Quantifying the reduction in potential infection risks from non-O157 Shiga toxin producing Escherichia coli in strawberries by low dose electron beam processing

Strawberries are vulnerable to harboring microbial pathogens because they are generally not washed due to their perishable nature. The focus of this study was to quantify the reduction in infection risks associated with non-O157 Shiga toxin producing Escherichia coli serotypes contaminated strawberries if the strawberries are exposed to low doses ∼1 kGy (kiloGray) of electron beam (eBeam) irradiation. A cocktail of six serotypes of non O157 E. coli namely, O26:H11, O45:H2, O103:H2, O111:NM, O121:H19, and O145 was employed. Strawberry puree rather than whole strawberries were used in this study to ensure dose uniformity that is critical for accurate interpretation of microbial reduction. The results show that when these serotypes are exposed to ≤1 kGy eBeam dose, there is approximately 4-log reduction in their numbers when they are present within a strawberry matrix (puree). Quantitative microbial risk assessments suggest that if a typical strawberry serving (150 g) was heavily contaminated (∼10⁵ CFU/serving size), 2 out of 10 susceptible individuals (20%) would get sick (without eBeam treatment). However, if these contaminated strawberries had been treated with 1 kGy of eBeam dose, the infection risks would have be significantly reduced to approximately 4 out of every 100,000 individuals (0.004%). Similarly, even at low levels of contamination (∼10² CFU/serving), the infection risks would be reduced from 6 out of 10,000 susceptible individuals to approximately 4 out of 100 million susceptible individuals.     

Growth characteristics of Shiga toxin-producing Escherichia coli (STEC) stressed by chlorine,sodium chloride,acid, and starvation on lettuce and cantaloupe

Shiga toxin-producing Escherichia coli (STEC) is a major foodborne pathogen causing serious illnesses and hospitalizations in the United States. Bacteria that are exposed to environmental stresses during food processing may exhibit different growth patterns in the subsequent growth environment. The purpose of this study was to examine the effect of environmental stresses on the growth of O15H and non-O157 STEC in lettuce or cantaloupe. Strains of O157:H7 and non-O157 STEC (O26:H11, O103:H1, O104:H4, and O145:NM) were subjected to four selected stresses including 2 ppm of chlorine, a_w of 0.97 (osmotic stress), and pH 5 (acid stress) at 22 °C for 24 h, or starvation (lack of nutrients) at 22 °C for 15 d. A cocktail mix of stressed or non-stressed (control) O157 or non-O157 at 3 log CFU/g (control or stressed) was inoculated on lettuce or cantaloupe and incubated at 10 and 22 °C for four weeks. While there were significant differences (p < 0.05) in the growth of stressed and unstressed cells of non-O157 STEC, no difference was observed in the growth of stressed and unstressed O157 STEC cells. Osmotic-stressed non-O157 STEC had significantly higher cell populations than control with 2 log difference (9.0 vs. 6.8 log CFU/g) at 10 °C on lettuce and 1 log difference (9.3 vs. 8.3 log CFU/g) at 22 °C on cantaloupe after 4 weeks. Acid-stressed non-O157 STEC had significantly higher cell populations than control at 10 °C after 4 weeks with >1 log difference (7.7 vs. 6.3 log CFU/ml) on cantaloupe. Starvation-stressed non-O157 STEC showed significantly higher cell populations than control with 1 log difference (8.4 vs. 7.2 log CFU/g) at 22 °C on cantaloupe after 4 weeks. The results indicated that osmotic, acid, or starvation stress may enhance the growth of non-O157 STEC on lettuce or cantaloupe and lead to a greater safety risk.     

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.     

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.     

Antimicrobial efficacy of cinnamon oil against Salmonella in almond based matrices

Reduced moisture enhances resistance of Salmonella and subsequently reduces the antimicrobial efficacy of thermal treatment. Alternative and supplementary non-thermal intervention methods are urgently needed. In this study, Cinnamonum cassia oil was tested for its antimicrobial effect against outbreak strains Salmonella Enteritidis PT30 and S. Tennessee K4643. Minimal inhibitory concentration and minimal bactericidal concentration for both strains were 0.05% (v/v) and 0.1% (v/v), respectively. Death curves showed that including 0.1% and 0.15% (v/v) C. cassia oil resulted in ∼7 Log reduction of bacteria within 2 h and 1 h, respectively. However, the antimicrobial efficacy of C. cassia oil was reduced when S. Enteritidis PT30 existed in low moisture condition. When S. Enteritidis PT30 was established on almonds/paper discs, 0.4% C. cassia oil resulted in ∼1.7 Log₁₀ CFU/almond or 3.2 Log₁₀ CFU/disc reduction within 2 h at room temperature, respectively. S. Enteritidis PT30 established on both almonds and paper discs were very stable, there was only a 0.80 Log₁₀ CFU/almond and 1.20 Log₁₀ CFU/disc reduction during 9-week and 7-week storage at room temperature, respectively. C. cassia oil intervention increased S. Enteritidis PT30 reduction on both almonds and paper discs during storage with more reduction on paper discs. 0.4% C. cassia oil treatment reduced S. Enteritidis PT30 on paper disc to undetectable level within 4 weeks, but only led to 2 Log₁₀ CFU reduction on almonds, indicating a protection effect from the almond matrix or almond surface components. Additionally, S. Enteritidis PT30 established on paper disc coated with almond surface components exhibited higher resistance to desiccation and C. cassia oil treatment, further demonstrating the protection role of food matrix. In conclusion, C. cassia oil is effective against S. Enteritidis PT30 and S. Tennessee K4643, but its antimicrobial efficacy against the tested Salmonella was compromised by low moisture environment and food matrix.     

Bactericidal effects of Cinnamon cassia oil against bovine mastitis bacterial pathogens

Organic food production is expanding rapidly. However, this industry is hampered by the lack of effective antimicrobial agents which can be used in organic food production. This study examined the antimicrobial activity of Cinnamon cassia oil against major pathogens causing bacterial bovine mastitis, its miscibility in milk and possible antimicrobial mechanisms. C. cassia oil had inhibitory activity against all tested pathogen isolates from bovine mastitis. We conducted disk diffusion assay and found that discs with 20 μL of 2% (v/v) C. cassia oil solution resulted in inhibition zones of 29.6, 19.1, 27.0, 33.3 and 30.7 mm for Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus hyicus, Staphylococcus xylosus and Escherichia coli 29, respectively. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of C. cassia oil was 0.00625% and 0.025% (v/v) for S. hyicus, 0.025% and 0.10% (v/v) for E. coli 29, and 0.0125% and 0.05% for S. aureus, S. epidermidis and S. xylosus, respectively. We selected two common mastitis pathogens, a representative S. aureus isolate and E. coli 29 for further analyses. Based on time-kill assay in LB broth with 0.15% agar, 2MBC of C. cassia oil generated bactericidal effects on S. aureus and E. coli 29 within 30 min, and 4MBC caused 6 log reduction of S. aureus and E. coli 29 within 30 min. In milk, C. cassia oil at 4MBC reduced ∼6.0 Log₁₀ CFU/ml of S. aureus and E. coli 29 to undetectable level within 8 h. Using propidium iodide staining, we observed membrane damage on both S. aureus and E. coli 29 cells during incubation with C. cassia oil. In addition, C. cassia oil treatment at MIC impaired membrane integrity of E. coli and S. aureus, which was followed by a decrease in ATP synthesis. Bacterial extracellular signaling quorum sensing orchestrates important events related to bacterial pathogeneses through excreting autoinducer (AI). Sub-inhibitory concentration of C. cassia oil repressed AI-2, a universal signal molecule mediating quorum sensing, production in S. aureus and E. coli 29 isolates. Collectively, our data show that C. cassia oil provides an exciting potential to be used as an alternative antimicrobial for bovine mastitis in organic dairy farms.     

Prevalence assessment of Coxiella burnetii and verocytotoxin-producing Escherichia coli in bovine raw milk through molecular identification

Raw milk has become increasingly appreciated by consumers and in the EU there is general acceptance of this product, the sale of which is regulated by EU Directives. However, unpasteurised milk can be contaminated by zoonotic agents, thus representing a risk for human health. The aim of our work was the assessment of Coxiella burnetii and verocytotoxin-producing Escherichia coli (VTEC) presence in bovine bulk tank milk of Marche region (Central Italy) destined to direct human consumption. PCR and real-time PCR well-established protocols have been used for pathogen identification, showing high sensitivity and specificity. C. burnetii prevalence was 27%, while VTEC serogroup were found as follows: 3.5% for both O157 and O145; 2.3% for O26; 4.7% for O103. In contrast, the immunomagnetic separation-based protocol (IMS) was able to identify only one sample (1.2%) contaminated by VTEC O157.These results indicate that a combination of real-time PCR and IMS proved to be more appropriate for VTEC serogroup identification, thanks to improved sensitivity. Moreover, the prevalence of these pathogens would suggest that non-O157 VTEC and C. burnetii should be included among microbiological criteria for raw milk, implementing control strategies to limit possible negative impact to consumers' health.     

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.     

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 malic acid against Listeria monocytogenes,Salmonella Enteritidis and Escherichia coli O157:H7 in apple,pear and melon juices

Minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations of malic acid against Listeria monocytogenes, Salmonella Enteritidis and Escherichia coli O157:H7 inoculated in apple, pear and melon juices stored at 5, 20 and 35 °C were evaluated. MICs and MBCs against L. monocytogenes, S. Enteritidis and E. coli O157:H7 were significantly affected by storage temperature, juice characteristics and type of microorganism. Malic acid was more effective at 35 and 20 °C than at 5 °C in all studied fruit juices. E. coli O157:H7 was more resistant to malic acid than S. Enteritidis and L. monocytogenes. Apple, pear and melon juices without malic acid were inhibitory to E. coli O157:H7, S. Enteritidis and L. monocytogenes at 5 °C, whereas, MBCs of 1.5% (v/v) of malic acid in apple and pear juices, and 2% (v/v) in melon juice at 5 °C were needed to reduce E. coli O157:H7, those concentrations being higher than those required to reduce S. Enteritidis and L. monocytogenes in those fruit juices. In addition, concentrations of 2%, 2.5% and 2.5% (v/v) of malic acid added to apple, pear and melon juices, respectively, were required to inactivate the three pathogens by more than 5 log cycles after 24 h of storage at 5 °C. Transmission electron microscopy showed that malic acid produced damage in the cell cytoplasm of pathogens without apparent changes in the cell membrane.     

Prevalence of molecular markers for Salmonella and Shiga toxigenic Escherichia coli (STEC) in whole-muscle beef cuts sold at retail markets in Costa Rica

The present study sought to determine the prevalence of molecular markers for Salmonella and Shiga toxigenic Escherichia coli (STEC) serogroups O26, O45, O103, O111, O121, O145, and O157 in whole-muscle beef cuts sold at retail in urban and semi-rural areas of Costa Rica. A total of 279 (171 urban, 108 semi-rural) samples were purchased from 93 butcher shops between August of 2012 and August of 2013 and tested for the presence of molecular markers characteristic of Salmonella and STEC using the DuPont Qualicon BAX^® System. The overall prevalence of Salmonella and STEC markers was 3.6% (10/279) and 4.7% (13/279), respectively. Salmonella markers were more frequently found in semi-rural (6.5%; 7/108) than in urban (1.8%; 3/171) areas. Similarly, STEC markers were more commonly detected in semi-rural (7.4%; 8/108) than in urban (2.9%; 5/171) areas. A marginal association was found between Salmonella markers and sampling location (P = 0.0496), whereas the presence of STEC markers and sampling location were considered independent (P = 0.1416). Among the 13 positive samples for STEC, 38 O-antigen gene fragments were amplified, with serogroups O45 and O121 being the predominant (28.9 and 21.1%, respectively). Markers for somatic antigens O111 and O157 were not detected in any of the samples. The present investigation is the first of its kind in Central America and shows that both Salmonella and STEC may be commonly present in whole-muscle raw beef cuts sold at retail markets in Costa Rica. Consequently, consumers may be directly at risk of foodborne illness due if meat products are not adequately cooked and handled in food service or domestic settings. Future work should emphasize continuous monitoring of the presence of these and other zoonotic pathogens in meat and meat products and on the implementation and validation of adequate food safety controls along the farm-to-table continuum.     

Synergetic antibacterial efficacy of cold nitrogen plasma and clove oil against Escherichia coli O157:H7 biofilms on lettuce

This study aims to evaluate the antimicrobial effects of cold nitrogen plasma (CNP) and clove oil against Escherichia coli O157:H7 (E. coli O157:H7) biofilm on lettuce. Both clove oil (1 mg/mL, 2 mg/mL and 4 mg/mL) and CNP (400–600 W) displayed significant eradication effect on E. coli O157:H7 biofilms in vitro (p < 0.001). Subsequently, the antibiofilm effect of combined treatment was studied as well. Compared with the respective treatment, combined treatment exhibited remarkable synergistic effect on eradicating E. coli O157:H7 biofilms. The confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) had also visually testified that the antibacterial effects of clove oil on E. coli O157:H7 biofilms (in vitro and on lettuce) were enhanced by CNP at 400 W for short treatment duration. The results of sensory evaluation indicated that combined treatment has mild negative effect on lettuce quality. Moreover, the synergetic antibacterial mechanism of clove oil and CNP against E. coli O157:H7 was concluded as that they could damage the bacterial cell wall and the outer membrane, leading to leakage of cellular components, such as nucleic acid and ATP.     

Antimicrobial activity of essential oils against Escherichia coli O157:H7 in organic soil

Soil can be a significant source of preharvest contamination of produce by pathogens. Demand for natural pesticides such as essential oils for organic farming continues to increase. We examined the antimicrobial activity of several essential oils against Escherichia coli O157:H7 in soil. Two essential oils (cinnamaldehyde and eugenol), two bio-pesticides (Ecotrol and Sporan) containing essential oils, and an organic acid (acetic acid) at 0.5%, 1.0%, 1.5% and 2.0%, were mixed with organic sandy soil and inoculated with five different strains of E. coli O157:H7. Soils were incubated at room temperature (22 °C) and samples obtained at 1, 7 and 28 days were enumerated to determine survival. E. coli O157:H7 populations in soil were reduced by up to 5 log cfu/g after 24 h incubation at room temperature with 2% cinnamanaldehyde, Ecotrol, Sporan or vinegar. Reduction in E. coli O157:H7 by eugenol was not significantly different from control. Overall, E. coli O157:H7 strain 4406 was the most sensitive of all the five strains tested and cinnamaldehyde was superior to other treatments in reducing E. coli O157:H7 in soil. In general, increases in essential oil concentrations corresponded to reduced survival of E. coli O157:H7 with all oils used in this study. The results suggest that oils can reduce potential contamination of fresh organic produce inadvertently contaminated by soil.     

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

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

Characteristics of coliphage ECP4 and potential use as a sanitizing agent for biocontrol of Escherichia coli O157:H7

Escherichia coli O157:H7 is an important pathogenic bacterium to humans because it produces various toxins, such as shiga-toxin. Coliphage ECP4, which belongs to the Siphoviridae family, was isolated from bovine feces to test its utility as a potential agent for the biocontrol of E. coli O157:H7. The burst size of coliphage ECP4 was about 80 PFU/cell, after a latent period of 30–35 min. Coliphage ECP4 was susceptible to temperatures above 70 °C; however, its stability was slightly reduced to 1–2 log PFU/ml after 30 min in 70% ethanol. In addition, the shiga toxin gene was not detected on coliphage ECP4. Coliphage ECP4 inhibited the growth of E. coli O157:H7 in vegetable juice, and was not detected in cabbage after 5 h. When coliphage ECP4 was applied to biofilm-formed E. coli O157:H7, E. coli O157:H7 was efficiently reduced. The newly identified coliphage ECP4 might effectively reduce E. coli O157:H7 or its biofilmed-form. Therefore, the coliphage ECP4 might be an efficient sanitizer for fresh produce contaminated with E. coli O157:H7 in the biofilm environment.     

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.     

Determination of antimicrobial effect of mint and basil essential oils on survival of E. coli O157:H7 and S. typhimurium in fresh-cut lettuce and purslane

In this research, mint and basil essential oils at concentrations of 0.01 ml/L, 0.032 ml/L or 0.08 ml/L were used for disinfection treatments of fresh-cut lettuce and purslane samples inoculated with Salmonella typhimurium or Escherichia coli 0157:H7. Disinfection treatment time was applied as 10 min (short) or 15 min (long). Disinfected samples were packaged aerobically and stored at refrigerator +4 °C for 7 days. It was observed that mint and basil essential oils showed antimicrobial effect on the survival of E. coli O157:H7 and S. typhimurium inoculated into lettuce and purslane samples during refrigerated storage. Mint essential oil showed higher antimicrobial effect on pathogens when compared to basil essential oil. Mint and basil essential oils at concentration of 0.08 ml/L were the most effective antimicrobial treatment against pathogens in two different vegetable. S. typhimurium was more resistant against basil oil in lettuce samples when compared to its resistance against basil oil in purslane samples, whereas E. coli O157:H7 was more resistant to mint oil in purslane samples when compared to its resistance against mint oil in lettuce samples.     

Antimicrobial efficacy of grape seed extract against Escherichia coli O157:H7 growth,motility and Shiga toxin production

Escherichia coli O157:H7 produces Shiga toxin (Stx) which is heat stable and causes Hemolytic Uremic Syndrome (HUS), a serious disease associated with bloody diarrhea and even death. To ensure food safety, both live E. coli O157:H7 and its toxin production in food products need to be controlled. Natural ingredients with inhibitory effects on E. coli O157:H7 growth and toxin production are top choices of antimicrobials for the food industry. The objectives of this study were to evaluate efficacy of grape seed extract (GSE) against the growth, swimming motility and Stx production of E. coli O157:H7. The disc diffusion assay indicated that 3.2 mg GSE per disc resulted in an inhibition zone of 14.8 ± 0.21 mm. The minimal inhibitory concentration of GSE against E. coli O157: H7 was 4.0 mg/ml. At high inoculation level (1 × 10⁷ CFU/ml), including GSE at 0.25–2.0 mg/ml reduced Stx production without inhibiting E. coli O157:H7 growth. At 5 × 10⁵ CFU/ml inoculation level, 2.0 and 4.0 mg/ml GSE effectively inhibited the growth of E. coli O157:H7 for at least 72 h, however, a low level of GSE (0.125–1.0 mg/ml) enhanced E. coli O157:H7 growth and Stx2 production. At 4 mg/ml, GSE completely abolished Stx2 production in addition to it bactericidal effect against E. coli O157:H7. In addition, GSE at concentration as low as 0.125% blocked the swimming motility, which is important for E. coli O157:H7 surface adherence. In conclusion, GSE is effective in inhibiting the motility of E. coli O157:H7, GSE shows potential to be used as a natural antimicrobial to control E. coli O157:H7.