Antimicrobial activity of mustard essential oil against Escherichia coli O157:H7 and Salmonella typhi

The aim of this study was to investigate how mustard essential oil (EO) affected the cell membrane of Escherichia coli O157:H7 and Salmonella typhi. Intracellular pH and ATP concentration and the release of cell constituents were measured when mustard EO was in contact with E. coli and S. typhi at its minimal inhibitory concentration (MIC) and maximal tolerated concentration (MTC). The treatment with mustard EO affected the membrane integrity of bacteria and induced a decrease of the intracellular ATP concentration. Also, the extracellular ATP concentration increased and a reduction of the intracellular pH was observed in both bacteria. A significantly (P ? 0.05) higher release of cell constituent was observed when both bacteria cells were treated with mustard EO. Electronic microscopy observations showed that the cell membranes of both bacteria were apparently damaged by mustard EO. In conclusion, mustard EO affects the concentration of intracellular component, such as ATP in both bacteria and affects the pH suggesting that cytoplasmic membrane is involved in the antimicrobial action of mustard EO. Mustard EO can be used as an effective antimicrobial agent. We have demonstrated that mustard EO affected the cell membrane integrity, resulting in a loss of cell homeostasis.     

Efficacy of sanitizers in reducing Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes populations on fresh-cut carrots

Shredded carrots were inoculated with Escherichia coli O157:H7, Salmonella or Listeria monocytogenes and washed for 1 or 2 min with chlorine (Cl; 200 ppm), peroxyacetic acid (PA; 40 ppm) or acidified sodium chlorite (ASC; 100, 200, 500 ppm) under simulated commercial processing conditions. After washed, the carrots were spin dried, packaged and stored at 5 °C for up to 10 days. Bacterial enumeration was significantly (P ⩽ 0.05) reduced by 1, 1.5 and 2.5 log CFU/g after washing with ASC 100, 250 and 500 ppm, respectively. All sanitizers reduced pathogen load below that of tap water wash and unwashed controls. During storage at 5 °C the bacterial load of all treatments increased gradually, but to different extent in different treatments. ASC inhibited bacterial growth more effectively than the other sanitizers and also maintained the lowest pathogen counts (<1 log CFU/g) during storage. Organic matter in the process water significantly (P ⩽ 0.05) reduced the antibacterial efficacy of Cl, but not that of PA or ASC. Therefore, ASC shows the potential to be used as a commercial sanitizer for washing shredded carrots.     

The bactericidal activity of acidic electrolyzed oxidizing water against Escherichia coli O157:H7, Salmonella Typhimurium,and Listeria monocytogenes on raw fish,chicken and beef surfaces

The bactericidal efficacy of acidic electrolyzed oxidizing water (AC-EW) (pH = 2.30, free chlorine = 38 ppm) and sterile distilled water (DW) on three pathogens (Escherichia coli O157:H7 Salmonella Typhimurium, and Listeria monocytogenes) inoculated on raw trout skin, chicken legs and beef meat surfaces was evaluated. The decontaminating effect of AC-EW and DW was tested for 0 (control), 1, 3, 5 and 10 min at 22 °C. AC-EW significantly (P < 0.05) reduced the three pathogens in the inoculated samples compared to the control and DW. The level of reduction ranged between ca.1.5–1.6 logs for E. coli O157:H7 and S. Typhimurium in the inoculated foods. However, AC-EW exhibited less bactericidal effect against L. monocytogenes (1.1–1.3 logs reduction). AC-EW elicited about 1.6–2.0 log reduction in the total mesophilic count. Similar treatment with DW reduced pathogens load by ca. 0.2–1.0 log reduction and total mesophiles by ca. 0.5–0.7 logs. No complete elimination of the three pathogens was obtained using AC-EW possibly because of the level of organic matter and blood moving from food samples to the AC-EW solution. This study demonstrates that AC-EW could considerably reduce common foodborne pathogens in fish, chicken and beef products.     

Incidence of Listeria monocytogenes and Escherichia coli O157:H7 in two Kasar Cheese processing environments

This study was designed to determine the presences of two environmental pathogens in two dairy factories in Sakarya, Turkey. A total of 264 environmental samples, raw milk and cheese samples were taken at four different seasons. According to the results, Listeria monocytogenes or Escherichia coli O157:H7 was isolated from 26 or 2.7% of the samples collected from both factories, respectively. None of the cheese or curd samples were found to be positive for Listeria or E. coli O157:H7. However, 50% of raw milk samples contained Listeria innocua. Listeria was mostly isolated from the swap samples taken from the drains or the floors in processing or packaging areas. However, E. coli was also isolated from the swap samples taken from the workers’ hands and gloves as well as the drains and the floor. Only one raw milk sample contained E. coli O157:H7. A higher prevalence of both pathogens was observed in the summer months than in the other months.     

Efficacy of aqueous chlorine dioxide and fumaric acid for inactivating pre-existing microorganisms and Escherichia coli O157:H7, Salmonella typhimurium,and Listeria monocytogenes on broccoli sprouts

The combined effect of aqueous chlorine dioxide (ClO₂) and fumaric acid as a chemical treatment to inactivate pre-existing microorganisms was evaluated using broccoli sprouts. Broccoli sprouts were treated with distilled water, 50 ppm ClO₂, 0.5% fumaric acid, and a combination of 0.5% fumaric acid and 50 ppm ClO₂. Treatment with 50 ppm ClO₂ and 0.5% fumaric acid reduced the initial populations of total aerobic bacteria, yeasts and molds, and coliforms in broccoli sprouts by 2.70, 2.46, and 1.71 log CFU/g, respectively. In addition, the combined treatment of 50 ppm ClO₂ and 0.5% fumaric acid reduced the initial populations of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes inoculated on broccoli sprouts by 2.39, 2.74, and 2.65 log CFU/g, respectively, compared to the control. These results suggest that the combination of aqueous ClO₂ and fumaric acid can be useful as a hurdle for extending the shelf life of broccoli sprouts during storage.     

Simultaneous detection of Escherichia coli O175:H7, Salmonella spp., and Listeria monocytogenes by multiplex PCR

The wide application of nucleic acid amplification techniques and the increasing industrial interest toward rapid methods has led to the development and application of PCR based methods for the detection of microbial pathogens in food. In the present paper we describe the development of a multiplex PCR method for simultaneous detection of Salmonella enterica serovar Typhimurium, Listeria monocytogenes and Escherichia coli O157:H7 in a complex food matrix (liquid whole egg).Four different DNA extraction procedures were evaluated for their application on food and, among these, Chelex resin combined with a DNA purification step were found to better perform on the food system considered.A multiplex PCR system was developed, based on the evaluation and combination of published primer sets, and applied to the simultaneous detection of the target pathogens plus an internal amplification control, both in culture media and in a model food system.The overall system proposed, based on an overnight enrichment step followed by DNA isolation and multiplex PCR, was satisfactorily tested for its specificity and sensitivity and allowed the detection of the presence of bacterial DNA and the identification of the target pathogens down to 10 cells/25 g liquid whole egg.     

Survival of Escherichia coli O157:H7 and Listeria monocytogenes during kimchi fermentation supplemented with raw pork meat

Kimchi, a traditional Korean food, is fermented by lactic acid producing bacteria. Among the many types of kimchi, soongchimchae is a typical type of kimchi that combines fermented vegetables and meat. We aimed to investigate the survival of Escherichia coli O157:H7 and Listeria monocytogenes during the fermentation of kimchi supplemented with pork meat. Regardless of whether it was assessed in cabbage kimchi or radish kimchi, in which pH levels differ, the population of E. coli O157:H7 gradually decreased during the fermentation at 4 °C and was no longer detected in cabbage samples after 14 post-fermentation days (PFDs). The pH of cabbage kimchi and radish kimchi were 5.8 and 6.0, respectively, at 0 PFDs, changing to 3.9 and 4.1 at 15 PFDs. Although the population of L. monocytogenes gradually decreased, L. monocytogenes did not survive in cabbage kimchi or radish kimchi after 15 PFDs. Compared with radish kimchi, the pH of cabbage kimchi dropped rapidly during the early fermentation period and reached a pH of 3.9 at 15 PFDs. We observed that pH changes during fermentation were associated with a reduction in foodborne bacterial pathogens. Antimicrobial factors and inhibitory mechanisms against foodborne bacteria need to be investigated in the different types of kimchi.     

Effect of combined ozone and organic acid treatment for control of Escherichia coli O157:H7 and Listeria monocytogenes on enoki mushroom

This study evaluated the effects of ozonated water (1, 3, and 5 ppm) alone with different exposure times (0.5, 1, 3, or 5 min), and combinations of 3 ppm ozone with 1% organic acids (acetic, citric, or lactic acids) during 5-min exposure for control of Escherichia coli O157:H7 and Listeria monocytogenes on enoki mushroom and to observe the regrowth of these pathogenic bacteria on treated enoki mushroom during storage for 10 days at 15 °C. Results showed that ozone treatment gave less than 1.0- and 0.5-log count reductions on E. coli O157:H7 and L. monocytogenes, respectively. Efficacy was improved with combined 3 ppm ozone and 1% citric acid treatment, resulting in 2.26- and 1.32-log count reductions, respectively. During storage at 15 °C (10 days) after combined treatment and packaging, populations of E. coli O157:H7 and L. monocytogenes increased to more than 8.0 log cfu/g, indicating that the combined treatment did not have a residual antimicrobial effect during storage. Although the storage study did not show control of these pathogens, the combined ozone–organic acid treatment was more effective than individual treatments in reducing initial population levels of these pathogens on enoki mushroom.     

Effects of lactic acid and lauricidin on the survival of Listeria monocytogenes,Salmonella enteritidis and Escherichia coli O157:H7 in chicken breast stored at 4 °C

Lauricidin and lactic acid were evaluated for their effects on growth and survival of Listeria monocytogenes (L55), Salmonella enteritidis (S552) and Escherichia coli O157:H7 (E19) inoculated onto raw chicken breast. Fresh, raw chicken breasts were purchased immediately after slaughter and transported on ice to the laboratory within 20 min. Each chicken breast was decontaminated by briefly dipping in 70% ethanol and passed through a flame of a Bunsen burner and then allowed to cool. The decontaminated Chicken breast was dipped in TSB broth, at room temperature (25 °C) for 15 min, containing approximately log 9 CFU/ml of L. monocytogenes, S. enteritidis or E. coli O157:H7. Initial counts of L. monocytogenes, S. enteritidis or E. coli O157:H7 counts in chicken breast immediately after dipping in TSB broth were in the range of log 7–log 8 CFU/g. After inoculation, the chicken breasts were kept at room temperature for 20 min to allow attachment. Each inoculated chicken breast (25 °C) was dipped in 0 (control – sterile water), 0.5%, 1%, 1.5% or 2% of lauricidin (w/v) or lactic acid (v/v) for 10, 20 or 30 min and then individually placed in oxygen-permeable polyethylene bags. Breasts were subjected to microbiological analyses after treatment (day 0) and after storage for 2, 5, 7, 10 and 14 d at 4 °C. Initial counts of L. monocytogenes, S. enteritidis and E. coli O157:H7, in chicken breast treated with lauricidin decreased by 2.90, 1.31 and 2.27 log CFU/g, respectively. Lauricidin was more effective in reducing L. monocytogenes population than S. enteritidis and E. coli O157:H7 population. Dipping chicken breast in lauricidin for 30 min caused a significant reduction of L. monocytogenes, S. enteritidis and E. coli O157:H7 population compared to 10 and 20 min dipping. Initial L. monocytogenes, S. enteritidis and E. coli O157:H7 counts on chicken breast treated with lactic acid decreased by 1.97, 1.71 and 2.59 log CFU/g, respectively. Lactic acid caused a higher reduction in initial S. enteritidis and E. coli O157:H7 counts compared to lauricidin.     

Combined treatment with chlorine dioxide gas,fumaric acid,and ultraviolet-C light for inactivating Escherichia coli O157:H7 and Listeria monocytogenes inoculated on plums

Combined non-thermal treatment with chlorine dioxide (ClO₂) gas, ultraviolet-C (UV-C) light, and fumaric acid was performed to inactivate Listeria monocytogenes and Escherichia coli O157:H7 inoculated on plums. Plums were treated with ClO₂ gas (15 and 30 ppmv), fumaric acid (0.1, 0.3, and 0.5%), and by UV-C irradiation (3, 5, and 10 kJ/m²). The single treatments with 15 or 30 ppmv ClO₂ gas, 0.5% fumaric acid, and 10 kJ/m² UV-C decreased the population of L. monocytogenes by 1.78, 2.00, 1.65, and 1.62 log CFU/g, respectively, and the population of E. coli O157:H7 by 1.73, 1.81, 1.34, and 2.07 log CFU/g, respectively. In addition, combined treatments reduced the populations of the pathogenic bacteria more than each treatment alone. In particular, the combined treatment with ClO₂ gas (30 ppmv) for 20 min, fumaric acid (0.5%), and UV-C (10 kJ/m²) decreased the populations of L. monocytogenes and E. coli O157:H7 by 6.26 and 5.48 log CFU/g, respectively. These results suggest that combined treatment with ClO₂ gas, UV-C light, and fumaric acid may be a useful hurdle technology to enhance the microbiological safety of plums.     

Antimicrobial activity of ascorbic acid alone or in combination with lactic acid on Escherichia coli O157:H7 in laboratory medium and carrot juice

The antimicrobial effects of ascorbic acid alone and in combination with lactic acid, against Escherichia coli O157:H7 in Brain Heart Infusion (BHI) broth and in carrot juice as a food model was investigated. In control samples, E. coli O157:H7 continued to growth from 3.98 ± 0.2 log CFU and reached to 8.88 ± 0.1 log₁₀ CFU after 8 h at 37° C; however, bacterial population was undetectable level in BHI in the presence of 0.4% ascorbic acid and 0.2% lactic acid. In carrot juice, E. coli O157:H7 continue to grow from initial population count of 4.41 ± 0.9 log₁₀ CFU to 8.75 ± 0.07 log₁₀ CFU at 37 °C for 24 h. Similarly, the bacteria population was undetectable when 0.2 or 0.4% ascorbic acid and 0.2% lactic acid applied. Our findings suggest the application of ascorbic acid, in combination with lactic acid, may have potential as preservative to inhibit the growth of E. coli O157:H7 in food.     

Quantification of Salmonella spp., Listeria monocytogenes and Escherichia coli O157:H7 in non-spiked food products and evaluation of real-time PCR as a diagnostic tool in routine food analysis

Escherichia coli O157:H7, Listeria monocytogenes and Salmonella spp. are foodborne pathogens frequently associated with foods such as poultry, ready-to-eat products, fruits and vegetables. PCR-based procedures are rapid, sensitive and accurate; in particular, real-time PCR (qPCR), which besides being an automated high-throughput technique, allows quantification of foodborne pathogens. In the present work, qPCR-based methods were applied for the quantitative detection of E. coli O157:H7, Salmonella spp. and L. monocytogenes in a total of 306 non-spiked food samples in a study carried out in two laboratories simultaneously. qPCR allowed the detection of the three pathogens in around 20% of the analyzed samples for each pathogen. Quantification results revealed the presence of the three pathogens mostly at levels between 10² and 10⁴ cells/g. Besides quantification, the qPCR results (presence/absence) were compared with those of the standard mini-VIDAS system. In order to determine which were the “true” positive samples, conventional PCR was carried out after the corresponding enrichment for each pathogen. These results were considered as the gold standard for further analysis. The statistical analysis of global data recording the presence of E. coli O157:H7 and L. monocytogenes, together with data previously obtained for Salmonella spp., revealed that qPCR outperformed the mini-VIDAS procedures, in terms of both time and accuracy. Thus, these results proved qPCR to be useful as a rapid diagnostic test for the direct detection of pathogens in food, without the need for enrichment steps.     

The effect of pulsed UV light on Escherichia coli O157:H7, Listeria monocytogenes,Salmonella Typhimurium,Staphylococcus aureus and staphylococcal enterotoxin A on sliced fermented salami and its chemical quality

Pulsed UV light (PL) applied at a fluence of 3 J/cm² was effective to reduce Listeria monocytogenes, Escherichia coli 0157:H7, Salmonella Typhimurium and Staphylococcus aureus for 2.24, 2.29, 2.25 and 2.12 log CFU/g on the surface of dry fermented salami. Further increase in the fluence of PL treatment did not increase levels of microbial inactivation. However, the time interval between the contamination and PL treatment was found to have a significant impact on the efficacy of PL treatment and should be kept as short as possible. After initial PL treatment slices of fermented salami were packed in vacuum or in 80%CO₂/20%N₂ modified atmosphere and stored at 4 °C to investigate the effect of PL treatment on protein and lipid oxidation as the shelf life of fermented salami is not usually limited by microbial deterioration, but by chemical and sensory alterations. In this study observed lipid oxidation values for PL treated vacuum and modified atmosphere packed fermented salami slices fall within the acceptable threshold for the rancid odor, except for the sample treated with the highest fluence tested (15 J/cm²), packed in modified atmosphere and kept in cold storage for 9 weeks (1.23 mg MDA/kg). All values were below the threshold for rancid flavor, too. The significant rise in protein oxidation of PL treated fermented salami slices, perceived as 28% increase of carbonyl content compared to untreated samples, was observed only after 9 weeks of cold storage in both vacuum and modified atmosphere packed samples. The results of chemical analysis are in agreement with previously published results of sensory analysis. Current results show the applicability of PL to improve microbial safety of sliced fermented salami that are prone to cross-contamination without affecting quality attributes by lipid and protein oxidation.     

Addition of phytochemical-rich plant extracts mitigate the antimicrobial activity of essential oil/wine mixtures against Escherichia coli O157:H7 but not against Salmonella enterica

Marinades for preparing raw meats for cooking are frequently made of wine and herbs. We simulated several formulations of potential antimicrobial marinades with these components and other food compatible/food derived extracts. Red wine formulations containing essential oils from oregano or thyme, or their primary active components carvacrol and thymol, respectively, and a mixture of plant extract powders from phytochemical-rich apple skin, green tea, and olive, were evaluated for inhibitory activity against the foodborne pathogens Escherichia coli O157:H7 and Salmonella enterica. Red wine alone exhibited low activity, as did the plant extract suspended in the wine. Surprisingly, the high activity of oregano or thyme essential oils in red wine was reduced in E. coli, but not in Salmonella, by addition of the plant extract. This study shows that essential oils in red wine can be an effective antimicrobial in food, however the possibility exists that phytochemicals, added to the treatment solution or natively present in the food itself, could adversely impact the antimicrobial activity and should be addressed with future studies.     

Inhibitory effects of selected plant essential oils on the growth of four pathogenic bacteria: E. coli O157:H7, Salmonella Typhimurium,Staphylococcus aureus and Listeria monocytogenes

Twenty eight essential oils were evaluated for their antibacterial properties, against four pathogenic bacteria (Escherichia coli O157:H7, Listeria monocytogenes 2812 1/2a, Salmonella Typhimurium SL 1344 and Staphylococcus aureus). Essential oils were introduced into Brain Heart Infusion agar (BHI) (15 ml) at a concentration of 0.003%, 0.006%, 0.013%, 0.025%, 0.05%, 0.1%, 0.2%, 0.4% and 0.8% (vol/vol) to determine the minimum inhibitory concentration (MIC) and the maximal tolerated concentration (MTC) for each pathogen evaluated. Results showed that the most active essential oils against bacteria tested were Corydothymus capitatus, Cinnamomum cassia, Origanum heracleoticum, Satureja montana, and Cinnamomum verum (bark). These showed a MIC ⩽ 0.05% (vol/vol) for all bacteria tested. For the MTC, with the exception of S. Typhimurium and L. monocytogenes where a MTC of 0.025% (vol/vol) was observed in presence of Cinnamomum verum and Cinnamomum cassia, respectively, a MTC ⩽ 0.013% (vol/vol) was observed for all other bacteria and the three other most active essential oils. Three oils (Satureja hortensis, Thymus vulgaris carvacroliferum, Origanum compactum) showed a MIC ⩽ 0.1% (vol/vol) for all bacteria tested. Seven oils (Thymus vulgaris thymoliferum, Thymus serpyllum, Thymus satureioides, Cymbopogon martinii, Pimenta dioica, Cinnamomum verum (leaf), Eugenia caryophyllus) showed a lower antimicrobial activity showing a MIC ⩽ 0.4% (vol/vol) against the four bacteria tested. Finally, 13 essential oils were less active showing a MIC value ⩾ 0.8% (vol/vol) against at least one bacterium.     

Antimicrobial effects of modified chitosan based coating containing nanoemulsion of essential oils,modified atmosphere packaging and gamma irradiation against Escherichia coli O157:H7 and Salmonella Typhimurium on green beans

The antibacterial activity of modified chitosan-based coatings containing nanoemulsion of essential oils (EOs), gamma irradiation, modified atmosphere packaging (MAP), alone or in combinations, against Escherichia coli O157:H7 and Salmonella Typhimurium was evaluated on inoculated green bean samples. Firstly, four different nanoemulsions, made of carvacrol, mandarin, bergamot and lemon Eos, respectively, were compared in terms of minimum inhibitory concentration (MIC) against the two bacteria evaluated in vitro using the micro-broth dilution method. Carvacrol nanoemulsion resulted to be the most effective antibacterial agent and was therefore selected to be incorporated into modified chitosan (MC) to form a bioactive coating. Secondly, the radiosensitivity of E. coli and S. Typhimurium to gamma irradiation was evaluated on inoculated green beans after coating deposition and MAP. Results showed that, without MAP, MC-based coating containing carvacrol nanoemulsion significantly increased the radiosensitization of E. coli and S. Typhimurium by 1.32-fold and 1.30-fold, respectively. Remarkably, the use of bioactive coating under MAP caused a synergistic effect with an increase in radiosensitivity by 1.80-fold and 1.89-fold for E. coli and S. Typhimurium, respectively. Thirdly, the antibacterial effects of the antimicrobial coating, gamma irradiation, MAP alone and their combinations were evaluated against these two bacteria during a 13-days storage of green beans at 4 °C. Bioactive coating deposition or gamma irradiation treatment resulted effective in controlling the growth of the two bacteria during the entire shelf-life. Moreover, it was also found that the combined treatment of antimicrobial coating, gamma irradiation and MAP caused the reduction of microbial population to undetectable levels during the whole storage period for E. coli and from day 7 to the end of storage for S. Typhimurium. The obtained results can be interested to food companies aiming to ensure the food safety with a prolonged shelf life.     

Combined treatment with silver ions and organic acid enhances growth-inhibition of Escherichia coli O157:H7

Individual and combined treatment with silver ions and selected organic acids were evaluated for growth-inhibition of Escherichia coli O157:H7. The concentrations of silver ion were 0.1, 0.3, 0.5, and 1.0 ppm and, citric, lactic, maleic, succinic, and tartaric acids (0.05% and 0.1%) were used. The inhibitory effect was measured during the growth of E. coli O157:H7 in LB broth by optical density at 600 nm. For individual treatments, silver ion at all concentrations and organic acids at 0.1% had a stronger inhibitory effect than untreated control and 0.05% organic acid treatments. For combined treatments, 1.0 ppm of silver ion with 0.1% of organic acids had the greatest inhibitory effect on E. coli O157:H7 growth. With different concentrations, combination with 1.0 ppm of silver ion and 0.05% of organic acids showed greater inhibitory effect than combination with 0.3 ppm of silver ion and 0.1% of organic acids. Combined treatment with silver ion and organic acid showed the enhanced inhibitory effect of E. coli O157:H7 compared to individual treatments. The present study indicated that growth-inhibiting effect of combined treatment was dependant on the concentration of silver ion rather than that of organic acid.     

Combined effects of heat,acetic acid,and salt for inactivating Escherichia coli O157:H7 in laboratory media

Heat, acid, and salt have been commonly used to ensure the microbial safety of foods and are often used in combinations in many food products. When combined, they can produce different results, such as additive, synergistic, and antagonistic effects. However, there has been little investigation into the effect of these combination treatments. Therefore, in this study, the effect of combined treatment of heat, acid, and salt was investigated in laboratory media. All possible paired combinations among three factors, heat (55 °C), acid (0.25% acetic acid, [v/v]) and salt (3%, [w/v]) were tested and compared with individual treatments for killing E. coli O157:H7 in laboratory media. When salt was combined with heat, there was no significant difference in reduction of E. coli O157:H7 (additive effect). However, when acid was combined with heat, there was a higher reduction of E. coli O157:H7 (synergistic effect). When salt was combined with acid treatment, salt gave protection against acid treatment (antagonistic effect), thus, there was lower reduction of E. coli O157:H7 in the combined treatment than in the single acid treatment. Depending on the combination of preserving factors, results were different.     

Antimicrobial effect of acidified sodium chlorite,sodium chlorite,sodium hypochlorite,and citric acid on Escherichia coli O157:H7 and natural microflora of fresh-cut cilantro

Fresh-cut cilantro is particularly susceptible to microbial growth and, therefore, use of an effective sanitizer on this product is of great importance. The objective of this study was to evaluate the efficacy of different sanitizing treatments on reducing Escherichia coli O157:H7 populations, aerobic mesophilic bacterial, yeast and mould counts on fresh-cut cilantro. Cut cilantro was treated with sodium hypochlorite (SH) at 0.2 g L^?1 free chlorine and acidified sodium chlorite (ASC) at 0.1, 0.25, 0.5 and 1 g L^?1, along with the components of ASC, i.e., citric acid (CA) at 6 g L^?1 and sodium chlorite (SC) at 1 g L^?1. In the present study, it was found that SH inactivated, at maximum, 1–1.3 log cfu g^?1 of background or pathogenic microflora present on cut cilantro. However, reductions of more than 3 log cfu g^?1 were observed after washing with 1 g L^?1 of ASC. Moreover, when lower concentrations of ASC were used (0.25 and 0.5 g L^?1), microbial populations were reduced by about 2 log cfu g^?1. SC was as effective as ASC at 1 g L^?1 in reducing aerobic mesophilic bacteria and E. coli O157:H7 populations, although it was not as effective as ASC in reducing yeast and mould populations.     

Cloth-based hybridization array system for the identification of Escherichia coli O157:H7

A simple cloth-based hybridization array system (CHAS) utilizing polyester cloth as the solid phase for DNA hybridizations has been adapted as a tool for the identification of presumptive verotoxigenic Escherichia coli O157:H7 colonies isolated from foods by standard culture techniques. Key indicator genes for this organism, rfbO157, fliCH7, vt1 and vt2 (encoding the O and flagellar antigenic determinants and verotoxin genes, respectively) were amplified in a multiplex PCR incorporating digoxigenin-dUTP, followed by hybridization of the amplicons with an array of specific oligonucleotide probes immobilized on polyester cloth, and subsequent immunoenzymatic assay of the bound digoxigenin label. This system includes a simple internal amplification control (IAC) to gauge PCR inhibition based on the incorporation of a primer pair with complementary 3′ ends, resulting in the generation of a unique “primer-dimer” detectable by hybridization with a specific capture probe immobilized on polyester cloth. The CHAS provided sensitive and specific detection of the E. coli O157:H7gene markers, exhibiting the expected patterns of reactivity with a panel of various target and non-target organisms.