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Papers by Joseph Dunn

Microbiology, 2016

The selection of a biological indicator organism for use with a new or existing sterilization met... more The selection of a biological indicator organism for use with a new or existing sterilization method is an important endeavor because it will serve as a benchmark for validation, safety, and quality assessments across a range of current and future sterilization systems and machines. By convention, the process for bioindicator selection is to choose an organism demonstrating high relative resistance for the sterilization agent and method under examination and, therefore, includes the evaluation and comparison of the resistance of multiple candidate organisms and spores. This report reviews the basic tenants and principles of modern sterilization science as they relate to the determination and comparison of microbial resistance, uses the pulsed light treatment of Bacillus pumilus spore preparations, and spore stocks prepared via different methods to illustrate how different preparation procedures can affect the results seen with resistance testing, particularly survival/end point testing, and provides insights and experiences into microbial spore resistance testing and examines relevant cases in point.

Pda Journal of Pharmaceutical Science and Technology Pda, 1997

A study was performed to assess the ability of pulsed light to sterilize water for injection in b... more A study was performed to assess the ability of pulsed light to sterilize water for injection in blow/fill/seal polyethylene containers. Pulsed light uses intense, short duration flashes of broad spectrum white light to produce high levels of microbial kill. In a first phase of testing, containers of 0.5, 5, 15, and 120 mL nominal volume were inoculated with Bacillus pumilus endospores, Bacillus subtilus variety niger strain globigii endospores, Bacillus stearothermophilus endospores, and Aspergillus niger conidiospores. Approximately 10(6) colony forming units of each test spore were individually inoculated into 22 replicate containers of each sample volume. Two of these containers served as inoculation recovery controls, and 10 were treated using each of two pulsed light exposure methods: single-sided treatment, or treatment within a reflective cavity. Both treatments employed flashes of intense broad spectrum pulsed light delivered at one flash per second. Cavity treatment used 10 flashes to treat each container within a reflective cavity containing a single lamp. Cavity treatment yielded no recoverable survivors for any of the challenge spores from the contents of any of the 160 total samples. Single-sided treatment used 20 approximately 1-J/cm2 flashes from a single lamp-reflector projecting onto one side of the container. Single-sided treatment yielded no recoverable survivors from the contents of the containers for any of the bacterial endospores tested, but Aspergillus niger survival was detected in 4 of the 40 single-side treated samples. A second phase of tests examined the pulsed light inactivation of Bacillus pumilus spores for a range of inoculation levels. High levels of Bacillus pumilus spore kill were obtained using only a few cavity flashes. The results show that pulsed light can provide high levels of microbial lethality and possesses potential for use as a terminal sterilization method for water for injection in filled, sealed polyethylene containers.

Journal of Food Science, 2009

This study investigated microbial inactivation via surface-active peracids and used electron spin... more This study investigated microbial inactivation via surface-active peracids and used electron spin resonance spectroscopy to characterize the active components and free radical formation. Bacillus atrophaeus spores were injected directly into 3 different concentrations of the peracid disinfectant (1.1%, 1.3%, or 1.5%) for various times (5, 10, 15, or 20 s) at 3 different temperatures (50, 60, or 70 • C) to evaluate the sporicidal activity of the disinfectant mixture. Spectroscopy revealed that the combination of hydrogen peroxide, peracetic acid, and octanoic acid were highly effective at forming a complex mixture of sporicidal, free radical intermediates including hydroxyl and superoxide radicals. Individual components of this mixture alone were not as effective as the final combination. This information has practical applications in the food industry for design of effective sanitation and disinfection agents and suggests that kinetic models could be developed to account for both the physical removal and localized inactivation of spores on food-contact surfaces.

Journal of Food Science, 2004

ABSTRACT: Formulae for the prediction of inactivation and accumulated lethality of bacterial spor... more ABSTRACT: Formulae for the prediction of inactivation and accumulated lethality of bacterial spores under moist heat and high pressures were derived on the basis of classic thermodynamic and kinetics principles. The capability of the model to describe the inactivation of bacterial spores was verified using 2 independent data sets corresponding to Clostridium botulinum processed at 60°C to 75°C and Bacillus stearothermophilus processed at 92°C to 110°C. Both sets included pressures between 5 × 108 Pa and 7 × 108 Pa. The equation fit explained more than 86% of the variation of the rate constant data. The developed equations establish a strong foundation on which to compare high-pressure processing treatments of different systems. This is especially useful because most systems have different transient temperature-pressure conditions.

Human Gene Therapy, 1993

Dependent on the viral vector and the specific assay used, viral titers produced from commonly us... more Dependent on the viral vector and the specific assay used, viral titers produced from commonly used retroviral packaging cell lines have an upper limit in the range of 10(5) to 10(7) infectious units/ml. We have developed a generally applicable method, using hollow-fiber filtration technology, which allows for the concentration of infectious virus derived from packaging lines. This method resulted in a reproducible 10- to 30-fold increase in viral titer and can readily be scaled to accommodate larger input volumes. Over 80% of the input virus is recovered in an infectious form in the concentrate. Concentrated virus containing media was seen to produce higher infection frequencies in Jurkat T cells as compared to unconcentrated virus containing media; however, this was not proportional to the differences in viral titer observed by limiting dilution analysis on NIH-3T3 cells. These results are discussed in relation to the importance of factors other than viral titer in determining transduction frequencies.

Microbiology, 2016

The selection of a biological indicator organism for use with a new or existing sterilization met... more The selection of a biological indicator organism for use with a new or existing sterilization method is an important endeavor because it will serve as a benchmark for validation, safety, and quality assessments across a range of current and future sterilization systems and machines. By convention, the process for bioindicator selection is to choose an organism demonstrating high relative resistance for the sterilization agent and method under examination and, therefore, includes the evaluation and comparison of the resistance of multiple candidate organisms and spores. This report reviews the basic tenants and principles of modern sterilization science as they relate to the determination and comparison of microbial resistance, uses the pulsed light treatment of Bacillus pumilus spore preparations, and spore stocks prepared via different methods to illustrate how different preparation procedures can affect the results seen with resistance testing, particularly survival/end point testing, and provides insights and experiences into microbial spore resistance testing and examines relevant cases in point.

Pda Journal of Pharmaceutical Science and Technology Pda, 1997

A study was performed to assess the ability of pulsed light to sterilize water for injection in b... more A study was performed to assess the ability of pulsed light to sterilize water for injection in blow/fill/seal polyethylene containers. Pulsed light uses intense, short duration flashes of broad spectrum white light to produce high levels of microbial kill. In a first phase of testing, containers of 0.5, 5, 15, and 120 mL nominal volume were inoculated with Bacillus pumilus endospores, Bacillus subtilus variety niger strain globigii endospores, Bacillus stearothermophilus endospores, and Aspergillus niger conidiospores. Approximately 10(6) colony forming units of each test spore were individually inoculated into 22 replicate containers of each sample volume. Two of these containers served as inoculation recovery controls, and 10 were treated using each of two pulsed light exposure methods: single-sided treatment, or treatment within a reflective cavity. Both treatments employed flashes of intense broad spectrum pulsed light delivered at one flash per second. Cavity treatment used 10 flashes to treat each container within a reflective cavity containing a single lamp. Cavity treatment yielded no recoverable survivors for any of the challenge spores from the contents of any of the 160 total samples. Single-sided treatment used 20 approximately 1-J/cm2 flashes from a single lamp-reflector projecting onto one side of the container. Single-sided treatment yielded no recoverable survivors from the contents of the containers for any of the bacterial endospores tested, but Aspergillus niger survival was detected in 4 of the 40 single-side treated samples. A second phase of tests examined the pulsed light inactivation of Bacillus pumilus spores for a range of inoculation levels. High levels of Bacillus pumilus spore kill were obtained using only a few cavity flashes. The results show that pulsed light can provide high levels of microbial lethality and possesses potential for use as a terminal sterilization method for water for injection in filled, sealed polyethylene containers.

Journal of Food Science, 2009

This study investigated microbial inactivation via surface-active peracids and used electron spin... more This study investigated microbial inactivation via surface-active peracids and used electron spin resonance spectroscopy to characterize the active components and free radical formation. Bacillus atrophaeus spores were injected directly into 3 different concentrations of the peracid disinfectant (1.1%, 1.3%, or 1.5%) for various times (5, 10, 15, or 20 s) at 3 different temperatures (50, 60, or 70 • C) to evaluate the sporicidal activity of the disinfectant mixture. Spectroscopy revealed that the combination of hydrogen peroxide, peracetic acid, and octanoic acid were highly effective at forming a complex mixture of sporicidal, free radical intermediates including hydroxyl and superoxide radicals. Individual components of this mixture alone were not as effective as the final combination. This information has practical applications in the food industry for design of effective sanitation and disinfection agents and suggests that kinetic models could be developed to account for both the physical removal and localized inactivation of spores on food-contact surfaces.

Journal of Food Science, 2004

ABSTRACT: Formulae for the prediction of inactivation and accumulated lethality of bacterial spor... more ABSTRACT: Formulae for the prediction of inactivation and accumulated lethality of bacterial spores under moist heat and high pressures were derived on the basis of classic thermodynamic and kinetics principles. The capability of the model to describe the inactivation of bacterial spores was verified using 2 independent data sets corresponding to Clostridium botulinum processed at 60°C to 75°C and Bacillus stearothermophilus processed at 92°C to 110°C. Both sets included pressures between 5 × 108 Pa and 7 × 108 Pa. The equation fit explained more than 86% of the variation of the rate constant data. The developed equations establish a strong foundation on which to compare high-pressure processing treatments of different systems. This is especially useful because most systems have different transient temperature-pressure conditions.

Human Gene Therapy, 1993

Dependent on the viral vector and the specific assay used, viral titers produced from commonly us... more Dependent on the viral vector and the specific assay used, viral titers produced from commonly used retroviral packaging cell lines have an upper limit in the range of 10(5) to 10(7) infectious units/ml. We have developed a generally applicable method, using hollow-fiber filtration technology, which allows for the concentration of infectious virus derived from packaging lines. This method resulted in a reproducible 10- to 30-fold increase in viral titer and can readily be scaled to accommodate larger input volumes. Over 80% of the input virus is recovered in an infectious form in the concentrate. Concentrated virus containing media was seen to produce higher infection frequencies in Jurkat T cells as compared to unconcentrated virus containing media; however, this was not proportional to the differences in viral titer observed by limiting dilution analysis on NIH-3T3 cells. These results are discussed in relation to the importance of factors other than viral titer in determining transduction frequencies.