Genomic and phenotypic analysis of heat and sanitizer resistance in Escherichia coli from beef in relation to the locus of heat resistance

The locus of heat resistance (LHR) can confer heat resistance to Escherichia coli to various extents. This study investigated the phylogenetic relationships, and genomic and phenotypic characteristics of E. coli with or without LHR recovered from beef by direct plating or from enrichment broth at 42°C. LHR-positive E. coli isolates (n=24) were whole genome-sequenced by short- and long-reads. LHR-negative isolates (n=18) from equivalent sources as LHR-positive isolates were short-read sequenced. All isolates were assessed for decimal reduction time at 60°C ( D 60°C ) and susceptibility to E-SAN and Perox-E. Selected isolates were evaluated for growth at 42°C. The LHR-positive and negative isolates were well separated on the core genome tree, with 22/24 of the positive isolates clustering into three clades. Isolates within clade 1 and 2, despite their different D 60°C values, were clonal, as determined by subtyping (MLST, core genome MLST, and serotyping). Isolates within each clade are of one serotype. The LHR-negative isolates were genetically diverse. The LHR-positive isolates had a larger (p<0.001) median genome size by 0.3 Mbp (5.0 vs 4.7 Mbp), and overrepresentation of genes in plasmid maintenance, stress response and cryptic prophages, but underrepresentation of genes involved in epithelial attachment and virulence. All LHR-positive isolates harbored a chromosomal copy of LHR, and all clade 2 isolates had an additional partial copy of LHR on conjugative plasmids. The growth rates at 42°C were 0.71±0.02 and 0.65±0.02 logOD h −1 for LHR-positive and negative isolates. No meaningful difference in sanitizer susceptibility was noted between LHR-positive and negative isolates. Importance Resistant bacteria are serious food safety and public health concerns. Heat resistance conferred by the LHR varies largely among different strains. The findings in this study show that genomic background and composition of LHR, in addition to the presence of LHR, play an important role in the degree of heat resistance in E. coli , and that strains with certain genetic background are more likely to acquire and maintain the LHR. Also, caution should be exercised when recovering E. coli at elevated temperatures as the presence of LHR may confer growth advantages to some strains. Interestingly, the LHR harboring strains seem to have evolved further from their primary animal host to adapt to their secondary habitat, as reflected by fewer genes in virulence and epithelial attachment. The phylogenetic relationships among the isolates point towards multiple mechanisms for acquiring LHR, likely prior to their deposition on meat.

Survival of Escherichia coli O157:H7 during Moderate Temperature Dehydration of Plant-Based Foods

The effect of moderate-temperature (≤60 °C) dehydration of plant-based foods on pathogen inactivation is unknown. Here, we model the reduction of E. coli O157:H7 as a function of product-matrix, aw, and temperature under isothermal conditions. Apple, kale, and tofu were each adjusted to aw 0.90, 0.95, or 0.99 and inoculated with an E. coli O157:H7 cocktail, followed by isothermal treatment at 49, 54.5, or 60.0 °C. The decimal reduction time, or D-value, is the time required at a given temperature to achieve a 1 log reduction in the target microorganism. Modified Bigelow-type models were developed to determine D-values which varied by product type and aw level, ranging from 3.0–6.7, 19.3–55.3, and 45.9–257.4 min. The relative impact of aw was product dependent and appeared to have a non-linear impact on D-values. The root mean squared errors of the isothermal-based models ranged from 0.75 to 1.54 log CFU/g. Second, we performed dynamic drying experiments. While the isothermal results suggested significant microbial inactivation might be achieved, the dehydrator studies showed that the combination of low product temperature and decreasing aw in the pilot-scale system provided minimal inactivation. Pilot-scale drying at 60 °C only achieved reductions of 3.1 ± 0.8 log in kale and 0.67 ± 0.66 log in apple after 8 h, and 0.69 ± 0.67 log in tofu after 24 h. This illustrates the potential limitations of dehydration at ≤60 °C as a microbial kill step.

Fungicidal Activity of Five Disinfectants on Isolates of Candida Species

Determine fungicidal activity of five disinfectants on Candida auris of clinical and environmental origin. Assess fungicidal efficiency of each disinfectants on the microorganism. Calculate percentage of efficiency (% E) of each disinfectants on Candida strain and determine specific death rate (k) and decimal reduction time for the microorganism. An analytic and experimental research with quantitative methods. We realized a strains workbench by culturing it in corresponding culture media. Analysis was a challenge essay, performed on four surfaces and at different exposure times; 1, 5, 15 and 30 minutes of contact between disinfectant and yeast. Once disinfection process was carried out, what was expected was that after 15 minutes of contact between the yeasts and the disinfectants, a percentage of inhibition of the microorganism between 90 and 95% was presented, thus guaranteeing the duration of elimination of the infectious agent by disinfectants. Results shows that after one minute of contact between Candida auris and the disinfectant in a gloved hand, there was a removal of the yeast, when the clinical and environmental strain were analyzed. Data showing disinfectants efficiency percentages greater than 90% over strains of Candida used in the study. Decimal reduction times in seconds of the strains of Candida against the disinfectants used in the study were between 9.3 and 14.04 s. It was possible to evaluate effectiveness by means inhibition percentage of each disinfectants on the strains of Candida auris of clinical and environmental origin. Similarly, specific death rate and decimal reduction time in seconds were determined for strains under study.

Modelling the inactivation of Staphylococcus aureusat moderate heating temperatures

The survival of bacterial contaminants at moderate processing temperatures is of interest to many food producers, especially in terms of the safety and quality of the final products. That is why the heat resistance of Staphylococcus aureus 2064, an isolate from artisanal Slovakian cheese, was studied in the moderate temperature range (57–61 °C) by the capillary method. The fourth decimal reduction time t_4D- and z-values were estimated in two steps by traditional log-linear Bigelow and non-linear Weibull models. In addition, a one-step fitting procedure using the Weibull model was also applied. All the approaches provided comparable t_4D-values resulting in the following z-values of 11.8 °C, 12.3 °C and 11.3 °C, respectively. Moreover, the one-step approach takes all the primary data into z-value calculation at once, thus providing a more representative output at the reasonable high coefficient of determination R₂ = 0.961

Microorganisms Photocatalytic Inactivation on Ag3PO4 Sub-microcrystals Under WLEDs Light Source

In this article, we report the silver orthophosphate (Ag3PO4) photocatalytic inactivation properties on strains Gram-positive Saprophyte B. subtilis, a diploid fungus Candida albicans and Gram-negative Pseudomonas aeruginosa, using as irradiation source white-light-emitting diodes (WLEDs) with luminous flux (Φ v) of 1.3 x 103 Lumens and relative power density of 15 mW m− 2. Microorganisms death curves and the kinetic constants (Kd) indicated that the inhibitory effect of the Ag3PO4 under WLEDs irradiation is well pronounced to C. albicans (6.6 x 10− 2 min− 1) in relation to P. augenosas (4.6 x 10− 2 min− 1) and B. subitilis (2.5 x 10− 2 min− 1). Decimal reduction time (Dt) were 34.4 min to C. albicans, 50.1 min P. augenosas and 92.1 min to B.subitilis The micrographs obtained by scanning electron microscopy with field emission gun (SEM-FEG) demonstrated that there was cell wall permeability and consequently total rupture in the C. albicans, suggesting the lipid peroxidation phenomenon and protein oxidation promoted by the presence of reactive oxygen species (ROS). Furthermore, it was observed the Ag3PO4 when irradiated by WLEDs demonstrates important sporicidal activity in related to B. subtilis, promoting the endospore wall rupture.

Application of a roller conveyor type plasma disinfection device with fungus-contaminated citrus fruits

Efficient methods to achieve the safe decontamination of agricultural products are needed. Here, we investigated the decontamination of citrus fruits to test the antifungal potential of a novel non-thermal gas plasma apparatus, termed a roller conveyer plasma instrument. This instrument generates an atmospheric pressure dielectric barrier discharge (APDBP) plasma on a set of rollers. Penicillium venetum was spotted onto the surface of the fruit or pericarps, as well as an aluminium plate to act as a control, before performing the plasma treatment. The results showed that viable cell number of P. venetum decreased with a decimal reduction time (D value or estimated treatment time required to reduce viable cell number by 90%) of 0.967 min on the aluminium plate, 2.90 min and 1.88 min on the pericarps of ‘Kiyomi’ (Citrus unshiu × C. sinensis) and ‘Kawano-natsudaidai’ (C. natsudaidai) respectively, and 2.42 min on the surface of ‘Unshu-mikan’ (C. unshiu). These findings confirmed a fungicidal effect of the plasma not only on an abiotic surface (aluminium plate) but also on a biotic surface (citrus fruit). Further development of the instrument by combining sorting systems with the plasma device promises an efficient means of disinfecting citrus fruits during food processing.

Electrically Charged Disinfectant Containing Calcium Hydrogen Carbonate Mesoscopic Crystals as a Potential Measure to Control Xanthomonas campestris pv. campestris on Cabbage Seeds

Xanthomonas campestris pv. campestris (Xcc) is an important seed-borne bacterial pathogen that causes black rot in brassica. Current seed disinfection methods for Xcc have disadvantages; chemical treatment has associated environmental risks, hot water immersion reduces germination, and dry heat treatment is protracted. Here, we treated Xcc-contaminated seeds with CAC-717, a recently developed disinfectant produced by applying an electric field and water flow to distilled water containing calcium hydrogen carbonate to produce mesoscopic crystals. The decimal reduction time (D-value) of Xcc suspension (8.22 log10 colony forming units (CFU)/mL) by CAC-717 treatment was 0.319 min. Treatment of Xcc-contaminated cabbage seeds at 25 °C for 30 min with CAC-717 significantly reduced bacterial cell numbers recovered from the seeds (0.36 log10 CFU/mL (SEM (standard error of the mean) = 0.23 log10 CFU/mL)) compared with distilled water treatment (3.52 log10 CFU/mL (SEM = 0.12 log10 CFU/mL)). Moreover, there was a lower incidence of black rot after treatment with CAC-717 (26.67% ± 3.33%) versus distilled water (56.67% ± 8.82%). For non-contaminated seeds, there was no significant difference in germination rate and plant stem length between distilled water and CAC-717 treatment after 5 days of cultivation. In conclusion, CAC-717 is a promising seed disinfectant without deleterious effects on germination or plant growth.

Kinetics of the thermal degradation of lycopene in tomatoes

This research studied the kinetics of the thermal degradation of lycopene in tomatoes using elevated temperature testing. Understanding the nature and the extent of sensitive nutrient degradation in tomatoes will assist in reducing postharvest nutrient losses during storage and processing. Ripe tomatoes were sorted, washed, and blinded. Juice was obtained by filtering the blinded pulp through a muslin cloth. The samples were heated using a water bath at 70, 80, 90, and 100 °C for 20, 40, 60, and 80 minutes. The determination of lycopene was done using spectrophotometric methods at 503 nm, in hexane: ethanol: acetone (2:1:1 v/v/v) lycopene extract. The concentrations of lycopene were determined immediately after processing. The data was found to fit into first order equations. Degradation constants (k), D-value, and half-life for the thermal degradation of lycopene were determined at each processing temperature. Models were also developed for each of the chosen temperatures, which can be used to predict the degradation pattern of lycopene at other processing conditions. Z-value, Q10, and activation energy for the degradation of lycopene were also determined. Analyses showed a considerable decrease in lycopene concentration and decimal reduction time (D-value), and a significant increase in the thermal degradation rate (k) during heating from 70 to 100 °C. The finding shows that the degradation of lycopene in tomatoes followed the first order kinetics and it shows that the lycopene content decreased at 80 to 100 °C.

Bionanotechnology: Silver Nanoparticles Supported on Bovine Bone Powder Used as Bactericide

Bionanotechnology is a relatively new term that implies the use of some biological material or organisms in order to prepare nanosystems or nanoparticles. This work presents the preparation and bactericide application of a sustainable nanometric system (silver nanoparticles) using a waste biological support (bovine bone powder). This system was prepared by the method of metallic salt reduction, using NaBH4 as reducing agent and AgNO3 as metallic salt. Two silver contents were analyzed, 1% and 5% weight. The latter was found to be more efficient than the former. Transmission electronic microscopy shows an average size of 10.5 ± 3.3 nm and quasi-sphere morphology. The antimicrobial assay shows that a 5% weight content of silver had a bactericide effect for Escherichia coli at 46.8 min of exposure. The minimum inhibitory concentration (MIC) of silver nanoparticles supported on bovine bone powder for Escherichia coli was 7.5 µg/mL. The biocomposite exhibits a specific antibacterial kinetics constant (k) of 0.1128 min−1 and decimal reduction time (DRT) of 20.39 min for Escherichia coli. Thus, it was concluded that a biocomposite was prepared with a biodegradable, waste, and low-cost support, under mild conditions (room temperature and atmospheric pressure) and using water as solvent.

Inactivation kinetics and thermodynamic properties of polygalacturonase produced by Aspergillus awamori CICC 2040 on pretreated orange and plantain peels

This study investigated the effect of pretreatment of orange and plantain peels on the inactivation kinetics and thermodynamic properties of polygalacturonase (PG) produced by Aspergillus awamori CICC 2040. Orange and plantain peel powders were subjected to microwave-assisted NaOH pretreatment and used as substrates for PG production. Un-treated peels served as controls. The PG was purified using acetone precipitation and column chromatography, and the inactivation kinetics, temperature dependency, and thermodynamic properties of the crude and purified PGs were determined. Higher inactivation rate constant was obtained for crude PG produced using pretreated orange peel (CPOF) and plantain peel (CPPF) compared to PG produced using untreated orange peel (Uo) and plantain peel (Up). At all the temperatures considered, higher half-life and decimal reduction time were recorded for CPOF and CPPF compared to Uo and Up. The highest half-life (45.60 min) and decimal reduction time (151.49 min) were recorded for CPOF at 60 ?C. Lower half-life and decimal reduction time were obtained for purified PGs compared to the crude PG. Polygalacturonase produced from pretreated peels had lower activation energy than those produced from untreated ones. The higher activation energy was recorded for the PG produced using orange peel compared to the one from plantain peels. The enthalpy of CPOF and CPPF was slightly lower than Uo and Up. The pretreatment of the peels resulted in a reduction of Gibbs free energy (?G ) and entropy (?S) of crude and purified PG. Higher ?G and ?S were recorded for the purified PG compared to the crude PG. Negative entropy and enthalpy were recorded for all the PGs. The findings from this study showed that the kinetic and thermodynamic properties of PG, produced by Aspergillus awamori CICC 2040, were enhanced by the pretreatment of orange and plantain peels.