Comparison of antimicrobial resistance patterns and phage types of Salmonella Typhimurium isolated from pigs,pork and humans in Belgium between 2001 and 2006

Infections with non-typhoid Salmonella represent a major problem in industrialized countries.The emergence and spread of antimicrobial-resistant pathogens, among them Salmonella, has become a serious health hazard worldwide. One of the most commonly isolated non-typhoid Salmonella serovars in pigs, pork and humans is Salmonella Typhimurium. In this study the comparison of the incidences of resistance to nine antimicrobials, resistance patterns and phage types between S. Typhimurium isolated from pigs (n = 581), pork (n = 255) and humans (n = 1870) in Belgium in the period 2001 to 2006 was performed.Resistance to the antimicrobials ampicillin, chloramphenicol, streptomycin, sulfonamides and tetracycline was frequently observed and varied between 23.5% and 83.1%. Resistance ranged from 15.6% to 20.7% for the combination trimethoprim–sulfonamides and from 3.4% to 5.8% for nalidixic acid. Resistance to the critical important antimicrobials cephalosporins and fluoroquinolones was found sporadically (≤ 1.2%). Resistance to the different antimicrobials was observed to be similar in S. Typhimurium isolates from the various origins. Twenty-seven antimicrobial resistance patterns representing in total 75.2%, 89.0% and 89.6% of the isolates from pigs, pork and humans respectively were found to be common among the three groups and 73 combinations antimicrobial resistance pattern/phage type were found to be common among pork and human isolates, representing 70.1% of the pork isolates and 51.0% of the human isolates. The high percentage of isolates that have a common resistance pattern, and in a less pronounced way a common combination phage type/resistance pattern, are in agreement with the hypothesis of transfer of antimicrobial resistant Salmonella from pigs via the consumption of pork to humans as one of the possible pathways. The most prevalent combination in Belgium within both the pork isolates (7.4%) and the human isolates (13.2%) was S. Typhimurium DT104 resistant to ampicillin, chloramphenicol, streptomycine, sulfonamides and tetracycline.     

Salmonella contamination of laying-hen flocks in two regions of Algeria

A preliminary epidemiological study of Salmonella contamination in laying-hen flocks was carried out in the regions of Annaba and Eltarf, Algeria, from March to October 2008 and March to November 2009. Our objectives were (i) to estimate the prevalence of infection by Salmonella spp. in seven pooled samples during the hens' laying period (ii) to identify the serotypes and antimicrobial resistance phenotypes of isolates, and (iii) to characterize the factors that may be related to Salmonella contamination in Algerian henhouses. For this purpose, 18 out of 22 operational laying-hen houses were sampled one to three times during these periods: once at the start of laying (pullets aged 22–31 weeks), once in the middle of laying (47–60 week) and once at the end of laying prior to depopulation (70–86 week). The flocks'Salmonella status was assessed by collecting 2754 environmental samples that were analyzed according to the ISO 6579 method. The antibiotic resistance of Salmonella strains was tested as per the guidelines of the Clinical and Laboratory Standards Institute (CLSI). The relationship between each potential risk factor and the Salmonella status of laying-hen flocks was evaluated by calculating the relative risk with 95% confidence intervals. Eight flocks tested positive for Salmonella spp., with a higher prevalence at the end of laying than at either the beginning or middle. Only 19 isolates were recovered from the 2754 samples analyzed and nine different serotypes identified. S. enteritidis (n = 4) was the most prevalent serovar, along with S. Kentucky and S. Hadar (n = 3), followed by S. Heidelberg, S. Manhattan and S. Virchow (n = 2), whereas S. Dublin, S. Typhimurium and S. Albany were found only once. Thirteen isolates were resistant to at least one antimicrobial agent. Of these, six were resistant to at least three different antimicrobial classes. Salmonella serovar Kentucky isolates were resistant to fluoroquinolones with ciprofloxacin MIC ≥ 8 mg/L. Six risk indicators were identified as potentially related to the Salmonella status of layer houses.     

Radio-sensitivity of pathogens in inoculated prepared foods of animal origin

The effectiveness of irradiation for inactivating Staphylococcus aureus, Listeria ivanovii, Salmonella Typhimurium, and Escherichia coli in the prepared foods of animal origin was investigated. Commercially available seasoned and cooked beef, fried egg, and ham were purchased, radiation-sterilized, and inoculated at 10⁶–10⁷ CFU/g with each of the four pathogens and stored at three storage conditions at 10 °C, 20 °C, and 30 °C. D₁₀-values of S. aureus, L. ivanovii, Salmonella Typhimurium, and E. coli were 0.34±0.01, 0.24±0.02, 0.24±0.01, and 0.27±0.01 kGy, respectively. No viable cells were detected at 3 kGy of irradiation. Salmonella mutagenicity assay (Ames test) indicated that the 10 kGy irradiated samples were statistically similar to non-irradiated control samples in the Salmonella mutagenicity assay (Ames test). These studies demonstrate that irradiation can be used as an additional safety tool to produce microbiologically safe and wholesome prepared foods of animal origin.     

Application of bacteriophages during depuration reduces the load of Salmonella Typhimurium in cockles

As bivalve molluscs are filter feeder, often consumed raw or lightly cooked and are frequently cultivated in contaminated waters, they are implicated in food-borne disease transmission to human. The present study investigated the potential application of bacteriophage (or phage) phSE-2, phage phSE-5 and phage cocktail phSE-2/phSE-5 to decrease the concentration of Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) during the depuration of natural and artificially contaminated cockles (Cerastoderma edule). Cockles were artificially infected with 10⁵ and 10⁶ colony-forming units (CFU)/mL of S. Typhimurium in static seawater and infected group were treated with phages at four different MOI values: 0.1, 1, 10 and 100. Depuration in static seawater at multiplicity of infection (MOI) of 0.1 with single phage suspensions of phSE-2 and phSE-5 provided the best results, as it decreased by ~ 1.3 and 1.7 log CFU/g, respectively, the concentration of Salmonella spp. after a 4 h treatment. At a MOI of 0.1, the rate of inactivation with single phage suspensions was higher when compared with the results obtained using the phage cocktail. However, in naturally contaminated cockles treated in static seawater with single phage suspensions and phage cocktail phSE-2/phSE-5, similar decreases in cultivable bacteria concentration (~ 0.7–0.9 log CFU/g) were achieved after 6 h of treatment. When artificially contaminated cockles were depurated with phage phSE-5 in a recirculated seawater system (mimicking industrial depuration conditions), a 0.9 and 2.0 log CFU/g reduction of Salmonella spp. was reached after 4 and 6 h treatment. Once the depuration process was performed without phage, a 6 h treatment was needed to obtain a 1.1 log CFU/g reduction of Salmonella spp. Results indicated that combining phage biocontrol with depuration procedures enhance bivalve microbial safety for human consumption by improving decontamination efficiency, proving that this technology can be transposed to the bivalves industry. Moreover, this approach also displays the advantage of reducing the time required for depuration and consequently its associated costs.     

Integrated surveillance of Salmonella along the food chain using existing data and resources in British Columbia,Canada

Integrated surveillance of pathogens along the food chain and the multidisciplinary investigation of food hazards are considered international best practices. Integrated surveillance of Salmonella was initiated in British Columbia (BC), Canada in 2006. The objectives of this paper were 1) to describe the BC integrated surveillance experience, 2) to present findings from the integrated surveillance of Salmonella, and 3) to identify the components that enabled the program. Data about BC animal, food and human Salmonella isolates from 2006 to 2010 (n = 5003) were centrally collated and analysed. Among chickens, chicken meat and humans, the most common serotypes identified were S. Enteritidis, S. Typhimurium and S. Heidelberg. An increase in S. Enteritidis in all three sectors in 2007–9 led to a multi-disciplinary and multi-sectoral investigation. An evaluation of the integrated surveillance program helped identify four critical program elements: dedicated people, cross-sectoral sharing and integration of data, multi-disciplinary analysis and interpretation of findings, and collaborative multi-sectoral response. Ongoing challenges include lack of resources and infrastructure to sustain the program.     

Effect of temperature,pH and presence of nisin on inactivation of Salmonella Typhimurium and Escherichia coli O157:H7 by pulsed electric fields

The aim of this investigation is to evaluate the concurrent influence of temperature (4–50 °C), pH (3.5–7.0), and the presence of nisin (up to 200 μg/mL) on the inactivation of two PEF-resistant Gram-negative, pathogenic bacteria, Salmonella Typhimurium STCC 878 and Escherichia coli O157:H7, using a PEF treatment of 30 kV/cm and 99 μs. A response surface model using a central composite design was developed for the purpose of understanding the individual effects and interactions of these factors.The models showed that temperature was the factor with the greatest influence on the PEF inactivation in the two strains investigated. Increasing the treatment temperature from 4 to 50 °C increased the lethality of PEF up to at least 4 Log₁₀ reductions for both microorganisms at all pH levels investigated. PEF lethality varied with the square of the pH observing the highest microbial PEF sensitivity at pH 5.25 at all temperatures. The addition of nisin to the treatment medium did not influence the PEF lethality independently of the temperature.PEF induced 1.0–1.5 Log₁₀ cycles of damaged cells at pH 3.5 for Salmonella Typhimurium STCC 878 and at pH 5.25 for E. coli O157:H7, independently of the temperature or the presence of nisin in the treatment medium.The application of PEF at 50 °C permitted the achievement of 5 Log₁₀ reductions of Salmonella Typhimurium STCC 878 and E. coli O157:H7 in a range of pH from 4.2 to 6.7 and from 4.5 to 6.0, respectively. Therefore, the application of PEF at moderate temperatures has great potential for achieving effective control of Gram-negative pathogenic microorganisms in the range of pH found in most foods.     

Decontamination of Salmonella enterica Typhimurium on green onions using a new formula of sanitizer washing and pulsed UV light (PL)

Pathogenic bacteria such as Salmonella and Shigella flexneri have been linked to green onion contamination. This study was conducted to evaluate decontamination of Salmonella Typhimurium using a new formula of sanitizer washing (0.4 mg/mL thymol and five new formula sanitizers including 300 ppm H₂O₂ + 4% SDS, 2 mg/mL citric acid + 4% SDS, 0.2 mg/mL thymol + 4% SDS, 0.2 mg/mL thymol + 2 mg/mL citric acid and 0.2 mg/mL thymol + 2 mg/mL acetic acid), pulsed UV light (PL) as well as synergy between the sanitizer wash and PL. New formula sanitizers based on decontamination efficacy of single washing solutions (organic acids, hydrogen peroxide (H₂O₂), essential oil or surfactant) were applied to decontaminate spot inoculated green onions. PL, the novel technique, alone has been applied to inactivate Salmonella on both dip and spot inoculated green onions. Salmonella inactivation of PL–new formula sanitizer combinations on dip inoculated green onions was investigated for their potential synergy. As a result, for spot inoculated green onions, 0.4 mg/mL thymol individually and the five new formula sanitizers all achieved higher log reduction of Salmonella (4.5–5.3 log 10 CFU/g reduction) than the 200 ppm chlorine washing. These new formulas of sanitizer would be potential alternatives to chlorine. The 5 s dry PL (4.6 log 10 CFU/g) or 60 s wet PL treatment (3.6 log 10 CFU/g) was better or comparable as chlorine washing. The sanitizer combinations did not provide significantly higher log reduction than PL, and PL has the potential of being used in the green onion industry for decontamination purpose. For dip inoculated green onions, none of our treatment provided > 0.8 log 10 CFU/g (0.6–0.8 log 10 CFU/g) reduction of Salmonella. As a result, the PL–new formula sanitizer combinations had no or minimal synergy to inactivate Salmonella dip inoculated on green onions.     

Effect of reducing nitrate and nitrite added to dry fermented sausages on the survival of Salmonella Typhimurium

Salmonella is one of the pathogens that most frequently contaminate pork processing lines. Several hurdles can control this organism in dry fermented sausages, among them is nitrite. However, the traditional use of nitrate/nitrite in the meat industry is being questioned due to their involvement in nitrosamine formation. In this study, minced pork and sausages inoculated with Salmonella Typhimurium were prepared with 150 ppm NaNO₃ and 150 ppm NaNO₂ (maximum amounts allowed by EU), and with a reduction of 25% and 50%. The absence of nitrate/nitrite favored Salmonella growth, with 2–2.5 log cfu/g higher counts at the end of ripening, compared to nitrate/nitrite added batches. The 50% reduction showed the same inhibitory effect as the maximum amounts. Nitrate/nitrite represented an essential hurdle to control Salmonella even when pH and a_w were below the values considered as minimum for its growth. The effect of this reduction on other pathogens should be considered.     

Examination of the internalization of Salmonella serovar Typhimurium in peanut,Arachis hypogaea,using immunocytochemical techniques

A variety of products of plant origin, such as tomatoes, melons, peppers, and peanuts, have been implicated in Salmonella spp. associated outbreaks in recent years. Although these bacteria have been found to internalize within some plants associated with foodborne-related outbreaks, the internalization in peanut plants has not been examined to date. To investigate internalization and where the bacteria localize within the plant, intact peanut seeds were contaminated with Salmonella serovar Typhimurium expressing green fluorescent protein (GFP) for 30 min and immunocytochemical techniques were used to localize the bacterium within the stem tissue of 16 day-old peanut plants. An average of 13.6 bacteria/mm³ were localized within the sampled tissue. The bacteria were found to be associated with every major tissue (cortical, vascular, epidermal, and pith) and corresponding cell type. The cortical cells located to the outside of the vascular bundles contained the majority of the Salmonella cells (72.4%). Additional growth experiments demonstrated peanut seedlings could support the reproduction of Salmonella to high levels (10⁹ CFU/plant) after 2 days following seed contamination. Together these results show that Salmonella Typhimurium can internalize within many different plant tissue types after a brief seed contamination event and that the bacteria are able to grow and persist within the plant.     

A meta-analytical estimation of the detection limits of methods for Salmonella in food

The validation of microbial detection methods for foods does not typically state a limit of detection value. Therefore performances of rapid and reference methods for Salmonella detection in foods were compared retrospectively using data from 49 published studies. A total of 576 values for the limit of detection (LOD₅₀) were calculated. The major scientific variables in these independent validation studies were food matrices, Salmonella serovars, and method types (reference, cultural and immunological and nucleic acid based). The basic design feature of the original studies was comparison of the performances of new methods with those of cultural reference methods. A major experimental design variable was the number of laboratories per study. There were 29 single laboratory studies with 20 replicates per level of Salmonella spiked into the food matrix. The 20 multi-laboratory (N ≥ 10) studies had 5–6 replicates per level of Salmonella. The LOD₅₀ values of the dataset had a mean value of 0.021 MPN g^? 1 (standard deviation range (0.013–0.036) and the distribution of their logarithms was symmetrical about the logarithm of the mean if the outlier values were discounted. Eighty-nine percent of the values ranged from 0.01 to 0.04 MPN g^? 1. On this basis about 11% of the values were deemed outliers. About three-quarters of them were > 0.04 MPN g^? 1. The distribution derived in this study can be used as a bench mark against which to evaluate LOD₅₀ data generated in future studies of detection methods for Salmonella in foods and potentially offers a possible way to streamline method validation study experimental design.     

Inactivation of Salmonella Typhimurium and Staphylococcus aureus by pulsed electric fields in liquid whole egg

In this study, the lethal effectiveness of pulsed electric fields (PEF) on the inactivation of Salmonella enterica subs. enterica ser. Typhimurium and Staphylococcus aureus in liquid whole egg (LWE) has been investigated. Maximum inactivation levels of 4 and 3 Log₁₀ cycles of the population of Salmonella Typhimurium and S. aureus were achieved with treatments of 45 kV/cm, 30 μs and 419 kJ/kg, and 40 kV/cm for 15 μs and 166 kJ/kg, respectively. The non-linear kinetics of inactivation observed for both microorganisms at all the investigated electric field strengths were described by mathematical equations based on the Weibull distribution. The developed equations enabled to compare the microbial resistance to PEF and to establish the most suitable treatment conditions to achieve a determined level of microbial inactivation. PEF treatments varying from 30 kV/cm, 67 µs and 393 kJ/kg to 45 kV/cm, 19 µs and 285 kJ/kg allow to reduce 3 Log₁₀ cycles the population of the microorganism of concern in PEF food processing of LWE, Salmonella Typhimurium.Industrial relevanceThe data presented in this investigation in terms of electric field strength, specific energy and treatment time result of relevance to evaluate the possibilities of PEF technology to pasteurize LWE with this technology. The models developed in this study can be applied to engineering design, and for the evaluation and optimization of the PEF technology as a new technique to obtain Salmonella free LWE.Based on our results it is not recommended to apply treatments of energy levels higher than 250 kJ/kg, since PEF lethality hardly increased but markedly augmented the energetic costs. For these energy values, PEF technology by itself is not sufficient (3 Log10 cycles in the best case scenario) to assure the safe security of LWE. Therefore, intelligent combinations of PEF with other preservation technologies have to be developed in order to use pulsed electric fields as an alternative to heat pasteurization of LWE.     

Fat contributes to the buffering capacity of chicken skin and meat but enhances the vulnerability of attached Salmonella cells to acetic acid treatment

Chicken skin and chicken meat display different buffering effects which may impact the survival of Salmonella attached to them when treated with acids. This study investigated the role that differences in fat composition of chicken skin and meat play in their buffering capacity. The survival of Salmonella attached to chicken skin and meat in the presence of fat, and treated with acetic acid was also investigated. Fat was extracted from chicken skin and meat and the buffering capacities of chicken skin, meat, extracted fat and their respective remnants were determined. Two strains of Salmonella Typhimurium and two strains of S. Enteritidis were attached independently to each of the chicken component listed above and enumerated before and after treatment with 0.3 M acetic acid. Chicken skin has a higher fat content as compared to chicken meat. Skin (13 mmol H⁺/(pH1 kg)) had a stronger buffering capacity (p < 0.05) than the extracted fat alone and skin remnants alone (7.0 mmol H⁺/(pH 1 kg) and 6.9 mmol H⁺/(pH 1 kg) respectively). From an initial inoculum (~ 9 log CFU/g), Salmonella cells attached better (p < 0.05) to chicken meat (~ 8 log CFU/g) and chicken skin (~ 7 log CFU/g) than extracted fat (~ 1.5 log CFU/g). Skin remnants without fat were better (p < 0.05) at protecting attached Salmonella than other chicken components. For example S. Typhimurium ATCC 33062 decreased ~ 1 log CFU/g (p < 0.05) on skin remnants after acetic acid treatment while its viable counts on other components decreased from ~ 1.5 to 7 log CFU/g (p < 0.05). We suggest that the fat content present in the skin may enhance the vulnerability of attached cells to acetic acid.     

Effect of Quillaja saponaria dietary administration on colour,oxidative stability and volatile profile of muscle longissimus dorsi of Barbarine lamb

Eighteen Barbarine lambs were assigned during 77 days to three dietary treatments (n = 6): control, oat hay ad libitum and 400 g of concentrate; QS60 and the QS90 control diet supplemented with 60 mg and 90 mg Quillaja saponaria (QS) bark extract/kg dry matter, respectively. The analysis of pre-frozen longissimus dorsi muscle showed that the QS90 treatment reduced meat redness (a*) and saturation (C*) measured after 2 h of blooming. It also reduced the rate of decrease in a* values (P = 0.02) during 14 days of refrigerated storage. Supplementation with QS extended meat colour stability by reducing (P < 0.05) the rate of increase in hue angle (H*) values. Neither the rate of metmyoglobin accumulation at the meat surface nor lipid peroxidation over storage duration differed between treatments. The overall meat volatile compound profile was similar between the groups. We conclude that supplementing QS affects meat colour development at the meat surface and extends its stability without producing detrimental effects on meat volatile compounds.     

Modeling inactivation kinetics and occurrence of sublethal injury of a pulsed electric field-resistant strain of Escherichia coli and Salmonella Typhimurium in media of different pH

A study of the effect of pulsed electric fields (PEF) on the kinetics of inactivation and the occurrence of cell damage in Escherichia coli O157:H7 and Salmonella Typhimurium 878 treated in McIlvaine buffer covering a range from pH 3.5 to 7.0 was conducted. Mathematical equations based on the Weibull distribution were developed to describe the influence of the electric field strength, treatment time and pH of the treatment medium on the lethality and generation of cell damage of both Gram negative pathogenic bacteria after the application of PEF treatments. E. coli O157:H7 was more PEF resistant than Salmonella Typhimurium at all pH investigated. PEF resistance of E. coli was influenced by the pH but the pH hardly affected the PEF resistance of Salmonella Typhimurium 878. After 150 μs at 35 kV/cm, 1 and 5 log₁₀ cycles of inactivation of E. coli O157:H7 were observed in the range of pH 3.5–4.5 and 5.5–6.5, respectively. Cell damage increased with the field strength and treatment time. A maximum cell damage level of 4.2 and 2.7 log₁₀ cycles for E. coli O157:H7 and Salmonella Typhimurium was observed respectively after a treatment of 30 kV/cm at pH 3.5. PEF induced cell damage was not detected at pH higher than 5.0 for both microorganisms. The developed equations can be applied to design combining processes which can increase the lethality of PEF or to reduce the intensity of PEF treatments to achieve a determine level of microbial inactivation.Industrial relevanceThis study demonstrates that when the influence of several factors on the microbial behavior is investigated, the development of mathematical models is a very useful tool to evaluate the influence of each parameter and their interactions. In this study, it has been mathematically described for first time the influence of the pH of the treatment medium and the occurrence of sublethal injury in a wide range of electric field strengths and treatment times in two Gram negative pathogenic bacteria, Escherichia coli O157:H7 and Salmonella Typhimurium 878. These models would also be of interest for engineering design, evaluation and optimization of PEF process as a new technique for food preservation.     

Volatile components and antibacterial effects of pine needle (Pinus densiflora S. and Z.) extracts

The antibacterial effects of the volatile components extracted from Pinus densiflora S. and Z., by simultaneous steam distillation and solvent extraction (SDE), were examined on six foodborne bacteria using Bioscreen C (a computer-controlled shake–incubator–reader). The SDE extracts of P. densiflora obtained after 1.5 or 2.0 h at pH 3.6 exhibited a strong growth inhibitory effect on Escherichia coli O157:H7 and their overall antibacterial activities against the various bacteria tested tended to increase with increased extraction time and with a lower extraction pH. The major volatile components of the SDE extracts obtained at pH 3.6 and 1.5 h, as determined by gas chromatography, were α-ocimene (29.3%), sabinene (10.9%), β-myrcene (9.6%), β-caryophyllene (8.0%), β-cadinene (7.3%), α-terpinolene (4.9%), 2-hexanal (4.5%), and β-pinene (4.3%). The addition of 8% or 10% (v/v) of the SDE extracts to culture broth completely inhibited the growths of Bacillus cereus, Salmonella Typhimurium, and Staphylococcus aureus. The intracellular adenosine triphosphate (ATP) concentration of S. Typhimurium treated with P. densiflora extract reduced to 0.165 μm from 0.595 μm, whereas the ATP concentration in culture supernatants was increased to 0.469 μm form 0.065 μm.     

Salmonella in meat from hunted game: A Central European perspective

The occurrence of Salmonella in meat from game hunted in Europe is reviewed, with a focus on Central Europe. Prevalence in fecal samples is different according to region and game species, ranging from < 5 (wild ruminants) to ca. 20% (wild boar). The pathogen is rarely recovered from carcasses or meat cuts of wild ruminants (< 1%). Prevalences on wild boar carcasses have been reported to range from < 1 to ca. 7%, the tonsils presumably constituting a main reservoir on the eviscerated carcass. On meat cuts from game, recent German and EU (EFSA) reports indicate a prevalence of < 1%. A number of Salmonella enterica serovars can be isolated, with highest prevalences of S. Typhimurium and S. Enteritidis. Persistence of these pathogens in wildlife is a less pressing issue for biology and wildlife conservation than for public health experts, which has been recognized in the framework of zoonoses legislation. On one hand, wildlife is exposed to salmonellae originating from farm animals and humans, and on the other hand, game can be a source of Salmonella in farm animals. Breeding game under intensified conditions (farmed game) as well as extensive breeding of farm animals, notably pigs, can create new epidemiological situations. The pathway of Salmonella from intestinal content of the live animal to individual meat cuts can be described in qualitative terms, yet the relative contribution of the various factors remains to be quantified, which complicates proper risk assessment. Control of Salmonella in the game meat chain is in part based on Good Hygiene Practice from killing and evisceration to chilling and skinning, whereas more detailed data are needed in order to allow risk-based meat inspection.     

A risk characterization model of Salmonella Typhimurium in Irish fresh pork sausages

A second-order simulation model was built to estimate the risk of Salmonella Typhimurium associated with the consumption of Irish fresh pork sausages. To select appropriate hazard characterization models, an initial appraisal of the current dose-response models was conducted. The cooking modality of grilling was associated with a higher mean risk of infection per serving (1.399 × 10^? 6; 95% CI: 7.54 × 10^? 7–2.65 × 10^? 6) than frying (6.246 × 10^? 7, 95% CI: 2.78 × 10^? 7–1.17 × 10^? 6). When the risk was extrapolated over the consumption in a year period, the mean risk of infection increased considerably to 8.541 × 10^? 5 with an expected number of infections and illnesses of 184.3 (95% CI: 26–664) and 17 (95% CI: 2–63), respectively. Results highlighted the importance of consumer education, as scenario analysis predicted that, for the current level of Salmonella in pork sausage, decreasing the product's cold storage by approximately 8 h and cooking for an additional half minute can reduce the current risk level by ～ 50%.     

Inactivation kinetics of Listeria monocytogenes,Salmonella enterica serovar Typhimurium,and Campylobacter jejuni in ready-to-eat sliced ham using UV-C irradiation

To investigate the applicability of UV-C irradiation on the inactivation of foodborne pathogenic bacteria in ready-to-eat sliced ham, UV-C treatment was evaluated. Irradiation dose required for 90% reduction of the populations of Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and Campylobacter jejuni were determined to be 2.48, 2.39, and 2.18 J/m². Ready-to-eat sliced hams were inoculated with the pathogens and irradiated with UV-C light of 1000, 2000, 4000, 6000, and 8000 J/m². Microbiological data indicated that foodborne pathogen populations significantly (p < 0.05) decreased with increasing UV-C irradiation. In particular, UV-C irradiation at 8000 J/m² reduced the populations of L. monocytogenes, S. Typhimurium, and C. jejuni in the ham by 2.74, 2.02, and 1.72 log CFU/g. The results indicate that UV-C irradiation can be used as a microbial inactivation method for ready-to-eat sliced ham, and inactivation kinetics of the foodborne pathogens fit the Weibull model better than the first-order kinetics model.     

Application of PCR for rapid detection and serotyping of Salmonella spp. from porcine carcass swabs following enrichment in semi-solid agar

A new procedure for the detection and serotyping of Salmonella spp. based on PCR was developed and applied to porcine carcass swabs. Detection was based on a two-step enrichment using Buffered Peptone Water (BPW) and Modified Semi-solid Rappaport Vassiliadis (MSRV) agar followed by real time PCR targeting the genus specific hilA gene. In addition, pUC19 plasmid DNA was included as an extraction and internal amplification control (IAC). Serotyping consisted of multiplex PCR and capillary electrophoresis (CE) based on the method of Leader, Frye, Hu, Fedorka-Cray, & Boyle, 2009. To validate this method, 271 porcine carcass swabs were examined in tandem by the conventional culture method using MSRV (ISO 6579:2002; Annex D) followed by serotyping using slide agglutination and classification according to the White–Kauffmann–Le Minor scheme. Results showed 100% agreement between the conventional culture method and PCR, with 27 samples positive for Salmonella spp. by both methods.Using slide agglutination, full antigenic formulas were obtained for 25 of the 27 isolates (14 S. Typhimurium, 6 S. Infantis, 3 S. Derby, 1 S. Virchow and 1 S. Livingstone), while two isolates were not fully typeable and were designated S. Unnamed. PCR serotyping discriminated 7 different molecular code patterns, of which 2 were identical to those described by Leader et al. (2009), namely S. Typhimurium (ST) and S. Virchow (SV), found in 16 and one, respectively, of the 27 isolates. Both S. Unnamed isolates were identified as ST by the PCR method, therefore improving the identification of ST over the conventional method. The remaining 10 isolates shared four PCR patterns and although consistent codes were generally observed, discrepancies were observed compared to Leader et al. (2009). MSRV-PCR followed by serotyping using multiplex PCR and CE is rapid with final results obtained in 2 days from receipt of samples compared with 6–9 days using the conventional methods. The inclusion of the pUC19 plasmid DNA as an extraction and IAC demonstrated the robustness of the PCR procedure, with consistent Ct values obtained for both the hilA and pUC19 targets. This procedure could be particularly useful for surveillance and outbreak investigations by tracking sources of S. Typhimurium contamination, thus improving Salmonella control activities.