Suitability of Rapid Detection Methods for Salmonella in Poultry Slaughterhouses

A duplex real-time NASBA assay targeting serotype-specific gene for rapid detection of viable S. enterica serovar Paratyphi C in retail foods of animal origin

Salmonella enterica serovars Paratyphi C is highly adapted to humans and can cause a typhoid-like disease with high mortality rates. In this study, three serovar-specific genes were determined for S. Paratyphi C, SPC_0871，SPC_0872, and SPC_0908, by comparative genomics method. Based on SPC_0908 and xcd gene for testing Salmonella spp., we have developed a duplex real-time nucleic acid sequence-based amplification (real-time NASBA) with molecular beacon approach for simultaneous detection of viable cells of Salmonella spp. and serotype Paratyphi C. The test selectively and consistently detected 53 Salmonella spp. (representing 31 serotypes) and 18 non-Salmonella strains. Additionally, the method showed high resistance to interference by natural background flora in pork and chicken samples. The sensitivity of the established approach was determined to be 4.89 CFU/25 g in artificially contaminated pork and chicken samples after pre-enrichment. We propose this NASBA-based protocol as a potential detection method for Salmonella spp. and serotype Paratyphi C in food of animal origin.

Characterization of chicken meat contaminated with Salmonella by fluorescence spectroscopy

Contaminated poultry products as eggs and meat are the primary vehicles of Salmonella infection. Conventional methods for microorganisms detections involve multiple steps, and despite its accuracy, these assays are time-consuming. Biosensing methods have shown great potential for the rapid detection of foodborne pathogens. Some of the biosensors are based on fluorescence. Various fluorophores such as collagen, elastin, NAD(P)H, and porphyrins can be used to evaluate possible chemical changes in meat. In this manuscript, the fluorescence properties of chicken meat contaminated with Salmonella enterica (ATCC 14028) cell suspensions (500; 5000; 50,000 and 500,000 cells/mL) were obtained and compared with non-contaminated control, for meat kept at 25 °C for 24 and 48 h. The effects of ambient light were also considered. Our results indicated that free NAD(P)H and coproporphyrin emission bands present in contaminated meat, increased over time, and can provide access to valuable information for the detection of Salmonella in chicken meat.

Advancement in Salmonella Detection Methods: From Conventional to Electrochemical-Based Sensing Detection

Large-scale food-borne outbreaks caused by Salmonella are rarely seen nowadays, thanks to the advanced nature of the medical system. However, small, localised outbreaks in certain regions still exist and could possess a huge threat to the public health if eradication measure is not initiated. This review discusses the progress of Salmonella detection approaches covering their basic principles, characteristics, applications, and performances. Conventional Salmonella detection is usually performed using a culture-based method, which is time-consuming, labour intensive, and unsuitable for on-site testing and high-throughput analysis. To date, there are many detection methods with a unique detection system available for Salmonella detection utilising immunological-based techniques, molecular-based techniques, mass spectrometry, spectroscopy, optical phenotyping, and biosensor methods. The electrochemical biosensor has growing interest in Salmonella detection mainly due to its excellent sensitivity, rapidity, and portability. The use of a highly specific bioreceptor, such as aptamers, and the application of nanomaterials are contributing factors to these excellent characteristics. Furthermore, insight on the types of biorecognition elements, the principles of electrochemical transduction elements, and the miniaturisation potential of electrochemical biosensors are discussed.

An electrochemical biosensor for the detection of pathogenic bacteria based on dual signal amplification of Cu3(PO4)2-mediated click chemistry and DNAzymes

A novel electrochemical biosensor for detecting pathogenic bacteria was designed based on specific magnetic separation and highly sensitive click chemistry. Instead of enzyme-antibody conjugates, organic-inorganic hybrid nanoflowers [concanavalin A (Con A)-Cu3(PO4)2] were used as the signal probe of the sandwich structure. The inorganic component, the copper ions of hybrid nanoflowers, was first used to amplify signal transduction for enzyme-free detection. Sodium ascorbate could dissolve Cu3(PO4)2 of the signal probe to produce Cu2+, which was subsequently converted to Cu+, triggering the Cu+-catalyzed alkyne-azide cycloaddition (CuAAC) reaction between azide-functionalized ssDNA (a fragment of the DNAzyme-containing sequence) and alkyne-functionalized ssDNA immobilized onto the electrode surface. As a result, the DNAzyme was immobilized onto the gold electrode, which produced a positive and stable electrical signal. An exceptional linear relationship was observed between the electrical signal and the concentration of Salmonella typhimurium (101-107 CFU mL-1) with a detection limit of 10 CFU mL-1. The developed electrochemical biosensor based on dual signal amplification of Cu3(PO4)2-mediated click chemistry and DNAzymes exhibited good results in detecting S. typhimurium in milk samples.

Characterization of Salmonella Isolates Recovered from Stages of the Processing Lines at Four Broiler Processing Plants in Trinidad and Tobago

This cross-sectional study determined the prevalence, characteristics, and risk factors for contamination of chicken with Salmonella at four operating broiler processing plants in Trinidad. Standard methods were used to isolate and characterize the Salmonella isolates. The overall prevalence of Salmonella at the four processing plants was 27.0% (107/396). The whole carcass enrichment (WCE) method yielded a statistically significantly (p = 0.0014) higher frequency of isolation (53.9%; 97/180) than the whole carcass rinse (35.0%; 63/180) and neck skin methods (42.2%; 38/90). S. enterica serotypes Enteritidis, Javiana, and Infantis were the predominant serotypes isolated accounting for 20.8%, 16.7% and 12.5%, respectively, of the serotyped isolates. Risk factors included the use of over 100 contract farmers (OR 4.4), pre-chiller (OR 2.3), addition of chlorine to chiller (OR 3.2), slaughtering sick broilers (OR 4.4), and flocks with >50% mortality. Multi-drug resistance was detected in 12.3% (14/114) of the isolates of Salmonella. Resistance was high to kanamycin (85.7%) and doxycycline (74.6%) but low to amoxicillin-clavulanic acid (2.4%) and sulphamethoxazole-trimethoprim (0.8%). The occurrence of resistant Salmonella in chickens processed at commercial broiler processing plants has implications for salmonellosis and therapeutic failure in consumers of improperly cooked contaminated chickens from these plants in the country.

Evaluation of a commercial loop-mediated isothermal amplification assay, 3MTM Molecular Detection Assay 2 - Campylobacter, for the detection of Campylobacter from poultry matrices

1. The objective of this study was to evaluate performance of a commercial loop-mediated isothermal amplification (LAMP) method as an alternative method for the detection of Campylobacter spp. in primary production samples, poultry rinses and raw poultry products, as compared to the US Department of Agriculture Food Inspection Service Microbiology Laboratory Guide Book PCR reference method, MLG 41A.2. The Campylobacter spp. LAMP was used in conjunction with a ready-to-use enrichment broth that does not require microaerophilic incubation. After enrichment, boot swabs from poultry farms, carcase rinses and raw poultry products were tested by the LAMP method and the MLG 41A PCR method.3. The ready-to-use enrichment broth enabled the growth of Campylobacter spp. within 22 to 28 hours under aerobic incubation conditions. The LAMP method enabled Campylobacter detection in the enriched samples of various poultry matrices and had equivalent sensitivity and specificity to the MLG 41A PCR method.4. No significant difference (95% confidence interval) was found between the alternative and the MLG 41A PCR method, as determined by probability of detection analysis, except for neutralising buffered peptone water post-chill rinsates. For the post-chill neutralising buffered peptone water rinsates, the LAMP method had significantly higher confirmed portions.

A sensitive biosensor for determination of pathogenic bacteria using aldehyde dehydrogenase signaling system

Aldehyde dehydrogenase (ALDH) was first developed as an enzymatic signaling system of a biosensor for sensitive point-of-care detection of pathogenic bacteria. ALDH and specific aptamers to Salmonella typhimurium (S. typhimurium), as organic components, were embedded in organic-inorganic nanocomposites as a biosensor signal label, integrating the functions of signal amplification and target recognition. The biosensing mechanism is based on the fact that ALDH can catalyze rapid oxidation of acetaldehyde into acetic acid, resulting in pH change with portable pH meter readout. The altered pH exhibited a linear relationship with the logarithm of S. typhimurium from 10² to 10⁸ CFU/mL and detection limit of 46 CFU/mL. Thus, the proposed biosensor has potential application in the diagnosis of pathogenic bacteria.

Evaluation of 3M™ loop-mediated isothermal amplification-based kit and 3M™ ready-to-use plating system for detection of Listeria in naturally contaminated leafy vegetables, chicken, and their related processing environments

The effectiveness of two different rapid methods involving the 3M™ molecular detection assay Listeria and the 3M™ Petrifilm environmental Listeria Plate were evaluated for the rapid detection of Listeria from naturally contaminated vegetables and chicken-processing environments against the standard culture-based method. A total of 178 samples were examined for the presence of Listeria. A total of 47/178 (26.4%) by standard ISO culture-based method (EN ISO 11290-1), 42/178 (23.6%) by 3M™ MDA Listeria and 40/178 (22.5%) by 3M™ Petrifilm EL Plate showed positive results, respectively. The accuracy, sensitivity, specificity, positive predictive value, and negative predictive value for 3M™ MDA Listeria and 3M™ Petrifilm EL Plate were 97.2, 89.4, 99.3, 97.7, 96.4% and 96.1, 85.1, 100.0, 100.0, 94.9%, respectively. Based on the Cohen's Kappa value, there was a complete and robust concordance between 3M™ MDA Listeria (0.911) and 3M™ Petrifilm EL Plates (0.894) as compared to the standard culture-based method.

QCM-based immunosensor for rapid detection of Salmonella Typhimurium in food

Salmonella Typhimurium is one of the main causes of outbreaks and sporadic cases of human gastroenteritis. At present, the rapid detection of this pathogen is a major goal of biosensing technology applied to food safety. In fact, ISO standardized culture method takes up to ten days to provide a reliable response. In this paper, we describe a relatively simple protocol for detecting Salmonella Typhimurium in chicken meat based on a Quartz-Crystal Microbalance (QCM), which leads to a limit of detection (LOD) less than of 10° CFU/mL and requires a pre-enrichment step lasting only 2 h at 37 °C. The reliability of the proposed immunosensor has been demonstrated through the validation of the experimental results with ISO standardized culture method. The cost-effectiveness of the procedure and the rapidity of the QCM-based biosensor in providing the qualitative response make the analytical method described here suitable for applications in food inspection laboratory and throughout the chain production of food industry.

Antibody-conjugated ferromagnetic nanoparticles with lateral flow test strip assay for rapid detection of Campylobacter jejuni in poultry samples

The aim of this study was to develop a nanoparticle-based cell capture system combined with a lateral flow test strip (LFT) assay for rapid detection of Campylobacter jejuni from poultry samples. The developed assay was bench-marked against the standard modified Charcoal Cefoperazone Deoxycholate Agar (mCCDA) method according to ISO16140:2003 procedures. The synthesized ferromagnetic nanoparticles (FMNs) were modified with glutaraldehyde, then functionalized with polyclonal antibodies for specific C. jejuni capture and concentration from poultry samples. After lysing captured cells, DNA from C. jejuni was amplified by PCR using the primers designed to target the hipO gene, and the PCR amplicons were detected with the lateral flow test strip assay. Following the ISO16140:2003 guidelines, the relative detection limit, and the inclusivity and exclusivity tests were determined. The results showed that the limit of detection (LOD) of the assay was 10⁰ or 1 cfu/ml with C. jejuni in pure culture and 10¹-10² cfu/ml with target cells spiked in poultry sample. In addition, the inclusivity and exclusivity tests were found to be 100%. Using field chicken samples (n = 60), the assay showed relative accuracy, relative specificity, and relative sensitivity of 96.67%, 100% and 93.33%, respectively. The positive predictive values (PPV) and negative predictive values (NPV), and the kappa index of concordance (k) were calculated as 100% and 93.75%, and 0.93, respectively. The developed assay required approximately 3 h to complete and gave results comparable to those analyzed by the standard culture method, which required 5-7 days. The assay is rapid, easy-to-use, and has potential to be directly applied to C. jejuni detection in various categories of poultry samples.

Electrochemical biosensors for Salmonella: State of the art and challenges in food safety assessment

According to the recent statistics, Salmonella is still an important public health issue in the whole world. Legislated reference methods, based on counting plate methods, are sensitive enough but are inadequate as an effective emergency response tool, and are far from a rapid device, simple to use out of lab. An overview of the commercially available rapid methods for Salmonella detection is provided along with a critical discussion of their limitations, benefits and potential use in a real context. The distinguished potentialities of electrochemical biosensors for the development of rapid devices are highlighted. The state-of-art and the newest technologic approaches in electrochemical biosensors for Salmonella detection are presented and a critical analysis of the literature is made in an attempt to identify the current challenges towards a complete solution for Salmonella detection in microbial food control based on electrochemical biosensors.

Detection of Salmonella enterica in Meat in Less than 5 Hours by a Low-Cost and Noncomplex Sample Preparation Method

Salmonella is recognized as one of the most important foodborne bacteria and has wide health and socioeconomic impacts worldwide. Fresh pork meat is one of the main sources of Salmonella, and efficient and fast methods for detection are therefore necessary. Current methods for Salmonella detection in fresh meat usually include >16 h of culture enrichment, in a few cases <12 h, thus requiring at least two working shifts. Here, we report a rapid (<5 h) and high-throughput method for screening of Salmonella in samples from fresh pork meat, consisting of a 3-h enrichment in standard buffered peptone water and a real-time PCR-compatible sample preparation method based on filtration, centrifugation, and enzymatic digestion, followed by fast-cycling real-time PCR detection. The method was validated in an unpaired comparative study against the Nordic Committee on Food Analysis (NMKL) reference culture method 187. Pork meat samples (n = 140) were either artificially contaminated with Salmonella at 0, 1 to 10, or 10 to 100 CFU/25 g of meat or naturally contaminated. Cohen's kappa for the degree of agreement between the rapid method and the reference was 0.64, and the relative accuracy, sensitivity, and specificity for the rapid method were 81.4, 95.1, and 97.9%, respectively. The 50% limit of detections (LOD50s) were 8.8 CFU/25 g for the rapid method and 7.7 CFU/25 g for the reference method. Implementation of this method will enable faster release of Salmonella low-risk meat, providing savings for meat producers, and it will help contribute to improved food safety.IMPORTANCE While the cost of analysis and hands-on time of the presented rapid method were comparable to those of reference culture methods, the fast product release by this method can provide the meat industry with a competitive advantage. Not only will the abattoirs save costs for work hours and cold storage, but consumers and retailers will also benefit from fresher meat with a longer shelf life. Furthermore, the presented sample preparation might be adjusted for application in the detection of other pathogenic bacteria in different sample types.

Prevalence and Serogroup Diversity of Salmonella for Broiler Neck Skin, Whole Carcass Rinse, and Whole Carcass Enrichment Sampling Methodologies following Air or Immersion Chilling

The purpose of this study was to evaluate neck skin (NS), whole carcass rinse (WCR), and whole carcass enrichment (WCE) sampling procedures for Salmonella isolation and serogroup identification from the same broiler chicken carcass treated with air or immersion chilling. Commercially processed and eviscerated broiler carcasses were collected from a commercial processing plant, individually bagged, and transported to the pilot processing plant. In experiment 1, carcasses were air chilled to 4°C. In experiment 2, carcasses were immersion chilled with or without chlorine. After air chilling, Salmonella was detected on 78% of NS and 89% of WCE samples. Only one Salmonella serogroup was detected from each of 13 Salmonella-positive NS samples, and two serogroups were detected on 1 Salmonella-positive NS sample. Only one Salmonella serogroup was detected from each of 13 Salmonella-positive WCE samples, and two serogroups were detected from 3 Salmonella-positive WCE samples. After immersion chilling without chlorine, Salmonella was detected on 38% of NS, 45% of WCR, and 100% of WCE samples. Without chlorine, the 15 Salmonella-positive NS samples included 14 samples with one serogroup and 1 sample with two serogroups. Only one Salmonella serogroup was detected from WCR samples after immersion chilling. Of 40 Salmonella-positive WCE samples, 23 had a one, 14 had two, and 3 had three Salmonella serogroups. After immersion chilling with chlorine, Salmonella was detected on 35% of NS, 0% of WCR, and 90% of WCE samples. With chlorine, the 14 Salmonella-positive NS samples included 11 samples with one serogroup and 3 samples with two serogroups. No Salmonella serogroups were detected from WCR samples after immersion chilling with 20 mg/liter free chlorine. The 36 Salmonella-positive WCE samples included 21 samples with one serogroup and 15 samples with two serogroups. NS and WCE sampling methodologies yielded similar prevalence and serogroup diversity after air chilling. However, after immersion chilling with or without chlorine, WCE sampling yielded significantly higher (α ≤ 0.05) prevalence and serogroup diversity than either NS or WCR sampling methodologies.

Application of Molecular Approaches for Understanding Foodborne Salmonella Establishment in Poultry Production

Salmonellosis in the United States is one of the most costly foodborne diseases. Given that Salmonella can originate from a wide variety of environments, reduction of this organism at all stages of poultry production is critical. Salmonella species can encounter various environmental stress conditions which can dramatically influence their survival and colonization. Current knowledge of Salmonella species metabolism and physiology in relation to colonization is traditionally based on studies conducted primarily with tissue culture and animal infection models. Consequently, while there is some information about environmental signals that control Salmonella growth and colonization, much still remains unknown. Genetic tools for comprehensive functional genomic analysis of Salmonella offer new opportunities for not only achieving a better understanding of Salmonella pathogens but also designing more effective intervention strategies. Now the function(s) of each single gene in the Salmonella genome can be directly assessed and previously unknown genetic factors that are required for Salmonella growth and survival in the poultry production cycle can be elucidated. In particular, delineating the host-pathogen relationships involving Salmonella is becoming very helpful for identifying optimal targeted gene mutagenesis strategies to generate improved vaccine strains. This represents an opportunity for development of novel vaccine approaches for limiting Salmonella establishment in early phases of poultry production. In this review, an overview of Salmonella issues in poultry, a general description of functional genomic technologies, and their specific application to poultry vaccine developments are discussed.

Vidas UP-enzyme-linked fluorescent immunoassay based on recombinant phage protein and fluorescence in situ hybridization as alternative methods for detection of Salmonella enterica serovars in meat

Several methods for the rapid and specific detection of Salmonella spp. in meat have been described. This study was conducted to evaluate the capability of the VIDAS(®) UP (SPT [Salmonella Phage Technology]), an enzyme-linked fluorescent immunoassay method, and fluorescence in situ hybridization (FISH) to complement the International Organization for Standardization Method 6579 (ISO) in detecting Salmonella spp. from beef, pork, and poultry meat samples. The meat was inoculated with a mixture of Salmonella spp. on three levels of contamination. It was also checked that the tests did not produce cross-reactions with other Enterobacteriaceae rods. On the basis of the results, the relative specificity, relative accordance, and relative sensitivity of the method were determined. In meat samples, Vidas UP and FISH detection results were in substantial agreement with ISO, with relative specificity, accordance, and sensitivity rates of 90%, 96.3%, and 100%, respectively, for Vidas UP and 100%, 100%, and 99.4%, respectively, for FISH. This is the first report on the evaluation of both Vidas UP and FISH compared to ISO for the rapid detection of Salmonella enterica serovars in meat.

Validation of an open-formula, diagnostic real-time PCR method for 20-h detection of Salmonella in animal feeds

A comparative study of a 20-h, non-commercial, open-formula PCR method and the standard culture-based method NMKL 187, for detection of Salmonella, was performed according to the validation protocol from the Nordic organisation for validation of alternative microbiological methods (NordVal) on 81 artificially or naturally contaminated animal feed samples. The PCR method is based on culture enrichment in buffered peptone water for 16 ± 2 h followed by a magnetic beads based semi automated DNA extraction and real-time PCR analysis, including an internal amplification control. The limit of detection (LOD50) was found to be 7.19 and 7.24 CFU/sample for the PCR method and NMKL187, respectively. A very good correlation between results obtained by the two methods was found (Cohen's kappa=0.92). The relative accuracy, relative sensitivity and relative specificity were found to be 97.5%, 102.0% and 96.6%, respectively. This method is the fastest open PCR based analysis protocol for detection of Salmonella in feed samples. Implementing rapid methods such as the one validated in this study can speed up Salmonella testing of feed for food-producing animals.

Rapid detection of E. coli O157:H7 on turnip greens using a modified gold biosensor combined with light microscopic imaging system

This research aims to demonstrate the feasibility of a modified gold biosensor to detect E. coli O157:H7 in leafy turnip greens. The gold biosensor was modified with dithiobis-succinimidyl propionate (DSP) and/or protein A or G. The gold biosensor modified with DSP (Gold-DSP) was combined with a light microscopic imaging system (LMIS). The optimal concentration and specificity of anti-E. coli O15 polyclonal antibodies (pAbs) on the biosensor were determined. The reliability of Gold-DSP biosensor was investigated by determining the sensitivity, specificity, and limit of detection (LOD) of the Gold-DSP combined with LMIS. The Gold-DSP combined with LMIS was applied to turnip greens for E. coli O157:H7 detection. The modification of Gold biosensor with DSP significantly increased the detected number of E. coli O157:H7. The specificity of pAbs was sufficient to react with target E. coli O157:H7 among the tested bacterial culture. The optimum concentration of pAbs was determined as 200 μg/mL. The sensitivity, specificity, and LOD of Gold-DSP combined with LMIS were determined as 100%, 90%, and 10(3) CFU/25 mm(2) , respectively. When applied to turnip greens, the Gold-DSP combined with LMIS could detect 2641 ± 394 and 15383 ± 3853 cell/mm(2) with the initial concentrations of 10(1) and 10(2) CFU/25 g turnip greens, respectively, after 10 h-enrichment. Overall, this research suggested that the Gold-DSP combined with LMIS could be used to detect E. coli O157:H7 on turnip greens qualitatively and quantitatively.

The need and potential of biosensors to detect dioxins and dioxin-like polychlorinated biphenyls along the milk, eggs and meat food chain

Dioxins and dioxin-like polychlorinated biphenyls (DL-PCBs) are hazardous toxic, ubiquitous and persistent chemical compounds, which can enter the food chain and accumulate up to higher trophic levels. Their determination requires sophisticated methods, expensive facilities and instruments, well-trained personnel and expensive chemical reagents. Ideally, real-time monitoring using rapid detection methods should be applied to detect possible contamination along the food chain in order to prevent human exposure. Sensor technology may be promising in this respect. This review gives the state of the art for detecting possible contamination with dioxins and DL-PCBs along the food chain of animal-source foods. The main detection methods applied (i.e., high resolution gas-chromatography combined with high resolution mass-spectrometry (HRGC/HRMS) and the chemical activated luciferase gene expression method (CALUX bioassay)), each have their limitations. Biosensors for detecting dioxins and related compounds, although still under development, show potential to overcome these limitations. Immunosensors and biomimetic-based biosensors potentially offer increased selectivity and sensitivity for dioxin and DL-PCB detection, while whole cell-based biosensors present interpretable biological results. The main shortcoming of current biosensors, however, is their detection level: this may be insufficient as limits for dioxins and DL-PCBs for food and feedstuffs are in pg per gram level. In addition, these contaminants are normally present in fat, a difficult matrix for biosensor detection. Therefore, simple and efficient extraction and clean-up procedures are required which may enable biosensors to detect dioxins and DL-PCBs contamination along the food chain.

Scientific and technical factors affecting the setting of Salmonella criteria for raw poultry: a global perspective

Concerns about foodborne salmonellosis have led many countries to introduce microbiological criteria for certain food products. If such criteria are not well-grounded in science, they could be an unjustified obstacle to trade. Raw poultry products are an important part of the global food market. Import and export ambiguities and regulatory confusion resulting from different Salmonella requirements were the impetus for convening an international group of scientific experts from 16 countries to discuss the scientific and technical issues that affect the setting of a microbiological criterion for Salmonella contamination of raw chicken. A particular concern for the group was the use of criteria implying a zero tolerance for Salmonella and suggesting complete absence of the pathogen. The notion can be interpreted differently by various stakeholders and was considered inappropriate because there is neither an effective means of eliminating Salmonella from raw poultry nor any practical method for verifying its absence. Therefore, it may be more useful at present to set food safety metrics that involve reductions in hazard levels. Such terms as "zero tolerance" or "absence of a microbe" in relation to raw poultry should be avoided unless defined and explained by international agreement. Risk assessment provides a more meaningful approach than a zero tolerance philosophy, and new metrics, such as performance objectives that are linked to human health outcomes, should be utilized throughout the food chain to help define risk and identify ways to reduce adverse effects on public health.

Comparison of neck skin excision and whole carcass rinse sampling methods for microbiological evaluation of broiler carcasses before and after immersion chilling

Sampling protocols for detecting Salmonella on poultry differ among various countries. In the United States, the U.S. Department of Agriculture Food Safety and Inspection Service dictates that whole broiler carcasses should be rinsed with 400 ml of 1% buffered peptone water, whereas in the European Union 25-g samples composed of neck skin from three carcasses are evaluated. The purpose of this study was to evaluate a whole carcass rinse (WCR) and a neck skin excision (NS) procedure for Salmonella and Escherichia coli isolation from the same broiler carcass. Carcasses were obtained from three broiler processing plants. The skin around the neck area was aseptically removed and bagged separately from the carcass, and microbiological analysis was performed. The corresponding carcass was bagged and a WCR sample was evaluated. No significant difference (alpha </= 0.05) in Salmonella prevalence was found between the samples processed by the two methods, but both procedures produced many false-negative Salmonella results. Prechill, 37% (66 carcasses), 28% (50 carcasses), and 51% (91 carcasses) of the 180 carcasses examined were positive for Salmonella by WCR, NS, and both procedures combined, respectively. Postchill, 3% (5 carcasses), 7% (12 carcasses), and 10% (17 carcasses) of the 177 carcasses examined were positive for Salmonella by the WCR, NS, and combination of both procedures, respectively. Prechill, E. coli plus coliform counts were 3.0 and 2.6 log CFU/ml by the WCR and NS methods, respectively. Postchill, E. coli plus coliform counts were 1.7 and 1.4 log CFU/ml by the WCR and NS methods, respectively.

A validated miniaturized MPN method, based on ISO 6579:2002, for the enumeration of Salmonella from poultry matrices

AIMS

To validate the effectiveness of a miniaturized most probable number method (mMPN) in enumerating Salmonella from poultry matrices.

METHODS AND RESULTS

A MPN was developed, based on the ISO 6579:2002 method using modified semi-solid Rappaport-Vassiliadis media as the sole selective medium. The validation of the mMPN was shown to not differ significantly from, at the 95% confidence level (Student's t-test P = 0·357) to, the traditional 9-tube MPN (tMPN) using pure cultures of Salmonella ser. Typhimurium, Infantis, Montevideo, Muenster and Salmonella subsp II 1,4,12,27:b:[e,n,x] (Sofia). The validation of naturally and artificially contaminated poultry matrices (carcasses, scald tank water, faeces, caeca and feed) showed that detection using the mMPN compared well to the ISO 6572:2002; sensitivity (92%), specificity (97%) and agreement (KAPPA 0·72). The quantitative comparison between the tMPN and mMPN methods showed that 92% of enumerations were less than ± 1 log different (Student's t-test = 0·13). Financial analysis showed that the mMPN required 64% less media and 56% less labour than the tMPN.

CONCLUSION

The mMPN is a consistent, easy to automate method for the enumeration of Salmonella from different poultry matrices.

SIGNIFICANCE AND IMPACT OF STUDY

The miniaturized MPN reduces the material and labour cost of the method and enables the uniform and accurate measurement of the effectiveness of intervention strategies in the control of Salmonella colonization of poultry.