Chlorine and ozone disinfection of Encephalitozoon intestinalis spores

Microsporidia are intracellular eukaryotic parasites which have the potential for zoonotic and environmental, including waterborne, transmission. Encephalitozoon intestinalis is a microsporidian pathogen of humans and animals and has been detected in surface water. It is also on the Contaminant Candidate List of potential emerging waterborne pathogens for the US EPA. We performed disinfection studies using chlorine and ozone on E. intestinalis spores with a cell-culture most-probable-number assay to determine infectivity. Chlorine experiments were performed at 5 degrees C at pH of 6, 7, and 8 with 1mg/L initial chlorine concentrations, while ozone experiments were performed at 5 degrees C and pH 7 with initial ozone doses of 1 and 0.5mg/L, both in buffered water. A derivation of Hom's model for disinfection kinetics under dynamic disinfectant concentrations was used to fit observed data and calculate concentration-time product (C*t) values. Chlorine C*t values varied with pH such that 99% (2-log(10)) C*t ranged from 12.8 at pH 6 to 68.8 at pH 8 (mg min/L). Ozone C*t values were approximately an order of magnitude less at 0.59--0.84 mg min/L, depending on initial concentration.     

Influence of pH on bioactivity of cinnamon oil against Legionella pneumophila and its disinfection efficacy in hot springs

Cinnamon oil extracted from leaves of Cinnamomum osmophloeum has recently been proved as a promising antibacterial agent against Legionella pneumophila, an etiological agent of human pneumonia known as Legionnaires' disease. However, the pH effects on the efficacy of cinnamon oil against L. pneumophila and its applicability to recreational spring water remain unknown. We therefore determined the bactericidal activity of cinnamon oil at pH 3-10 in phosphate-buffered saline (PBS) and in four kinds of springs with various conductivity (259-5595 μs cm⁻¹) and pH (2.1-7.7) levels. Results show L. pneumophila cells were more susceptible to cinnamon oil at pH 8-10 than at pH 4-6 in PBS, which became more evident as increasing contact time from 10 to 60 min. An increase in concentration of cinnamon oil and contact time significantly increased the anti-L. pneumophila activity (P ≤ 0.001), indicating a consistent biocidal effect regardless of pH. Interestingly, this dose-response biocidal effect was also observed in spring waters. Moreover, L. pneumophila of 4 log CFU ml⁻¹ in spring waters was completely inactivated within 60 min by cinnamon oil at 300-750 μg ml⁻¹, with the highest inactivation in alkaline hydrogen carbonate spring. The great bioactivity of cinnamon oil demonstrates its potential to be used to control Legionella growth in recreational spring water and possibly other niches generally at basic pH, e.g., cooling towers.     

A simulation on PSB biofilm formation with considering cell inactivation

A differential-discrete mathematical model is developed to predict the photosynthetic bacteria (PSB) Rhodopseudomonas palustris CQK 01 biofilm formation. In this model, with the consideration of the light decay in the photobioreactor, PSB inactivation and cellular automata (CA) rules along with the previously obtained growth kinetics parameters of PSB are used to simulate biofilm growth. With this model, the effects of illumination intensity, pH value and initial inoculation on the biofilm morphology, active cell biomass as well as some characteristic parameters such as porosity, roughness and thickness is investigated. Numerical results show that cell inactivation occurs within the biofilm and the biofilm morphology varies with the operating conditions. Moreover, the roughness and thickness increase, but the porosity decreases as the biofilm grows. The amount of active cells is increasing with time. It is also found that the optimal conditions for PSB biofilm formation are the illumination intensity of 6000 lx, the initial inoculation of 60 and the substrate solution pH value of 7.0.     

The inactivation of Bacillus subtilis spores at low concentrations of hydrogen peroxide vapour

Spores of the bacterium Bacillus subtilis were deposited onto the surface of membranes by a process of filtration and exposed to concentrations of hydrogen peroxide vapour between 10 and 90 mg/m³ (ppm) for times ranging from 1.5 to 48 h. The inactivation data obtained in this way was modelled using the Weibull, Series-Event and Baranyi inactivation models. The Weibull model provided the best fit, and its use was extended to previously published literature obtained at higher hydrogen peroxide concentrations to produce a correlation yielding D (decimal reduction value) values over a range from 10 to almost 4000 ppm.     

Accelerated inactivation of Geobacillus stearothermophilus spores by ohmic heating

Until recently, ohmic heating was commonly thought to kill microorganisms through a thermal effect. However a growing body of evidence suggests that non-thermal effects may occur. Our aim was to determine the kinetics of inactivation of Geobacillus stearothermophilus spores (ATCC 7953) under ohmic and conventional heating using a specially constructed test chamber with capillary sized cells to eliminate potential sources of error and ensure that identical thermal histories were experienced both by conventionally and ohmically heated samples. Ohmic treatments at frequencies of 60 Hz and 10 kHz were compared with conventional heating at 121, 125 and 130 °C for four different holding times. Both ohmic treatments showed a general trend of accelerated spore inactivation. It is hypothesized that vibration of polar dipicolinic acid molecules (DPA) and spore proteins to electric fields at high temperature conditions may result in the accelerated inactivation.     

Effectiveness of chitosan on the inactivation of enteric viral surrogates

Chitosan is known to have bactericidal and antifungal activity. Although human noroviruses are the leading cause of non-bacterial gastroenteritis, information on the efficacy of chitosan against foodborne viruses is very limited. The objective of this work was to determine the effectiveness of different molecular weight chitosans against the cultivable human norovirus and enteric virus surrogates, feline calicivirus, FCV-F9, murine norovirus, MNV-1, and bacteriophages, MS2 and phiX174. Five purified chitosans (53, 222, 307, 421, ∼1150 kDa) were dissolved in water, 1% acetic acid, or aqueous HCl pH = 4.3, sterilized by membrane filtration, and mixed with equal volume of virus to obtain a final concentration of 0.7% chitosan and 5 log₁₀ PFU/ml virus. Virus-chitosan suspensions were incubated for 3 h at 37 °C. Untreated viruses in PBS, in PBS with acetic acid, and in PBS with HCl were tested as controls. Each experiment was run in duplicate and replicated at least twice. Water-soluble chitosan (53 kDa) reduced phiX174, MS2, FCV-F9 and MNV-1 titers by 0.59, 2.44, 3.36, and 0.34 log₁₀ PFU/ml respectively. Chitosans in acetic acid decreased phiX174 by 1.19–1.29, MS2 by 1.88–5.37, FCV-F9 by 2.27–2.94, and MNV-1 by 0.09–0.28 log₁₀ PFU/ml, respectively. Increasing the MW of chitosan corresponded with an increasing antiviral effect on MS2, but did not appear to play a role for the other three tested viral surrogates. Overall, chitosan treatments showed the greatest reduction for FCV-F9, and MS2 followed by phiX174, and with no significant effect on MNV-1.     

Survival of manure-borne E. coli in streambed sediment: Effects of temperature and sediment properties

Escherichia coli bacteria are commonly used as indicator organisms to designate of impaired surface waters and to guide the design of management practices to prevent fecal contamination of water. Stream sediments are known to serve as a reservoir and potential source of fecal bacteria (E. coli) for stream water. In agricultural watersheds, substantial numbers of E. coli may reach surface waters, and subsequently be deposited into sediments, along with fecal material in runoff from land-applied manures, grazing lands, or wildlife excreta. The objectives of this work were (a) to test the hypothesis that E. coli survival in streambed sediment in the presence of manure material will be affected by sediment texture and organic carbon content and (b) to evaluate applicability of the exponential die-off equation to the E. coli survival data in the presence of manure material. Experiments were conducted at three temperatures (4 °C, 14 °C, and 24 °C) in flow-through chambers using sediment from three locations at the Beaverdam Creek Tributary in Beltsville, Maryland mixed with dairy manure slurry in the proportion of 1000:1. Indigenous E. coli populations in sediments ranged from ca. 10¹ to 10³ MPN g⁻¹ while approx 10³ manure-borne E. coli MPN g⁻¹ were added. E. coli survived in sediments much longer than in the overlaying water. The exponential inactivation model gave an excellent approximation of data after 6-16 days from the beginning of the experiment. Slower inactivation was observed with the increase in organic carbon content in sediments with identical granulometric composition. The increase in the content of fine particles and organic carbon in sediments led not only to the slower inactivation but also to lower sensitivity of the inactivation to temperature. Streambed sediment properties have to be documented to better evaluate the role of sediments as reservoirs of E. coli that can affect microbiological stream water quality during high flow events.     

Comparison of the inactivation kinetics of pectin methylesterases from carrot and peach by high-pressure carbon dioxide

The inactivation of pectin methylesterases (PMEs) from carrot and peach in buffer by high-pressure carbon dioxide (HPCD) at 55 °C was investigated. The two PMEs were effectively inactivated by HPCD, their residual activity (RA) decreasing with increasing pressures. The RA of the two PMEs exhibited a fast decrease firstly and reached a constant after a prolonged treatment time; their inactivation kinetics was adequately modelled by a fractional-conversion model. The non-zero RA(A_∞)of the two PMEs was 6–7%, with increasing pressures the kinetic rate constant, k, increased and the decimal reduction time, D, decreased for the HPCD-labile fraction of the two PMEs. The labile fraction of carrot PME was more susceptible to HPCD than that of peach PME; the activation volume, V_a, and Z_P (the temperature increase needed for a 90% reduction of D) was −1079.37 cm³/mol and 5.80 MPa for carrot PME, and −130.51 cm³/mol and 48.31 MPa for peach PME.     

Inactivation kinetics of Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and Campylobacter jejuni in ready-to-eat sliced ham using UV-C irradiation

To investigate the applicability of UV-C irradiation on the inactivation of foodborne pathogenic bacteria in ready-to-eat sliced ham, UV-C treatment was evaluated. Irradiation dose required for 90% reduction of the populations of Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and Campylobacter jejuni were determined to be 2.48, 2.39, and 2.18 J/m². Ready-to-eat sliced hams were inoculated with the pathogens and irradiated with UV-C light of 1000, 2000, 4000, 6000, and 8000 J/m². Microbiological data indicated that foodborne pathogen populations significantly (p < 0.05) decreased with increasing UV-C irradiation. In particular, UV-C irradiation at 8000 J/m² reduced the populations of L. monocytogenes, S. Typhimurium, and C. jejuni in the ham by 2.74, 2.02, and 1.72 log CFU/g. The results indicate that UV-C irradiation can be used as a microbial inactivation method for ready-to-eat sliced ham, and inactivation kinetics of the foodborne pathogens fit the Weibull model better than the first-order kinetics model.     

Recent Advances in the Use of High Pressure as an Effective Processing Technique in the Food Industry

High pressure processing is a food processing method which has shown great potential in the food industry. Similar to heat treatment, high pressure processing inactivates microorganisms, denatures proteins and extends the shelf life of food products. But in the meantime, unlike heat treatments, high pressure treatment can also maintain the quality of fresh foods, with little effects on flavour and nutritional value. Furthermore, the technique is independent of the size, shape or composition of products. In this paper, many aspects associated with applying high pressure as a processing method in the food industry are reviewed, including operating principles, effects on food quality and safety and most recent commercial and research applications. It is hoped that this review will promote more widespread applications of the technology to the food industry.