Growth and biofilm formation by Listeria monocytogenes in cantaloupe flesh and peel extracts on four food-contact surfaces at 22 °C and 10 °C

The nationwide listeriosis outbreak that occurred in the United States during 2011 highlighted the importance of preventing cantaloupe contamination with Listeria monocytogenes (Lm) within farm and processing environments. The objectives of this study were to determine the effects of strain and temperature on growth and biofilm formation of Lm in cantaloupe flesh and peel extracts on different food-contact surfaces. Growth of Lm strains was markedly greater at high concentration of cantaloupe extracts and temperature in comparison to low concentration and temperature. For 50 mg/ml of cantaloupe extract inoculated with 3 log CFU/ml, the growth of Lm was 8.5 log CFU/ml in 32 h at 22 °C and 6–7 log CFU/ml in 72 h at 10 °C. For 2 mg/ml of cantaloupe extract that was inoculated with Lm, the growth was 7–7.5 log CFU/ml in 72 h at 22 °C and 3.5 log CFU/ml in 72 h at 10 °C. There were no differences (P > 0.05) among Lm strains for biofilm formation in cantaloupe extracts, but biofilm formation was greater at high temperature and high concentration. For 50 mg/ml cantaloupe extracts inoculated with 3 log CFU/ml, the biofilm formation of Lm on stainless steel surface was approximately 7 log CFU/coupon at 22 °C in 4–7 days and 5–6 log CFU/coupon at 10 °C in 7 days. For 2 mg/ml cantaloupe extracts, the biofilm formation of Lm on the stainless-steel surface was approximately 5–6 log CFU/coupon at 22 °C and 4–4.5 log CFU/coupon at 10 °C in 7 days. The biofilm formation by cantaloupe outbreak strain Lm 2011L-2625 in cantaloupe extracts was least on buna-n rubber when compared to stainless steel, polyethylene and polyurethane surfaces (P < 0.05). These findings show that a very low concentration of nutrients from cantaloupe flesh or peel can induce Lm growth and subsequent biofilm formation on different food-contact processing surfaces.     

Comparison of effects of mild heat combined with lactic acid on Shiga toxin producing Escherichia coli O157:H7, O103, O111, O145 and O26 inoculated to spinach and soybean sprout

The aim of the present study was to investigate the effect of lactic acid against Shiga toxin producing Escherichia coli (O157:H7 and non-O157 serogroups including O103, O111, O145 and O26) at different conditions. Soybean sprouts and spinach leaves inoculated with each serogroup of E. coli (∼7.00 + 1.00 log₁₀ cfu/g) were treated with the lactic acid solutions at different concentrations (0% (control), 1.5%, 2.0%, or 2.5%) and at different temperatures (20, 40, or 50 °C) for 3 min. Results indicated that regardless of the treatment temperature, no significant reduction in the numbers of any serogroup occurred in the control group (0%) (p > 0.05). However, lactic acid at concentration of 1.5%, 2% and 2.5% was found to be effective against all organisms tested. There was no significant difference (p > 0.05) between E. coli O157:H7 and non-O157 STEC serogroups at any treatment group. The highest reductions (ca. 4.00 log₁₀ cfu/g) of all serotypes in both produces were observed after immersing into 2.5% lactic acid at 50 °C. The results of this study showed that decontamination of fresh produces such as spinach and soybean sprout with lactic acid solutions prepared at mild temperatures (40 °C and 50 °C) might be an effective safety measure in preventing public health risks associated with these products contaminated with STEC.     

Quality attributes and thermal inactivation of Shiga toxin-producing Escherichia coli in moisture enhanced,non-intact beef products are affected by pump rate,internal temperature,and resting time after cooking

Escherichia coli O157:H7 (ECOH) and non-O157-Shiga toxin-producing E. coli (STEC) may move from the surface of beef to the internal tissue during non-intact moisture enhancement processes. Little is known about the thermal inactivation of ECOH and non-O157-STEC in moisture-enhanced, non-intact beef. Our study evaluated the pump rate, internal temperature, resting time to inactivate ECOH and non-O157-STEC, and the resulting quality attributes of non-intact beef. Fresh 1 kg coarse-ground beef knuckles, inoculated with ECOH or a six-strain mixture of non-O157-STEC, were mixed with sodium chloride and sodium tripolyphosphate solutions to reach a 10 or 18% pump rate. The semi-frozen beef was cut, vacuum-packaged, frozen, and tempered before double pan-broiling to internal temperatures of 55, 60, 65, or 71.1 °C with 0.5 or 3.5 min rest. We analyzed pathogen survival on tryptic soy agar, MacConkey agar, and sorbitol MacConkey agar plus sodium pyruvate (0.1%). We also monitored color changes in the raw and cooked beef. We analyzed our data (two replicates of three samples each) using the Mixed Model Procedure of SAS including independent variables and interactions. ECOH and non-O157-STEC respond similarly (P = 0.518) to thermal treatments. Cooked internal temperatures of 65 and 71.1 °C achieved higher reductions in the pathogen (4.76–5.21 log CFU/g) compared to temperatures of 55 and 60 °C (2.43–3.53 log CFU/g) regardless of the pump rate and resting time (P = 0.001). A 3.5 min resting time (P = 0.007) or 18% pump rate (P = 0.008) achieved an additional 0.5 log CFU/g reduction among the various internal temperatures. The beef maintained a similar internal color regardless of the pump rate or cooked internal temperatures. These findings will be useful for the U.S. Department of Agriculture, Food Safety and Inspection Service to develop risk assessments for ECOH and non-O157-STEC on non-intact beef.     

Inhibitory effect of Cinnamomum cassia oil on non-O157 Shiga toxin-producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) have caused numerous foodborne outbreaks. Compared with the most well-known STEC E. coli O157:H7, importance of non-O157 STEC has been underestimated and they have gained far less attention till increasing outbreaks recently. Using natural plant materials as antimicrobial agents is a heated area. Therefore in this study, Cinnamomum cassia, a widely used spice in cuisine, was tested for its antibacterial efficacy on CDC “top six” non-O157 STECs including O26, O45, O103, O111, O121, O145. Gas chromatography-mass spectrometry analysis showed that the major component of C. cassia oil was cinnamaldehyde (59.96%). The disk diffusion assay indicated that 20 μL 4% (v/v) C. cassia oil per disk resulted in inhibition zones of 15.0 mm, 18.5 mm, 15.7 mm, 19.3 mm, 18.8 mm, and 25.3 mm for O26:H11, O45:NM, O103:H2, O111:H2, O121:H19, and O145:NT, respectively. Minimum inhibitory concentration for all tested non-O157 STECs were 0.025% (v/v). Minimum bactericidal concentration was strain dependent, which was 0.05% (v/v) for O26:H11, O121:H19, O145:NT, while 0.1% (v/v) for O45:NM, O103:H2 and O111:H2. Growth kinetics showed that at the low inoculation of approximate 2.5 × 10⁵ CFU/mL, C. cassia oil at the concentration of 0.01875% (v/v) completely inhibited the growth of O26:H11 and O145:NT for at least 24 h, and increased the duration of lag phase of O45:NM, O103:H2, O111:H2, O121:H19 by18, 12, 6, and 16 h, respectively. Including 0.025% (v/v) C. cassia oil completely inhibited the growth of all tested non-O157 STECs for at least 24 h. At high inoculation of 5 × 10⁶ CFU/mL, inhibition effect of C. cassia oil decreased. Death curve showed that including as low as 0.05% (v/v) C. cassia oil could kill non-O157 STECs. 0.1% (v/v) C. cassia oil showed bactericidal effects on all tested non-O157 STECs within 15 min. C. cassia oil at the concentration of 0.15% (v/v) killed all O26:H11, O121:H19 and O145:NT within 30 min, while O45:NM, O103:H2 and O111:H2 at 120, 60, and 60 min, respectively. In conclusion, C. cassia oil can effectively inhibit the growth of non-O157 STECs at concentration as low as 0.025% (v/v). Our data suggest that C. cassia oil has the potential to be used as a natural antibacterial agent in food industry.     

Inactivation of Shiga toxin-producing and nonpathogenic Escherichia coli in non-intact steaks cooked in a radio frequency oven

This study evaluated the thermal inactivation of Shiga toxin-producing Escherichia coli (O157:H7, O26:H11 and O111) (STEC) and non-pathogenic E. coli in non-intact beefsteaks (NIBS) cooked by radio frequency (RF). Blade tenderized steaks were inoculated with nalidixic (Nal) acid resistant E. coli strains, vacuum packaged in thermal pouches and cooked using pre-determined cooking times to 60 °C (rare) or 65 °C (medium-rare) inside a RF oven. Log reduction ranged from 0.99, 3.08, 2.85 and 5.0 for O157:H7, O26:H11, O111 and non-pathogenic E. coli respectively at 60 °C and a 5.0 log reduction at 65 °C for all strains. Non-pathogenic E. coli strains selected for the present study did not behave similar to the pathogenic strains being significantly more sensitive; therefore, they were not considered for testing at 63 °C. A second part of the study focused on the extent of thermal inactivation of STEC when NIBS were cooked to 63 °C (minimum safe cooking temperature recommended by USDA-FSIS). There was a 5.0 log reduction for E. coli O157:H7 and E. coli O111; but not for E. coli O26:H11. The results indicated that cooking steaks to 65 °C with a holding time at room temperature of 5 min before refrigeration would be enough to reduce numbers of E. coli O157:H7, O26:H11 and O111 using RF. The cooking protocol developed on the present study, has a practical relevance for the industry since the experiments were carried on a pilot-scale RF oven and also pathogens were tested under realistic processing conditions.     

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.     

Pulsed electric field inactivation of E. coli O157:H7 and non-pathogenic surrogate E. coli in strawberry juice as influenced by sodium benzoate,potassium sorbate,and citric acid

Current FDA regulations require that juice processors achieve a 5 log CFU/ml reduction of a target pathogen prior to distributing products. Whereas thermal pasteurization reduces the sensory characteristics of juice, pulsed electric field (PEF) treatments can be conducted at lower temperatures and may preserve sensory characteristics.Escherichia coli O157:H7 (ATCC 43895) and a non-pathogenic E. coli (ATCC 35218), respectively, were inoculated into single-strength strawberry juice with or without 750 ppm sodium benzoate (SB), 350 ppm potassium sorbate (PS), and 2.7% citric acid (CA). Juice was treated at outlet temperatures of 45, 50 and 55 °C at a field strength of 18.6 kV/cm for 150 μs with a laboratory-scale PEF unit. Inactivation of surrogate E. coli at 45, 50, and 55 °C were 2.86, 3.12, and 3.79 log CFU/ml, respectively, in plain juice (pH 3.4), and 2.75, 3.52, and 5.11 with the addition of benzoic and sorbic acids (pH 3.5). Inactivation of E. coli O157:H7 under the same conditions were 3.09, 4.08, and 4.71 log CFU/ml, respectively, and 2.27, 3.29, and 5.40 with antimicrobials. E. coli O157:H7 in juice with antimicrobials and 2.7% CA (pH 2.7) treated with PEF was reduced by 2.60, 4.32 and 6.95 log CFU/ml at 45, 50 and 55 °C while the surrogate E. coli decreased by 3.54, 5.69, and 7.13 log under the same conditions. When juice (pH 2.7) was held for 6 h without PEF treatment, higher numbers of E. coli 35218 (7.17 log CFU/ml) were inactivated than of acid-resistant E. coli O157:H7 (3.89 log). Slightly greater PEF inactivation of E. coli O157:H7 than of the surrogate bacterium indicates that E. coli ATCC 35218 provides a margin of safety when used as a surrogate for O157:H7 in plain strawberry juice or in juice + SB + PS at 45–50 °C, or with SB + PS and CA at 55 °C.     

Effect of organic acids,hydrogen peroxide and mild heat on inactivation of Escherichia coli O157:H7 on baby spinach

Minimally processed baby spinach contaminated with Escherichia coli O157:H7 has been associated with multiple outbreaks of foodborne illnesses recently. Chlorinated water is widely used to wash vegetables commercially, but this washing procedure has limited efficacy and can lead to the formation of carcinogenic substances. This study was conducted to determine the effects of organic acids and hydrogen peroxide alone and in binary combinations with or without mild heat (40 and 50 °C) on the inactivation of Escherichia coli O157:H7 on baby spinach. 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. Individual washing solutions (1% and 2% lactic acid [LA], citric acid [CA], malic acid [MA], tartaric acid [TA], acetic acid [AA], hydrogen peroxide [H₂O₂] as well as binary combinations of LA, CA, MA and H₂O₂ at final concentrations of 1% were used to decontaminate spinach leaves at 22, 40 or 50 °C for 2–5 min to test their efficacy in reducing E. coli O157:H7. Chlorinated water (200 ppm free chlorine) decreased the population of E. coli O157:H7 on baby spinach by only 1.2–1.6 log CFU/g, which was not significantly different from DI water washing. Washing with 1% LA at 40 °C for 5 min was the most effective treatment achieving a 2.7 log reduction of E. coli O157:H7 which is significantly higher than chlorine washing. Washing with LA + CA or LA + HP at 40 °C for 5 min was equally effective against E. coli O157:H7, resulting in a 2.7 log reduction of E. coli O157:H7. The application of mild heat significantly enhanced the efficacy of washing solutions on the inactivation of E. coli O157:H7. There was, however, no significant difference between treatments at 40 °C for 5 min and 50 °C for 2 min. The results suggested that the use of organic acids in combination with mild heat can be a potential intervention to control E. coli O157:H7 on spinach.     

The influence of acid stress on the growth of Listeria monocytogenes and Escherichia coli O157:H7 on cooked ham

Acid solutions are increasingly being used for decontaminating meat surfaces. On the surfaces of acid-treated meat, the population of microorganism is reduced due to the low pH of acids, and the subsequent growth of the microorganism is reduced due to the residual acids on meat surfaces. Microbial cells on meat surfaces subjected to acid treatments may cross-contaminate untreated meat surfaces, e.g., microorganisms on the surfaces of acid-treated cooked ham cross contaminate the untreated surfaces during slicing. The objective of this study was to examine this scenario in determining the subsequent growth of acid-treated Listeria monocytogenes and Escherichia coli O157:H7 on the surfaces of untreated meat. Cells of multiple-strain L. monocytogenes or E. coli O157:H7 were exposed to HCl solutions of pH 3, 4, or 5 and deionized water at room temperature for 24 h. The acid or deionized water-treated cells were inoculated separately onto cooked ham. Samples inoculated with L. monocytogenes were stored at 4 and 8 °C and samples inoculated with E. coli O157:H7 were stored at 10 and 12 °C. Populations of the pathogens on ham were enumerated during storage, and the lag phase durations (LPD, h) and growth rates (GR, log CFU/h) of the pathogens were determined. The populations of L. monocytogenes and E. coli O157:H7 in pH 5, 4, and 3 solutions were 1.2–3.1 and 0.6–2.4 log CFU/ml, respectively, lower than those in deionized water, indicating an increased acid stress on both microorganisms at lower pHs. L. monocytogenes subjected to pH 3 and pH 4 stresses and E. coli O157:H7 subjected to pH 3 stress exhibited significantly (p < 0.05) extended LPDs and reduced GRs on cooked ham. The growth of L. monocytogenes on ham was more readily reduced by acid stress than that of E. coli O157:H7. This study showed that acid treatments reduced the viability of L. monocytogenes and E. coli O157:H7and the acid stress reduced their subsequent growth ability on untreated ham. Therefore, cross-contamination of L. monocytogenes or E. coli O157:H7 cells from acid-treated meat surfaces onto untreated meat surfaces may not impose increased risk to the product.     

Inactivation of Escherichia coli O157:H7 in vitro and on the surface of spinach leaves by biobased antimicrobial surfactants

This study was conducted to evaluate the effect of biosurfactants on the populations of Escherichia coli O157:H7 in suspension and on spinach leaves. Eight surfactants including four soybean oil-based biosurfactants, sodium dodecyl sulfate (SDS), polyoxyethylene sorbitan monooleate (Tween 80), sophorolipid (SO) and thiamine dilauryl sulfate (TDS) at concentrations of 0.1%, 0.5% and 1.0% were tested in bacterial suspension, and the most effective biosurfactants were applied on spinach leaves. Results showed that the soybean oil-based biosurfactants, SDS or Tween 80 did not significantly affect E. coli O157:H7 populations. SO and TDS at concentrations of 1.0% were effective in reducing E. coli O157:H7 populations in bacterial suspension. E. coli O157:H7 with an initial population of 7.1 log CFU/mL was not detectable (detection limit: 1 log CFU/mL) after 1 min in 1.0% TDS or after 2 h in 1.0% SO. On spinach leaves, SO at 1% did not significantly affect E. coli when compared to a water wash during 7 days post-treatment storage at 4 °C. However, TDS (1.0%) wash was as effective as 200 ppm chlorine in reducing population of spot inoculated E. coli O157:H7, achieving 3.1 and 2.7 log CFU/per leaf at day 0, and 1.4 and 1.9 log CFU/leaf at day 7 when compared with a water wash. No apparent change in spinach visual quality was observed. None of treatments caused changes in visual quality of spinach. Electron micrographs suggested ultrastructural damage of bacterial cells such as separation of the outer membrane from the cytoplasmic membrane. Overall, our results showed that SO and TDS may be potential sanitizers in inactivating human pathogens such as E. coli O157:H7 in wash water and on fresh produce.     

Evaluation of chlorine,benzalkonium chloride and lactic acid as sanitizers for reducing Escherichia coli O157:H7 and Yersinia enterocolitica on fresh vegetables

The effectiveness in the assurance of fresh vegetable microbiological quality of wash solutions containing 200 ppm free chlorine, 0.1 mg/ml benzalkonium chloride, 0.2% and 1% lactic acid was assessed on Escherichia coli O157:H7 and Yersinia enterocolitica contaminated lettuce and tomatoes. Y. enterocolitica reduction on tomatoes (5.08, 4.77 and 4.21 log after 0.2% lactic acid, 200 ppm chlorine and 0.1 mg/ml benzalkonium chloride treatments, respectively) were significantly higher than those for Y. enterocolitica on lettuce and E. coli O157:H7 on both vegetables. Antimicrobial treatment effects on bacterial counts and product quality after subsequent 7 day storage (4 °C and 22 °C) were determined. No pathogens were found in natural microflora of fresh vegetables.     

Molecular screening and characterization of Shiga toxin-producing Escherichia coli in retail foods

Shiga toxin-producing Escherichia coli (STEC) strains are one of the most important recently emerged groups of food borne pathogens. This study investigated the prevalence of molecular markers for STEC and characteristics of E. coli O157 isolates from foods sold at retail markets in Wuhan, China. A total of 489 samples (350 meat products and 139 raw vegetables) were purchased from 22 large scale markets between July of 2011 and September of 2013. The meat samples consisted of frozen chicken products, raw pork, raw beef, frozen fish products and processed duck products. The raw vegetable samples consisted of lettuce, bok choy, radish, spinach, cucumber, and tomato. Shiga toxin genes (stx1 and stx2) and an O-group marker of the seven main pathogenic STEC serogroups (O157, O26, O45, O103, O111, O121, and O145) were detected in the samples by using PCR. 100% agreement was obtained between the results of the PCR targeting for wzy_O157 and the PCR targeting for rfbE_O157 gene. The result demonstrated that PCR assay targeting for wzy_O157 gene can be employed as an effective screening method for E. coli O157 in food sample. In the study, E. coli O157 and non-O157 STEC were detected in 55 (11.2%) and 75 (15.3%) samples by PCR screening, respectively. There was significant difference in the occurrence of STEC contamination between supermarkets (19/127, 15.0%) and open markets (111/362, 30.7%) (P < 0.05). Out of 489 samples, 5 samples carried O45, 1 sample carried O145 and 1 sample carried O111. Markers for O103, O26 and O121 were not detected. This result differed from other reports. Immunomagnetic separation based cultivation technique was used to isolate E. coli O157 from 27 food samples collected in 2013. Finally 7 E. coli O157 isolates were obtained. Among the 7 isolates, the prevalent stx genotype was stx_1a and stx_2a. Four E. coli O157 strains exhibited toxic effects on Vero cells, while 3 isolates had no detectable cytotoxicity effects even though they contained stx genes. All E. coli O157 isolates were sensitive to the 12 antimicrobials tested except for roxithromycin. There are some inconsistencies between the PCR screening and culture results. Characteristics of STEC isolates should be evaluated and considered for monitoring STEC contamination in foods.     

Occurrence,serotypes and virulence genes of non-O157 Shiga toxin-producing Escherichia coli in fresh beef,ground beef,and beef burger

This study determined the prevalence, serotypes and virulence genes distribution of non-O157 Shiga toxin-producing Escherichia coli in meat products collected from butchers shops and supermarkets in Mansoura city, Egypt. We have characterized 18 non-O157 STEC strains among the identified 100 E. coli isolates recovered from the examined 87 meat product samples. The prevalence of non-O157 STEC strains in fresh beef, ground beef and beef burger samples were 11.1% (3/27), 16.7% (5/30), and 33.3% (10/30), respectively. The eighteen non-O157 STEC isolated strains were serotyped into seven (38.9%) O111:H8, six (33.3%) O26:H11, two (11.1%) O111:H–, and one (5.56%) for each of O55:H7, O126:H5 and O128:H2. PCR assays for different virulence genes showed that nine (50%), eleven (61.1%), and nine (50%) strains carry stx1, stx2, and eae genes, respectively. The distribution of shiga toxin genes among the isolated strains indicated that seven (38.9%) strains harbored stx1 only, nine (50%) strains harbored stx2 only, and two (11.1%) strains harbored both stx1 and stx2. The eae gene was present in association with five (27.8%), three (16.7%), and one (5.6%) strains that harbored stx1 only, stx2 only, and both stx1 and stx2, respectively. This study concluded that the examined meat products, particularly beef burger, consumed in Egypt are considerably contaminated with a variety of non-O157 STEC serotypes, and hence consumption of such products may constitute a potential health risk for consumers.     

Effects of UV-C treatment on inactivation of Salmonella enterica and Escherichia coli O157:H7 on grape tomato surface and stem scars,microbial loads,and quality

The purpose of this study was to investigate the effectiveness of ultraviolet-C (UV-C) light inactivation as affected by the location of pathogens on the surface and at stem scars of whole grape tomatoes. A mixed bacterial cocktail containing a three strain mixture of Escherichia coli O157:H7 (C9490, E02128 and F00475) and a three serotype mixture of Salmonella enterica (S. Montevideo G4639, S. Newport H1275, and S. Stanley H0558) were used. Tomatoes were spot inoculated using approximately 100 μL of inocula to achieve a population of about 10^7±1 CFU/tomato. Additionally, the effects of treatment on color, texture, lycopene content, and background microbial loads during post UV-C storage at 4 °C for 21 days were determined. Results showed that UV-C doses of 0.60–6.0 kJ/m² resulted in 2.3–3.5 log CFU per fruit reduction of E. coli O157:H7 compared to 2.15–3.1 log CFU per fruit reduction for Salmonella on the surfaces. Under the same conditions, log reductions achieved at stem scar were 1.7–3.2 logs CFU for E. coli O157:H7 and 1.9–2.8 logs CFU for Salmonella. The treatment was effective in controlling native microbial loads during storage at 4 °C as the total aerobic mesophilic organisms (PCA) and anaerobic lactic acid bacteria (LAB) counts of treated tomatoes were significantly (p < 0.05) lower during storage compared to the control group and the yeast and mold populations were reduced significantly below the detection limit. Furthermore, the firmness of tomato and its color was not affected by the UV-C doses during storage. UV-C radiation could potentially be used for sanitizing fresh tomatoes and extending shelf-life. The results of this study indicate that the specific location of pathogens on the produce influences the effectiveness of UV-C treatment, which should be taken into consideration for the design of UV-C systems for produce sanitization.     

Reuterin,lactoperoxidase, lactoferrin and high hydrostatic pressure on the inactivation of food-borne pathogens in cooked ham

The antimicrobial effect of high hydrostatic pressure (HHP) processing combined with reuterin, lactoperoxydase system (LPS) and lactoferrin (LF) on the survival of Listeria monocytogenes, Salmonella enterica subsp. enterica serovar Enteritidis and Escherichia coli O157:H7 in sliced cooked ham stored under strict refrigeration temperature (4 °C) and mild temperature abuse conditions (10 °C) was investigated. One day after treatment, L. monocytogenes counts in HHP at 450 MPa for 5 min were 0.8 log units lower, but a recovery was observed with counts not significantly different to those observed in control after 35 d. S. Enteritidis and E. coli O157:H7 levels were reduced around 5 log cfu/g by the pressure treatment (450 MPa/5 min) and the numbers of these pathogens did not increase significantly during the 35 d of storage at 4 °C. The individual application of reuterin and LPS influenced the survival of the three pathogens studied, extending the lag phase of L. monocytogenes and diminishing S. Enteritidis and E. coli levels throughout storage, whereas no effect was recorded when LF was added. When reuterin or LPS were applied in combination with HHP there was a synergistic antimicrobial effect against L. monocytogenes, avoiding at 4 °C the recovery observed with individual treatments. These combined treatments also kept the levels of S. Enteritidis and E. coli O157:H7 below the detection limit (<1 log unit) in cooked ham stored at 4 and 10 °C during 35 d. The results obtained in the present work suggest that HHP at 450 MPa for 5 min in combination with LPS or reuterin would be useful as a hurdle technology approach against L. monocytogenes, S. Enteritidis and E. coli O157:H7 in cooked ham.     

Quantitative study of cross-contamination with Escherichia coli,E. coli O157, MS2 phage and murine norovirus in a simulated fresh-cut lettuce wash process

The water management in fresh-cut produce processing is an important factor affecting the microbial quality and safety of fresh-cut produce. For this study, a commercial lettuce washing process was simulated using two subsequent washing baths (WB). The worst case scenario, when no sanitizers are used and still common in some European countries, was investigated to fully understand the potential for cross-contamination and to obtain baseline data for further risk assessment. The two cross-contamination processes (from lettuce to water and from water to lettuce) were included in the simulation study and the transfer of Escherichia coli, E. coli O157, MS2 phage and murine norovirus was quantified. The mean reduction of initially contaminated lettuce through the washing in two successive WB was limited: 0.3 ± 0.1 log CFU E. coli/g after washing in WB1 and an additional reduction of 0.2 ± 0.1 log after WB2. The microbial load of the water in the washing baths, initially starting off with potable water, increased rapidly during the washing process of the contaminated lettuce. Furthermore to quantify the transfer of the four implicated micro-organisms from contaminated water to the lettuce, the first washing bath was inoculated with either approximately 3.0, 4.0 and 5.0 log CFU E. coli/100 ml or 4.8, 5.6 or 6.7 log CFU E. coli O157/100 ml, 4.0, 5.1 or 6.5 log PFU MS2 phages/100 ml or 6.5 log PFU/100 ml norovirus surrogate MNV-1. The contamination of the subsequently washed lettuce portions resulted in levels of ca. 1.0 up to 1.9 log CFU E. coli/g after passing the two washing steps. In addition, after a rapid initial increase, due to spill over of water from WB 1 to WB2, the contamination of WB2 further augmented during the washing process to approximately 1.0 to 0.5 log below the inoculation level of WB1. Transfer of E. coli O157, MS2 phages or MNV-1 from the water to the lettuce was respectively 0.9% ± 0.3%, 0.5% ± 0.2% and 0.5 ± 0.1% after WB1 and resulted in a contamination level for the highest inoculum level of WB1 of respectively ca. 2.9 ± 0.1 log CFU/g, 3.7 ± 0.1 log PFU/g and 4.4 ± 0.1 log PFU/g lettuce. The quantitative data of lettuce contamination and transfers established in this study further highlight the vulnerability of fresh produce to cross-contamination during the washing stage and stresses that notwithstanding the use of initial potable water and partial refreshment of water but without the use of sanitizers, microbial pathogens (or indicator organisms) may easily be introduced and reside for prolonged periods in washing baths enabling cross-contamination to the final fresh-cut product.     

Thermal inactivation and growth of Listeria monocytogenes during production and storage of caramel apples

During the fall of 2014, commercially produced pre-packaged caramel apples were linked to 35 cases of listeriosis in 12 states. In response, this study aimed to assess 1) the reduction of different outbreak and non-outbreak strains of Listeria monocytogenes during caramel dipping of apples, and 2) subsequent growth of the apple outbreak strains within caramel apples during storage at 22 and 4 °C. In aim 1, three unwaxed Jonathan apples were dip-inoculated with three different 4-strain L. monocytogenes cocktails (apple outbreak, unrelated outbreak or unrelated environmental) at ∼8 log CFU/apple, dried for 1 h, dipped for 5 s in caramel at 82, 88, 93 or 99 °C, cooled for 1 h at room temperature and assessed for survivors. In aim 2, Jonathan apples were spot-inoculated with the apple outbreak cocktail (∼3 log CFU/apple) at the stem juncture, dried for 1 h, pushed onto wooden sticks, and dipped in caramel at 82 °C. During storage at 4 and 22 °C for 28 and 14 days, respectively, four different apple sections (top, middle, bottom and core) were cut from three apples, homogenized and plated for Listeria. After dipping apples in caramel at 82 and 99 °C, the apple outbreak, unrelated outbreak and environmental Listeria strains decreased 2.0 ± 0.6 and 2.7 ± 0.1, 1.8 ± 0.3 and 2.6 + 0.1, and 1.7 ± 0.1 and 2.9 ± 0.2 logs, respectively, with the environmental cocktail significantly less heat resistant (P < 0.05) at 99 °C compared to the other two cocktails. After 14 days of storage at 22 °C, Listeria populations were significantly higher (P < 0.05) in the core (7.4 ± 0.6 log CFU/g) compared to the other three sections (4.9–5.4 log CFU/g). The same trend was seen for the core (7.7 ± 0.6 log CFU/g) and the other three sections (5.0–5.4 log CFU/g) after 28 days of storage at 4 °C. Since dipping in hot caramel cannot ensure pathogen elimination, producers of caramel apples should implement good agricultural practices, post-harvest preventive controls and refrigeration of the final product to minimize the risks from Listeria.     

Adherence of cold-adapted Escherichia coli O157:H7 to stainless steel and glass surfaces

The effects of previous cold-induced cell elongation on adherence of Escherichia coli O157:H7 to glass slides and stainless steel surfaces was evaluated at 4 °C for ≤48 h. Planktonic E. coli O157:H7 with and without cold adaptation were prepared at 15 and 37 °C, respectively, and planktonic E. coli O157:H7 containing elongated (>4 ≤ 10 μm) and filamentous (>10 μm) cells were prepared at 6 °C. Despite morphological differences in planktonic E. coli O157:H7 preparations, all three cell types attached to a greater extent to glass than to the stainless steel surfaces. E. coli O157:H7 cells adapted to growth at 15 °C attached better to both glass and stainless steel surfaces (3.2 and 2.6 log cfu/cm², respectively) than cells of the other treatments at ≥24 h. Cells adapted at 6 °C attached to glass slides and stainless steel coupons at levels of 3.0 and 1.8 log cfu/cm², respectively, while E. coli O157:H7 cells grown at 37 °C attached to these surfaces at levels of 2.0 and 1.7 log cfu/cm², respectively. No further attachment of cells from any of the treatments was noted between 24 and 48 h at 4 °C. These results suggest that E. coli O157:H7 cells adapted at 6 °C–15 °C have greater potential to attach to food contact surfaces than those grown at higher temperature. The enhanced biofilm-forming ability of 6 °C or 15 °C-adapted, elongated and filamentous E. coli O157:H7 cells did not appear to be related to the greater entanglement of longer cells within biofilm matrices.     

Evaluation of a novel antimicrobial solution and its potential for control Escherichia coli O157:H7, non-O157:H7 shiga toxin-producing E. coli,Salmonella spp., and Listeria monocytogenes on beef

The goal of this study was to evaluate the efficacy of a novel antimicrobial solution made with chitosan, lauric arginate ester, and organic acids on Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, and non-O157 shiga toxin-producing E. coli cocktails and to test its potential to be used as a marinade for raw beef. Fresh beef top round steaks were surface-inoculated with the pathogen cocktails at approximately 2.5 or 4.5 Log CFU/cm², marinated with the antimicrobial solution (AMS), and then stored at 4 °C for 6, 24, and 48 h. Three commercially available marinades were used for comparison. Results revealed that AMS had the most antimicrobial effect regardless of the type or inoculation level of pathogens (P < 0.05). After 6 h, the AMS marination reduced all pathogens to levels below the limit of detection (<1 Log CFU/cm²), resulting in a 3.5 Log CFU/cm² reduction. When AMS was diluted with autoclaved distilled water by 5 times (AMS 1:5) or 10 times (AMS 1:10), its antimicrobial efficacy was impacted by marination time, the inoculated pathogens, and the inoculation levels. This study demonstrates that the developed antimicrobial solution has a great potential to be used during marination by consumers to ensure better food safety.