Qualitative exposure assessment for Salmonella spp. in shell eggs produced on the island of Ireland

A qualitative exposure assessment for Salmonella in eggs produced on the island of Ireland was developed. The assessment was divided into three main modules (production and packing, distribution and storage, and preparation and consumption), and each of these stages into defined steps in the exposure pathway. In the production and packing stage the initial prevalences of Salmonella in the contents and on the shell of eggs were estimated to be negligible and low respectively. Numbers of Salmonella both in and on eggs were estimated to be low. At each subsequent step in the pathway, qualitative assessments were made of the impact of events on the probability and level of Salmonella contamination on the shells and in the contents of eggs. At the end of each module assessments were combined to give an overall probability and level of Salmonella contamination. In the first two modules the assessment focused on the effect of the duration and temperature of storage on yolk membrane integrity and the likelihood of shell penetration. During the final stage the influence of factors such as safe-handling procedures, pooling practices, consumption patterns and the effectiveness of cooking, on the prevalence and level of Salmonella contamination in a food item at time of consumption was assessed. The outcome of this assessment was an estimate of a low probability and level of Salmonella contamination of egg-containing foods, prepared with eggs produced on the island of Ireland.     

Probabilistic model for contamination of egg dishes with Salmonella spp. made from shell eggs produced on the island of Ireland

A quantitative model was constructed to estimate the probability that a serving of food containing eggs produced on the island of Ireland is contaminated with Salmonella spp. The model is based on the prevalence of contaminated eggs at the time of lay and a set of parameters which describe the pooling of eggs in the home and in catering situations. Both external and internal contamination of the eggs by Salmonella spp. was considered. The model estimates that there is a 90% chance that the probability of a serving of food being contaminated is between 0.0043% and 0.038%. Sensitivity analysis demonstrated that egg prevalence drives this low probability and that, at the current level of egg prevalence at the time of lay, pooling of eggs has a minor effect. These results indicate the importance of maintaining the low prevalence of contaminated eggs at the time of lay to minimise the risk of human cases of salmonellosis from consumption of eggs.     

Non-thermal atmospheric gas plasma device for surface decontamination of shell eggs

A resistive barrier discharge (RBD) prototype able to generate gas plasma at atmospheric conditions was set up. The discharge was electrically characterized and the plasma glow was analysed by optical emission spectroscopy. The decontamination power of the device was assessed on samples of shell eggs experimentally inoculated with Salmonella Enteritidis and Salmonella Typhimurium (5.5–6.5 Log CFU/eggshell) and placed in the treatment chamber. Different decontamination times (10, 20, 30, 45, 60 and 90 min) and relative humidity values (RH) of the gas mixture in the chamber (i.e. 35% and 65%, at 25 °C) were considered. All samples were treated in the plasma after-glow chamber where the measured temperature was not much higher than the room temperature, minimizing the risk of egg quality alterations.     

含茶多酚的壳聚糖涂膜对鸡蛋保鲜效果的影响

用茶多酚和壳聚糖制成的复合涂膜液对鸡蛋进行涂膜处理,以感官指标、失重率、蛋黄指数、蛋清pH值、哈夫单位为质量指标定期取样分析测定,研究所制成的涂膜液在室温条件下对鸡蛋的保鲜效果。结果表明,和对照相比,含茶多酚的壳聚糖涂膜液能较好地保持鸡蛋的新鲜度和品质,尤其以1.5%的壳聚糖溶液联合200mg/kg茶多酚制得的涂膜液保鲜效果最好,经此涂膜液处理后的鸡蛋室温下贮存35d,失重率为1.89%,蛋黄指数为0.26,哈夫单位为60.109,蛋清pH值为8.20。     

Campylobacter contamination of broiler caeca and carcasses at the slaughterhouse and correlation with Salmonella contamination

In order to estimate the prevalence of Campylobacter spp. and Salmonella spp. on broiler chicken carcasses and the prevalence of Campylobacter spp. in caeca, 58 French slaughterhouses were investigated in 2008. Enumeration of Campylobacter spp. was also performed in order to study the relation between caeca and carcass contamination. A pool of 10 caeca and one carcass were collected from 425 different batches over a 12-month period in 2008. Salmonella was isolated on 32 carcasses leading to a prevalence of 7.5% ([5.0-10.0]_95%CI). The prevalence of Campylobacter was 77.2% ([73.2-81.2]_95%CI) in caeca and 87.5% ([84.4-90.7]_95%CI) on carcasses. No significant correlation was found between Campylobacter and Salmonella. Positive values of Campylobacter were normally distributed and the average level was 8.05 log₁₀ cfu/g ([7.94-8.16]_95%CI) in caeca and 2.39 cfu/g ([2.30-2.48]_95%CI) on carcasses. A positive correlation (r = 0.59) was found between the mean of Campylobacter in caeca and on carcasses (p < 0.001). Thus, carcasses from batches with Campylobacter-positive caeca had significantly (p < 0.001) higher numbers of Campylobacter per gram than batches with negative caeca. These results show that Campylobacter can be present in both matrices and reduction in caeca could be a possible way to reduce the amount of bacteria on carcasses. Of the 2504 identifications performed, 3 species of Campylobacter (Campylobacter jejuni, Campylobacter coli and Campylobacter lari) were identified. The main species recovered were C. jejuni and C. coli, which were isolated in 55.3% and 44.5% of positive samples, respectively. These two species were equally represented in caeca but C. jejuni was the most frequently isolated on carcasses with 57.1% and 42.5% of positive carcasses for C. jejuni and C. coli, respectively. This study underlines that target a reduction of Campylobacter on final products requires a decrease of contamination in caeca.     

High pressure treatments on the inactivation of Salmonella Enteritidis and the characteristics of beef carpaccio

The effect of high pressure (HP) on Salmonella enterica subsp. enterica serovar Enteritidis in beef carpaccio stored under temperature abuse conditions (8°C) during 30days was investigated. After treatment, reductions of S. Enteritidis were 3.68 and 5.94 log cfu/g in samples pressurized at 450MPa for 5 and 10min, respectively, whereas the pathogen was only detected after enrichment of samples treated at 450MPa for 15min. During storage, counts of S. Enteritidis decreased 0.26 log cfu/g in non-pressurized carpaccio, 1.33 log cfu/g in carpaccio treated at 450MPa for 5min and were only detected after enrichment in carpaccio pressurized at 450MPa for 10 or 15min. Color (L*, a* and b*) varied with pressurization and storage, with higher changes in carpaccio treated at longer pressurization times. Shear resistance was slightly lower in treated samples just after pressurization, but increased at the end of the storage period. Maximum force was less affected by treatment.     

High pressure treatments on the inactivation of Salmonella Enteritidis and the physicochemical, rheological and color characteristics of sliced vacuum-packaged dry-cured ham

The effect of high pressure (HP) on Salmonella Enteritidis in sliced dry-cured ham stored under temperature abuse (8°C) during 60d was investigated. After treatment, reductions of S. Enteritidis were 1.06, 2.54 and 4.32 log units in ham treated at 400, 500 and 600MPa for 5min at 12°C, compared to non-pressurized samples. After 60d, counts of S. Enteritidis in ham treated at 400 and 500MPa were 2.56 and 2.66 log units lower than in non-treated ham, whereas the pathogen was only detected after enrichment in ham treated at 600MPa. Lipid oxidation increased with storage and pressurization, whereas total free amino acid contents were similar in HP and control samples after 60d. Dry-cured ham treated at the highest pressures exhibited lower shear resistance, whereas the maximum force to compress the sample was slightly changed. Color (L*, a* and b*) varied with pressurization and storage. Changes induced by HP in dry-cured ham were attenuated during storage.     

Transfer of Salmonella Enteritidis to four types of surfaces after cleaning procedures and cross-contamination to tomatoes

The objectives of the present study were to evaluate the spread of Salmonella Enteritidis to different cutting boards (wood, triclosan-treated plastic, glass, and stainless steel) from contaminated poultry skin (5 log CFU/g) and then to tomatoes and to analyze the effect of different protocols used to clean these surfaces to control contamination. The following procedures were simulated: (1) no cleaning after handling contaminated poultry skin; (2) rinsing in running water; (3) cleaning with dish soap and mechanical scrubbing; and (4) cleaning with dish soap and mechanical scrubbing, followed by disinfection with hypochlorite. The pathogen was recovered from all surfaces following procedure 1, with counts ranging from 1.90 to 2.80 log, as well as from the tomatoes handled on it. Reduced numbers of S. Enteritidis were recovered using the other procedures, both from the surfaces and from the tomatoes. Counts were undetectable after procedure 4. From all surfaces evaluated, wood was the most difficult to clean, and stainless steel was the easiest. The use of hypochlorite as a disinfecting agent helped to reduce cross-contamination.     

Effects of chitosan coating and storage position on quality and shelf life of eggs

Effects of chitosan coating and storage positions (small-end down, small-end up or horizontal) on internal quality and shelf life of eggs were evaluated during 5 weeks of storage at 25 °C. Compared with noncoated eggs, all chitosan-coated eggs, irrespective of storage positions, had significantly lesser weight loss, higher Haugh units and higher yolk index throughout the storage. Chitosan coating, irrespective of storage positions, extended the egg shelf life by at least 3 weeks at 25 °C compared with noncoated eggs. Noncoated and chitosan-coated eggs placed small-end down tentatively showed better quality than eggs placed small-end up after 3 and 4 weeks of storage. After 5 weeks of storage, storage positions did not significantly affect quality of noncoated and chitosan-coated eggs. There were no notable differences in total amino acid content of the albumen and fatty acid composition of the yolk between noncoated and chitosan-coated eggs after 5 weeks of storage.     

肠炎沙门菌感染与鸡蛋污染相互作用机制的研究进展

被污染的鸡蛋与人类肠炎沙门菌病感染之间存在明显的联系,鸡蛋和鸡蛋产品是肠炎沙门菌暴发最主要的食品源头。本文主要阐述肠炎沙门菌病原与蛋鸡及鸡蛋之间的相互作用,揭示肠炎沙门菌菌株比其他血清型菌株更易污染鸡蛋的原因。     

Characterization and horizontal transfer of class 1 integrons in Salmonella strains isolated from food products of animal origin

A total of 81 Salmonella isolates from retail meats and seafood in Hebei province, China, were assayed for the presence of and horizontal transfer of class 1 integrons. By the PCR screening for the integrons, class 1 integron was detected from strains in serotypes of Derby, Indiana, London and Choleraesuis, which were isolated from pork, chicken or seafood; however, two isolates contained the empty integron that lacked the resistance cassette, a potential hotspot for development of the multidrug resistance. In contrast, two other isolates had the antibiotic resistance gene cassettes within the class 1 integron, which were dfrA1-aadA1 and aadB-cmlA, respectively. The conjugation experiments demonstrated the plasmid-mediated transfer of the class 1 integrons. Furthermore, each of the integrons was transmitted to Streptococcus mutans via natural gene transformation. These findings suggest the possible transfer of class 1 integrons from foodborne pathogens to human residential bacteria via horizontal gene transfer.     

The combination of CRISPR-MVLST and PFGE provides increased discriminatory power for differentiating human clinical isolates of Salmonella enterica subsp. enterica serovar Enteritidis

Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis) is a major cause of foodborne salmonellosis. Rapid, efficient and accurate methods for identification are required to track specific strains of S. Enteritidis during outbreaks of human salmonellosis. By exploiting the hypervariable nature of virulence genes and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs), we previously developed a powerful sequence-based subtyping approach, designated CRISPR-MVLST. To substantiate the applicability of CRISPR-MVLST, we analyzed a broad set of S. Enteritidis isolates collected over a six-year period. Among 141 isolates we defined 22 Enteritidis Sequence Types (ESTs), the majority of which were novel. Notably, strains exhibiting the common PFGE pattern, JEGX01.0004 (characteristic of ∼40% of S. Enteritidis isolates in the United States), were separated into twelve distinct sequence types. Conversely, isolates of EST4, the most predominant EST we observed, comprised eight different PFGE patterns. Importantly, we showed that some genotypes that were previously associated with the food supply chain at the farm level have now been identified in clinical samples.     

Individual-based modelling of growth and migration of Salmonella enteritidis in hens' eggs

An individual-based model (IbM) was developed to describe the growth and migration of Salmonella enteritidis in hens' eggs. The Bacteria Simulator (BacSim) environment was used to implement the model; the bacteria are represented by spheres that grow by nutrient uptake and divide in two daughter cells upon exceeding a certain threshold volume. Motility of the Salmonella bacteria was described by a run and tumble mechanism. For the sake of simplicity, the bacteria were assumed to grow exponentially, an appropriate assumption for the initial phase of growth relevant for shelf-life predictions. Both albumen and yolk were assumed to be homogeneous. The impact of several model parameters (chemotaxis, growth rate, initial contamination numbers and bacterial swimming speed) was assessed by a sensitivity analysis. The results show that chemotaxis towards the yolk would have a strong effect on the time needed to reach the vitelline membrane, an aspect that future research should focus on. The contamination position had less impact on the time to reach the vitelline membrane. The simulation results illustrate the need for more detailed knowledge on the subject of bacterial migration in hens' eggs. Our model can easily incorporate this knowledge when it becomes available.     

Quantification of contamination of lettuce by GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium

The primary objective of this study was to determine the possibility of internalization of GFP-expressing Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium (S. Typhimurium) strains MAE 110 (multi-cellular morphology) and 119 (wild type morphology) into lettuce seedlings (Lactuca sativa cv. Tamburo) grown in an inoculated hydroponic and soil system. The second aim was to quantify the level of contamination with the use of a proper surface sterilization method. Silver nitrate was superior in reducing the number of viable bacteria on leave surfaces compared to sodium hypochlorite and ethanol. With the hydroponic system internal colonization of lettuce only occurred at high densities with S. Typhimurium MAE 119. With the soil system E. coli O157:H7, S. Typhimurium 110 and S. Typhimurium 119 were found at considerable densities in sterilized leaf samples (respectively, 3.95, 2.57 and 2.37 log cfu/g on average) with prevalences of 0.29, 0.23 and 0.15, respectively. No statistical differences were observed between the Salmonella strains. A negative correlation was observed between shoot weight and leaf contamination. The observed presence of the pathogens in lettuce, after thorough surface sterilization, demonstrates the possible presence of human pathogens in locations were they are unlikely to be removed by the actions of consumer washing and therefore pose a serious threat when occurring in field situations.     

Phenotypic and genetic characterization of antimicrobial resistance in Salmonella serovars isolated from retail meats in Alberta, Canada

This study determined the prevalence of Salmonella serovars, antimicrobial resistance (AMR) and resistance genes in Salmonella isolated from retail meats purchased in Alberta, Canada. Samples were collected during one year period (May 2007–April 2008) on weekly basis from 19 census divisions in Alberta. A total of 564 samples including chicken (n = 206), turkey (n = 91), beef (n = 134) and pork (n = 133) were purchased. Salmonella were recovered from chicken (40%), turkey (27%) and pork (2%) samples and was not found in ground beef. A total of 21, 8, and 3 different serovars were recovered from chicken, turkey and pork meats, respectively. Salmonella Hadar was most common in chicken whereas S. Heidelberg was common in turkey meat. Overall 29% (32/110) of isolates were susceptible to tested antimicrobials and resistance to ciprofloxacin, amikacin and nalidixic acid was not found in any isolate. Multiresistance (≥2 antimicrobials) was found in 56% of isolates. Resistance to amoxicillin–clavulanic acid (AMC), ceftiofur (TIO), and ceftriaxone (CRO) was found in about 21% of chicken and 25% of turkey isolates. Resistance to either of tetracycline (TET), streptomycin (STR) or ampicillin (AMP) was unconditionally associated with S. Hadar but resistance to either of TET, AMP, AMC, TIO, CRO or cefoxitin was associated with S. Heidelberg. The strA/B (42% isolates), tet(A) (28% isolates), bla_CMY-2 (21% isolates) and bla_TEM (17% isolates) were the most common resistance genes found. The bla_CMY-2 and bla_TEM genes were unconditionally associated with S. Heidelberg; tet(A) and strA/B with S. Hadar and tet(B) gene with S. Kentucky. The strA/B genes were not associated with S. Heidelberg. Our data suggests that the prevalence of Salmonella serovars varied by the meat type and that AMR and resistance genes varied by the Salmonella serovars.     

Influences of preharvest spraying Cryptococcus laurentii combined with postharvest chitosan coating on postharvest diseases and quality of table grapes in storage

The effects of preharvest spray with Cryptococcus laurentii combined with chitosan coating after harvest on decay and quality of table grapes during storage periods were evaluated in the present study. Preharvest spray with C. laurentii (PreA) significantly decreased decay index (DI), and postharvest chitosan coating (PCC) enhanced the effectiveness of the pre-harvest spray when fruits were stored at 0 °C. PreA combination with PCC increased the activities of polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) of fruit in storage. PreA + PCC treatment was effective in reducing weight loss of fruits by 85% at 17 d storage and 38% at 42 d storage as compared to PreA alone at the same stage. In addition, PreA enhanced the ratio of soluble solids content (SSC) to titratable acid (TA) by 12% at harvest time, 7% at 17 d storage and 25% at 42 d storage, mainly by increasing SSC and decreasing TA in fruit stored at 0 °C. These results suggested that integration of preharvest spray with C. laurentii and postharvest chitosan coating treatment may be a promising management strategy for decay control and quality maintenance of table grapes.     

Detection of eggs of stored-product insects in flour with staining techniques

Chemical stains were investigated with the aim of developing a method for detecting eggs of stored-product insects in refined wheat flour (white flour), so that eggs and flour particles could be distinguished easily. Eggs of the rust-red flour beetle, Tribolium castaneum, the saw-toothed grain beetle, Oryzaephilus surinamensis and the rice moth, Corcyra cephalonica were detected by staining with 0.1% bromocresol green or 1:1 mixture of bromocresol green+0.5% orange G solution after acid digestion of the flour particles. In contrast to the standard AACC method of staining with iodine solution where both eggs and flour particles were stained brownish-yellow or yellow, bromocresol green alone or in mixture with orange G, differentially stained the insect eggs and the flour particles distinct orange and green, respectively. Eggs in flour could also be detected using 0.05% acid fuchsin but both eggs and flour particles were stained uniformly pink.     

The effect of X-ray irradiation on Salmonella inactivation and sensory quality of almonds and walnuts as a function of water activity

The overall goal of this study was to develop a set of process design principles for low-energy X-ray irradiation of tree nuts. Almonds and walnuts were inoculated with Salmonella Enteritidis PT30 and Salmonella Tennessee, and conditioned to four different water activities (0.23, 0.45, 0.64, and 0.84 a_w). Thereafter, the inoculated/conditioned samples were irradiated to achieve up to a 5-log reduction in Salmonella using a pilot scale low-energy X-ray food irradiator. Greater efficacy (D₁₀-value: the dose required to eliminate 90% of the microbial population) for inactivating SE PT30 and S. Tennessee was seen on the surface of almonds (0.226-0.431 kGy) than on walnuts (0.474-0.930 kGy) at all water activities. Also, the efficacy did not change monotonically with water activity. Overall, no significant difference (P > 0.05) in sensory characteristics was seen between non-irradiated almonds and those irradiated to achieve a 5 log reduction in Salmonella. However, irradiating walnuts to the dose corresponding to a 5 log reduction caused a perceivable change in flavor. Post-irradiation storage tests revealed that surviving bacterial counts did not change over 120 days, regardless of nut type, Salmonella serovar, and a_w. Therefore, low-energy X-ray irradiation technology appears to be a promising non-thermal pasteurization strategy for certain types of nuts.     

Surfactant-disinfectant resistance of Salmonella and Staphylococcus adhered and dried on surfaces with egg compounds

To confirm the importance of eliminating food sediments from the surfaces of food-related environments, we examined the resistance of pathogenic bacteria (Salmonella Typhimurium and Staphylococcus aureus) cells, dried and adhered on glass with 25% w/v egg albumen, 25% yolk or 50% whole egg solutions, against benzalkonium chloride and alkyldiaminoethylglycine hydrochloride. Bacterial suspensions (0.1 ml of 8 log cfu/ml) were put on 47 mmφ glass dishes and dried at room temperature (20-24 °C) for 180 min in a bio safety cabinet with ventilation. Although the viable cells in distilled water decreased 2.0 (S. aureus)-3.5 (S. Typhimurium) log fold during the drying period, the egg compounds protected the bacteria. The disinfectant treatments (2.0 mg/ml for 10 min) showed a clear bactericidal effect in the absence of egg compounds. However, the bactericidal effect disappeared in the presence of yolk and whole egg. Imaging before and after drying and the disinfectant treatments were carried out using a phase-contrast microscope and an atomic force microscope. The protective effect of egg compounds on bacterial viability disappeared with a proper washing process.     

Antimicrobial susceptibility of Salmonella from organic and conventional dairy farms

The objective of this study was to compare antimicrobial susceptibility of Salmonella isolated from conventional and organic dairy farms in the Midwest and Northeast United States. Environmental and fecal samples were collected from organic (n = 26) and conventional (n = 69) farms in Michigan, Minnesota, New York, and Wisconsin every 2 mo from August 2000 to October 2001. Salmonella isolates (n = 1,243) were tested using a broth microdilution method for susceptibility to amoxicillin-clavulanic acid, ampicillin, ceftiofur, ceftriaxone, cephalothin, chloramphenicol, ciprofloxacin, gentamicin, kanamycin, nalidixic acid, streptomycin, sulfamethoxazole, tetracycline, and trimethoprim-sulfamethoxazole. Herd-level logistic regression and logistic proportional hazards multivariable models were used to examine the association between farm management type and susceptibility to antimicrobial agents. For most antimicrobial agents tested, susceptibility of Salmonella isolates was similar on organic and conventional herds when controlling for herd size and state. Conventional farms were more likely to have at least one Salmonella isolate resistant to streptomycin using logistic regression (odds ratio = 7.5; 95% confidence interval = 1.7-5.4). Conventional farms were more likely to have Salmonella isolates with greater resistance to streptomycin (odds ratio = 5.4; 95% confidence interval = 1.5-19.0) and sulfamethoxazole (odds ratio = 4.2; 95% confidence interval = 1.2-14.1) using logistic proportional hazards models. Although not statistically significant, conventional farms tended to be more likely to have at least one Salmonella isolate resistant to 5 or more antimicrobial agents when compared with organic farms.