A proposed cleaning classification system for reusable medical devices to complement the Spaulding classification.

A central tenet in infection prevention is application of the Spaulding classification system for the safe use of medical devices. Initially defined in the 1950s, this system defines devices and surfaces as being critical, semi-critical or non-critical depending on how they will be used on a patient. Different levels of antimicrobial treatment, defined as various levels of disinfection or sterilization, are deemed appropriate to reduce patient risk of infection. However, a focus on microbial inactivation is insufficient to address this concern, which has been particularly highlighted in routine healthcare facility practices, emphasizing the underappreciated importance of cleaning and achieving acceptable levels of cleanliness. A deeper understanding of microbiology has evolved since the 1950s, which has led to re-evaluation of the Spaulding classification along with a commensurate emphasis on achieving appropriate cleaning. Albeit underappreciated, cleaning has always been important as the presence of residual materials on surfaces can interfere with the efficacy of the antimicrobial process to inactivate micro-organisms, as well as other risks to patients including device damage, malfunction and biocompatibility concerns. Unfortunately, this continues to be relevant, as attested by reports in the literature on the occurrence of device-related infections and outbreaks due to failures in processing expectations. This reflects, in part, increasing sophistication in device features and reuse, along with commensurate manufacturer's instructions for use. Consequently, this constitutes the first description and recommendation of a new cleaning classification system to complement use of the traditional Spaulding definitions to help address these modern-day technical and patient risk challenges. This quantitative risk-based classification system highlights the challenge of efficient cleaning based on the complexity of device features present, as an isolated variable impacting cleaning. This cleaning classification can be used in combination with the Spaulding classification to improve communication of cleaning risk of a reusable medical device between manufacturers and healthcare facilities, and improve established cleaning practices. This new cleaning classification system will also inform future creation, design thinking and commensurate innovations for the sustainable safe reuse of important medical devices.

Use of real-time immersive digital training and educational technologies to improve patient safety during the processing of reusable medical devices: Quo Vadis?

Hospital acquired infections stemming from contaminated reusable medical devices are of increasing concern. This issue is exaggerated with the introduction of complex medical devices like endoscopes and robotic instrumentation. Although medical device manufacturers validate their cleaning instructions for use, evidence in the literature demonstrates that effective device processing is not being performed consistently within sterile processing departments in clinical settings. The result is increased risks to patient safety. As a solution to this problem, focused one-on-one training increases compliance to the medical device manufacturer's processing instruction. However, often this is not a practical solution for the volume of healthcare staff responsible for device processing activities. This constitutes the first paper to address the blended use of educational and digital technologies to address these challenges and as a result inform safety and sustainability for the medical device sector. Cognitive learning theory is an evidence-based framework for learning. It supports the use of immersive educational experiences using emerging extended reality technologies (e.g., virtual or augmented reality) to increase learning comprehension. The delivery of educational content via these technologies provides an innovative option for repeatable leaning and training outcomes. The motivation is to decrease patient risk of contaminated reusable medical devices. The proposed approach while primary motivated by safety can also enhance sustainability and efficiency enabled by artificial intelligence and robotic instrumentation.

Studies on the novel effects of electron beam treated pollen on colony reproductive output in commercially-reared bumblebees (Bombus terrestris) for mass pollination applications.

Commercially-reared bumblebees provide an important pollinator service that helps support food production and security. The deployment of an appropriate non-thermal disinfection technology for the bulk treatment of pollen collected from honeybees for the feeding of commercial bumblebees is important in order to mitigate against complex diseases and unwanted pathogen spillover to native bees. High level disinfection of pollen was achieved using an electron (e)-beam dose of 100 kGy that corresponded to 78 % loss of cellular viability of bee pathogens before feeding to bumblebees as measured by the novel in vitro use of flow cytometry (FCM). Novel findings showed that e-beam treated-pollen that was fed to bumblebees produced fewer females, gynes and exhibited an absence of males when compared to control bumblebee colonies that were fed untreated commercial pollen. A similar trend emerged in bumblebee colony reproductive outputs when using membrane filtered washed pollen. Proteomic analysis of bumblebees from individual colonies fed with treated-pollen revealed a differential abundance of proteins associated with stress, immunity and metabolism when compared to the untreated pollen control group. Microbiome analysis of the bumblebee gut content revealed differences in microbiota between treated and untreated pollen in bumblebee colony studies. This novel study evaluated the impact of industrial e-beam treated-pollen on complex bee disease mitigation where physically treated-pollen fed to bumblebees was shown to substantially affect colony reproductive outputs.

A review of Spaulding's classification system for effective cleaning, disinfection and sterilization of reusable medical devices: Viewed through a modern-day lens that will inform and enable future sustainability.

Despite advances in medicine and innovations in many underpinning fields including disease prevention and control, the Spaulding classification system, originally proposed in 1957, remains widely used for defining the disinfection and sterilization of contaminated re-usable medical devices and surgical instruments. Screening PubMed and Scopus databases using a PRISMA guiding framework generated 272 relevant publications that were used in this review. Findings revealed that there is a need to evolve how medical devices are designed, and processed by cleaning, disinfection (and/or sterilization) to mitigate patient risks, including acquiring an infection. This Spaulding Classification remains in use as it is logical, easily applied and understood by users (microbiologists, epidemiologists, manufacturers, industry) and by regulators. However, substantial changes have occurred over the past 65 years that challenge interpretation and application of this system that includes inter alia emergence of new pathogens (viruses, mycobacteria, protozoa, fungi), a greater understanding of innate and adaptive microbial tolerance to disinfection, toxicity risks, increased number of vulnerable patients and associated patient procedures, and greater complexity in design and use of medical devices. Common cited examples include endoscopes that enable non- or minimal invasive procedures but are highly sophisticated with various types of materials (polymers, electronic components etc), long narrow channels, right angle and heat-sensitive components and various accessories (e.g., values) that can be contaminated with high levels of microbial bioburden and patient tissues after use. Contaminated flexible duodenoscopes have been a source of several significant infection outbreaks, where at least 9 reported cases were caused by multidrug resistant organisms [MDROs] with no obvious breach in processing detected. Despite this, there is evidence of the lack of attention to cleaning and maintenance of these devices and associated equipment. Over the last few decades there is increasing genomic evidence of innate and adaptive resistance to chemical disinfectant methods along with adaptive tolerance to environmental stresses. To reduce these risks, it has been proposed to elevate classification of higher-risk flexible endoscopes (such as duodenoscopes) from semi-critical [contact with mucous membrane and intact skin] to critical use [contact with sterile tissue and blood] that entails a transition to using low-temperature sterilization modalities instead of routinely using high-level disinfection; thus, increasing the margin of safety for endoscope processing. This timely review addresses important issues surrounding use of the Spaulding classification system to meet modern-day needs. It specifically addresses the need for automated, robust cleaning and drying methods combined with using real-time monitoring of device processing. There is a need to understand entire end-to-end processing of devices instead of adopting silo approaches that in the future will be informed by artificial intelligence and deep-learning/machine learning. For example, combinational solutions that address the formation of complex biofilms that harbour pathogenic and opportunistic microorganisms on the surfaces of processed devices. Emerging trends are addressed including future sustainability for the medical devices sector that can be enabled via a new Quintuple Helix Hub approach that combines academia, industry, healthcare, regulators, and society to unlock real world solutions.

Effects of climate and environmental variance on the performance of a novel peatland-based integrated multi-trophic aquaculture (IMTA) system: Implications and opportunities for advancing research and disruptive innovation post COVID-19 era.

Advancing wet peatland 'paludiculture' innovation present enormous potential to sustain carbon-cycles, reduce greenhouse-gas (GHG) gas emissions and to transition communities to low-carbon economies; however, there is limited scientific-evidence to support and enable direct commercial viability of eco-friendly products and services. This timely study reports on a novel, paludiculture-based, integrated-multi-trophic-aquaculture (IMTA) system for sustainable food production in the Irish midlands. This freshwater IMTA process relies on a naturally occurring ecosystem of microalgae, bacteria and duckweed in ponds for managing waste and water quality that is powered by wind turbines; however, as it is recirculating, it does not rely upon end-of-pipe solutions and does not discharge effluent to receiving waters. This constitutes the first report on the effects of extreme weather events on the performance of this IMTA system that produces European perch (Perca fluviatilis), rainbow trout (Oncorhynchus mykiis) during Spring 2020. Sampling coincided with lockdown periods of worker mobility restriction due to COVID-19 pandemic. Observations revealed that the frequency and intensity of storms generated high levels of rainfall that disrupted the algal and bacterial ecosystem in the IMTA leading to the emergence and predominance of toxic cyanobacteria that caused fish mortality. There is a pressing need for international agreement on standardized set of environmental indicators to advance paludiculture innovation that addresses climate-change and sustainability. This study describes important technical parameters for advancing freshwater aquaculture (IMTA), which can be future refined using real-time monitoring-tools at farm level to inform management decision-making based on evaluating environmental indicators and weather data. The relevance of these findings to informing global sustaining and disruptive research and innovation in paludiculture is presented, along with alignment with UN Sustainable Development goals. This study also addresses global challenges and opportunities highlighting a commensurate need for international agreement on resilient indicators encompassing linked ecological, societal, cultural, economic and cultural domains.

Opportunities for the application of real-time bacterial cell analysis using flow cytometry for the advancement of sterilization microbiology.

Medical devices provide critical care and diagnostic applications through patient contact. Sterility assurance level (SAL) may be defined as the probability of a single viable micro-organism occurring on an item after a sterilization process. Sterilization microbiology often relies upon using an overkill validation method where a 12-log reduction in recalcitrant bacterial endospore population occurs during the process that exploits conventional laboratory-based culture media for enumeration. This timely review explores key assumptions underpinning use of conventional culture-based methods in sterilization microbiology. Consideration is given to how such methods may limit the ability to fully appreciate the inactivation kinetics of a sterilization process such as vaporized hydrogen peroxide (VH2O2) sterilization, and consequently design efficient sterilization processes. Specific use of the real-time flow cytometry (FCM) is described by way of elucidating the practical relevance of these limitation factors with implications and opportunities for the sterilization industry discussed. Application of FCM to address these culture-based limitation factors will inform real-time kinetic inactivation modelling and unlock potential to embrace emerging opportunities for pharma, medical device and sterilization industries including potentially disruptive applications that may involve reduced usage of sterilant.

Purified ß-glucans from the Shiitake mushroom ameliorates antibiotic-resistant Klebsiella pneumoniae-induced pulmonary sepsis.

Bacterial infection remains the main cause of acute respiratory distress syndrome and is a leading cause of death and disability in critically ill patients. Here we report on the use of purified ß-glucan (lentinan) extracts from Lentinus edodes (Shiitake) mushroom that can reduce infection by a multidrug-resistant clinical isolate of Klebsiella pneumoniae in a rodent pneumonia model, likely through immunomodulation. Adult male Sprague-Dawley rats were subjected to intra-tracheal administration of K. pneumoniae to induce pulmonary sepsis and randomized to three groups; vehicle control (Vehicle, n = 12), commercial lentinan (CL, n = 8) or in-house extracted lentinan (IHL, n = 8) were administered intravenously 1 h postinfection. Physiological parameters and blood gas analysis were measured, bacterial counts from bronchoalveolar-lavage (BAL) were determined, along with differential staining of white cells and measurement of protein concentration in BAL 48 h after pneumonia induction. Use of IHL extract significantly decreased BAL CFU counts. Both CL and IHL extractions reduced protein concentration in BAL. Use of IHL resulted in an improvement in physiological parameters compared to controls and CL. In conclusion, administration of lentinan to treat sepsis-induced lung injury appears safe and effective and may exert its effects in an immunomodulatory manner.

Terminal sterilization of medical devices using vaporized hydrogen peroxide: a review of current methods and emerging opportunities.

Medical devices are an important and growing aspect of healthcare provision and are increasing in complexity to meet established and emerging patient needs. Terminal sterilization plays a vital role in the provision of safe medical devices. While terminal sterilization technologies for medical devices include multiple radiation options, ethylene oxide remains the predominant nonthermal gaseous option, sterilizing c. 50% of all manufactured devices. Vaporized hydrogen peroxide (abbreviated VH2O2 by the International Organization for Standardization) is currently deployed for clinical sterilization applications, where its performance characteristics appear aligned to requirements, constituting a viable alternative low-temperature process for terminal processing of medical devices. However, VH2O2 has operational limitations that create technical challenges for industrial-scale adoption. This timely review provides a succinct overview of VH2O2 in gaseous sterilization and addresses its applicability for terminal sterilization of medical devices. It also describes underappreciated factors such as the occurrence of nonlinear microbial inactivation kinetic plots that may dictate a need to develop a new standard approach to validate VH2O2 for terminal sterilization of medical devices.

Investigation of critical inter-related factors affecting the efficacy of pulsed light for inactivating clinically relevant bacterial pathogens.

AIMS: To investigate critical electrical and biological factors governing the efficacy of pulsed light (PL) for the in vitro inactivation of bacteria isolated from the clinical environment. Development of this alternative PL decontamination approach is timely, as the incidence of health care-related infections remains unacceptably high. METHODS AND RESULTS: Predetermined cell numbers of clinically relevant Gram-positive and Gram-negative bacteria were inoculated separately on agar plates and were flashed with

Evidence of lethal and sublethal injury in food-borne bacterial pathogens exposed to high-intensity pulsed-plasma gas discharges.

AIMS: To apply scanning electron microscopy, image analysis and a fluorescent viability stain to assess lethal and sublethal injury in food-borne bacteria exposed to pulsed-plasma gas discharges (PPGD). METHODS AND RESULTS: The fluorescent redox probe 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) was used for enumerating actively respiring cells of Campylobacter jejuni, Escherichia coli, Listeria monocytogenes, Staphylococcus aureus and Salmonella enterica serovar Typhimurium that were suspended in sterile water at 4 degrees C and exposed to separate PPGD and heat treatments. While there was good agreement between use of respiratory staining (RS) and direct-selective agar plate counting (PC) for enumerating untreated bacteria, there were c. 1 and 3 log-unit differences in surviving cell numbers per millilitre for test organisms subjected to PPGD and heat treatments respectively, when enumerated by these different viability indicators. PPGD-treated bacteria were markedly altered at the cellular level when examined by scanning electron microscopy. CONCLUSIONS: Use of this RS method revealed that substantial subpopulations of test bacteria rendered incapable of forming colonies by separate PPGD and heat treatments may remain metabolically active. SIGNIFICANCE AND IMPACT OF THE STUDY: Use of this RS method offers interesting perspectives on assessing established and novel microbial inactivation methods, and may also provide a better understanding of mechanisms involved in microbial inactivation induced by high-intensity PPGD treatments.

Pulsed-plasma gas-discharge inactivation of microbial pathogens in chilled poultry wash water.

A pulsed-plasma gas-discharge (PPGD) system was developed for the novel decontamination of chilled poultry wash water. Treatment of poultry wash water in the plasma generation chamber for up to 24 s at 4 degrees C reduced Escherichia coli NCTC 9001, Campylobacter jejuni ATCC 33560, Campylobacter coli ATCC 33559, Listeria monocytogenes NCTC 9863, Salmonella enterica serovar Enteritidis ATCC 4931, and S. enterica serovar Typhimurium ATCC 14028 populations to non-detectable levels (< or = 8 log CFU/ml). Although similar PPGD treatments at 4 degrees C also produced significant reductions (> or = 3 log CFU/ml) in recalcitrant B. cereus NCTC 11145 endospore numbers within 30 s, the level of endospore reduction was dependent on the nature of the sparged gas used in the plasma treatments. Scanning electron microscopy revealed that significant damage occurred at the cellular level in PPGD-treated test organisms. This electrotechnology delivers energy in intense ultrashort bursts, generating products such as ozone, UV light, acoustic and shock waves, and pulsed electric fields that have multiple bactericidal properties. This technology offers an exciting complementary or alternative approach for treating raw poultry wash water and for preventing cross-contamination in processing environments.

Use of a fluorescent viability stain to assess lethal and sublethal injury in food-borne bacteria exposed to high-intensity pulsed electric fields.

AIMS: To apply scanning electron microscopy, image analysis and a fluorescent viability stain to assess lethal and sublethal in food-borne bacteria exposed to high-intensity pulsed electric fields (PEF). METHODS AND RESULTS: A rapid cellular staining method using the fluorescent redox probes 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) and 4',6-diamidino-2-phylindole was used for enumerating actively respiring cells of Listeria mononcytogenes, Bacillus cereus and Escherichia coli. This respiratory staining (RS) approach provided good agreement with the conventional plate count agar method for enumerating untreated and high-intensity PEF-treated bacteria suspended in 0.1% (w/v) peptone water. However, test organisms subjected to similar levels of lethality by heating at 56 degrees C resulted in ca 3-log-unit difference in surviving cell numbers ml(-1) when enumerated by these different viability indicators. PEF-treated bacteria were markedly altered at the cellular level when examined by scanning electron microscopy. CONCLUSIONS: While PEF-treatment did not produce sublethally injured cells (P < 0.05), substantial subpopulations of test bacteria rendered incapable of forming colonies by heating may remain metabolically active. SIGNIFICANCE AND IMPACT OF THE STUDY: The fluorescent staining method offers interesting perspectives on assessing established and novel microbial inactivation methods. Use of this approach may also provide a better understanding of the mechanisms involved in microbial inactivation induced by PEF.

Putative virulence factor expression by clinical and food isolates of Bacillus spp. after growth in reconstituted infant milk formulae.

Forty-seven strains representing 14 different Bacillus species isolated from clinical and food samples were grown in reconstituted infant milk formulae (IMF) and subsequently assessed for adherence to, invasion of, and cytotoxicity toward HEp-2 and Caco-2 cells. Cell-free supernatant fluids from 38 strains (81%) were shown to be cytotoxic, 43 strains (91%) adhered to the test cell lines, and 23 strains (49%) demonstrated various levels of invasion. Of the 21 Bacillus cereus strains examined, 5 (24%) were invasive. A larger percentage of clinically derived Bacillus species (20%) than of similar species tested from the food environment were invasive. Increased invasion occurred after growth of selected Bacillus species in reconstituted IMF containing glucose. While PCR primer studies revealed that many different Bacillus species contained DNA sequences encoding the hemolysin BL (HBL) enterotoxin complex and B. cereus enterotoxin T, not all of these isolates expressed these diarrheagenic genes after growth in reconstituted IMF. Of the 47 Bacillus isolates examined, 3 isolates of B. cereus and 1 isolate of B. subtilis produced the HBL enterotoxin after 18 h of growth in brain heart infusion broth. However, eight isolates belonging to the species B. cereus, B. licheniformis, B. circulans, and B. megaterium were found to produce this enterotoxin after growth in reconstituted IMF when assessed with the B. cereus enterotoxin (diarrheal type) reversed passive latex agglutination (RPLA) kit. It is concluded that several Bacillus species occurring occasionally in clinical specimens and food samples are of potential medical significance due to the expression of putative virulence factors.

Inactivation of Mycobacterium paratuberculosis by pulsed electric fields.

The influence of treatment temperature and pulsed electric fields (PEF) on the viability of Mycobacterium paratuberculosis cells suspended in 0.1% (wt/vol) peptone water and in sterilized cow's milk was assessed by direct viable counts and by transmission electron microscopy (TEM). PEF treatment at 50 degrees C (2,500 pulses at 30 kV/cm) reduced the level of viable M. paratuberculosis cells by approximately 5.3 and 5.9 log(10) CFU/ml in 0.1% peptone water and in cow's milk, respectively, while PEF treatment of M. paratuberculosis at lower temperatures resulted in less lethality. Heating alone at 50 degrees C for 25 min or at 72 degrees C for 25 s (extended high-temperature, short-time pasteurization) resulted in reductions of M. paratuberculosis of approximately 0.01 and 2.4 log(10) CFU/ml, respectively. TEM studies revealed that exposure to PEF treatment resulted in substantial damage at the cellular level to M. paratuberculosis.

Cellular morphology of rough forms of Listeria monocytogenes isolated from clinical and food samples.

Transmission electron microscopy (TEM) studies revealed that rough cell-forms of L. monocytogenes (designated FR variants), isolated from clinical and food samples (and under conditions of sublethal heat stress), consist of either single or paired long-filaments. These FR variants markedly contrast in cell morphology from other previously described avirulent rough-mutants of L. monocytogenes that form long chains consisting of multiple cells of similar size (designated MCR variants). The identity of these Listeria isolates was determined using a commercially available, anti-Listeria polyclonal KPL antibody and by the API Listeria biochemical gallery. This study shows that filamentous rough-forms of L. monocytogenes may occur in clinical and food samples that are of undetermined pathogenicity.

Pulsed electric field inactivation of diarrhoeagenic Bacillus cereus through irreversible electroporation.

The physical effects of high-intensity pulsed electric fields (PEF) on the inactivation of diarrhoeagenic Bacillus cereus cells suspended in 0.1% peptone water were examined by transmission electron microscopy (TEM). The levels of PEF-induced microbial cell death were determined by enumeration on tryptone soy yeast extract agar and Bacillus cereus-selective agar plates. Following exposure to lethal levels of PEF, TEM investigation revealed irreversible cell membrane rupture at a number of locations, with the apparent leakage of intracellular contents. This study provides a clearer understanding of the mechanism of PEF-induced cellular damage, information that is essential for the further optimization of this emerging food-processing technology.

Virulent rough filaments of Listeria monocytogenes from clinical and food samples secreting wild-type levels of cell-free p60 protein.

Atypical rough cell filaments of Listeria monocytogenes (designated FR variants), isolated from clinical and food samples, form long filaments up to 96 microm in length and demonstrated wild-type levels of adherence, invasion, and cytotoxicity to human epithelial HEp-2, Caco-2, and HeLa cells. Unlike previously described avirulent rough mutants of L. monocytogenes that secrete diminished levels of the major extracellular protein p60 and that form long chains that consist of multiple cells of similar size (designated MCR variants), FR variants secreted wild-type or greater levels of p60. This study shows that virulent filamentous forms of L. monocytogenes occur in clinical and food environments and have atypical morphological characteristics compared to those of the wild-type form.

Prediction of toxigenic fungal growth in buildings by using a novel modelling system.

There is growing concern about the adverse effects of fungal bioaerosols on the occupants of damp dwellings. Based on an extensive analysis of previously published data and on experiments carried out within this study, critical limits for the growth of the indoor fungi Eurotium herbariorum, Aspergillus versicolor, and Stachybotrys chartarum were mathematically described in terms of growth limit curves (isopleths) which define the minimum combination of temperature (T) and relative humidity (RH) at which growth will occur. Each growth limit curve was generated from a series of data points on a T-RH plot and mathematically fitted by using a third-order polynomial equation of the form RH = a(3)T(3) + a(2)T(2) + a(1)T + a(0). This fungal growth prediction model was incorporated within the ESP-r (Environmental Systems Performance [r stands for "research"]) computer-based program for transient simulation of the energy and environmental performance of buildings. For any specified location, the ESP-r system is able to predict the time series evolution of local surface temperature and relative humidity, taking explicit account of constructional moisture flow, moisture generation sources, and air movement. This allows the predicted local conditions to be superimposed directly onto fungal growth curves. The concentration of plotted points relative to the curves allows an assessment of the risk of fungal growth. The system's predictive capability was tested via laboratory experiments and by comparison with monitored data from a fungus-contaminated house.

Pulsed-light inactivation of food-related microorganisms.

The effects of high-intensity pulsed-light emissions of high or low UV content on the survival of predetermined populations of Listeria monocytogenes, Escherichia coli, Salmonella enteritidis, Pseudomonas aeruginosa, Bacillus cereus, and Staphylococcus aureus were investigated. Bacterial cultures were seeded separately on the surface of tryptone soya-yeast extract agar and were reduced by up to 2 or 6 log10 orders with 200 light pulses (pulse duration, approximately 100 ns) of low or high UV content, respectively (P < 0.001).

Light inactivation of food-related pathogenic bacteria using a pulsed power source.

The effects of high intensity light emissions, produced by a novel pulsed power energization technique (PPET), on the survival of bacterial populations of verocytotoxigenic Escherichia coli (serotype 0157:H7) and Listeria monocytogenes (serotype 4b) were investigated. Using this PPET approach, many megawatts (MW) of peak electrical power were dissipated in the light source in an extremely short energization time (about 1 microsecond). The light source was subjected to electric field levels greater than could be achieved under conventional continuous operation, which led to a greater production of the shorter bacteriocidal wavelengths of light. In the exposure experiments, pre-determined bacterial populations were spread onto the surface of Trypone Soya Yeast Extract Agar and were then treated to a series of light pulses (spectral range of 200-530 nm) with an exposure time ranging from 1 to 512 microseconds. While results showed that as few as 64 light pulses of 1 microsecond duration were required to reduce E. coli 0157:H7 populations by 99.9% and Listeria populations by 99%, the greater the number of light pulses the larger the reduction in cell numbers (P < 0.01). Cell populations of E. coli 0157:H7 and Listeria were reduced by as much as 6 and 7 log10 orders at the upper exposure level of 512 microseconds, respectively. Survival data revealed that E. coli 0157:H7 was less resistant to the lethal effects of radiation (P < 0.01). These studies have shown that pulsed light emissions can significantly reduce populations of E. coli 0157:H7 and L. monocytogenes on exposed surfaces with exposure times which are 4-6 orders of magnitude lower than those required using continuous u.v. light sources.