Modelling the inactivation of Listeria monocytogenes and Salmonella typhimurium in simulated egg wash water

The inactivation of Listeria monocytogenes Scott A and Salmonella typhimurium in synthetic egg washwater was studied under varying conditions of temperature (38°C to 46°C), egg solids (0%, 2%), pH (9·5 to 10·5) and chlorine concentration (0 to 10 μg ml^-1 [ppm]) using a full factorial design. Survival was measured as the logarithm of the time required for a 4-log reduction in viable counts. Both pathogens were significantly affected by temperature and the presence of egg, while the survival of S. typhimurium was significantly reduced by pH and chlorine alone. Both pathogens were affected by second order interactions involving egg and either pH or chlorine. Egg was the most significant factor, reducing the survival of L. monocytogenes while promoting the survival of S. typhimurium. Two linear equations were derived to describe the decrease in survival of L. monocytogenes and S. typhimurium as a function of the 4 factors. These equations were used to estimate conditions which would reduce the time for a 4-log reduction in viable counts to <30 min. In the absence of egg solids, chlorine (20 μg ml^-1) can be used to control L. monocytogenes and S. typhimurium using moderate temperature (42°C) and pH (10·5). When egg is present in wash water, increased temperature (47·4°C) and pH (10·8) are required.     

Irradiation inactivation of four Salmonella serotypes in orange juices with various turbiditiest

Reconstituted orange juice inoculated with Salmonella Anatum, Salmonella Infantis, Salmonella Newport, or Salmonella Stanley was treated with gamma radiation at 2 degrees C. To determine the relationship between juice antioxidant power and Dgamma (dose required to achieve 90% mortality), juice solids were removed prior to inoculation by centrifugation and/or filtration to create juice preparations of varying turbidity. In unadulterated orange juice, Salmonella Anatum (Dgamma = 0.71 kGy) was significantly more resistant than the other species tested. Salmonella Newport (Dgamma = 0.48 kGy) and Salmonella Infantis (Dgamma = 0.35 kGy) were significantly different, while Salmonella Stanley (Dgamma = 0.38 kGy) was intermediate between the two. Neither the resistance of each isolate nor the pattern of relative resistance among isolates was altered in reduced turbidity juice preparations. Although total antioxidant power was associated with the level of juice solids resuspended in phosphate buffer, antioxidant power was not significantly associated with turbidity in the juice preparations or with Dgamma of any species. The variable resistance to irradiation of the Salmonella isolates suggests this as a more significant factor than turbidity or antioxidant power in designing antimicrobial juice irradiation protocols.     

高效液相色谱测定食品中非食用色素皂黃

建立了食品中非食用色素皂黄的高效液相色谱检测方法.样品经丙酮超声波提取,以乙睛-5mmol/L乙酸铵 0.06%三乙胺水溶液为流动相,XDB-C18色谱柱分离,二极管阵列检测器检测,检测波长为418nm.该方法线性范围为0.5～15μg/mL,最低检出浓度为O.08mg/L,变异系数为0.4%～3.6%,加标平均回收率为102.29%,方法准确可靠,精密度较高.     

食品中碱性橙、皂黄、丽舂红2R等色素的同时薄层色谱定性分析

开发了利用薄层色谱技术同时检测豆制品中碱性橙、皂黄、柠檬黄、日落黄四种色素和辣椒粉中酸性橙Ⅱ、丽春红2R、罗丹明B三种非食用色素的方法.结果表明,豆制品经丙酮和乙醇-氨溶液提取,辣椒粉经乙醇-氨溶液提取,采用硅胶G薄层板,正丁醇-无水乙醇-1%氨水(6:2:2)为展开剂上行展开,混合色素能够有效分离.碱性橙、皂黄、柠檬黄、日落黄、丽春红2R的最低检出量均为0.04μg,酸性橙Ⅱ的最低检出量为0.10μg,罗丹明B最低检出量为0.02μg.利用该方法对市售的辣椒面和豆腐干进行了检测,检测结果与高效液相色谱法的检测结果相符.因此.该方法可以快速有效地对辣椒面和豆制品中的碱性橙等色素进行定性分析.     

热-超声波联合对鼠伤寒沙门氏菌的杀菌效果研究

研究了32⁵2℃条件下,热处理以及热-超声波联合处理对鼠伤寒沙门氏菌的杀菌效果,分析了温度对热-超声波联合杀菌效果的影响。结果表明:32⁵2℃热处理杀菌效果远远达不到卫生标准;而热-超声波联合作用杀菌效果显著增强,在52℃下,190、380、570W分别处理40、30min和30min即可达到平板菌落计数法检测限;在热-超声波联合处理中,较低温度（32⁴7℃）对鼠伤寒沙门氏菌的杀菌效果贡献较小,杀菌效果主要取决于超声波作用;而致死温度（52℃）体现协同杀菌效应,增强杀菌效果,提高杀菌速率。      

热-超声波联合对鼠伤寒沙门氏菌的杀菌效果研究

研究了32~52℃条件下,热处理以及热-超声波联合处理对鼠伤寒沙门氏菌的杀菌效果,分析了温度对热-超声波联合杀菌效果的影响。结果表明:32~52℃热处理杀菌效果远远达不到卫生标准;而热-超声波联合作用杀菌效果显著增强,在52℃下,190、380、570W分别处理40、30min和30min即可达到平板菌落计数法检测限;在热-超声波联合处理中,较低温度(32~47℃)对鼠伤寒沙门氏菌的杀菌效果贡献较小,杀菌效果主要取决于超声波作用;而致死温度(52℃)体现协同杀菌效应,增强杀菌效果,提高杀菌速率。     

高效液相色谱法测定果汁、果酱中的皂黄

目的建立高效液相色谱法检测果汁、果酱中皂黄含量的分析方法。方法试样经20%(V:V)甲醇溶液超声提取,离心取上清液,高效液相色谱—二极管阵列检测器分析。结果皂黄在0.50～100μg/mL浓度范围内呈现良好的线性关系(r~20.9999),具有较高的分离度且峰型对称,果汁和果酱的标准物质加入实验的回收率分别在96.1%～101.9%和79.2%～99.4%之间,相对标准偏差(relative standard deviation,RSD)分别为1.1%～2.3%和4.3%～7.4%。结论该方法具有操作简便、准确度高、灵敏度高和稳定性好等优点,适用于果汁、果酱中皂黄含量的测定。     

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.     

Sensitivity of multidrug-resistant Salmonella typhimurium DT104 to organic acids and thermal inactivation in liquid egg products

A mixture of four Salmonella typhimurium DT104 strains and a mixture of four S. typhimurium non-DT104 strains were examined for their ability to grow in tryptic soy broth (TSB) acidified with acetic, lactic, citric, or malic acids at pH 5·4, 4·4, and 3·7. Significantly (P<0·05) higher numbers of S. typhimurium DT104 cells were detected at pH 4·4 and 4·0 in TSB acidified with acetic acid and at pH 4·4 and 3·7 in TSB acidified with lactic acid compared to non-DT104 cells. Acid-shocked and non-shocked (control) cells were plated on TSA (pH 7·3) acidified with lactic acid at pH 5·4, 4·4, and 4·0 and on TSA (pH 7·0±0·2) containing 0·5, 2·5, and 5% sodium chloride. Populations of acid-shockedS. typhimurium DT104 and non DT104 cells recovered on acidified or salt-supplemented TSA were significantly (P<0·05) lower than those of non-shocked cells. A significantly lower number of acid-shocked non-DT104 cells recovered on TSA at pH 5·4, compared to acid-shocked DT104 cells, suggests that DT104 cells may be more resistant to acid shock and subsequent exposure to acid pH. D values and z values of acid-shocked or non-shocked cells of DT104 and non-DT104 strains in liquid whole egg (WE), egg yolk (EY), egg white (EW), whole egg+10% salt (WES), and egg yolk+10% salt (EYS) were determined. Differences in thermal sensitivity of the two types of cells were few. Rates of thermal inactivation of S. typhimurium DT104 cells indicate that the USDA pasteurization process would eliminate >8 log₁₀cfu ml⁻¹of EW heated at 57°C and >11 log₁₀cfu ml⁻¹of WE, EY, WES, or EYS heated at 61°C. D values of acid-shocked DT104 and non-DT104 cells heated in liquid egg products were significantly (P<0·05) lower than those of respective non-shocked cells.     

Adhesion of Salmonella typhimurium var. copenhagen in the intestines of pigeons.

The attachment of Salmonella typhimurium var. copenhagen to the intestinal epithelium of pigeons was studied. After experimental infection, the intestines of both young and adult pigeons were examined in vivo and in vitro. Investigations were carried out by electron and immunofluorescence microscopy. Attachment of the Salmonella strain to duodenal epithelium was established. Following repeated washing after inoculation, bacterial cells could be seen by SEM and TEM in association with the surface structure of the tissue. The adhesive properties of fimbriae, which are also involved in haemagglutination, could be demonstrated.     

固相萃取-HPLC测定食品中皂黄的含量

建立食品中非食用色素皂黄的固相萃取-高效液相色谱检测方法.样品经丙酮提取,固相萃取小柱净化,以乙腈-5 mmol/L乙酸铵 0.06%三乙胺水溶液为流动相,XDB-C18色谱柱分离,二极管阵列检测器418 nm检测.该方法线性范围为0.5～15 μg/mL,最低检出浓度为0.07 mg/L,RSD为2.5～3.4%,加标平均回收率为83.97%,方法准确可靠,精密度较高.     

Elucidation of the inhibitory factors of yogurt against Salmonella typhimurium.

The inhibitory nature of yogurt against contaminating microorganisms has been studied extensively. Nevertheless, the factors responsible for the death of Salmonella typhimurium in yogurt have not been elucidated. An understanding of these factors is important for the determination of yogurt's safety to consumer health. Yogurt fermented for 18 h at 42 C had a stable environment with the following conditions: pH 3.85, oxidation-reduction potential -80 mV, lactic acid concentration 158 mM, and acetic acid concentration 3.7 mM. Under these conditions, lactic acid was responsible for virtually all of yogurt's bactericidal activity against S. typhimurium at 37 C. Die-off rates were observed when these conditions were reproduced artificially in milk (artificial milk yogurt) and when lactic acid was added back to 18-h yogurt from which acids were removed by passage of the whey through a Dowex 1 (Cl-) anion exchange column (cationic yogurt). Factors that augmented lactic acid inhibition of S. typhimurium were low pH and low oxidation-reduction potential. The die-off rate of S. typhimurium was more rapid in yogurt whey (yogurt minus the casein fraction) than in whole yogurt, indicating that the casein fraction was partially able to protect Salmonella.     

Effects of pH and temperature on inactivation of Salmonella typhimurium DT104 in liquid whole egg by pulsed electric fields

Pulsed electric field (PEF) exposes a fluid or semi-fluid product to short pulses of high-energy electricity, which can inactivate microorganisms. The efficacy of PEF treatment for pasteurisation of liquid eggs may be a function of processing temperature. In this study, effects of PEF, temperature, pH and PEF with mild heat (PEF + heat) on the inactivation of Salmonella typhimurium DT104 cells in liquid whole egg (LWE) were investigated. Cells of S. typhimurium were inoculated into LWE pH adjusted to 6.6, 7.2 or 8.2 at 15, 25, 30 and 40 °C. The PEF field strength, pulse duration and total treatment time were 25 kV cm⁻¹, 2.1 μs and 250 μs respectively. Cells of S. typhimurium in LWE at pH 7.2 were reduced by 2.1 logs at 40 °C and 1.8 logs at 30 °C. The PEF inactivation of S. typhimurium cells at 15 or 25 °C was pH dependent. Heat treatment at 55 °C for 3.5 min or PEF treatment at 20 °C resulted in c. 1-log reduction of S. typhimurium cells. Combination of PEF + 55 °C achieved 3-log reduction of S. typhimurium cells and was comparable to the inactivation by the heat treatment at 60 °C for 3.5 min. With further development, PEF + heat treatment may have an advantage over high-temperature treatment for pasteurisation of liquid eggs.     

Mutagenicity evaluation of nitroanilines and nitroaminophenols in Salmonella typhimurium

In our studies of structure-activity relationships, three nitroanilines and nine nitroaminophenols were tested for their ability to induce mutations in Salmonella typhimurium strains TA1535, TA100, TA1537, TA1538 and TA98. The compounds m -nitroaniline, 4-nitro-2-aminophenol, and 3-nitro-6-aminophenol were active in two or more of these strains. The compounds o -nitroaniline, 2-nitro-3-aminophenol, 3-nitro-4-aminophenol, 4-nitro-3-aminophenol, 3-nitro-2-aminophenol, 2-nitro-6-aminophenol, 2-nitro-4-aminophenol and 2-nitro-5-aminophenol were inactive, both in the presence and in the absence of S9 mix. The compound p -nitroaniline was also inactive in all tests with the possible exception of that in strain TA98 in the presence of S9 mix, where it was either very weakly mutagenic or non-mutagenic. The mutagenic activity or inactivity of these compounds appears to be dependent on the positions of the amino, nitro, and hydroxy groups in their chemical structures.
Etude en mutagénèse des nitroanilines et nitroaminophénols sur Salmonella typhimurium .     

Distribution of Salmonella typhimurium in romaine lettuce leaves

Leafy greens are occasionally involved in outbreaks of enteric pathogens. In order to control the plant contamination it is necessary to understand the factors that influence enteric pathogen-plant interactions. Attachment of Salmonella enterica serovar typhimurium to lettuce leaves has been demonstrated before; however, only limited information is available regarding the localization and distribution of immigrant Salmonella on the leaf surface. To extend our knowledge regarding initial pathogen-leaf interactions, the distribution of green-fluorescent protein-labeled Salmonella typhimurium on artificially contaminated romaine lettuce leaves was analyzed. We demonstrate that attachment of Salmonella to different leaf regions is highly variable; yet a higher attachment level was observed on leaf regions localized close to the petiole (7.7 log CFU g⁻¹) compared to surfaces at the far-end region of the leaf blade (6.2 log CFU g⁻¹). Attachment to surfaces located at a central leaf region demonstrated intermediate attachment level (7.0 log CFU g⁻¹). Salmonella displayed higher affinity toward the abaxial side compared to the adaxial side of the same leaf region. Rarely, Salmonella cells were also visualized underneath stomata within the parenchymal tissue, supporting the notion that this pathogen can also internalize romaine lettuce leaves. Comparison of attachment to leaves of different ages showed that Salmonella displayed higher affinity to older compared to younger leaves (1.5 log). Scanning electron microscopy revealed a more complex topography on the surface of older leaves, as well as on the abaxial side of the examined leaf tissue supporting the notion that a higher attachment level might be correlated with a more composite leaf landscape. Our findings indicate that initial attachment of Salmonella to romaine lettuce leaf depends on multiple plant factors pertaining to the specific localization on the leaf tissue and to the developmental stage of the leaf.     

四重荧光定量PCR法鉴定肠炎、鼠伤寒以及伤寒沙门氏菌

目的建立四重荧光定量PCR体系鉴定肠炎沙门氏菌、鼠伤寒沙门氏菌以及伤寒沙门氏菌。方法针对沙门氏菌属特异性ompC基因、肠炎沙门氏菌sdf基因、鼠伤寒沙门氏菌STM4495和伤寒沙门氏菌STY2021序列设计引物和TaqMan探针,建立多重荧光定量PCR体系,进行特异性与敏感性研究。结果 28株不同血清型的沙门氏菌均扩增出ompC基因,其他13株非沙门氏菌均未出现ompC的非特异性扩增。sdf、STM4495、STY2021的探针和引物分别特异性扩增出肠炎沙门氏菌、鼠伤寒沙门氏菌以及伤寒沙门氏菌,而25株其他血清型沙门氏菌以及13株非沙门氏菌均未见扩增曲线。敏感性试验显示,该体系的最低检测限分别为48 pg/mL(ompC)、560 pg/mL(sdf)、530 pg/mL(STM4495)、35 pg/mL(STY2021)。结论该方法特异好、灵敏高、能够快速检测沙门氏菌并鉴定肠炎沙门氏菌、鼠伤寒沙门氏菌以及伤寒沙门氏菌。     

PCR amplification of the Salmonella typhimurium fimY gene sequence to detect the Salmonella species

This study evaluated the suitability of fimY gene amplification by PCR as an effective means of detecting Salmonella species. Although fimY gene of Salmonella typhimurium is involved in regulating type 1 fimbrial expression, the amino acid sequence of FimY shares very little homology with other known prokaryotic proteins in the GenBank database. Therefore, fimY is a promising target gene to detect the presence of Salmonella species. Herein, two primers internal to the fimY gene of S. typhimurium are used to investigate the distribution of the fimY homologous sequence among 45 Salmonella serovars and 20 non-Salmonella species by using PCR. Experimental results indicated that only Salmonella species possessed the fimY homologous sequence, subsequently generating the specific 526-bp DNA fragments. The sensitivity of the fmY-specific primer set was demonstrated on a Salmonella-free swab sample from a pork carcass surface, which was then artificially contaminated with different concentrations of S. typhimurium. A combining of pre-enrichment step in buffered peptone water and PCR amplification of fimY allowed the detection of S. typhimurium at the concentration of 3.4 x 10(0) CFU/ml from the swab sample. With an additional enrichment step in Rappaport-Vassiliadis (RV) broth, this procedure can also detect pork carcass surface naturally contaminated with Salmonella species in a slaughterhouse. Results in this study demonstrate that fimY is unique to Salmonella species and is an appropriate PCR target for detecting these microorganisms.     

PCR法检测肉鸭屠宰加工生产链中沙门氏菌的污染

为建立肉鸭加工中快速、准确的沙门氏菌PCR 检测方法,并应用于肉鸭屠宰生产加工链沙门氏菌的实时监测。采用Primer Premier 5.0 软件针对沙门氏菌特有的fimY 基因设计合成一对引物5′- GCATTCCGCTCATTAGAT-3′和5′-TGGAGGCTGATAACAAGG-3′,并对沙门氏菌DNA 扩增PCR 体系的退火温度、引物浓度、Mg2+ 浓度和聚合酶浓度进行优化。结果表明：成功扩增出沙门氏菌标准株和分离株的2 7 5b p 目的片段,灵敏度达到了1.2pg;应用建立的PCR 方法对国内某典型肉鸭屠宰厂的肉鸭屠宰链环节进行沙门氏菌污染的检测,发现在屠宰环境、拔毛浸烫水、浸蜡冷却水、清洗池水、宰前毛、食道、粪便和沥水体腔内共有25 个样品中扩增出了275bp大小的特异性片段,而空白对照无扩增条带。     

Magnetoelastic biosensor for the detection of Salmonella typhimurium in food products

In this article, a magnetoelastic sensor immobilized with polyclonal antibody for the detection of Salmonella typhimurium in food products is described. The remote query nature of magnetoelastic sensors enables the detection of bacterial species in sealed and opaque containers. Bacterial binding to the antibody on the sensor surfaces changed the resonance parameters, and these changes were quantified by the shift in the sensor’s resonance frequency. Response of the sensors to increasing concentrations (5 × 10¹–5 × 10⁸ cfu/ml) of S. typhimurium in three different food products (water, fat-free milk and apple juice) was studied and similar responses were observed. These results were also further ascertained by Scanning Electron Microscopy (SEM) studies. A detection limit of 5 × 10³ cfu/ml, with a sensitivity of 139 Hz/decade was obtained for the sensors tested in water samples, as compared to 129 Hz/decade in apple juice and 127 Hz/decade in fat free milk. A 2 × 0.4 × 0.015 mm sensor was employed in all the investigations. The dissociation constant K _d and the binding valencies for S. typhimurium spiked in water samples was 435 cfu/ml and 2.33 respectively; as compared to 309 cfu/ml and 2.38 for apple juice; and 1389 cfu/ml and 1.85 for fat free milk samples. Bacterial binding was specific and a divalent binding was observed.     

Thermal pasteurization requirements for the inactivation of Salmonella in foods

Thermal processing is still one of the most effective methods for inactivating undesirable microorganisms in foods. Heat is used to inactivate pathogens and in developing typical flavours, aromas, texture and colour of a cooked food. Pasteurization produces safer foods with longer shelf-life. Since mild temperatures are applied for a specified time, complementary food preservation techniques such as modified atmospheres, addition of preservatives or the use of refrigerated storage and distribution, might be needed to control the growth of the surviving microorganisms. This review starts by addressing food contamination by Salmonella spp., referring to some examples of outbreaks, and the benefits of pasteurization in terms of Salmonella inactivation. A section covering the thermal resistance studies of Salmonella in poultry and other animal-based foods is presented. Based on Salmonella thermal resistance data, minimum pasteurization times are suggested at different heating temperatures, to meet the guidelines and recommendations of governmental food agencies for meat products (7 log reduction). Validation of a minimum pasteurization time must be done for each specific food-thermal process, by inserting a thermocouple into the “coldest” spot of the food , and ensuring that this point is submitted to the minimum pasteurization value required. This procedure will guarantee food safety with respect to Salmonella. Salmonella pasteurization requirements of low moisture foods such as some nuts, chocolate and peanut butter are also reviewed.