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.     

Assessment of Escherichia coli O157:H7 transference from soil to iceberg lettuce via a contaminated field coring harvesting knife

The potential for lettuce field-coring harvesting knives to cross-contaminate lettuce heads with pathogens was evaluated. Rings and blades of the harvest knives artificially contaminated with Escherichia coli O157:H7 (EHEC), were used to core three successive heads of iceberg lettuce. The coring rings and blades were inoculated by dipping into soils containing EHEC at concentration ranges of 1-10⁵ MPN/g soil. Factors that influenced EHEC transference from soil to iceberg lettuce via contaminated coring knife blade, included water content (WC) of clay and sandy soils, EHEC concentration, and degree of blade contact (stem, medium, and heavy) with edible tissue. High moisture content clay soil was positively associated with high pathogen transference. No EHEC were detected on any cut heads when clay soil contaminated with 10⁵ MPN/g EHEC had WC of 20% or less, or when the knife blade was dipped into sandy soil contaminated with EHEC at the same level, regardless of percent WC. The extent to which the harvesting knife blade cut across edible lettuce tissues was also an important factor in the amount of pathogen transference that occurred. EHEC were detectable on first and second sequentially cut lettuce heads when medium-contact was made between knife blade and edible tissues and on all three sequentially cut lettuce heads using the heavy-contact cutting scenario, when the blade was contaminated with 10⁴ cfu/g EHEC in clay soil (25% WC). However, when the blade, contaminated at the same soil EHEC level, was used to cut only the stem and had no contact with the edible portion of the lettuce head, no pathogen transference was detected. Under the current CIF harvesting practice, the cutting blade has a higher potential than the coring ring to be contaminated by the soil, but less opportunity to transfer pathogens to harvested lettuce. However, once contaminated, the coring ring has much higher potential than the blade to transfer pathogens to the harvested lettuce.     

Quantification of Campylobacter jejuni cross-contamination via hands, cutlery, and cutting board during preparation of a chicken fruit salad

Using artificially contaminated chicken, the quantitative overall effect of Campylobacter jejuni cross-contamination, either via cutlery, cutting board, or hands, on the microbiological quality of a chicken salad was tested to identify the most critical transfer route. The end contamination level of salads prepared according to different scenarios, with or without cross-contamination, was compared. It was shown that the mean transfer rate calculated for all salads prepared allowing cross-contamination was 0.12% of the initial number of C. jejuni on the chicken fillet (8.8 +/- 0.2 log CFU). The difference in calculated transfer rates for the tested cross-contamination routes was not significantly different (P > 0.05). The prevention of cross-contamination by replacing cutlery and cutting board after handling raw chicken and the prevention of hand contact resulted in considerably reduced end contamination levels (< 2.4 log CFU) or noncontaminated end products. The results of this study emphasize the importance of preventing cross-contamination during food handling in reducing the risks of foodborne infections, and they provide useful data for quantitative microbiological risk assessment.     

Modeling the growth rate and lag time of different strains of Salmonella enterica and Listeria monocytogenes in ready-to-eat lettuce

The growth parameters (growth rate, μ and lag time, λ) of three different strains each of Salmonella enterica and Listeria monocytogenes in minimally processed lettuce (MPL) and their changes as a function of temperature were modeled. MPL were packed under modified atmosphere (5% O₂, 15% CO₂ and 80% N₂), stored at 7–30 °C and samples collected at different time intervals were enumerated for S. enterica and L. monocytogenes. Growth curves and equations describing the relationship between μ and λ as a function of temperature were constructed using the DMFit Excel add-in and through linear regression, respectively. The predicted growth parameters for the pathogens observed in this study were compared to ComBase, Pathogen modeling program (PMP) and data from the literature. High R² values (0.97 and 0.93) were observed for average growth curves of different strains of pathogens grown on MPL. Secondary models of μ and λ for both pathogens followed a linear trend with high R² values (>0.90). Root mean square error (RMSE) showed that the models obtained are accurate and suitable for modeling the growth of S. enterica and L. monocytogenes in MP lettuce. The current study provides growth models for these foodborne pathogens that can be used in microbial risk assessment.     

基于FSO值对生熟食品交叉污染中单增李斯特菌的危害识别

为定性分析生熟食品中单增李斯特菌在不同案板材质上的交叉污染,选定木制、塑料及不锈钢案板为材质研究对象,设置4种常见场景,并测定各案板材质不同场景下卤猪舌、案板与黄瓜中单增李斯特菌的污染水平(lg CFU/g)。同时,选择一级Baranyi模型修改式,二级主参数模型对黄瓜中单增李斯特菌的生长进行模拟。此外,根据食品安全目标(FSO)计算整个交叉污染过程的污染水平,并以即食食品中单增李斯特菌的FSO值2(lg CFU/g)为标准,与12种交叉污染情景(4种场景×3种材质)比较,并进行风险等级排序。结果表明:木质案板场景1(S1w)、塑料案板场景1(S1p)和不锈钢案板场景1(S1s)风险等级最高;场景2、3和4下,木质案板风险等级分别为2、3和3,高出塑料和不锈钢案板(3、4和4)一个风险等级。本研究表明对案板不进行任何清洗处理最易引发交叉污染,木质案板相较于其他2种案板材质的风险较大。     

Detection of Salmonella enteritidis and Salmonella typhimurium in foods using a rapid,multiplex real-time recombinase polymerase amplification assay

Salmonella has been recognized as a major foodborne pathogen for humans and animals. In this study, a multiplex real-time recombinase polymerase amplification (RPA) was developed for simultaneous detection of Salmonella enterica serovars, Salmonella enteritidis and Salmonella typhimurium, from chicken, eggs, lettuce, and papaya. The reaction was performed for 20 min at 35°C, and the detection limit of the assay was 10² CFU/ml for pure culture. In food application, the limit of detection (LOD) of S. enteritidis and S. typhimurium using multiplex real-time RPA without enrichment procedure was 10² CFU/25 g, respectively. After enrichment, the LOD of S. enteritidis and S. typhimurium was 10 CFU/25 g. Moreover, the result for Salmonella spp. was not significantly different from those obtained using a culture-based method. Additionally, the assay has a lower cross-reactivity with other pathogenic microorganisms and a good stability performance. Thus, the developed multiplex RPA assay could be used as a rapid tool for the detection of S. enteritidis and S. typhimurium in food.     

High hydrostatic pressure processing reduces Salmonella enterica serovars in diced and whole tomatoes

Fresh and fresh-cut tomatoes have been associated with numerous outbreaks of salmonellosis in recent years. One effective post harvest treatment to reduce Salmonella enterica in tomatoes may be high pressure processing (HPP). The objectives of the study were to determine the potential for HPP to reduce S. enterica serovars Newport, Javiana, Braenderup and Anatum in tryptic soy broth (TSB) and to determine the effect of HPP to reduce the most pressure resistant of the four serovars from fresh diced and whole tomatoes. To evaluate pressure resistance, TSB containing 8 log CFU/ml of one of the four serovars was packaged in sterile stomacher bags and subjected to one of three different pressures (350, 450 or 550 MPa) for 120 s. The most pressure resistant S. enterica serovar evaluated was Braenderup. Subjecting the broth culture to 350, 450 and 550 MPa resulted in a 4.53, 5.74 and 7.09 log reduction in S. Braenderup, respectively. Diced tomatoes (150 g) and whole red round tomatoes (approximately 150 g) were inoculated with 0.1 ml of 9.1 log CFU/ml S. Braenderup, and subjected to the same pressure treatments (350, 450 or 550 MPa). Significant reductions of S. Braenderup concentrations in diced tomatoes (P < 0.05) were seen after processing at 350 (0.46 CFU/g), 450 (1.44 log CFU/g), and 550 MPa (3.67 log CFU/g). In whole tomatoes, significant reductions (P < 0.05) were also seen at 350 (1.41 log CFU/g), 450 (2.25 log CFU/g) and 550 MPa (3.35 log CFU/g). HPP may be an effective post harvest strategy to reduce low levels of S. enterica contamination in whole and diced tomatoes.     

Salmonella surveillance and control at post-harvest in the Belgian pork meat chain

Salmonella remains the primary cause of reported bacterial food borne disease outbreaks in Belgium. Pork and pork products are recognized as one of the major sources of human salmonellosis. In contrast with the primary production and slaughterhouse phases of the pork meat production chain, only a few studies have focussed on the post-harvest stages. The goal of this study was to evaluate Salmonella and Escherichia coli contamination at the Belgian post-harvest stages. E. coli counts were estimated in order to evaluate the levels of faecal contamination. The results of bacteriological analysis from seven cutting plants, four meat-mincing plants and the four largest Belgian retailers were collected from official and self-monitoring controls. The prevalence of Salmonella in the cutting plants and meat-mincing plants ranged from 0% to 50%. The most frequently isolated serotype was Salmonella typhimurium. The prevalence in minced meat at retail level ranged from 0.3% to 4.3%. The levels of Salmonella contamination estimated from semi-quantitative analysis of data relating to carcasses, cuts of meat and minced meat were equal to −3.40 ± 2.04 log CFU/cm², −2.64 ± 1.76 log CFU/g and −2.35 ± 1.09 log CFU/g, respectively. The E. coli results in meat cuts and minced meat ranged from 0.21 ± 0.50 to 1.23 ± 0.89 log CFU/g and from 1.33 ± 0.58 to 2.78 ± 0.43 log CFU/g, respectively. The results showed that faecal contamination still needs to be reduced, especially in specific individual plants.     

Efficacy of neutral electrolyzed water for sanitization of cutting boards used in the preparation of foods

The effectiveness of neutral electrolyzed water (NEW) to sanitize cutting boards used for food preparation was investigated. Cutting boards made of hardwood and bamboo were inoculated with Escherichia coli K12 and Listeria innocua, dried for 1 h, washed, rinsed and sanitized with NEW, sodium hypochlorite (NaClO) solution, or tap water (control). After each washing protocol, surviving bacterial populations were determined. Results showed that both NEW and NaClO sanitizing solutions produced similar levels of bacterial reductions. In manual washing, the population reductions by NEW and NaClO were 3.4 and 3.6 log₁₀ CFU/100 cm² for E. coli, and 4.1 and 3.9 log₁₀ CFU/100 cm² for L. innocua, respectively. In the automatic washing, the reductions by NEW and NaClO were 4.0 and 4.0 log₁₀ CFU/100 cm² for E. coli, and 4.2 and 3.6 log₁₀ CFU/100 cm² for L. innocua, respectively. No significant differences (P > 0.05) were observed in surviving bacteria counts when comparing board material types.     

Efficacy of Cetylpyridinium Chlorine on Salmonella Typhimurium and Escherichia coli O157:H7 in Immersion Spray Treatment of Fresh-Cut Lettuce

Fresh‐cut lettuce inoculated with Salmonella enterica serovar Typhimurium and Escherichia coli O157:H7 was treated using cetylpyridinium chlorine (CPC) solution in a laboratory‐scale immersion spray system. With 0.7 kg/cm² spray pressure and 1.5‐min spray time (ST), both bacteria were significantly reduced (P < 0.05) in 0.1% to 0.3% CPC spray treatments, compared with water spray controls. At the same ST, increasing spray pressure from 0.7 to 2.1 kg/cm² further reduced bacteria by 0.5 to 1.5 log colony‐forming units (CFU)/g. The 0.2% and 0.3% CPC treatments resulted in the greatest reduction of S. serovar Typhimurium and E. coli O157:H7, respectively. Similar bacterial reduction could be achieved using shorter ST with extended post‐spray exposure time. No color change on the lettuce was observed after CPC treatment.