Alterations of the phylloepiphytic bacterial community associated with interactions of Escherichia coli O157:H7 during storage of packaged spinach at refrigeration temperatures

This study investigated the effects of packaging and storage temperature on the spinach phylloepiphytic bacterial community and fate of Escherichia coli O157:H7. Freshly harvested spinach was rinsed and/or disinfected, packaged and stored under typical retail conditions (4 °C) or under temperature abuse conditions (10 °C) for a period of 15 days. The final population size of culturable epiphytic bacteria after 15 days of storage was not affected by the temperature of storage or the presence of E. coli O157:H7. However, analysis of the bacterial community using denaturing gradient gel electrophoresis of 16s rDNA revealed changes with time of storage and the presence of E. coli O157:H7. Excision and sequencing of prominent DGGE bands identified that the majority of sequences belonged to the phyla Actinobacteria, Bacteroidetes, Firmicutes and Alphaprotebacteria. After 10 days of storage at 4 °C or 10 °C the population became more dominated by psychrotrophic bacteria. Removal of the epiphytic bacteria resulted in significant increases in numbers of E coli O157:H7 at 10 °C and was associated with decreased expression of E. coli O157:H7 virulence (stxA, curli, eaeA) and stress response (rpoS, sodB) genes. In conclusion, storage temperature and time of storage of packaged spinach affected the diversity of the epiphytic spinach microbiota which influenced the growth, establishment, physiology and potentially virulence of E. coli O157:H7.     

Detection of 5 CFU/g of Escherichia coli O157:H7 on lettuce using activated charcoal and real-time PCR without enrichment

A sample treatment method which separates Escherichia coli O157:H7 from lettuce and removes PCR inhibitors allowing 5 CFU/g of target cells to be detected using real-time PCR is described. Lettuce leaves inoculated with E. coli O157:H7 were rinsed with 0.025% sodium dodecyl sulfate (SDS). In this study, there were two major factors that strongly affected the recovery of E. coli O157:H7 during sample preparation, the amount of bentonite coated activated charcoal used to remove PCR inhibitors and the agitated contact time of the samples with the coated charcoal. When 3.0 g of activated carbon coated with bentonite were mixed with target cell suspensions (30 ml) derived from 50 g of lettuce, a high recovery of E. coli O157:H7 (93%) was obtained. Sample agitation with bentonite coated activated charcoal for 15 min resulted in 95% recovery of E. coli O157:H7. When a commercial DNA purification resin was used for detection of E. coli O157:H7 without the use of the bentonite treated charcoal, the real-time PCR (Rti-PCR) failed to detect 1 × 10² CFU/g. In contrast, with the use of use of bentonite coated activated charcoal and a commercial DNA purifying resin together, Rti-PCR was able to detect 5 CFU of E. coli O157:H7/g of lettuce which was equivalent to 2.8 CFU/Rti-PCR. Such a successful detection level was the result of the bentonite coated activated charcoal’s ability to absorb the PCR inhibitors released from seeded lettuce during detachment. A standard curve was generated by plotting the Ct values against the log of CFU of target bacterial cells. A linear range of DNA amplification was exhibited from 5.0 × 10⁰ to 1.0 × 10⁴ CFU/g by using Rti-PCR.     

Transcriptional and functional responses of Escherichia coli O157:H7 growing in the lettuce rhizoplane

Lettuce and spinach are increasingly implicated in foodborne illness outbreaks due to contamination by Escherichia coli O157:H7. While this bacterium has been shown to colonize and survive on lettuce leaf surfaces, little is known about its interaction with the roots of growing lettuce plants. In these studies, a microarray analyses, mutant construction and confocal microscopy were used to gain an understanding of structure and function of bacterial genes involved in the colonization and growth of E. coli O157:H7 on lettuce roots. After three days of interaction with lettuce roots, 94 and 109 E. coli O157:H7 genes were significantly up- and down-regulated at least 1.5 fold, respectively. While genes involved in biofilm modulation (ycfR and ybiM) were significantly up-regulated, 40 of 109 (37%) of genes involved in protein synthesis were significantly repressed. E. coli O157:H7 was 2 logs less efficient in lettuce root colonization than was E. coli K12. We also unambiguously showed that a ΔycfR mutant of E. coli O157:H7 was unable to attach to or colonize lettuce roots. Taken together these results indicate that bacterial genes involved in attachment and biofilm formation are likely important for contamination of lettuce plants with Shiga toxin-producing E. coli strains.     

Inhibition of polymerase chain reaction for the detection of Escherichia coli O157:H7 and Salmonella enterica on walnut kernels

The aim of this study was to determine whether Escherichia coli O157:H7 can be reliably detected and isolated from walnut kernels using standard methods of analysis. The limit of detection approached 1 cell per analytical unit (25 g) for E. coli O157:H7 on walnut kernels enriched in modified tryptic soy broth with 20 μg/ml novobiocin and plating onto selective agar media. The presence of PCR inhibitors in walnut kernels was indicated by the failure to detect E. coli O157:H7 from culture positive enrichment broths analysed by PCR, with two separate polymerase and reagent compositions (Dupont BAX E. coli O157:H7 MP system, Promega GoTaq Green for stx) and three methods of template preparation (DuPont BAX, Qiagen DNeasy, Bio-Rad InstaGene). PCR inhibition was overcome by 1:100 dilution in TE buffer of the DNeasy or InstaGene template. PCR inhibition was not relieved by dilution of the BAX template. Similar results were observed for walnut kernels inoculated with Salmonella enterica and analysed for invA, indicating that PCR inhibition is not specific to the organism or primer/template. These results indicate that analysis of walnut kernels for pathogens should be with culture based methods or use protocols for DNA template preparation modified to remove or dilute inhibitors and the need for internal amplification controls in PCR methods.     

The physiologic state of Escherichia coli O157:H7 does not affect its detection in two commercial real-time PCR-based tests

Multiplex real-time PCR detection of Escherichia coli O157:H7 is an efficient molecular tool with high sensitivity and specificity for meat safety assurance. The Biocontrol GDS^® and DuPont Qualicon BAX^®-RT rapid detection systems are two commercial tests based on real-time PCR amplification with potential applications for quantification of specific E. coli O157:H7 gene targets in enriched meat samples. However, there are arguments surrounding the use of these tests to predict pre-enrichment concentrations of E. coli O157:H7, as well as arguments pertaining to the influence of non-viable cells causing false positive results. The present study attempts to illustrate the effects of different bacterial physiologic states and the presence of non-viable cells on the ability of these systems to accurately measure contamination levels of E. coli O157:H7 in ground beef. While the PCR threshold cycle (C_T) values of these assays showed a direct correlation with the number of bacteria present in pure cultures, this was not the case for ground beef samples spiked with various levels of injured or healthy cells. Furthermore, comparison of post-enrichment cell densities of bacteria did not correlate with injured or healthy cell numbers inoculated before enrichment process. Ground beef samples spiked with injured or healthy cells at different doses could not be distinguished by C_T values from either assay. In addition, the contribution of nonviable cells in generating positive real-time PCR signals was investigated using both assays on pre-enriched and post-enriched beef samples, but only if inoculated at levels of 10⁶ cells/sample or higher, which are levels not typically seen in ground beef.     

Characterization of interactions between Escherichia coli O157:H7 with epiphytic bacteria in vitro and on spinach leaf surfaces

This study characterized the types of interactions between Escherichia coli O157:H7 and spinach phylloepiphytic bacteria and identified those that influence persistence of E. coli O157:H7 on edible plants. A total of 1512 phylloepiphytic bacterial isolates were screened for their ability to inhibit or to enhance the growth of E. coli O157:H7 in vitro and on spinach leaf surfaces. Fifteen different genera, the majority belonging to Firmicutes and Enterobacteriaceae, reduced growth rates of E. coli O157:H7 in vitro by either nutrient competition or acid production. Reduced numbers of E. coli O157:H7 were recovered from detached spinach leaves that were co-inoculated with epiphytic isolates belonging to five genera. A 1.8 log reduction in E. coli O157:H7 was achieved when co-inoculated with Erwinina perscinia and 20% cellobiose, a carbon source used by the phylloepiphytes but not E. coli O157:H7. The reduction on leaves was significantly less than reduction measured in vitro. Phylloepiphytic bacteria belonging to eight different genera, increased numbers of E. coli O157:H7 when co-cultured in vitro on spent medium and when co-cultured on detached spinach leaves. The results, showing reduction of E. coli O157:H7 numbers by natural epiphytic bacteria, support the hypothesis that native plant microbiota can be used for bio-control of foodborne pathogens, however, other epiphytes may promote the persistence of enteric pathogens on the phyllosphere.     

Inactivation of Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on spinach leaves by X-ray

Several recent foodborne disease outbreaks associated with leafy green vegetables, including spinach, have been reported. X-ray is a non-thermal technology that has shown promise for reducing pathogenic and spoilage bacteria on spinach leaves. Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on spinach leaves using X-ray at different doses (0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0 kGy) was studied. The effect of X-ray on color quality and microflora counts (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated spinach was also determined. A mixture of three strains of each tested organism was spot inoculated (100 μl) onto the surface of spinach leaves (approximately 8–9 log ml⁻¹), separately, and air-dried, followed by treatment with X-ray at 22 °C and 55–60% relative humidity. Surviving bacterial populations on spinach leaves were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacteria; E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). More than a 5 log CFU reduction/leaf was achieved with 2.0 kGy X-ray for all tested pathogens. Furthermore, treatment with X-ray significantly reduced the initial inherent microflora on spinach leaves and inherent levels were significantly (p < 0.05) lower than the control sample throughout refrigerated storage for 30 days. Treatment with X-ray did not significantly affect the color of spinach leaves, even when the maximum dose (2.0 kGy) was used.     

Efficacy of washing with hydrogen peroxide followed by aerosolized antimicrobials as a novel sanitizing process to inactivate Escherichia coli O157:H7 on baby spinach

Aerosolization was investigated as a potential way to apply allyl isothiocyanate (AIT), hydrogen peroxide (H₂O₂), acetic acid (AA) and lactic acid (LA) on fresh baby spinach to control Escherichia coli O157:H7 during refrigeration storage. In this study, baby spinach leaves were dip-inoculated with E. coli O157:H7 to a level of 6 log CFU/g and stored at 4 °C for 24 h before treatment. Antimicrobials were atomized into fog-like micro-particles by an ultrasonic nebulizer and routed into a jar and a scale-up model system where samples were treated. Samples were stored at 4 °C for up to 10 days before the survival of the cells was determined. A 2-min treatment with 5% AIT resulted in a > 5-log reduction of E. coli O157:H7 on spinach after 2 days refrigeration regardless if the samples were pre-washed or not; however, this treatment impaired the sensory quality of leaves. Addition of LA to AIT improved the antimicrobial efficacy of AIT. In the jar system, washing with 3% H₂O₂ followed by a 2-min treatment of 2.5% LA + 1% AIT or 2.5% LA + 2% AIT reduced E. coli O157:H7 population by 4.7 and > 5 log CFU/g, respectively, after 10 days refrigeration. In the scale-up system, up to 4-log reduction of bacterial population was achieved for the same treatments without causing noticeable adverse effect on the appearance of leaves. Thus, this study demonstrates the potential of aerosolized AIT + LA as a new post-washing intervention strategy to control E. coli O157:H7 on baby spinach during refrigeration storage.     

Comparison of multiple chemical sanitizers for reducing Salmonella and Escherichia coli O157:H7 on spinach (Spinacia oleracea) leaves

Effectiveness of multiple chemical sanitizers on the reduction of Salmonella spp. and Escherichia coli O157:H7 on spinach was compared. Fresh spinach (Spinacia oleracea) was inoculated with a bacterial suspension containing multiple strains of rifampin-resistant Salmonella and E. coli O157:H7. Inoculated spinach leaves were treated with a water wash or water wash followed by 2% L-lactic acid at 55 °C, peroxyacetic acid (80 mg/L), calcium hypochlorite (200 mg/L), ozonated water (mg/L) or ClO₂ gas (1.2 or 2.1 mg/L). The l-lactic acid produced a 2.7 log CFU/g reduction for E. coli O157:H7 and a 2.3 log CFU/g reduction for Salmonella, statistically significant compared to water wash alone (P < 0.05), which resulted in a reduction of 0.7 log CFU/g for both pathogens. These findings indicate that 2% l-lactic acid at 55 °C may be an effective treatment for reducing pathogens on spinach leaves.     

Occurrence of Escherichia coli O157, O111 and O26 in raw ewe's milk and performance of two enrichment broths and two plating media used for its assessment

The occurrence of Escherichia coli O157, O111 and O26 in 159 raw ewe's milk samples was examined. Sample-aliquots were incubated simultaneously in TSB added with yeast extract (YETSB) and mTSB with novobiocin (N-mTSB). Serogroup-specific immunomagnetic separation (IMS) was then used and IMS beads were plated in a cefixime tellurite (CT)-containing media (CT-SMAC, CT-SBMAC and CT-RMAC for E. coli O157, O111 and O26, respectively) and E. coli O157:H7 chromogenic ID agar. A sweep of confluent growth from each medium was examined for the presence of E. coli O157 and O111 using PCR, and for E. coli O26 using a latex agglutination test. Enumeration of E. coli O157 and O111 was performed in the samples tested positive for the correspondent serogroup using the most probable number (MPN) method combined with PCR. Percentage occurrences of E. coli O157, O111 and O26 were 18.2, 8.2 and 5.7, respectively. Mean E. coli O157 and O111 levels were 0.22 and < 0.04 MPN/mL, respectively. Enrichment in YETSB resulted in higher detection rates of E. coli O157 and O26 than in N-mTSB. When YETSB was used as enrichment broth and for these last two serogroups, the analysis of the confluent growth from the CT-media gave more positive results than that from E. coli O157:H7-ID medium.     

Lactic acid resistance of Shiga toxin-producing Escherichia coli and multidrug-resistant and susceptible Salmonella Typhimurium and Salmonella Newport in meat homogenate

This study compared lactic acid resistance of individual strains of wild-type and rifampicin-resistant non-O157 Shiga toxin-producing Escherichia coli (STEC) and of susceptible and multidrug-resistant (MDR) and/or MDR with acquired ampC gene (MDR-AmpC) Salmonella against E. coli O157:H7. After inoculation of sterile 10% beef homogenate, lactic acid was added to a target concentration of 5%. Before acid addition (control), after acid addition (within 2 s, i.e. time-0), and 2, 4, 6 and 8 min after addition of acid, aliquots were removed, neutralized, and analyzed for survivors. Of wild-type and of rifampicin-resistant non-O157 STEC strains, irrespective of serogroup, 85.7% (30 out of 35 strains) and 82.9% (29 out of 35 strains), respectively, reached the detection limit within 0–6 min. Of Salmonella strains, 87.9% (29 out of 33 isolates) reached the detection limit within 0–4 min, irrespective of antibiotic resistance phenotype. Analysis of non-log-linear microbial survivor curves indicated that non-O157 STEC serogroups and MDR and susceptible Salmonella strains required less time for 4D-reduction compared to E. coli O157:H7. Overall, for nearly all strains and time intervals, individual strains of wild-type and rifampicin-resistant non-O157 STEC and Salmonella were less (P < 0.05) acid tolerant than E. coli O157:H7.     

Production of biofilm and quorum sensing by Escherichia coli O157:H7 and its transfer from contact surfaces to meat,poultry, ready-to-eat deli,and produce products

Multistate outbreaks of Escherichia coli O157:H7 infections through consumption of contaminated foods including produce products have brought a great safety concern. The objectives of this study were to determine the effect of biofilm and quorum sensing production on the attachment of E. coli O157:H7 on food contact surfaces and to evaluate the transfer of the pathogen from the food contact to various food products. E. coli O157:H7 produced maximum levels of AI-2 signals in 12 h of incubation in tested meat, poultry, and produce broths and subsequently formed strong biofilm in 24 h of incubation. In general, E. coli O157:H7 formed stronger biofilm on stainless steel than glass. Furthermore, E. coli O157:H7 that had attached on the surface of stainless steel was able to transfer to meat, poultry, ready-to-eat deli, and produce products. Strong attachment of the transferred pathogen on produce products (cantaloupe, lettuce, carrot, and spinach) was detected (>10³ CFU/cm²) even after washing these products with water. Our findings suggest that biofilm formation by E. coli O157:H7 on food contact surfaces can be a concern for efficient control of the pathogen particularly in produce products that require no heating or cooking prior to consumption.     

Survival of Escherichia coli O157:H7 in channel catfish pond and holding tank water

Survival of Escherichia coli O157:H7 in channel catfish (Ictalurus punctatus), pond and holding tank water was investigated. Water from three channel catfish ponds was inoculated with ampicillin/nalidixic acid-resistant E. coli O157:H7 transformed with a plasmid encoding for green fluorescent protein at 10⁵, 10⁶, and 10⁷ CFU/ml. Samples were taken from surface, internal organs, and skin scrape of fish and pond water for E. coli O157:H7 enumeration on brain heart infusion (BHI) agar containing ampicillin and nalidixic acid. To determine the survival of E. coli O157:H7 in catfish holding tank water from two farmers markets, the water was inoculated with 10⁷E. coli O157:H7 CFU/ml. E. coli O157:H7 were detected by direct plating for 33 and 69 d in pond and holding tank water, respectively. A rapid decrease of the pathogen was observed in the first 2 weeks to reach 2 log CFU/ml. When E. coli O157:H7 was not recovered by direct plating, the pathogen was isolated by enrichment in TSB for approximately another 30 d from pond and holding tank water. The populations of E. coli O157:H7 found in the internal organs and skin scrape were 5.5 log and 2.5 log CFU/ml, respectively. E. coli O157:H7 from internal organs and water were recovered for at least 12 d. Results suggest that E. coli O157:H7 can survive in channel catfish pond and holding tank water and channel catfish may become a potential carrier of the pathogen.     

Antibacterial activity of oregano and thyme essential oils against Listeria monocytogenes and Escherichia coli O157:H7 in feta cheese packaged under modified atmosphere

The antibacterial activity of the essential oils (EO) of oregano and thyme added at doses of 0.1 or 0.2 and 0.1 ml/100 g, respectively, to feta cheese inoculated with Escherichia coli O157:H7 or Listeria monocytogenes was investigated during cheese storage under modified atmosphere packaging (MAP) of 50% CO₂ and 50% N₂ at 4 °C. Compositional analysis showed that the predominant phenols were carvacrol and thymol for both EO. In control feta inoculated with the pathogens and stored under MAP, results showed that E. coli O157:H7 and L. monocytogenes strains survived up to 32 and 28 days of storage. However, in feta cheese treated with oregano EO at the dose of 0.1 ml/100 g, E. coli O157:H7 or L. monocytogenes survived up to 22 and 18 days, respectively, whereas at the dose of 0.2 ml/100 g up to16 or 14 days, respectively. Feta cheese treated with thyme EO at 0.1 ml/100 g showed populations of E. coli O157:H7 or L. monocytogenes not significantly different (P > 0.05) than those of feta cheese treated with oregano at 0.1 ml/100 g. Although both essential oils exhibited equal antibacterial activity against both pathogens, the populations of L. monocytogenes decreased faster (P < 0.05) than those of E. coli O157:H7 during the refrigerated storage, indicating a stronger antibacterial activity of both essential oils against the former pathogen.     

Prevalence and characterization of Escherichia coli O157:H7 isolates from meat and meat products sold in Amathole District,Eastern Cape Province of South Africa

Meat and meat products have been implicated in outbreaks of Escherichia coli O157:H7 in most parts of the world. In the Amathole District Municipality of the Eastern Cape Province of South Africa, a large number of households consume meat and meat products daily, although the microbiological quality of these types of food is questionable. The present study investigated the prevalence of E. coli O157:H7 isolated from selected meat and meat products (45 samples each of biltong, cold meat, mincemeat, and polony) sold in this area. Strains of E. coli O157:H7 were isolated by enrichment culture and confirmed by polymerase chain reaction (PCR). Also investigated were the antibiogram profiles of the E. coli O157:H7 isolates. Five (2.8%) out of 180 meat and meat products examined were positive for E. coli O157:H7 that carried the fliC_H7, rfbE_O157, and eaeA genes. Two of the E. coli O157:H7 isolates were resistant against all the eight antibiotics tested. To prevent E. coli O157:H7 infections, meat and meat products such as biltong, cold meat, mincemeat and polony should be properly handled, and packed in sterile polyvinyl wrappers.     

Survey of Listeria monocytogenes, Salmonella spp. and Escherichia coli O157:H7 in raw ingredients and ready-to-eat products by commercial real-time PCR kits

Real-time PCR (RTiPCR) assays including enrichment stage were evaluated for the rapid detection of Listeria monocytogenes, Salmonella spp. and Escherichia coli O157:H7 in raw ingredients and ready-to-eat products using molecular beacon probes available as commercial kits (WARNEX Genevision, Canada & AES Chemunex detection system, France). The accuracy of the assays was evaluated analyzing 1032 naturally contaminated food samples in combination to the conventional cultural methods. Presence/absence testing of the above pathogens was performed in 25 g samples of each product. In case of L. monocytogenes of 39 positive RTiPCR samples, 37 were confirmed by the cultural method (based on McNemar's test the difference between the two methods is insignificant). The highest incidence of L. monocytogenes in food products was found in desserts and the second highest in frozen pastries. None of the samples were cultural positive but negative in the RTiPCR test. One among the 343 investigated samples was positive for Salmonella spp. by RTiPCR and the cultural method. Out of 333 samples analyzed for E. coli O157:H7 no positive sample was detected. RTiPCR-based methods proved to be powerful tools for fast, sensitive and accurate pathogen detection in raw food ingredients and ready-to-eat products.     

Reduction of Escherichia coli O157:H7 viability on leafy green vegetables by treatment with a bacteriophage mixture and trans-cinnamaldehyde

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 has been recognized as a major foodborne pathogen responsible for frequent gastroenteritis outbreaks. Phages and essential oils can be used as a natural antimicrobial method to reduce bacterial pathogens from the food supply. The objective of this study was to determine the effect of a bacteriophage cocktail, BEC8, alone and in combination with the essential oil trans-cinnameldehyde (TC) on the viability of a mixture of EHEC O157:H7 strains applied on whole baby romaine lettuce and baby spinach leaves. The EHEC O157:H7 strains used were Nal^R mutants of EK27, ATCC 43895, and 472. Exponentially growing cells from tryptic soy (TS) broth cultures were spot inoculated on leaves and dried. EHEC cells were placed at low, medium, and high inoculum levels (10⁴, 10⁵, and 10⁶ CFU/mL, respectively). Appropriate controls, BEC8 (approx. 10⁶ PFU/leaf), and TC (0.5% v/v) were applied on treated leaves. The leaves were incubated at 4, 8, 23, and 37 °C in Petri dishes with moistened filter papers. EHEC survival was determined using standard plate count on nalidixic acid (50 μg/mL) Sorbitol MacConkey agar. No survivors were detected when both leaves were treated with BEC8 or TC individually at low inoculum levels after 24 h at 23 and 37 °C. When the EHEC inoculum size increased and/or incubation temperature decreased, the efficacy of BEC8 and TC decreased. However, when the two treatments were combined, no survivors were detected after 10 min at all temperatures and inoculum levels on both leafy greens. These results indicated that the BEC8/TC combination was highly effective against EHEC on both leafy greens. This combination could potentially be used as an antimicrobial to inactivate EHEC O157:H7 and reduce their incidence in the food chain.     

Monitoring of Escherichia coli O157:H7 in food samples using lectin based surface plasmon resonance biosensor

A novel surface plasmon resonance (SPR) biosensor using lectin as bioreceptor was developed for the rapid detection of Escherichia coli (E. coli) O157:H7. The selective interaction of lectins with carbohydrate components from bacterial cells surface was used as the recognition principle for the detection. Five types of lectins from Triticum vulgaris, Canavailia ensiformis, Ulex europaeus, Arachis hypogaea, and Maackia amurensis, were employed to evaluate the selectivity of the approach for binding E. coli O157:H7 effectively. A detection limit of 3 × 10³ cfu mL^?1 was obtained for determination of E. coli O157:H7 when used the lectin from T. vulgaris as the binding molecule. Furthermore, the proposed biosensor was used to detect E. coli O157:H7 in real food samples. Results showed that the lectin based SPR biosensor was sensitive, reliable and effective for detection of E. coli O157:H7, which hold a great promise in food safety analysis.     

Detection of Escherichia coli via VOC profiling using secondary electrospray ionization-mass spectrometry (SESI-MS)

Escherichia coli O157:H7 (EC O157:H7), as well as its recently emerging non-O157 relatives, are a notorious group of pathogenic bacteria associated with foodborne outbreaks. In this study, we demonstrated that secondary electrospray ionization mass spectrometry (SESI-MS) could be a rapid and accurate detection technology for foodborne pathogens. With SESI-MS volatile organic compound (VOC) profiling, we were able to detect and separate a group of eleven E. coli strains from two major foodborne bacteria, Staphylococcus aureus and Salmonella Typhimurium in three food modeling media. In addition, heatmap analysis of relative peak intensity show that there are six core peaks (m/z of 65, 91, 92, 117, 118 and 119) present and at a similar intensity in all eleven E. coli strains at the experimental conditions we tested. These peaks can be considered conserved VOC biomarkers for E. coli species (robustly produced after just 4 h of growth). Bacterial strain-level differentiation was also attempted via VOC profiling, and we found that EC O157:H7 and EC O145 were differentiable from all other EC strains under the conditions investigated.     

Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes in milk by caprylic acid and monocaprylin

Listeria monocytogenes and Escherichia coli O157:H7 are major foodborne pathogens implicated in various outbreaks involving pasteurized or unpasteurized milk, and various dairy products. The objective of this study was to determine the antibacterial effect of caprylic acid (CA, C_8:0) and its monoglyceride, monocaprylin (MC) on L. monocytogenes and E. coli O157:H7 in whole milk. A five-strain mixture of E. coli O157:H7 or L. monocytogenes was inoculated in autoclaved milk (10⁶ CFU/ml) containing 0, 25, or 50 mM of CA or MC. At 37°C, all the treatments, excepting 25 mm CA, reduced the population of both pathogens by approximately 5.0 log CFU/ml in 6 h. At 24 h of storage at 8°C, MC at both levels and CA at 50 mM decreased L. monocytogenes and E. coli O157:H7, respectively by >5.0 log CFU/ml. At 48 h of 4°C storage, populations of L. monocytogenes and E. coli O157:H7 were decreased to below detection level (enrichment negative) by 50 mm of MC and CA, respectively. Results indicate that MC could potentially be used to inhibit L. monocytogenes and E. coli O157:H7 in milk and dairy products, but sensory studies need to be conducted before recommending their use.