Browsing by Subject "Feline calicivirus"

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    Decontamination of food and food-processing surfaces from norovirus by cold atmospheric-pressure gaseous plasma
    (2017-12) Aboubakr, Hamada
    Human Norovirus (HuNoV) is a leading cause of acute foodborne gastroenteritis outbreaks and sporadic cases. The estimated burden of HuNoV on public health is 685 million and 20 million illnesses each year in the world and the US, respectively. This results in approximately $4.3 billion and $60.3 billion in direct and indirect annual costs worldwide. In the USA, the annual economic burden of foodborne gastroenteritis illness has been estimated to be $77 billion. Most of the foodborne outbreaks are due to fresh produce and contaminated food contact surfaces. Obviously, heat cannot be used to decontaminate fresh fruits and vegetables and hence there is a need for novel non-thermal technologies that can inactivate noroviruses on food and food-processing surfaces. Cold atmospheric pressure gaseous plasma (CAP) is one such technology that has showed strong antibacterial and antifungal effects. However, studies on virucidal activity of CAP are lacking. In this thesis, we studied the in vitro virucidal efficacy of CAP against feline calicivirus (FCV), as a cultivable surrogate of HuNoV. Our results showed that >6 log10 TCID50 of FCV could be inactivated in liquid by a radio-frequency driven plasma jet after 15s exposure to Ar-1%O2 plasma. CAP generated from other feed gas mixtures (i.e. pure Ar, Ar+1% air, Ar+0.27% water) showed lower efficacies than Ar+1% O2. The virucidal efficacy is dependent on the exposure power, exposure distance, and virus-suspending medium. A combination of detailed scavenger measurements combined with positive controls of CAP reactive species allowed us to identify two distinctive pathways that lead to virus inactivation. The first mechanism depends on singlet oxygen in case of Ar+1% O2 plasma. In the presence of air, however, there is a significant reduction in pH and peroxynitrous acid is the key virus inactivating species. Smaller effects of H2O2, O3 and NO2− were also found. By employing different cultural, morphological, molecular and proteomic techniques, we found that reactive species of CAP generated from Ar+O2 are targeting mainly the virus capsid. The CAP was found to inactivate FCV by damaging and disintegrating the virus capsid and oxidizing specific functional peptide residues on major capsid proteins that are important for the attachment and entry of virus into the host cell. Using another CAP generation setup (two-dimensional air-based plasma microdischarge array or 2D-APMA), we were able to inactivate >5 logs of FCV on the surface of stainless steel discs after 3 min of wet exposure at 12.9 W discharge power, and 16.4 slm air flow rate without any significant effect of exposure distances (from 0.5 to 40 cm). Unlike wet exposure, the 2D-APMA showed no efficacy against FCV on dry surface. By using ethidium monoazido-coupled RT-qPCR (EMA-RT-qPCR) method for titrating HuNoV inactivation, CAP showed only 2.6 log reduction in HuNoV GII-4 on the surface of stainless steel and Romaine lettuce leaves under the same operational conditions as mentioned above. The lower inactivation of HuNoV GII-4 by CAP as compared to FCV was due to underestimation by the EMA-RT-qPCR method. The presence of fecal impurities in the HuNoV sample was also found to partially suppress the effect of CAP against HuNoV. This may be due to the competition of organic impurities with the virus particles on reaction with the reactive species of CAP. In a comparison study between the virucidal efficacy of CAP and UVC, as another non-thermal technology, we found that UVC could inactivate FCV on both dry and wet surfaces while CAP was effective only under wet conditions. However, CAP was able to inactivate FCV at both direct and indirect exposures while UVC could inactivate the virus under direct exposure only. This indicates that CAP may be useful for decontamination of rough surfaces with irregularities, which UV may not be able to penetrate. In terms of the power consumption, UVC inactivated FCV at much lower power than needed by CAP to inactivate the same titers of FCV. However, this limitation can be overcome by additional modifications in the design of the CAP setup to be less power consuming. In general, CAP has many advantages and holds promise as a viral decontamination technique.
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    Two-Dimensional Microdischarge Jet Array in Air: Characterization and Inactivation of Virus
    (2016-06) Nayak, Gaurav
    Cold atmospheric pressure plasmas (CAPs) have proven to be quite effective for surface disinfection, wound healing and even cancer treatment in recent years. One of the major societal challenges faced today is related to illness caused by food-borne bacteria and viruses, particularly in minimally processed, fresh or ready-to-eat foods. Gastroenteritis outbreaks, caused, for example, by the human Norovirus (NV) is a growing concern. Current used technologies seem not to be fully effective. In this work we focus on a possible solution based on CAP technology for surface disinfection. Many discharge sources have been studied for disinfection and the two major challenges faced are the use of expensive noble gases (Ar/He) by many plasma sources and the difficulty to scale up the plasma devices. The efficacies of these devices also vary for different plasma sources, making it difficult to compare results from different research groups. Also, the interaction of plasma with the biological matter is not understood well, particularly for virus. In this work, a two-dimensional array of micro dielectric barrier discharge is used to treat Feline Calicivirus (FCV), which is a surrogate for human Norovirus. The plasma source can be operated with an air flow rate (up to 94 standard liters per minute or slm). The use of such discharge source also raises important scientific questions which are addressed in this work. These questions include the effect of gas flow rate on discharge properties and the production of reactive species responsible for virus inactivation and the underlying inactivation mechanism. The plasma source is characterized via several diagnostic techniques such as current voltage measurements for electrical characterization and power measurements, optical emission spectroscopy (OES) to determine the gas temperature, cross-correlation spectroscopy (CCS) for microdischarge evolution and timescales, UV absorption spectroscopy to measure the O3 density, absolute IR OES to measure the O2(a 1Δg) density and spectrophotometry to estimate the NOx species density in aqueous medium. The results show that the discharge activity is strongly dependent on the gas flow rate particularly for gas residence times comparable to the applied high voltage cycle. The maximum difference in gas temperature at extreme plasma conditions do not exceed 50 K. The NO density is found to be reducing with smaller gas residence time. It is found that the reduced field E/N is dependent on the flow rate. The observed variation in the electric field is attributed to the change in the neutral gas densities. Both gas residence time and humidity have an impact on the space-charge distribution. The O3 density is found to increase with increasing power density and saturates at higher power above 12 W, and the maximum density of 1022 m-3 is achieved at an intermediate flow rate of 20 slm. An optimal condition for O2(a 1Δg) generation is found that is a balance between power and gas residence. Higher specific energy leads to higher increase of O2(a 1Δg) density as compared to the O3 density. It is also observed that the O2(a 1Δg) to O3 density ratio could be controlled by the flow rate from 0.7 to almost 0. The discharge source is used for FCV inactivation on surfaces (in the gas phase) and suspended in solution. Discharge power and treatment time have strong effect on the reduction in virus titer, while exposure distance or flow rate have negligible effect. Humidity plays a major effect on FCV inactivation on surfaces, leading to complete inactivation (>4 log10) within 3 minutes of treatment. FCV inactivation can be explained by O3 in gas phase and RNS in liquid phase. Nonetheless synergistic effects of ROS and RNS cannot be excluded, as similar production rates of O3 and NOx in discharge are determined. The O2(a 1Δg) density at conditions used for FCV treatment is at least 2 orders of magnitude lower than the ozone density and is not a dominant factor in the inactivation.