Inactivation of Bacillus subtilis spores on packaging surfaces by u. v. excimer laser irradiation

Sterilization effects of UV laser irradiation on Bacillus atrophaeus spore viability, structure, and proteins

Bacillus spores are highly resistant to toxic chemicals and extreme environments. Because some Bacillus species threaten public health, spore inactivation techniques have been intensively investigated. We exposed Bacillus atrophaeus spores to a 266 nm Nd:YVO₄ laser at a laser power of 1 W and various numbers of scans. As a result, the UV laser reduced the viability of Bacillus atrophaeus spores. Although the outer coat of spores remained intact after UV laser irradiation of 720 scans, damage inside the spores was observed. Spore proteins were identified by matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry during the course of UV laser irradiation. Photochemical and photothermal processes are believed to be involved in the UV laser sterilization of Bacillus spores. Our findings suggest that a UV laser is capable of sterilizing Bacillus atrophaeus spores.

Bacillus spores: a review of their properties and inactivation processing technologies

Many factors determine the resistance properties of a Bacillus spore to heat, chemical and physical processing, including thick proteinaceous coats, peptidoglycan cortex and low water content, high levels of dipicolinic acid (DPA), and divalent cations in the spore core. Recently, attention has been focused on non-thermal inactivation methods based on high pressure, ultrasonic, high voltage electric fields and cold plasmas for inactivating Bacillus spores associated with deterioration in quality and safety. The important chemical sporicides are glutaraldehyde, chorine-releasing agents, peroxygens, and ethylene oxide. Some food-grade antimicrobial agents exhibit sporostatic and sporicidal activities, such as protamine, polylysine, sodium lactate, essential oils. Surfactants with hydrophilic and hydrophobic properties have been reported to have inactivation activity against spores. The combined treatment of physical and chemical treatment such as heating, UHP (ultra high pressure), PEF (pulsed electric field), UV (ultraviolet), IPL (intense pulsed light) and natural antimicrobial agents can act synergistically and effectively to kill Bacillus spores in the food industry.

Inactivation of Listeria monocytogenes on and within Apples Destined for Caramel Apple Production by Using Sequential Forced Air Ozone Gas Followed by a Continuous Advanced Oxidative Process Treatment

This study evaluated the efficacy of using sequential forced air ozone followed by an advanced oxidative process (AOP) treatment to inactivate Listeria monocytogenes on and within Empire apples. The forced air ozone treatment consisted of a reactor that introduced ozone (6 g/h) into an airstream that flowed through an apple bed (ca. 30 cm in depth). Before treatment, the apples were conditioned at 4°C to ensure that condensate had formed before the apples were transferred to the reactor. The condensate ensured sufficient relative humidity to enhance the antimicrobial action of ozone. Air was passed through the apple bed at 9.3 m/s, and the ozone was introduced after 10 min. The ozone concentration measured after exiting the apple bed reached a steady state of 23 ppm. A 20-min ozone treatment supported a 2.12- to 3.07-log CFU reduction of L. monocytogenes, with no significant effect of apple position within the bed. The AOP-based method was a continuous process whereby hydrogen peroxide was introduced as a vapor into a reactor illuminated by UV-C and ozone-emitting lamps that collectively generated hydroxyl radicals. Operating the AOP reactor with UV-C light (54-mJ cm² dose), 6% (v/v) hydrogen peroxide, 2 g/h ozone, and a chamber temperature of 48°C resulted in a 3-log CFU reduction of L. monocytogenes on the surface of the apples and internally within the scar tissue. Applying a caramel coating, from a molten solution (at 80°C), resulted in a 0.5-log CFU reduction of L. monocytogenes on the apple surface. In apples treated with the sequential process, L. monocytogenes could only be recovered sporadically by enrichment and did not undergo outgrowth when the caramel apples were stored at 22°C for 19 days. However, growth of L. monocytogenes within the core, but not the surface, was observed from caramel apples prepared from nontreated control fruit.

Assessing microbial decontamination of indoor air with particular focus on human pathogenic viruses

Transmission of bacterial, fungal, and viral pathogens is of primary importance in public and occupational health and infection control. Although several standardized protocols have been proposed to target microbes on fomites through surface decontamination, use of microbicidal agents, and cleaning processes, only limited guidance is available on microbial decontamination of indoor air to reduce the risk of pathogen transmission between individuals. This article reviews the salient aspects of airborne transmission of infectious agents, exposure assessment, in vitro assessment of microbicidal agents, and processes for air decontamination for infection prevention and control. Laboratory-scale testing (eg, rotating chambers, wind tunnels) and promising field-scale methodologies to decontaminate indoor air are also presented. The potential of bacteriophages as potential surrogates for the study of airborne human pathogenic viruses is also discussed.

Modification of bacterial structures by a low-temperature gas plasma and influence on packaging material

AIMS

To investigate the effect of a cascaded dielectric barrier discharge (CDBD) treatment on the biological structure of a selected bacterium and on the properties of different polymer films.

METHODS AND RESULTS

Inactivation kinetics were measured using air as the process gas and using Bacillus atrophaeus spores and vegetative cells, which had been homogeneously distributed on a surface. The changes to the outer coats and the DNA of the endospores and cells after plasma treatment were determined using biomolecular and chemical methods. The experiments showed that damage to the DNA molecules and changes in the cell walls can be observed as a consequence of the CDBD treatment. Furthermore, the influence of the plasma treatment on the properties of various polymer films was investigated using a variety of test methods. Except the sealing strength where a slight decrease was observed (max. 20%), no negative changes of the material properties have occurred.

CONCLUSIONS

CDBD treatment can affect the DNA of spores and cells, depending on the treatment time. At the same time, practically relevant inactivation rates on packaging materials were observed, without any significant changes to the material properties.

SIGNIFICANCE AND IMPACT OF THE STUDY

Knowledge about CDBD mechanisms was acquired from a biological point of view, and the suitability of the method for treating polymer films was demonstrated.

Inactivation of food-borne spoilage and pathogenic micro-organisms on the surface of a photoactive polymer

The photodynamic action of a novel photoactive polymer comprising covalently bound anthraquinone (AQ) moieties was evaluated after developing a methodology to reliably immobilize viable micro-organisms onto polymer film surfaces. The survival of Escherichia coli, Bacillus cereus (vegetative cells and spores), Fusarium oxysporum and Saccharomyces cerevisiae microbes inoculated on the surface of inert polymeric substrates was assessed to determine the effect of inoculum composition, drying rate and exposure to ultraviolet (UV-A) radiation. Their survival was highly dependent on microbial genus, with E. coli consistently displaying markedly shorter survival times than the other microbes, and B. cereus spores being the most resistant. Inoculation of the microbes onto the surface of the photoactive polymer films, followed by exposure to UV-A radiation, dramatically accelerated the inactivation of all microbial types studied compared with their survival on the surface of inert polymer substrates. Simultaneous exposure to both oxygen and UV-A radiation is required to affect cell survival, which is consistent with this effect most likely originating from the photoinduced production of singlet oxygen by the photoactive polymer. These results provide further compelling evidence that singlet oxygen produced exogenously by this photoactive polymeric substrate can successfully inactivate a broad spectrum of microbes on the substrate's surface.

Efficiency of KrCl excilamp (222 nm) for inactivation of bacteria in suspension

AIMS

To examine the killing efficiency of UV KrCl excilamp against gram-positive and gram-negative bacteria.

METHODS AND RESULTS

Vegetative cells of Bacillus cereus, Bacillus subtilis, Escherichia coli O157:H7, Staphylococcus aureus and Streptococcus pyogenes at initial populations from 10(2) to 10(7) colony-forming units (CFU) ml(-1) were treated by KrCl excilamp in sterile Ringer's solution with and without H(2)O(2). The number of viable cells was determined using spread plating techniques and nutrient agar method with subsequent incubation at 28 degrees C or 37 degrees C for 24 h. At estimated populations of 10(2)-10(5) CFU ml(-1) E. coli O157:H7 and Staph. aureus were the most sensitive and showed 100% disinfection within 15 s (29.2 mJ cm(-2)). Bacillus subtilis was more sensitive to UV treatment than B. cereus. The UV/H(2)O(2) inactivation rate coefficients within this population range were two times higher than those observed for UV treatment alone. No effect of H(2)O(2) was observed at 10(7) CFU ml(-1) for Bacillus sp. and Strep. pyogenes.

CONCLUSIONS

The narrow-band UV radiation at 222 nm was effective in the rapid disinfection of bacteria in aqueous suspensions.

SIGNIFICANCE AND IMPACT OF THE STUDY

KrCl excilamps represent UV sources which can be applied for disinfection of drinking water in advanced oxidation processes.

Effects of freezing on the survival of Escherichia coli and Bacillus and response to UV and chlorine after freezing

Escherichia coli (E. coli) and Bacillus megaterium bacteria were frozen at -15 degrees C using a freezer and a spray freezing method. The frozen Bacillus spores were also exposed to UV and free chlorine. An average of 4.7-log inactivation was obtained from the spray ice with 2-day storage time, while the freezer freezing only caused 0.84-log reduction with the same storage time. Significantly higher inactivation levels were observed for the E. coli cells with 2-day storage compared with those without storage. The spray freezing was found more effective in killing the E. coli cells, while more cells were sublethally injured by the freezer freezing. Freezing did not kill the Bacillus megaterium spores, but affected their response to UV and chlorine. Greater inactivation levels were observed at higher free chlorine doses or longer contact time, and the UV fluence-response curve showed initial rapid kill followed by tailing for the frozen spores.

Carton sterilization by u.v.-C excimer laser light: recovery of Bacillus subtilis spores on vegetable extracts and food simulation matrices

AIMS

To determine the recovery of Bacillus subtilis spores loaded onto preformed cartons and irradiated with u.v.-excimer laser (248 nm) light.

METHODS AND RESULTS

Bacillus subtilis spores irradiated with u.v.-excimer laser light retained phase brightness, but were blocked at various stages of germination. In the presence of germinant, the majority of spores began to lose phase brightness but only after an extended lag period (ca 90 min). After 6 h ca 9% of the spores had elongated but failed to form new cells, approx. 12% had undergone partial phase darkening (grey spores), 15% remained phase bright whilst the remainder had turned fully phase dark but failed to elongate. No enhanced recovery of u.v.-treated spores (with intact or permeabilized coats) occurred in media containing hen egg white lysozyme or vegetable extracts (celery, carrot, swede or turnip). However, recovery did occur when irradiated spores were incubated for 26 d, semiaerobically, within cartons containing nutrient broth or milk.

CONCLUSIONS

The germination ability of B. subtilis spores is altered following u.v.-excimer laser treatment. Recovery of treated spores was found in liquid systems but not on agar plates supplemented with vegetable extracts or lysozyme.

SIGNIFICANCE AND IMPACT OF THE STUDY

The potential recovery of u.v.-excimer laser-treated spores in a range of carton-packed food systems requires further investigation.

Examination of peak power dependence in the UV inactivation of bacterial spores

We examine whether the rate of delivery of photons from a UV radiation source has an effect on the inactivation of spores. We directly compare the output of a high-peak-power UV laser source at 248 nm to a low-power continuous lamp source (254 nm) in the inactivation of Bacillus subtilis spores. The two UV sources differ by a factor of 10(8) in peak power. Contrary to previous reports, no clear differences in spore survival were observed.

Low-temperature sterilization using gas plasmas: a review of the experiments and an analysis of the inactivation mechanisms

Utilizing an ionized gas (plasma) to achieve sterilization is an alternative to conventional sterilization means as far as sterilization of heat-sensitive materials and innocuity of sterilizing agents are concerned. The literature on plasma sterilization is reviewed. A major issue of plasma sterilization is the respective roles of UV photons and reactive species such as atomic and radicals. Insight into this matter is obtained by analyzing the survival curves of microorganisms. In contrast to classical sterilization where such plots show a unique straight line, plasma sterilization yields survival diagrams with two or three different linear segments. Three basic mechanisms are involved in the plasma inactivation of microorganisms: (A) direct destruction by UV irradiation of the genetic material of microorganisms; (B) erosion of the microorganisms atom by atom, through intrinsic photodesorption by UV irradiation to form volatile compounds combining atoms intrinsic to the microorganisms; (C) erosion of the microorganisms, atom by atom, through etching to form volatile compounds as a result of slow combustion using oxygen atoms or radicals emanating from the plasma. In some cases, etching is further activated by UV photons, increasing the elimination rate of microorganisms. These mechanisms make plasma sterilization totally different from classical sterilization techniques and suggest its use to inactivate nonconventional infectious agents such as the abnormal prions.