Bacillus Stearothermophilus Spores Research Articles

Photo-Fenton and TiO2 Photocatalytic Inactivation of Model Microorganisms under UV-A; Comparative Efficacy and Optimization.

Photocatalytic inactivation of pathogens in aqueous waste is gaining increasing attention. Several homogeneous and heterogeneous photocatalytic protocols exist using the Fenton's reagent and TiO2, respectively. A comprehensive study of homogeneous and heterogeneous photocatalysis on a range of microorganisms will significantly establish the most efficient method. Here, we report a comparative study of TiO2- and Fe+3-based photocatalytic inactivation under UV-A of diverse microorganisms, including Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, bacterial spores (Bacillus stearothermophilus spores) and viruses (MS2). We also present data on the optimization of TiO2 photocatalysis, including optimal catalyst concentration and H2O2 supplementation. Our results indicate that both photo-Fenton and TiO2 could be successfully applied for the management of microbial loads in liquids. Efficient microorganism inactivation is achieved with homogeneous photocatalysis (7 mg/L Fe+3, 100 mg/L H2O2, UV-A) in a shorter processing time compared to heterogeneous photocatalysis (0.5 g/L TiO2, UV-A), whereas similar or shorter processing is required when heterogenous photocatalysis is performed using microorganism-specific optimized TiO2 concentrations and H2O2 supplementation (100 mg/L); higher H2O2 concentrations further enhance the heterogenous photocatalytic inactivation efficiency. Our study provides a template protocol for the design and further application for large-scale photocatalytic approaches to inactivate pathogens in liquid biomedical waste.

Thermal processing of canned dika kernel (ogbono) soup and the neural prediction of its canning parameters

AbstractThe canning of dika kernel (ogbono) soup into a ready‐to‐eat form has been recommended because of the special skills and time required in preparing this popular West African soup. This study investigated the thermal processing of ogbono soup, calculated the lethality (F) and process time, and predicted same using the artificial neural network (ANN) model. A dataset of the processing time, cold point, and retort temperature obtained during the heat penetration study was used for the model training, validating, and testing steps. There was a 54%, 71%, and 75% log‐reduction of the surviving Bacillus stearothermophilus spores after heat processing of the canned soup at 110, 116, and 121°C respectively. Heat penetration parameters revealed that canning the soup at 121°C for a total process time of about 31 min was the best thermal processing condition. Results also showed that the ANN model was a useful and high‐reliability tool in predicting the sterilization value of the canned soup, with a high degree of accuracy (R2 closer to 1) at all the canning temperatures considered in the study. Unsupervised learning of the neurons models to predict the output data from the input data was also suggested in the thermal canning processes.Practical ApplicationsIn the canning industry, the sterilization process is aimed to inactivate potentially harmful microorganisms, leaving the food product safe and of good quality. This research evaluated the canning parameters to process dika kernel (ogbono) soup. The total processing time of 31 min at 121°C obtained in the study, indicate that higher temperature and shorter time would produce a commercially sterile soup. However, the heat penetration test requiring higher temperature and longer processing times could necessitate increased energy costs. This research shows that the use of the machine learning (artificial neural network) model could accurately predict lethality rate (F‐value) better than the non‐linear model like the response surface methodology (RSM), providing an advantage of estimating process time, thus reducing operational costs.

Comparing Sterilization of Endodontic Hand Files by Four Different Methods: An In Vitro Study.

The aim and objective of this study is to compare the efficacy of four various approaches of sterilizing endodontic hand files via Autoclave, Glass-bead sterilizer, Glutaraldehyde solution, and Diode laser. Fifty-two k-files of size #25 and length 21 mm were taken for the study. All the 52 files were presterilized in an endodontic instrument box via autoclave. Bacillus stearothermophilus spore suspension was prepared and all the presterilized files were contaminated with stearothermophilus spore suspension in a sterile Petri dish under vacuum hood safety. Later, the test files were randomly divided into four groups of 13 each and subjected to four different methods of sterilization- Autoclave, Glass-bead sterilizer, Glutaraldehyde solution, and Diode laser. Files were then be placed in thioglycollate media containing test tubes and incubated in an incubator at 55°C and checked for turbidity at 3 days and 21 days. The result revealed that there was no Turbidity present in test tubes on both the 3rd and 21st day for autoclave. In all the remaining sterilization procedures there was some amount of turbidity present. In terms of sterilization provided autoclave provides complete sterilization and glutaraldehyde solution is the least effective.The specificity of Bacillus stearothermophilus was then confirmed with a sugar test viz., starch hydrolysis test which gave a positive result confirming the presence of Bacillus stearothermophilus. We can conclude that autoclave is the perfect process of sterilization providing 100% sterility and although Glass-bead didn't provide 100% sterility, it can be used as an alternative if autoclave is not available. Ameer B, Khatib MS, Peerzade SM, et al. Comparing Sterilization of Endodontic Hand Files by Four Different Methods: An In Vitro Study. Int J Clin Pediatr Dent 2022;15(2):149-152.

Changes in Acid-pH Resistance of Food Spoilage and Pathogens Spore-Forming Bacteria in Cameroonian Indigenous Sorghum-Based Acidic Beers before and after Sublethal Thermal Stresses

Fermented alcoholic beverages play a major role in the socio-cultural lives of people of Northern Cameroon. However, reports of shelf-life and health problems associated with indigenous sorghum-based alcoholic beverages are a major call for concern. This study aimed to highlight the additional effects of sublethal temperatures (no thermal treatment and 10, 45, 50 and 60°C for 45, 90, 180 min) and acidic pH of beers (2.79 and 2.63 for 45, 90, 180 min) on fate of four food spoilage and pathogens spore-forming bacteria. The experiments were carried out on real food products formed by two indigenous sorghum-based alcoholic beverages. Pasteurized traditional beers were significantly efficient on all unstressed bacterial spores after 180 minutes of treatment. In addition, spores of B. megapterium and G. stearothermophilus were more sensitive in white beer pH 2.79 and red beer pH 2.63 respectively. Previous thermal treatments of spores at certain sublethal temperatures have significantly (P=0.05) decreased the effect of both acidic beers on stressed spores. It was noticed that the spores of B. subtilis stressed at 10°C, G. stearothermophilus (former Bacillus stearothermophilus) spores submitted at 45°C and the spores of B. cereus thermally stressed at 50°C and 60°C for 45, 90, 180 minutes were significantly (P=0.05) less affected by the white beer at pH 2.79. Whereas, in the red beer at pH 2.63, the spores of B. subtilis sublethally stressed at 10°C and the spores of B. cereus stressed at 45°C, 50°C and 60°C were more acid resistant and very weakly affected by acid pH of the alcoholic beverages. The study delivered some overview on the potential microbial (stability and safety) consequences of the current tendency towards milder cold and heat treatments which are greatly used in the food-grade industry.

Application of rapid biological monitoring for bacillus stearothermophilus spore in the management of surgical instruments

Objective To compare the applications of four types of bacillus stearothermophilus spore reagents, in order to provide basis for the safe management of surgical instruments. Methods From September to December 2015, four types of bacillus stearothermophilus spore reagents that were often used in the disinfection supply center of Jiaozuo People's Hospital of He'nan province were investigated. They were SSI.K31 type bacillus stearothermophilus spore tablet of Beijing Sihuan (common bacterial tablet) , self-contained Bacillus stearothermophilus spore reagent of Beijing Sihuan (48 h self-contained agent) , 1292 biological reagent of American 3M company (3M1292) , and 1492 biological reagent of American 3M company (3M1492) . They were cultured by steam sterilization of 132℃ for 480 seconds. The culture results were obtained at different time according to the different types of reagents. The number of vacuum and sterilization time were adjusted. The spore killing situation was recorded and analyzed. Results In the experimental tube culture of four types bacillus stearothermophilus spore reagents, the difference occurred in the common bacterial tablets because they were susceptible to other factors. The culture results of three self-contained reagents were in agreement. The time of common spore tablets was the longest. The time of 3M1492 was the shortest. Conclusions For common bacterial tablets, 7 days is needed for the bacterial culture. In the transplantation process there is potential contamination chance, which might result in false positive results. The application of self-contained spore biological reagents can avoid false positive results and it is convenient and fast. The super rapid biological monitoring can interpret monitoring results in the shortest time so that the seamless joint of the surgical instruments can be achieved, which speeds up the turnover and produces higher practical value. Key words: Disinfection; Environmental monitoring; Bacillus stearothermophilus; Surgical instruments

Evaluation of Nanoparticles as Carrier for Bacillus Stearothermophilus Spore Preservation in Bioindicator System

A precise assessment of sterilization processes is very essential in the pharmaceutical and biological industry, because a wrong treatment could result in the spoilage of a product due to microorganism development. Bacillus Stearothermophilus has been established as an industrial bacterium in the production of biological sterilization indicators. The production of biological indicators involving bacterial spore production which is dormant and are extremely resistant to heat stresses. Bacillus Stearothermophilus ATCC 7953 spores are used to monitor the efficacy of steam heat and hydrogen peroxide sterilization processes. In this study, efficacy of replacing nanomaterial as carrier instead of regular paper strip was investigated. For this purpose, the effect of nanomaterial on thermal resistance parameters and spore absorption was assessed and compared with common paper strips of this product.

Effect of High Pressure Homogenization Process on Bacillus Stearothermophilus and Clostridium Sporogenes Spores in Skim Milk

High pressure homogenization (HPH) is an alternative food processing technique. As product heating is minimum, its characteristics are not affected in a large extend. This characteristic makes the HPH an interesting process to guarantee the safety of thermo-labile food. Inactivation of Bacillus stearothermophilus ATCC 7953 and Clostridium sporogenes PA 3679 spores in skim milk by HPH was studied. Results showed that pressures up to 300 MPa were not able to cause any reduction on spore counts or promote changes on its thermal resistance. The application of heat shock (100°C/15 min) before HPH treatment and the homogenization process realized at mild inlet temperature (45°C) – which results in homogenization temperature of around 84°C at 300 MPa - also did not cause reduction on viable spores counts. A few spores reduction (0.67 logarithmic cycles) were only observed when the milk samples were subjected to homogenization treatment 16 times (multiple passes) at 300 MPa. Therefore, although HPH be recognized as an effective method for milk pasteurization, it was conclude that the HPH process is not able to guarantee the commercial sterility of milk, being necessary the association of the homogenization with another preservative method, as refrigeration.

The effect of organic acid type on thermal inactivation of Geobacillus stearothermophilus spores

The effect of organic acid (either citric or acetic) on thermal inactivation of Geobacillus stearothermophilus (former Bacillus stearothermophilus) spores was analysed focusing on individuals of population with different thermal sensitivity. The survival of spores was investigated in media (tryptone solution, red beet juice) of natural pH or acidified with organic acid at pH ranging from 6.0 to 4.0. Thermal sterilisation was carried out in the temperature range from 115 °C to 125 °C. It was confirmed that survival curves of G. stearothermophilus spores could have three stages, which caused that the decimal reduction time was not always a proper parameter to set the conditions required for the media sterilisation. Based on performed experiments it was found out that spore inactivation in acidified red beet juice medium was faster than in acidified tryptone solution. It was shown that the presence of both acetic and citric acids in tryptone solution had a similar influence on the rate of spore inactivation. However, in the case of red beet juice, the acetic acid had a stronger effect on spore destruction than the citric acid only at pH 4.0. It was proved that medium composition could accelerate the activation of dormant spores, what resulted in elimination of “tailing” on the spore survival curve and in shorter time necessary for inactivation of particular spore population.

Comparison of hydrogen peroxide and peracetic acid as isolator sterilization agents in a hospital pharmacy

The efficacy of hydrogen peroxide and peracetic acid as isolator sterilization agents was compared. Sterilization and efficacy tests were conducted in a flexible 0.8-m3 transfer isolator using a standard load of glass bottles and sterile medical devices in their packing paper. Bacillus stearothermophilus spores were placed in six critical locations of the isolator and incubated at 55 degrees C in a culture medium for 14 days. Sterilization by 4.25 mL/m3 of 33% vapor-phase hydrogen peroxide and 12.5 mL/m3 of 3.5% peracetic acid was tested in triplicate. Sterility was validated for hydrogen peroxide and peracetic acid at 60, 90, 120, and 180 minutes and at 90, 120, 150, 180, 210, and 240 minutes, respectively. In an efficacy test conducted with an empty isolator, the sterilization time required to destroy B. stearothermophilus spores was 90 minutes for both sterilants, indicating that they have comparable bactericidal properties. During the validation test with a standard load, the sterilization time using hydrogen peroxide was 150 minutes versus 120 minutes with peracetic acid. The glove cuff was particularly difficult for hydrogen peroxide to sterilize, likely due to its slower diffusion time than that of peracetic acid. Hydrogen peroxide is an environmentally safer agent than peracetic acid; however, its bacteriostatic properties, lack of odor, and poor diffusion time may limit its use in sterilizing some materials. Hydrogen peroxide is a useful alternative to peracetic acid for isolator sterilization in a hospital pharmacy or parenteral nutrition preparation unit.

Comparison of two radio-frequency plasma sterilization processes using microspot evaluation of microbial inactivation

In this study, we evaluated gas plasma surface sterilization methods in a specific sterilizer. We have introduced a new monitoring method using 0.4 microm pore size membranes, which in this study gave the information corresponding to 3000 exposed biological indicators per treatment cycle. This enabled us to compare the fraction of inoculates that showed no growth after exposure for 30 different locations in the chamber, and hereby identify weak and strong spots in the chamber with regard to sporicidal effect. Membranes were also used to expose a broad spectrum of soil bacteria for plasma treatment at four different conditions. The organisms were identified using PCR and sequencing. The test showed that Bacillus stearothermophilus spores were inactivated at the slowest rate among the tested microorganisms. Further alpha-proteobacteria (Gram negative) seemed more sensitive than the rest of the tested organisms. The microspot evaluation approach has been a most useful tool in the assessment of sterilization performance in sterilizers that do not have clear measurable parameters related to the sterilization.

Effects of oxygen radicals in low-pressure surface-wave plasma on sterilization

The effects of oxygen radicals on sterilization were studied using a 2.45GHz surface-wave oxygen plasma. A population of 1.5×106 Bacillus stearothermophilus spores was irradiated for 3min or more with oxygen plasma, generated at pressures between 6 and 14Pa. The decimal reduction value (D value), a measure of the effectiveness of sterilization, was determined to be about 15–25s. Using only oxygen radicals, excluding all charged particles, the 1.5×106 spores were sterilized with a D value of 30–45s after 5min or more of irradiation. On scanning electron microscopy, the length and width of the spores changed significantly due to chemical etching by oxygen radicals.

The dependence of the sporicidal effects on the power and pressure of RF‐generated plasma processes

The sporicidal effect of 20 different radio-frequency plasma processes produced by combining five different gas mixtures [O(2), Ar/H(2) (50/50%), Ar/H(2) (5/95%), O(2)/H(2) (50/50%), O(2)/H(2) (95/5%)] with four power/pressure settings were tested. Sporicidal effects of oxygen-containing plasmas were dependent on power at low pressure settings but not at high pressure settings. In the absence of oxygen no power dependency was observed at either high or low pressure settings. Survivor curves obtained with the use of nonoxygen plasmas typically had a tailing tendency. Only a mixture-optimized Ar/H(2) (15/85%) plasma process was not encumbered by tailing, and produced a decimal reduction time (D value) below 2 min for Bacillus stearothermophilus spores. Scanning electron microscopy showed that a CF(4)/O(2) plasma did more damage to the substrate than the 15/85% Ar/H(2) plasma. The present results indicate that UV irradiation inactivation is swift and power and pressure independent. Additionally, it is produced at low energy. However, it is not complete. Inactivation through etching is highly power and pressure dependent; finally, inactivation by photodesorption is moderately power and pressure dependent. A sterilization process relying on this mechanism is very advantageous because it combines a highly sporicidal effect with low substrate damage.

LETHALITY CONTRIBUTION FROM THE TUBULAR HEAT EXCHANGER DURING HIGH‐TEMPERATURE SHORT‐TIME PROCESSING OF A MODEL LIQUID FOOD

ABSTRACT Experiments were conducted using Bacillus stearothermophilus spores in 0.5% w/w carboxymethylcellulose suspension to evaluate come‐up contributions from the tubular heat exchanger. A lab‐scale UHT/HTST simulator that allowed samples to be collected at the exit of the heat exchanger and holding tube was used with operating temperatures up to 270F. The bulk mean residence time in the heat exchanger ranged from 30 to 89 sec, while that in the holding tube ranged from 4 to 14 sec. It was observed that between 40% and 51% of the cumulative lethality ( ) at the exit of the holding tube, was contributed by come‐up in the tubular heat exchanger. This come‐up contribution was determined on the basis of having an of 8.5 min in the holding tube alone. It was evident that come‐up lethality will depend on product initial temperature, residence time and temperature history in the heat exchanger, with higher temperatures obviously contributing more lethality. Therefore, the entire aseptic system becomes even more complex since several critical parameters need to be monitored, controlled and documented. Experimental data compared favorably with computer‐simulated data using the AseptiCAL™ software, with the software package giving more conservative results. Ultimately, come‐up credit (CUC) should be tested on a pilot scale or industrial setup by way of reduced residence time (i.e. increased fluid flow rate), reduced holding tube length or temperature in order to determine if CUC can be applied towards the lethality required for the product. Monitoring and control devices become critical to ensure consistency and reproducibility in product residence time and time–temperature history, in the tubular heat exchanger.

Theoretical and experimental investigation of the thermal inactivation of Bacillus stearothermophilus in food pouches

Numerical simulations are used to profile temperature, velocity vector and viable bacteria (Bacillus stearothermophilus spores) concentration in a three-dimensional pouch filled with beef–vegetable soup during thermal sterilization. The partial differential equations of the continuity, momentum and energy equations are solved numerically, together with an equation defining viable bacteria concentration, based on finite volume method of analysis. Saturated steam at 121°C is used as a heating medium, and the model liquid is assumed to have constant properties except for the viscosity (temperature dependent) and density (Boussinesq approximation). The simulations show clearly the dependency of the concentration of live bacteria on both the temperature distribution and the flow pattern as sterilization proceeds. Experimental measurements are done to validate the bacteria concentration profiles. The experimental measurements are conducted at the Biotechnology Laboratory located at the Chemical and Materials Engineering Department, University of Auckland in New Zealand. The measured concentrations of B. stearothermophilus spores at different periods of heating are compared with those obtained from simulations, showing good agreements.

Sporicidal activity of a new low-temperature sterilization technology: the Sterrad 50 sterilizer.

This study was undertaken to evaluate the efficacy of a new low-temperature sterilization system that recently has been cleared by the Food and Drug Administration, the Sterrad 50. Flat stainless steel carriers were inoculated with approximately 10(6) Bacillus stearothermophilus spores. These carriers were placed aseptically in the middle of 40-cm-long stainless steel-lumened test units of varying diameters (1 mm, 2 mm, and 3 mm). After inoculation, the test units were processed in the Sterrad 50. After sterilization, the carriers were assayed for growth of the B. stearothermophilus spores. Our data demonstrated that the Sterrad 50 was highly effective in killing the B. stearothermophilus spores (no positive carriers with 30 tests of each lumen-diameter test unit). The Sterrad 50 is likely to be clinically useful for the sterilization of heat-sensitive medical equipment.

A Method for Radioactive Containment during Biological Inactivation of Radioactive-Biomedical Mixed Waste

A waste container that can contain the radioactive component of a radioactive-biomedical mixed waste while the biological component of the waste is inactivated was designed, fabricated, and validated. Bacillus stearothermophilus spore indicator strips were used to validate the biological inactivation through autoclaving of a given biomedical waste mixture. Repeated experiments indicated that a ninety minute autoclave sterilization cycle was sufficient to effect biological inactivation of the biomedical waste. The experiments also validated that any radioactivity placed within the container was contained during the autoclaving process. Any volatilization of radionuclides was contained within the container or adsorbed onto a charcoal filter column attached to the container. Experiments were performed using varying activities of three common radionuclides used in research at the National Cancer Institute-Frederick Cancer Research and Development Center (NCI-FCRDC). The majority of this research was performed using 125l; subsequent validation studies were also conducted using 3H and 35S.

Comparative evaluation of the sporicidal activity of new low-temperature sterilization technologies: Ethylene oxide, 2 plasma sterilization systems, and liquid peracetic acid

Objective: This study was undertaken to evaluate the efficacy of 4 new low-temperature sterilization technologies: ethylene oxide with hydrochlorofluorocarbons, a liquid peracetic acid immersion system (Steris System 1 Processor), and 2 plasma sterilization processes that use vaporized hydrogen peroxide (Sterrad 100 and the Sterrad 100S). The Sterrad 100S system potentially improves sterilizer efficacy by using 2 cycles of a diffusion stage and a plasma stage per sterilization cycle. Methods: Flat stainless steel carriers were inoculated with approximately 10 6 Bacillus stearothermophilus spores. These carriers were aseptically placed in the middle of 40 cm long stainless steel lumens (hollow tubes). Two types of lumen were used: (1) a lumen test unit with a removable 5 cm center piece (1.2 cm diameter) of stainless steel sealed to the narrower steel tubing by hard rubber septums and (2) a straight lumen. Three different diameters of the lumen test unit (1, 2, and 3 mm) and a single diameter of the straight lumen (3 mm) were studied. At least 40 replicates were performed for each type of lumen and sterilization method. After inoculation, the test unit was evaluated in 1 of the low-temperature sterilization technologies. After sterilization, the carriers were cultured in trypticase soy broth for 14 days at 55°C and assessed for growth of B stearothermophilus spores. Results: Our results demonstrated that ethylene oxide with hydrochlorofluorocarbons, the Sterrad 100S, and the Sterrad 100S half cycle were highly effective in killing approximately 10 6 B stearothermophilus spores present in the center of narrow-lumen stainless steel tubes. As the lumen diameter decreased with the lumen test unit, the Sterrad 100 demonstrated reduced ability to kill B stearothermophilus spores present on the carrier. At the smallest diameter tested (1 mm), the Sterrad 100 system failed 74% of the time. The Steris System 1 was not effective in completely eliminating the 10 6 inoculum under test conditions. Conclusion: The Sterrad 100S was significantly superior to the Sterrad 100 system and equivalent to ethylene oxide with hydrochlorofluorocarbons. Introduction of this new Sterrad 100S system should improve the margin of safety and reduce processing costs by its use of a shorter cycle time. The Steris System 1 is limited by diffusion of the chemical sterilant into the interior of the lumen test unit. (AJIC Am J Infect Control 1998;26: 393-8)

HOW WELL DOES THE CHEMICLAVE STERILIZE HANDPIECES?

Using the Food and Drug Administration's protocol for testing health care sterilizers, the author investigated the ability of chemical vapor and steam to sterilize handpieces. Five internal sites of six high-speed handpiece models and four internal positions of one low-speed handpiece model were each inoculated with 10(6) Bacillus stearothermophilus spores. Half-cycle challenges were conducted with Chemiclave models EC 5500 and 8000 (Barnstead/Thermolyne) and with two autoclaves, Tuttnauer 2540M (large chamber) (Tuttnauer USA Co., Ltd.) and Statim Cassette (SciCan USA). Experiments with spores either openly exposed or partially enclosed prove that chemical vapor is an excellent lethal agent, but strongly suggest penetration weakness [corrected].

Apparent thermal resistance of Bacillus stearothermophilus spores recovered under anaerobic conditions

The effect of recovering Bacillus stearothermophilus spores under anaerobic conditions on their apparent thermal resistance was studied. Spores were suspended in bidistilled water as a reference medium, heated at 115, 117, 119, 121, 123 and 125°C and recovered under aerobic and anaerobic conditions. D values (decimal reduction time) obtained following recovery under anaerobic conditions were lower than those obtained under aerobic conditions. Reductions of between 31 and 48% were found for all the temperatures studied. When spores were suspended in mushroom extract and recovered under anaerobic conditions the apparent heat resistance was much lower than that obtained under aerobic conditions (D121°C was 4.3 min and 1.7 min, under aerobic and anaerobic conditions, respectively). Heating the spores in mushroom extract and recovering the spores under anaerobic conditions produced an additive effect, decreasing the apparent heat resistance of the B. stearothermophilus spores.

Room temperature sterilization of surfaces and fabrics with a one atmosphere uniform glow discharge plasma.

We report the results of an interdisciplinary collaboration formed to assess the sterilizing capabilities of the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP). This newly-invented source of glow discharge plasma (the fourth state of matter) is capable of operating at atmospheric pressure in air and other gases, and of providing antimicrobial active species to surfaces and workpieces at room temperature as judged by viable plate counts. OAUGDP exposures have reduced log numbers of bacteria, Staphylococcus aureus and Escherichia coli, and endospores from Bacillus stearothermophilus and Bacillus subtilis on seeded solid surfaces, fabrics, filter paper, and powdered culture media at room temperature. Initial experimental data showed a two-log10 CFU reduction of bacteria when 2 x 10(2) cells were seeded on filter paper. Results showed > or = 3 log10 CFU reduction when polypropylene samples seeded with E. coli (5 x 10(4)) were exposed, while a 30 s exposure time was required for similar killing with S. aureus-seeded polypropylene samples. The exposure times required to effect > or = 6 log10 CFU reduction of E. coli and S. aureus on polypropylene samples were no longer than 30 s. Experiments with seeded samples in sealed commercial sterilization bags showed little or no differences in exposure times compared to unwrapped samples. Plasma exposure times of less than 5 min generated > or = 5 log10 CFU reduction of commercially prepared Bacillus subtilis spores (1 x 10(5)); 7 min OAUGDP exposures were required to generate a > or = 3 log10 CFU reduction for Bacillus stearothermophilus spores. For all microorganisms tested, a biphasic curve was generated when the number of survivors vs time was plotted in dose-response cures. Several proposed mechanisms of killing at room temperature by the OAUGDP are discussed.