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.     

The effects of X-ray radiation on Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri inoculated on whole Roma tomatoes

In the last two decades several foodborne disease outbreaks associated with produce were reported. Tomatoes, in particular, have been associated with several multi-state Salmonella outbreaks. Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on whole Roma tomato surfaces by X-ray at 0.1, 0.5, 0.75, 1.0, and 1.5 kGy was studied. The main purpose of this study was to achieve a 5 log reduction in consistent with the recommendations of the National Advisory Committee on Microbiological Criteria for Foods. Moreover, the effect of X-ray on inherent microflora (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated Roma tomatoes, during storage at ambient temperature (22 °C) for 20 days was also determined. Mixtures of three or two strains of each tested organism was spot inoculated (100 μl) onto the surface of Roma tomatoes (approximately 7–9 log per tomato), separately, and air-dried, followed by treatment with X-ray doses at 22 °C and 55–60% relative humidity. Surviving bacterial populations on tomato surfaces 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). Treatment with X-ray significantly reduced the population of the tested pathogens on whole Roma tomato surfaces, compared with the control. Approximately 4.2, 2.3, 3.7 and 3.6 log CFU reduction of E. coli O157:H7, L. monocytogenes, S. enterica and S. flexneri per tomato were achieved by treatment with 0.75 kGy X-ray, respectively. More than a 5 log CFU reduction per tomato was achieved at 1.0 or 1.5 kGy X-ray for all tested pathogens. Furthermore, treatment with X-ray significantly reduced the inherent microflora on Roma tomatoes. Inherent levels were significantly (p < 0.05) lower than the control sample throughout storage for 20 days.     

Comparative efficacy of Zataria multiflora Boiss., Origanum compactum and Eugenia caryophyllus essential oils against E. coli O157:H7, feline calicivirus and endogenous microbiota in commercial baby-leaf salads

Ready-to-eat salads using baby-leaf and multi-leaf mixes are one of the most promising developments in the fresh-cut food industry. There is great interest in developing novel decontamination treatments, which are both safe for consumers and more efficient against foodborne pathogens. In this study, emulsions of essential oils (EOs) from Origanum compactum (oregano), Eugenia caryophyllus (clove), and Zataria multiflora Boiss (zataria) were applied by spray (0.8 ml) after the sanitizing washing step. The aim was to investigate their ability to control the growth of potentially cross-contaminating pathogens and endogenous microbiota in commercial baby leaves, processed in a fresh-cut produce company. Zataria EO emulsions of 3%, 5% and 10% reduced Escherichia coli O157:H7 by 1.7, 2.2 and 3.5 log cfu/g in baby-leaf salads after 5 days of storage at 7 °C. By contrast, reductions in E. coli O157:H7 counts remained the same when clove was applied at concentrations of 5% and 10% (2.5 log cfu/g reduction). Oregano (10%) reduced inoculated E. coli O157:H7 counts in baby-leaf salads by a maximum of 0.5 log cfu/g after 5 days of storage. Zataria showed strong antimicrobial efficacy against E. coli O157:H7 and also against the endogenous microbiota of baby-leaf salads stored for 9 days. Feline calicivirus (FCV), a norovirus surrogate, survived on inoculated baby-leaf salads during refrigerated storage (9 days at 7 °C) regardless of treatment. Refrigeration temperatures completely annulled the effectiveness of the EOs against FCV inoculated in baby-leaf salads as occurred in FCV cultures. This study shows that EOs, and zataria in particular, have great potential use as an additional barrier to reduce contamination-related risks in baby-leaf salads. However, further research should be done into foodborne viruses in order to improve food safety.     

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.     

Effect of selected autochthonous starter cultures on processing and quality characteristics of Greek fermented sausages

Selected autochthonous starter (SAS) cultures (i.e. Lactobacillus sakei 8416, Lactobacillus sakei 4413, and L. sakei 8426, L. plantarum 7423 and L. curvatus 8427) were used as starter cultures in addition to a control treatment in the production of fermented sausages. The SAS cultures had a rapid growth and dominated the fortuitous population of LAB during the whole fermentation and ripening process improving the sensory attributes in comparison to control. Apart from the treatment produced with L. sakei 8416, all other SAS cultures prevented the lipid oxidation to values lower than 1 mg malonaldehyde/kg. The Micrococcaceae count and the redness of the sausages was not affected by the smoking and the acidification during the fermentation in the treatments produced with L. sakei 8416 and L. sakei 4413. The treatment of L. sakei 4413 had the lowest (*P < 0.05) content of all biogenic amines. In comparison to the control, the reduction of tyramine was 13%, tryptamine 55%, cadaverine 60% and putrescine 72%. Sausages produced with SAS cultures L. sakei 4413 and L. sakei 8416 had the highest scores for all sensory attributes. The results indicated that the SAS culture of L. sakei 4413 is the best autochthonous starter culture for fermented sausages.     

Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on fresh-cut celery

Illnesses from Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella have been associated with the consumption of numerous produce items. Little is known about the effect of consumer handling practices on the fate of these pathogens on celery. The objective of this study was to determine pathogen behavior at different temperatures under different storage conditions. Commercial fresh-cut celery was inoculated at ca. 3 log CFU/g onto either freshly cut or outer uncut surfaces and stored in either sealed polyethylene bags or closed containers. Samples were enumerated following storage for 0, 1, 3, 5, and 7 days when held at 4 °C or 12 °C, and after 0, 8, and 17 h, and 1, and 2 days when held at 22 °C. At 4 °C, all populations declined by 0.5–1.0 log CFU/g over 7 days. At 12 °C, E. coli O157:H7 and Salmonella populations did not change, while L. monocytogenes populations increased by ca. 0.5 log CFU/g over 7 days. At 22 °C, E. coli O157:H7, Salmonella, and L. monocytogenes populations increased by ca. 1, 2, or 0.3 log CFU/g, respectively, with the majority of growth occurring during the first 17 h. On occasion, populations on cut surfaces were significantly higher than those on uncut surfaces. Results indicate that populations are reduced under refrigeration, but survive and may grow at elevated temperatures.     

Effects of X-ray radiation on Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri inoculated on shredded iceberg lettuce

The main goal of this investigation was to study the efficacy of X-ray doses (0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 1.5 and 2.0 kGy) on inoculated Escherichia coli O157: H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on shredded iceberg lettuce. The second goal was to study the effect of X-ray on the inherent microflora counts and visual color of shredded iceberg lettuce during storage at 4 °C for 30 days. Treatment with 1.0 kGy X-ray significantly reduced the population of E. coli O157: H7, L. monocytogenes, Salmonella enterica and S. flexneri on shredded iceberg lettuce by 4.4, 4.1, 4.8 and 4.4-log CFU 5 cm⁻², respectively. Furthermore, more than a 5 log CFU reduction of E. coli O157: H7, L. monocytogenes, S. enterica and S. flexneri was achieved with 2.0 kGy X-ray. Treatment with X-ray reduced the initial microflora on iceberg lettuce and kept them significantly (p < 0.05) lower than the control during storage at 4 °C and 90% RH for 30 days. Treatment with X-ray did not significantly (p > 0.05) change the green color of iceberg lettuce leaves. Treatment with X-ray significantly reduced selected pathogens and inherent microorganisms on shredded iceberg lettuce leaves, which could be a good alternative to other technologies for produce (lettuce) industry.     

Resistance of Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter jejuni after exposure to repetitive cycles of mild bactericidal treatments

While maintaining nutritional and sensorial attributes of fresh foods mild processing technologies generally deliver microbiologically perishable food products. Currently little information exists on possible increase in the resistance of pathogens after repetitive exposure to mild (sub-lethal) treatments. Multiple strain-cocktails of Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter jejuni were exposed to 20 consecutive cycles of sub-lethal inactivation by three different techniques. Used techniques comprised inactivation with lactic acid (LA), chlorine dioxide (ClO₂) and intense light pulses (ILP). Results showed that the selection of resistant cells was both species and technique dependent. While repetitive cycles of ClO₂ treatment did not result in increased resistance, repetitive inactivation with LA yielded L. monocytogenes culture of higher resistance in comparison to the parental culture. The increased resistance, expressed as decreased level of reduction in bacterial counts in subsequent inactivation cycles, was also observed with ILP for both L. monocytogenes and E. coli O157:H7 strains. Visual trend observations were confirmed through statistical linear regression analysis. No such effects were noted for C. jejuni which became undetectable after first 2–5 cycles. Current findings indicate the ability of foodborne pathogens to adapt to mild bactericidal treatments creating new challenges in risk assessment and more specifically in hazard analysis.     

Inactivation of Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes in apple juice with gaseous ozone

This research was initiated to assess the efficacy of gaseous ozone for inactivation Escherichia coli O157:H7, Salmonella typhimurium and Listeria monocytogenes in apple juice. Juice samples with solids content of 18, 36, and 72 °Brix inoculated with a culture cocktail of three foodborne pathogens were treated with gaseous ozone at a flow rate of 3.0 L/min and an ozone generation rate of 0.10, 0.90, 3.51, and 5.57 g/h for 0.5, 1, 5, and 10 min, respectively. The inactivation kinetics of gaseous ozone on foodborne pathogens conformed to the Weibull model. The time required to achieve a 5 log reduction (t_5d) was estimated using the parameters of the Weibull model. The t_5d increased with increasing solids content of apple juice. The ozone generation rate did not impart a significant effect (p > 0.05) on t_5d. Gaseous ozone is effective at inactivating foodborne pathogens in apple juice but the efficacy is dependent on the solids content of the juice sample.     

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 Salmonella and Escherichia coli O157:H7 on artificially contaminated alfalfa seeds using high hydrostatic pressure

Alfalfa sprouts contaminated with Salmonella and Escherichia coli O157:H7 have been implicated in several outbreaks of foodborne illnesses in recent years. The seed used for sprouting appears to be the primary source of pathogens. Seed decontamination prior to sprouting presents a unique challenge for the sprouting industry since cells of the pathogenic survivors although undetectable after sanitizing treatments, can potentially multiply back to hazardous levels. The focus of this study was to therefore test the efficacy of high hydrostatic pressure to eliminate a ∼5 log CFU/g load of Salmonella and E. coli O157:H7 on alfalfa seeds. Pressure treatment of 600 MPa for up to 25 min at 20 °C could not result in complete inactivation of Salmonella. High-pressure treatment was then carried out either at sub-ambient (4 °C) or elevated (40, 45 and 50 °C) temperatures to test the ability of high pressure to eliminate Salmonella. Pressure treatment at 4 and 20 °C did not deliver any satisfactory inactivation of Salmonella while high pressure at elevated temperatures achieved complete kill. Pre-soaking seeds prior to high-pressure treatment also enhanced pressure inactivation of Salmonella but at the expense of seed viability. High-pressure treatment of 500 MPa for 2 min at 45 °C was able to eliminate wild-type Salmonella and E. coli O157:H7 strains without bringing about any appreciable decrease in the seed viability.     

Antibacterial effects of natural tenderizing enzymes on different strains of Escherichia coli O157:H7 and Listeria monocytogenes on beef

This study determined the efficacy of actinidin and papain on reducing Listeria monocytogenes and three mixed strains of Escherichia coli O157:H7 populations on beef. The average reduction of E. coli O157:H7 was greater than that of L. monocytogenes and higher concentrations of either protease yielded greater reduction in bacterial populations. For instance, actinidin at 700 mg/ml significantly (p ≤ 0.05) reduced the population of L. monocytogenes by 1.49 log cfu/ml meat rinse after 3 h at 25 & 35 °C, and by 1.45 log cfu/ml rinse after 24 h at 5 °C, while the same actinidin concentration significantly reduced the populations of three mixed strains of E. coli O157:H7 by 1.81 log cfu/ml rinse after 3 h at 25 & 35 °C, and 1.94 log cfu/ml rinse after 24 h at 5 °C. These findings suggest that, in addition to improving the sensory attributes of beef, proteolytic enzymes can enhance meat safety when stored at suitable temperatures.     

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.     

Microbial and chemical origins of the bactericidal activity of thermally treated yellow mustard powder toward Escherichia coli O157:H7 during dry sausage ripening

Work examines the origin of bactericidal activity in mustard flour and explores the relative contribution from starter cultures, E. coli O157:H7 itself and other sources. Bacteria can degrade naturally occurring glucosinolates in mustard and form isothiocyanates with antimicrobial activity. In the present work, 24 starter cultures (mostly from commercial mixtures) were screened for their capacity to decompose the glucosinolate, sinalbin. The most active pair, Pediococcus pentosaceus UM 121P and Staphylococcus carnosus UM 123M, were used together for the production of dry fermented sausage contaminated with E. coli O157:H7 (~ 6.5 log CFU/g). They were compared to industrial starters used previously (P. pentosaceus UM 116P and S. carnosus UM 109M) for their reduction of E. coli O157:H7 viability. Sausage batches containing hot mustard powder (active myrosinase), cold mustard powder (inactivated myrosinase), autoclaved mustard powder (inactivated myrosinase) and no mustard flour (control) were prepared. Interestingly, both pairs of starter cultures yielded similar results. Elimination of E. coli O157:H7 (> 5 log CFU/g) occurred after 31 days in the presence of hot flour and in 38 days when the cold flour was added. Reductions > 5 log CFU/g of the pathogen did not occur (up to 38 days) in the control group. It was found that E. coli O157:H7 itself had a greater effect on sinalbin conversion than either pair of starter cultures, and glucosinolate degradation by the starter cultures was less important in determining E. coli survival. The autoclaved powder caused more rapid bactericidal action against E. coli O157:H7, yielding a > 5 log CFU/g reduction in 18 days. This may have been a result of the formation and/or release of antimicrobial substances by the autoclave treatment. Autoclaved mustard powder could potentially solve an important challenge facing the meat industry as it strives to manufacture safe dry fermented sausages.     

Antibacterial effects of American cranberry (Vaccinium macrocarpon) concentrate on foodborne pathogens

Antibacterial effects of American cranberry (Vaccinium macrocarpon) concentrate on foodborne pathogens, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella Typhimurium, and Staphylococcus aureus in vitro were investigated. Cranberry concentrate at various concentrations was prepared in distilled water (DW) or Brain Heart Infusion (BHI) broth. Pathogens were inoculated in each sample and incubated at 21 and 4 °C for 0, 1, 5, 7, and 24 h (DW samples) and 0, 1, 3, and 5 days (BHI samples). Transmission electron microscopy (TEM) was used to study the effects of cranberry concentrate on cellular structure of pathogens. DW results showed that S. Typhimurium and L. monocytogenes were reduced to non-detectable levels at 5 h in 100 μl/ml treatment at 21 and 4 °C. At 24 h, no target pathogens were detected from the 100 μl/ml treatment. BHI data indicated that the 100 μl/ml treatment reduced the four pathogens by 3-8 log CFU/ml compared with the control on Day 5 at 21 and 4 °C. TEM revealed damage to the bacterial cell walls and membranes. Cranberry concentrate has antibacterial effects on the four foodborne pathogens. Based on potential health benefits and proven antimicrobial effects, American cranberry concentrate may have dual applications as a food preservative.     

Inactivation of Escherichia coli O157:H7 on stainless steel upon exposure to Paenibacillus polymyxa biofilms

We investigated the potential use of biofilm formed by a competitive-exclusion (CE) microorganism to inactivate Escherichia coli O157:H7 on a stainless steel surface. Five microorganisms showing inhibitory activities against E. coli O157:H7 were isolated from vegetable seeds and sprouts. The microorganism with the greatest antimicrobial activity was identified as Paenibacillus polymyxa (strain T5). In tryptic soy broth (TSB), strain T5 reached a higher population at 25 °C than at 12 or 37 °C without losing inhibitory activity against E. coli O157:H7. When P. polymyxa (6 log CFU/mL) was co-cultured with E. coli O157:H7 (2, 3, 4, or 5 log CFU/mL) in TSB at 25 °C, the number of E. coli O157:H7 decreased significantly within 24 h. P. polymyxa formed a biofilm on stainless steel coupons (SSCs) in TSB at 25 °C within 24 h, and cells in biofilms, compared to attached cells without biofilm formation, showed significantly increased resistance to a dry environment (43% relative humidity [RH]). With the exception of an inoculum of 4 log CFU/coupon at 100% RH, upon exposure to biofilm formed by P. polymyxa on SSCs, populations of E. coli O157:H7 (2, 4, or 6 log CFU/coupon) were significantly reduced within 48 h. Most notably, when E. coli O157:H7 at 2 log CFU/coupon was applied to SSCs on which P. polymyxa biofilm had formed, it was inactivated within 1 h, regardless of RH. These results will be useful when developing strategies using biofilms produced by competitive exclusion microorganisms to inactivate foodborne pathogens in food processing environments.     

Multiplex fiber optic biosensor for detection of Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica from ready-to-eat meat samples

Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica are the most common foodborne bacterial pathogens and are responsible for many outbreaks. Therefore, multiplex detection of these three using a single assay platform is highly desirable. The objective was to develop and optimize a fiber optic sensor for simultaneous detection of these three from food. The streptavidin coated optical waveguides were immobilized with biotinylated polyclonal antibodies and exposed to the bacterial suspensions or enriched food samples for 2 h. Pathogens were detected after reacting with Alexa-Fluor 647-labeled monoclonal antibodies. Ready-to-eat beef, chicken and turkey meats were inoculated with each pathogen (∼100 cfu/25 g), enriched in SEL (Salmonella, E. coli, Listeria), a multipathogen selective enrichment broth for 18 h and tested with the biosensor. The biosensor was able to detect each pathogen, individually or in a mixture with very little cross-reactivity. The limit of detection for the sensor was ∼10³ cfu/ml for all three pathogens. Furthermore, the biosensor successfully detected each pathogen, grown in a mixture from enriched meat samples under 24 h. The pathogen presence was further verified by PCR and immunofluorescence assay. The multiplex fiber optic sensor shows promise for detection of the three pathogens if present in the same sample eliminating the use of multiple single pathogen detection platforms.     

Control of foodborne pathogens on fresh-cut fruit by a novel strain of Pseudomonas graminis

The consumption of fresh-cut fruit has substantially risen over the last few years, leading to an increase in the number of outbreaks associated with fruit. Moreover, consumers are currently demanding wholesome, fresh-like, safe foods without added chemicals. As a response, the aim of this study was to determine if the naturally occurring microorganisms on fruit are “competitive with” or “antagonistic to” potentially encountered pathogens. Of the 97 and 107 isolates tested by co-inoculation with Escherichia coli O157:H7, Salmonella and Listeria innocua on fresh-cut apple and peach, respectively, and stored at 20 °C, seven showed a strong antagonistic capacity (more than 1-log unit reduction). One of the isolates, CPA-7, achieved the best reduction values (from 2.8 to 5.9-log units) and was the only isolate able to inhibit E. coli O157:H7 at refrigeration temperatures on both fruits. Therefore, CPA-7 was selected for further assays. Dose-response assays showed that CPA-7 should be present in at least the same amount as the pathogen to adequately reduce the numbers of the pathogen. From the results obtained in in vitro assays, competition seemed to be CPA-7's mode of action against E. coli O157:H7. The CPA-7 strain was identified as Pseudomonas graminis. Thus, the results support the potential use of CPA-7 as a bioprotective agent against foodborne pathogens in minimally processed fruit.     

Synergistic antimicrobial effect of pyrophosphate on Listeria monocytogenes and Escherichia coli O157 in modified atmosphere packaged and refrigerated seabass slices

Effect of pyrophosphate (PP) in combination with modified atmosphere (MAP) (80% CO₂, 10% O₂ and 10% N₂) on the survival of Listeria monocytogenes and Escherichia coli O157 inoculated on seabass slices stored at 4 °C was investigated. PP pretreatment showed the synergistic effect on microbiological inhibition with MAP as evidenced by the lowered TVC and LAB counts, compared with samples stored in air and those kept under MAP. Microbiological changes of seabass slices inoculated with different levels of L. monocytogenes or E.coli O157 (10³ and 10⁵ cfu/g) were monitored during storage. PP pretreatment reduced colony count of E. coli O157 and extended the lag phase of L. monocytogenes. Therefore, MAP in combination with PP pretreatment not only retarded microbiological deterioration of seabass slices but also reduced or inactivated some pathogenic bacteria to some extent.     

Salmonella, Escherichia coli O157:H7 and E. coli biotype 1 in a pilot survey of imported and New Zealand pig meats

A pilot survey for the pathogens Salmonella and Escherichia coli O157:H7, and E. coli biotype 1 was conducted on 100 New Zealand-produced (domestic) pig carcasses and 110 imported pig meat samples over an 8-month period to assess the likelihood of introduction of novel pathogen strains into New Zealand (NZ), and as a guide for development of a domestic pork National Microbiological Database programme. Salmonella was not isolated from domestic pig carcasses or from pig meat imported from Canada and the USA. The prevalence of Salmonella in imported pig meat was 3.6% (95% CI 1.0–9.0) with positive samples detected from Australian pig meat. The prevalence of E. coli O157:H7 on domestic pig carcasses was 1% (95% CI 0.03–5.4) while the overall prevalence of E. coli O157:H7 in imported pig meat was 1.8% (95% CI 0.2–6.4), detected mainly from Australian but not from Canadian or US pork. All except three samples have an E. coli biotype 1 count of <100 CFU cm⁻² or g⁻¹, indicating good hygiene quality of domestic and imported pig meat. The results demonstrated that importation of uncooked pig meat is a potential route for the introduction of new clones of Salmonella and E. coli O157:H7 into New Zealand.