitable microaerophilic environments or linking biomolecules to which the pathogen adheres. Therefore, biofilms appear to provide not only a safe haven for H. pylori but also a concentration mechanism so that subsequent sloughing releases a concentrated bolus of cells that might be infectious and that could escape routine grab sample microbiological analyses and be a cause of concern for public health.

The survival of Escherichia coli O157 on a range of metal surfaces.

Escherichia coli O157:H7 is a serious pathogen causing haemorrhagic colitis. It has been responsible for several large-scale outbreaks in recent years. E. coli O157:H7 is able to survive in a range of environments, under various conditions. The risk of infection from contaminated surfaces is recognised, especially due to the low infectious dose required. In this study, a high concentration (10(7) cells) of E. coli O157 was placed onto different metals and survival time measured. Results showed E. coli O157 to survive for over 28 days at both refrigeration and room temperatures on stainless steel. Copper, in contrast, has strong antibacterial properties (no bacteria can be recovered after only 90 min exposure at 20 degrees C, increasing to 270 min at 4 degrees C) but its poor corrosion resistance and durability make it unsuitable for use as a surface material. Other copper-containing alloys, such as copper nickels and copper silvers, have improved durability and anticorrosion properties and greatly reduce bacterial survival times at these two temperatures (after 120 min at 20 degrees C and 360 min at 4 degrees C, no E. coli could be detected on a copper nickel with a 73% copper content). Use of a surface material with antibacterial properties could aid in preventing cross-contamination events in food processing and domestic environments, if standard hygiene measures fail.

Die-off of enteric bacterial pathogens during mesophilic anaerobic digestion.

Conventionally treated sewage sludge may contain high concentrations of potentially pathogenic microorganisms and additional treatment is required to minimise the risks to health if it is to be recycled to agricultural land. Mesophilic anaerobic digestion (MAD) is the most widely used process in the UK for stabilising sludge prior to agricultural recycling, but little is known about the fate of a number of enteric pathogens as the sludge passes through the treatment processes. The aim of this study was to determine the efficiency of MAD in removing the bacterial enteric pathogens, Salmonella senftenberg, Listeria monocytogenes and Campylobacter jejuni which were added as a spike to the digester feedstock, together with the die-off of indigenous Escherichia coli already present in the sludge. The primary sludge digestion stage of MAD was found to achieve a log removal of 1.66 for E. coli, 2.23 for L. monocytogenes and 2.23 for S. senftenberg. However, the extent of die-off was a function of the numbers of pathogens in the feed and as these increased the log removal also increased. The numbers of C. jejuni were not affected by primary sludge digestion. Additional die-off was provided by secondary sludge digestion with log removals of 1.70 for E. coli, 2.10 for S. senftenberg and 0.36 for C. jejuni.