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Culturability and viability techniques such as plate count on solid agar (PC), Most Probable Number (MPN) and Direct Viable Count-Fluorescence in Situ Hybridation (DVC FISH) were used to study the inactivation of Salmonella typhimurium by photo-Fenton process at pH 5.5. In the presence of only simulated solar irradiation (500 W·m-2), S. typhimurim...
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... irradiation was simu- lated by a Hanau Suntest solar simulator (Germany) having a wavelength spectral distribution with about 0.5% of emitted photons <300 nm (UV-C range) and about 7% between 300 and 400 nm (UV-B, A range). The emission spectrum between 400 and 800 nm follows the solar spectrum (Figure 1). Light intensity in all ex- periments was 500 W·m −2 and it was monitored with a Kipp & Zonen (CM3) power meter (Omni instruments, Dundee, UK). ...
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... is well known that UV-C component (220 -280 nm) of UV light is the most lethal to the microorganisms since it might produce chemical changes on the DNA components [22]. Solar simulator emits few UV-C light irradiation (Figure 1) and this fact could explain why light irradiation did not affect in a larger extent of the initial concentration of S. typhimu- rium. However, the UV-A (320 -400 nm) is emitted by the solar simulator and some studies have argued that this UV component could affect the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase, and could also produce partial degradation of iron-con- taining proteins, releasing Fe (II) ions into the cell [23,24]. ...
Citations
... Salmonella can be found in many foods including beef, chicken, eggs, fruits, pork, sprouts, vegetables, and even processed foods, such as nut butters, frozen pot pies, chicken nuggets, and stuffed chicken entrees (CDC 2018). In addition to the familiar routine Salmonella contamination, the VBNC status of Salmonella is a potential safety concern (Asakura et al. 2002;Reissbrodt et al. 2002;Rengifo-Herrera et al. 2013;Roszak et al. 1984). VBNC state is a specific stage of bacterial survival, but a colony cannot be formed on conventional bacterial cultures that normally support its growth. ...
In this study, a rapid and sensitive real-time loop-mediated isothermal amplification (Rti-LAMP) assay was developed for quantitative and evaluation of viable but non-culturable (VBNC) Salmonella. Four micrograms per milliliter of ethidium bromide monoazide (EMA) could significantly inhibit DNA amplification derived from dead cells in Rti-LAMP assays. The EMA-Rti-LAMP was used to monitor the culturable and VBNC Salmonella cells induced by 4 °C and − 20 °C, as direct fluorescence method (DEM) and plate counting method as controls. When 1.3 × 10⁴ CFU/mL Salmonella was 5 cycles of freeze-thaw, the cells were all dead. However, Salmonella in 1.3 × 10⁶ CFU/mL gradually transferred into VBNC state reaching 6.0 × 10² CFU/mL (0.05%) after 5 cycles of freeze-thaw. Keeping Salmonella 1.3 × 10⁴ CFU/mL and 1.3 × 10⁶ CFU/mL in 0.85% NaCl at 4 °C, the culturable cells persistently decreased in plate counting. Meanwhile, the VBNC cells generated gradually from 0 to 4.2 × 10³ CFU/mL and 1.3 × 10⁵ CFU/mL detected by both EMA-Rti-LAMP and DEM up to 110-day storage, respectively. While in − 20 °C, 1.3 × 10⁴ CFU/mL Salmonella sharply inactivated during 20 days, but 1.3 × 10⁶ CFU/mL increasingly transferred into VBNC state reaching 3.5 × 10⁴ CFU/mL detected by both EMA-Rti-LAMP and DEM up to 110-day storage. The results indicated that the EMA-Rti-LAMP had similar accuracy with DEM in rapidly detecting viable including VBNC cells, and the former had specificity but the latter did not. The EMA-Rti-LAMP combined with bentonite-coated activated carbon (BCAC) treatment could detect as low as 35 CFU/g VBNC Salmonella derived from contaminated chicken, and the entire assay completed in 5 h. Furthermore, four identical samples were Salmonella positive from 24 retail frozen chicken samples detected by plate culture (GB4789.4-2016), BCAC-Rti-LAMP, and BCAC-EMA-Rti-LAMP. The BCAC-EMA-Rti-LAMP had one more sample for Salmonella positive than that of plate culture, but less two samples than that of BCAC-Rti-LAMP. Noticeably, the BCAC-EMA-Rti-LAMP had much more accuracy as plate counting than that of BCAC-Rti-LAMP in detection of viable Salmonella derived from chicken. These results strongly suggested that the BCAC-EMA-Rti-LAMP assay could be a rapid and sensitive method for detection of viable Salmonella including VBNC cells in chicken without enrichment.
... Several bacterial species have been reported to enter a VBNC state and regain culturability after 117 the elimination of the stress ( Keep et al., 2006;Oliver, 2000Oliver, , 2010 Gage et al., 2015;Reissbrodt et al., 2002;Rengifo-Herrera et al., 2013;Senoh et al., 2012), Shigella ...
By definition, foodborne outbreaks are illnesses affecting two or more people, correlated in terms of space and time, as a result of the ingestion of etiologic agents present in a common food. Ready-to-eat food products are normally subjected to treatments of sanitisation during processing that aims to miminise the microbial load. However, microorganisms have developed mechanisms to withstand adverse environmental conditions and fight for survival, including the ability to reduce their exposure to external attack through reversible modification of the morphology and physiology of their cell. This results in a significant change of their viability, which becomes undetectable through conventional culture techniques. Subsequent ‘resuscitation’ of these organisms in favourable food environment can represent a serious public health risk.
This review aims to examine the existing experimental evidence on the role of different sanitising approaches in inducing ‘viable but nonculturable’ state in microorganism and discuss possible approaches to reduce its occurrence.
... However, SPC is known to only consider cell culturability, neglecting the risk associated with persistence of bacterial viability. Rengifo-Herrera et al. (18) showed that photo-Fenton processes at pH 5.5 could induce viable but nonculturable state (VBNC) in Salmonella Typhimurium cells. Swetha et al. (19) suggested that inactivation of E. coli and S. aureus by photocatalytic reactions with TiO 2 nanoparticles could induce cells into VBNC state, thus producing differences between viability results and culturability results. ...
... This procedure was repeated three times, leaving the last cell pellet suspended in 10 mL of 0.1% peptonized bidistillated water. The final concentration of the washed cell suspension was adjusted according to the McFarland scale (18). 80 mL of a groundwater sample (with an initial pH of 7.1) containing 0.3 mg L À1 iron was added to a cylindrical Pyrex bottle. ...
Samples of natural groundwater (with low turbidity, neutral pH and 0.3 mg L(-1) iron concentration) inoculated with Escherichia coli K-12, were exposed to simulated solar light both in the presence and absence 10 mg L(-1) of H2 O2. Results demonstrated that the viability of E. coli (by DVC-FISH) was grounded to zero after 360 min of irradiation. This abatement could be caused by the oxidative stress induced by •OH radicals or another photo-induced reactive oxygen species. Two 2(3) factorial experimental designs enabled the evaluation of the effects of chemical factors on the inactivation of E. coli. The first experimental design considered the pH, iron and H2 O2 , while the second evaluated the ions fluoride, carbonate and phosphate found in groundwater. pH was found to play a key role in the inactivation of E. coli. The best reduction in viability was obtained at the lower pH (6.75), while a non-significant effect was observed when iron or H2 O2 concentrations were raised. At higher concentrations, anions such as carbonate and phosphate, negatively affected the E. coli abatement. However, a higher concentration of fluoride accelerated it. In all experiments, the pH was observed to rise to values higher than 8.0 units after 360 min of treatment. This article is protected by copyright. All rights reserved.
... Kumar D et al 44 studied the degradation of Basic Orange 2 in aqueous medium by use of photo-Fenton reagent. Julian et al 45 observed the cultivability and viability of Salmonella Typhimurium during photo-Fenton process at pH 5.5. It was reported that in S. typhimurium cellsugar metabolism was affected rather than amino-acids during photo-Fenton reaction. ...
Advanced Oxidation Processes (AOPs) have emerged as a promising technology for the treatment of wastewaters containing toxic, recalcitrant organic compounds such as dyes, pesticides etc. This review paper focuses on the Fenton and photo- Fenton technique which is one of the most efficient AOPs developed to decolorize and/or degrade organic pollutants. This oxidation method can produce biodegradable intermediates and mineralize complex organic pollutants effectively and efficiently. In this paper Fenton and photo-Fenton methods are categorised into two broad groups as homogeneous and heterogeneous Fenton and photo-Fenton processes. Applications of fundamental and advanced combined Fenton and photo-Fenton processes are also discussed.
