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Salmonella can enter hatcheries via contaminated eggs and other breaches of biosecurity. The study examined the prevalence and distribution of Salmonella in commercial hatcheries and assessed the effects of providing advice on Salmonella control. Intensive swab sampling was performed throughout 23 broiler hatcheries in Great Britain (GB). Swabs were cultured using a modified ISO6579:2017 method. After each visit, tailored advice on biosecurity and cleaning and disinfection procedures was provided to the hatchery managers. Repeat sampling was carried out in 10 of the 23 hatcheries. Salmonella prevalence ranged between 0% and 33.5%, with the chick handling areas, hatcher areas, macerator area, tray wash/storage areas, external areas and other waste handling areas being more contaminated than the setter areas. Salmonella Senftenberg and Salmonella 13,23:i:- were the most commonly isolated serovars. There was a reduction in Salmonella prevalence at the second visit in eight out of 10 premises, but prevalence values had increased again in all of the improved hatcheries that were visited a third time. One hatchery harboured a difficult-to-control resident Salmonella 13,23:i:- strain and was visited six times; by the final visit, Salmonella prevalence was 2.3%, reduced from a high of 23.1%. In conclusion, the study found low-level Salmonella contamination in some GB broiler hatcheries, with certain hatcheries being more severely affected. Furthermore, it was shown that Salmonella typically is difficult to eradicate from contaminated hatcheries, but substantial reductions in prevalence are possible with improvements to biosecurity, cleaning and disinfection.

Disinfectants for veterinary and livestock use, plus skin antiseptics, are critical elements for the control of infectious agents, including zoonotic and antimicrobial-resistant micro-organisms, in managed animal species. Such agents impact animal welfare, economic performance and human health. Testing of disinfectants is needed for safety, efficacy and quality control. The present review examines the principal types of test (carrier, suspension, surface and field) that have been developed or attempted, plus the features inherent in the respective tests, particularly with respect to variability. Elements of testing that have to be controlled, or which can be manipulated, are discussed in the context of real-world scenarios and anticipated applications. Current national and international testing regimes are considered, with an emphasis on the UK, continental Europe and North America, and with further detail provided in the Supporting Information. Challenges to disinfectant efficacy include: the nature of the biological targets (bacteria, fungi, yeasts, spores, viruses and prions), the need for economical and safe working concentrations, the physical and chemical nature of contaminated surfaces, constraints on contact times and temperatures, the presence of organic soil and other barrier or neutralising substances (including biofilms), and thoroughness of pre-cleaning and disinfectant application. The principal challenges with veterinary disinfectant testing are the control of test variability, and relating test results to likely performance in variable field conditions. Despite some ambitions to develop standardised field tests for disinfectants, aside from skin antiseptic trials the myriad problems such tests pose with respect to cost, reproducibility and generalisability remain intractable.

Reducing the risk of Salmonella contaminated pork products entering the food chain is important for improving food safety. This study aimed to evaluate the effectiveness of the short-duration use of three acidified feed interventions in finisher pigs for reducing the faecal shedding, caecal carriage and carcase contamination of Salmonella at slaughter. We also investigated the presence of Salmonella in transportation vehicles and abattoir lairages used prior to slaughter. In a series of seven farm trials, two groups of pigs received either their normal ration (control), or a ration containing one of three organic acid products (intervention) for a four-week period before slaughter. Product A was trialled on five farms, and Products B and C were trialled on one farm each, included in the ration of intervention pigs at the manufacturers recommended rate. Faecal samples were collected and examined before and after the four-week intervention; caecal content samples and carcase swab samples were collected at slaughter. The lorry used to transport pigs to slaughter and abattoir lairage pens used to hold pigs were also sampled. During one trial (farm ID: AT03), no Salmonella was detected during either farm visit, and therefore this farm was excluded from further analysis of the effectiveness of organic acid interventions. Overall regression analysis indicated there was no significant difference in faecal shedding between the control groups at the baseline visit and the follow-up visit in pigs which received Product A (P = 0.262) or Product B (P = 0.094) in comparison to the control groups. On the other hand, there was evidence to suggest that the use of Product C was associated with an increase in faecal shedding compared to the control groups (P0.001). Similarly, Product A was not significantly associated (P 0.05) with the caecal carriage of Salmonella. However, Product B (P = 0.029) and Product C (P = 0.050) were associated with an increase in caecal carriage in comparison to the control groups. These latter products were only trialled on one farm each, and these results may be attributable to natural random variation.

AIM: Shiga toxin-producing Escherichia coli (STEC) cause bloody diarrhoea, kidney failure and occasionally death. However, identifying the source of infection caused by STEC other than serogroup O157 is hampered by availability of sensitive methods for detecting these pathogens. In this study we developed novel tools for detecting E. coli O55 that is potentially associated with human outbreaks. METHOD AND RESULTS: Overall specificity of immuno-magnetic separation (IMS) beads coated with anti-O55 serum was good with exception of cross reactivity with E. coli O22 and O23, which was eliminated using an O55 specific PCR. Limit of detection for E. coli O55 using O55-IMS-beads in spiked cattle faeces was on average 50 CFU ml-1 (range 1-90), and improved to

This study compared a novel non-formaldehyde combination product developed for pathogen control in animal feed Finio (A), with a panel of three commonly used organic acid feed additive products: Fysal (B), SalCURB K2 (C) and Salgard (D). Products were evaluated for their ability to reduce Salmonella Typhimurium DT104 and avian pathogenic Escherichia coli in poultry feed. A commercial layer-hen mash was treated with each product and then mixed with feed previously contaminated (via inoculated meat and bone meal) with either Salmonella or E. coli. After 24 h at room temperature, 10 replicate samples were taken from each preparation and plate counts were performed using a selective agar. All concentrations of product A (0.5, 1.0, 1.5, 2.0 and 2.5 kg per metric tonne (MT)) plus the higher concentration of products B and D (6.0 kg MT−1) significantly reduced Salmonella counts compared with those in the untreated control group (p < 0.05). Product C did not significantly reduce levels of Salmonella under these conditions. Because of the poor recovery of E. coli, statistical comparisons for this organism were limited in scope, but only product A at the highest concentration appeared to have eliminated it.

SUMMARY While the consumption of duck eggs has gained popularity over the past few years, little is known about the prevalence of Salmonella in duck flocks and the associated potential Public Health impact. In order to detect Salmonella infection in duck flocks, sensitive sampling methods are essential; however, sampling costs and the practicalities of sampling have to be reasonable to allow testing on a large scale. In this study of 67 Salmonella-positive duck flocks, we assessed the suitability of several sample types. Different combinations of samples were also explored to produce advice on the most sensitive, yet practical sampling method. Overall, detecting all positive flocks proved challenging, and the number of samples collected from a flock appeared to influence the outcome rather than the actual type of sample. While a number of different sampling options proved successful to detect high prevalence flocks, low prevalence flocks were only detected satisfactorily if several sample types were taken and the results combined. It was concluded that the detection of Salmonella-positive breeding, laying or fattening duck flocks requires more samples compared to chicken or turkey flocks in order to achieve a meaningful outcome.

Following a rapid rise in cases of monophasic Salmonella Typhimurium DT193 (mST) in humans and pigs since 2007 a detailed study of the prevalence and persistence of mST on pig and cattle farms in Great Britain (GB) was undertaken. Thirteen commercial pig farms and twelve cattle farms, identified as mST-positive from surveillance data, were intensively sampled over a three year period. Five indoor and eight outdoor pig farms and four beef and eight dairy farms were included. Individual and pooled faecal samples were collected from each epidemiological group and environmental samples throughout each farm and the antimicrobial resistance profile determined for a selection of mST-positive isolates. Indoor pig farms had a higher mST prevalence than outdoor pig farms, and across both cattle and pig farms the juvenile animals had a higher mST prevalence than the adult animals. Overall, mST prevalence decreased with time across all pig farms, from 25% to less than 15% of environmental samples and 22% to 15% of pooled faecal samples; only one organic outdoor breeding farm was Salmonella-negative at the end of the study. Across the cattle farms no mST was detected by the end of the study, apart from one persistent farm. Clearance time of mST was between seven and twenty-five months. Farms were selected based on having the antimicrobial resistance profile ampicillin, streptomycin, sulphonamides and tetracycline (A, S, SU, T), although resistance to trimethoprim-potentiated sulphamethoxazole was also identified on five pig farms sampled. This study provided a detailed insight into the distribution and persistence of mST on individual pig and cattle farms in GB. It has identified variation in mST shedding of individual animals, and the data can be applied to the wider livestock industry when considering the distribution of mST once identified on an individual farm.

In the European Union, statutory control of Salmonella is in place in the chicken and turkey sectors, but not in the duck sector. In this study, 14 Salmonella-positive duck farms were sampled before and after cleaning and disinfection, and once the houses had been restocked with a new flock. The cleaning and disinfection programmes used were subdivided into two main categories: ones in which a final formaldehyde disinfection step was included (1) and ones in which it was not included (2). Several types of samples were collected during the study, and faecal samples were those more frequently positive (62% of faecal samples were positive for Salmonella in comparison to 2-23% of samples from all the other sample categories) (P 0.001). Independently of the cleaning and disinfection programme used, there was a statistically significant (P 0.001) reduction in the percentage of Salmonella-positive samples between before cleaning and disinfection (41.1%) and after cleaning and disinfection (3.1%). After restocking, the number of Salmonella-positive samples increased significantly (P 0.001), with 65.3% of the samples tested being positive for Salmonella. Farms in which disinfection programme 1 was used were 5.34 times less likely to have samples positive for Salmonella after cleaning and disinfection than farms which implemented programme 2. Formaldehyde acts effectively against Salmonella even in the presence of some residual organic matter. Limited residual contamination on farms after cleaning and disinfection represents a risk of infection for young ducklings, and thorough cleaning and disinfection procedures should be implemented to reduce the carry-over of infection between flocks.

In 2010, 81 confirmed cases of Salmonella Typhimurium DT8 were reported across England and Northern Ireland - an increase of 26% from 2009 and 41% since 2008. Five cases were hospitalized and one death reported, with a strong association found between cases and the consumption of duck eggs. Once present on farms, Salmonella may become persistent and can survive for long periods of time in residual organic matter, increasing risk of infection for follow-on flocks if cleaning and disinfection is not carried out effectively. The aim of this study was to investigate the efficacy of a range of disinfectants used by the duck industry against Salmonella using laboratory models. Sixteen products were selected from seven chemical groups and the Minimum Inhibitory Concentration and Minimum Bactericidal Concentrations determined. Each product was also tested at the recommended general orders (GO) concentration using a faecal suspension model to mimic boot dips and a surface contamination model to simulate contaminated building fabric and equipment. In the faecal suspension model, all products were effective at 2 × GO concentration, and activity was more inconsistent at GO concentration. At 0.5 × GO concentration, iodine-based and quaternary-ammonium-compound-based products were significantly less effective than products within other chemical groups (P 0.001). Glutaraldehyde-based products were significantly more effective than the other products in the surface contamination tests (P 0.001). Chlorocresol-based products were found to be most effective for use in boot dips and aldehyde-based products for surface disinfection, although there was variability between products within a chemical group.

The study examined the effects of a licensed live Salmonella Typhimurium vaccine, administered to sows and gilts on three commercial pig units experiencing clinical salmonellosis associated with S. Typhimurium or its monophasic variant. After vaccination, clinical salmonellosis resolved and shedding of S. Typhimurium declined markedly and persistently on all breeding or breeding-finishing units, during the one- to two-year monitoring period. On two finishing units supplied in part by one of the vaccinated herds, pigs from the vaccinated herd were less likely to shed Salmonella than those from non-vaccinating herds, and Salmonella counts in faeces were also lower from the vaccine-linked animals. Non-Typhimurium Salmonella serovars were isolated typically in fewer than 10% of samples, and showed no clear temporal changes in frequency. Vaccination of dams alone with S. Typhimurium was associated with reduced shedding of closely-related serovars among all age groups in this commercial setting.

Salmonella prevalence in UK pigs is amongst the highest in Europe, highlighting the need to investigate pig farms which have managed to maintain a low Salmonella seroprevalence. A total of 19 pig farms that had a consistently low (Salmonella compared with the Platinum farms (12.1% and 0.4% for pooled faecal samples, respectively) and were more likely to have serovars of public health importance detected (S. Typhimurium/ monophasic variants or S. Enteritidis). Considering the comprehensive on-farm sampling, the identification of farms negative for Salmonella, along with the identification of those that had maintained low prevalence over a long period is important. The risk factor analyses identified pelleted feed, feed deliveries crossing farm perimeter and regular antibiotic use as associated with being a Control farm. Performance data indicated that Platinum farms were performing better for slaughter live weight than Controls. Limited assessments of available pig movement records suggested that the source of pigs was not key to Platinum status, but further study would be needed to confirm this finding. These results emphasise that maintaining very low prevalence on UK farms is achievable.

SUMMARYAnecdotal evidence has suggested that outdoor-kept pigs show an improvement to health and productivity after being moved to a new site. This study explores whetherSalmonellaoccurrence reduced and was sustained after moving to a new site. Nine farms were followed for a year in which four sampling visits were completed. The highest detection ofSalmonellawas from pooled faecal dropping from pigs, run-off/ pooled water, rodents and wild birds. Descriptive summaries showed that the prevalence of both allSalmonellaand serovars of public health importance were lower at all visits after the move. Some variability was shown in results from individual farms, but a year after the move, six farms still maintained a lower prevalence. A risk factor model showed that the prevalence at visits 2 and 3 after the move was significantly lower than baseline, after accounting for a number of significant factors that were included in the model. These were sample type and seasonality (included asa priori), presence of coughing in the sampled group and Glasser's disease on the farm, and the use of tent or kennel accommodation. This finding provides important evidence that more frequent site moves may help reduceSalmonellaprevalence in outdoor herds.

High standards of biosecurity are known to reduce the risk of disease outbreaks; however, uptake of advice and implementation of biosecurity measures are dependent on many factors. This study assessed the uptake of targeted biosecurity advice by 60 laying hen farms provided during biosecurity audit visits. Advice was provided as bullet point cards focusing on specific areas identified as benefitting from improvement. These covered site entrance, site tidiness, vaccination, boot hygiene, hand hygiene, house tidiness, rodent control, fly control, red mite control and cleaning and disinfection between flocks. Background knowledge of Salmonella and biosecurity and farmers' willingness and intent to implement additional measures were assessed. About 50% of the principal decision-makers had basic background knowledge of Salmonella, with 22% considered well informed; almost all agreed that biosecurity could impact on Salmonella control and many appeared willing to implement additional biosecurity measures. Sixty-three per cent of study farms were categorised using the Defra Farmer Segmentation Model as Modern Family Businesses (MFBs), with 7-11% of farms being categorised as Custodian, Lifestyle Choice, Pragmatist or Challenged Enterprise; however, categorisation, did not determine uptake of advice. The most frequently used advice cards were boot hygiene, red mite control, hand hygiene, site entrance and cleaning and disinfection; uptake of advice ranged from 54 to 80% depending on the advice card. Uptake of advice by the farmers was encouraging, especially considering it was being provided by people other than their usual source of biosecurity information. Those who did not implement the recommended measures cited cost, difficulty of enforcement and practicality as the main reasons. However, the positive uptake of advice and implementation of recommended measures by many farmers demonstrates that targeted advice, discussed face to face with farmers, on a small number of key areas, is a potentially effective method of providing biosecurity information to complement more lengthy formal advisory reports.

In line with European legislation and the UK National Control Programme for Salmonella, poultry farms are sampled to establish their Salmonella status. Regular samples are collected by the farmer (operator), with annual routine (official) samples being collected by the competent authority to verify achievement of the Salmonella programme reduction target. To confirm sampling was being carried out effectively, a questionnaire-based survey was conducted. The aim was to identify any complicating factors the samplers encountered and the decisions made in these circumstances. There was good compliance with the official sampling visits, with few delays reported. However, farm-specific clothing/separate boots for non-caged houses were rarely provided by the operator, whereas boot dips and hand washing facilities were usually available. The collection of dust was often a problem for official samplers, operator boot swabs were not always moistened before sampling and both sampler groups did not always follow the recommended method for the collection of faeces from belts and scrapers. Overall, there was a good application of the sampling protocol, although a few areas for improvement were identified.

Salmonella Enteritidis (SE) and, to a lesser extent, Salmonella Typhimurium (ST) are associated with egg-related outbreaks in people. Recently, monophasic strains of ST (mST; lacking one phase of the flagellar antigen) have been described, and they have officially been classified as variants of ST and thus may contribute to human exposure to contaminated eggs. Currently used vaccination programmes are licensed for use against biphasic variants of ST, and their efficacy against mST has not yet been investigated. In this study, the effectiveness of four vaccination programmes currently in use in the UK poultry industry was evaluated against challenge with one SE strain, one ST strain and two mST strains. A Bayesian model was used to estimate the impact of vaccination on the rate of faecal shedding and on egg contamination. For the majority of vaccine/challenge strain combinations, there was little or no effect of vaccination on the proportion of birds shedding Salmonella for either biphasic or monophasic strains. However, vaccination was effective at reducing egg contamination. A significantly lower proportion of eggshells were positive for the vaccinated birds compared with non-vaccinated birds, including the mST strains (vaccination resulted in a 55% and 21% reduction for the two mST strains). Calculated across all strains, the estimated rate of positive egg contents was lower in vaccinated birds (Bayesian median was 0.13% for vaccinated birds versus 0.27% for non-vaccinated birds). For both vaccinated and unvaccinated birds, there was also an apparent difference in the proportion of positive organs between strains, with the SE strain resulting in a lower proportion of positive organs at post-mortem examination compared with the other strains.

Serological surveillance and vaccination are important strategies for controlling infectious diseases of food production animals. However, the compatibility of these strategies is limited by a lack of assays capable of differentiating infected from vaccinated animals (DIVA tests) for established killed or attenuated vaccines. Here, we used next generation phage-display (NGPD) and a 2-proportion Z score analysis to identify peptides that were preferentially bound by IgY from chickens infected with Salmonella Typhimurium or S. Enteritidis compared to IgY from vaccinates, for both an attenuated and an inactivated commercial vaccine. Peptides that were highly enriched against IgY from at least 4 out of 10 infected chickens were selected: 18 and 12 peptides for the killed and attenuated vaccines, respectively. The ten most discriminatory peptides for each vaccine were identified in an ELISA using a training set of IgY samples. These peptides were then used in multi-peptide assays that, when analysing a wider set of samples from infected and vaccinated animals, diagnosed infection with 100% sensitivity and specificity. The data describes a method for the development of DIVA assays for conventional attenuated and killed vaccines.

Mapping polyclonal antibody responses to infectious diseases to identify individual epitopes has the potential to underpin the development of novel serological assays and vaccines. Here, phage-peptide library panning coupled with screening using next generation sequencing was used to map antibody responses to bacterial infections. In the first instance, pigs experimentally infected with Salmonella enterica serovar Typhimurium was investigated. IgG samples from twelve infected pigs were probed in parallel and phage binding compared to that with equivalent IgG from pre-infected animals. Seventy-seven peptide mimotopes were enriched specifically against sera from multiple infected animals. Twenty-seven of these peptides were tested in ELISA and twenty-two were highly discriminatory for sera taken from pigs post-infection (P Salmonella enterica. Twenty-seven peptides were identified as being enriched specifically against IgY from multiple animals infected with S. Enteritidis compared to those infected with S. Hadar. Nine of fifteen peptides tested in ELISA were highly discriminatory for IgY following S. Enteritidis infection (p S. Hadar or S. Typhimurium.

Reports of Salmonella in ducks in the UK currently rely upon voluntary submissions from the industry, and as there is no harmonized statutory monitoring and control programme, it is difficult to compare data from different years in order to evaluate any trends in Salmonella prevalence in relation to sampling methodology. Therefore, the aim of this project was to assess the sensitivity of a selection of environmental sampling methods, including the sampling of faeces, dust and water troughs or bowls for the detection of Salmonella in duck flocks, and a range of sampling methods were applied to 67 duck flocks. Bayesian methods in the absence of a gold standard were used to provide estimates of the sensitivity of each of the sampling methods relative to the within-flock prevalence. There was a large influence of the within-flock prevalence on the sensitivity of all sample types, with sensitivity reducing as the within-flock prevalence reduced. Boot swabs (individual and pool of four), swabs of faecally contaminated areas and whole house hand-held fabric swabs showed the overall highest sensitivity for low-prevalence flocks and are recommended for use to detect Salmonella in duck flocks. The sample type with the highest proportion positive was a pool of four hair nets used as boot swabs, but this was not the most sensitive sample for low-prevalence flocks. All the environmental sampling types (faeces swabs, litter pinches, drag swabs, water trough samples and dust) had higher sensitivity than individual faeces sampling. None of the methods consistently identified all the positive flocks, and at least 10 samples would be required for even the most sensitive method (pool of four boot swabs) to detect a 5% prevalence. The sampling of dust had a low sensitivity and is not recommended for ducks.

Objective There is widespread and longstanding use of dogs in land search and rescue (SAR) operations, and their effectiveness is well accepted within the SAR community. However, very little published research exists that quantifies that effectiveness within a realistic SAR environment. Methods This study included 25 experiments, conducted between October 2013 and February 2014 with 10 dog/handler pairs, using randomized target placement to calculate the ratio of hits, misses, and false positives per dog. Each dog was fitted with a GPS receiver to record their paths and ambient temperature. Wind strength and humidity were recorded throughout each run. Results There was no identifiable correlation between humidity, temperature, or wind speed and effectiveness, but the age of the dog has a small positive correlation. Using a standard effectiveness formula, basic descriptive statistics were generated, which showed that the dogs tested were 76.4% successful overall, with an effectiveness of 62.9%. Dogs covered a mean distance 2.4 times greater than their human handlers but travelled at roughly average human walking speed. Conclusions This work represents a first attempt to quantify and understand levels of performance in lowland search dogs, and these results need to be understood within that context. A repeatable experimental framework has been demonstrated and provides a foundation for further work in this area.

SUMMARYThere has been a rapid rise in the prevalence of cases of monophasic Salmonella Typhimurium (mST) in both humans and farm animals, and it has been found in pigs, cattle and poultry. It is therefore vital to have a good understanding of how to efficiently detect infected farms. The objective of this project was to determine sample type sensitivity in the detection of Salmonella to detect infected groups of animals on both pig (breeder, grower and finisher sites) and cattle (beef and dairy) farms, using data collected from a study investigating farms that were positive for mST, and to explore any variation between different age groups and management practices. A Bayesian approach in the absence of a gold standard was adopted to analyse the individual and pooled faecal sample data collected from each epidemiological group on each of the farms. The sensitivity of pooled sampling depended on the prevalence of infection in the group being sampled, with a higher prevalence leading to higher sensitivity. Pooled sampling was found to be more efficient at detecting positive groups of animals than individual sampling, with the probability of a random sample from a group of animals with 5% prevalence testing positive being equal to 15·5% for immature pigs (3·6% for an individual faecal sample, taking into account the sensitivity and infection prevalence), 7·1% for adult pigs (1·2% for individual sampling), 30% for outdoor cattle (2% for individual sampling) and 34% for indoor cattle (1% for individual sampling). The mean prevalence of each epidemiological group was higher in outdoor farms than indoor for both pigs and cattle (mean within-farm prevalence of 29·4% and 38·7% for outdoor pigs and cattle, respectively, compared to 19·8% and 22·1% for indoor pigs and cattle)

Salmonella-contaminated poultry house dust plus 10 g chicken faeces inoculated with Salmonella Enteritidis and then frozen for storage and transport were used as candidate external quality assurance test samples. Variations in faeces sample preparation, storage and culture were examined initially. This indicated that, within modest limits, the age of the inoculating culture and of the faeces did not affect detection, nor did swirling the pre-enrichment culture or extending its duration. Under optimal conditions of preparation and storage, Salmonella numbers of 70 colony-forming units (CFU) and above were reliably detected at the originating laboratory. A ring trial was performed, involving 13 external UK laboratories plus the originating laboratory. Faeces samples inoculated with Salmonella Enteritidis were frozen, transported on dry ice and tested by the ISO 6579:2002 (Annex D) method. Detection by the originating laboratory was consistent with the previously established lower limit for reliability of 70 CFU. However, the sensitivity of detection by the external laboratories was apparently poorer in several cases, with significant interlaboratory variation seen at the lowest inoculum level, using Fisher's exact test. Detection of Salmonella in poultry house dust appeared to be more sensitive and uniform among laboratories. Significance and Impact of the Study Salmonella surveillance and control regimes in the European poultry industry and elsewhere require sensitive culture detection of Salmonella in environmental samples, including poultry faeces. A ring trial was conducted, and the results highlighted that some of the participating laboratories failed to identify Salmonella. This suggests that contaminated frozen faeces cubes could be beneficial to assess proficiency, according to the results of this preliminary study. The data obtained in this study can be used as an indication for the design of realistic external quality assurance for laboratories involved in official testing of Salmonella in poultry flocks.

Egg-related outbreaks of salmonellosis are a significant health concern. Although Salmonella Enteritidis (SE) is the major egg-associated serotype, Salmonella Typhimurium (ST) can also infect the hen's reproductive tract and contaminate eggs. Recently, monophasic and aphasic variants of ST have been reported with increased frequency in Europe, and the isolation of these variants from laying flocks triggers the same legislative restrictions associated with biphasic ST strains. However, little is known about the colonization, invasiveness and persistence of monophasic and aphasic ST strains in laying hens. In this study, seven groups of 1-day-old and point-of-lay commercial Hy-line chicken layers were separately challenged with four different strains of monophasic ST, one aphasic ST, one biphasic ST and one egg-invasive SE strain. Tissue samples and cloacal swabs (point-of-lay chickens only) were collected at regular intervals post challenge in order to recover the Salmonella challenge strains. In 1-day-old chicks, only the aphasic ST strain and the SE strain were recovered after direct plating, suggesting that the number of salmonellas colonizing the tissues of the chicks infected with the other strains was likely to be low. Interestingly, all of the strains colonized well in the point-of-lay chickens, and there was no statistical difference in the overall number of positive samples or Salmonella counts between the seven strains. Salmonella was recovered from the point-of-lay birds to the end of the study (20 days after challenge). Monophasic and aphasic ST strains colonized point-of-lay birds as efficiently as biphasic ST and SE strains. Further studies are necessary to estimate the invasiveness of these strains in naturally-infected vaccinated laying hens, and to assess the impact of natural infection on egg contamination.

Organic acid products are widely used in the UK poultry industry as feed or water additives. Claims for Salmonella control are made for some of these products, but there are few studies comparing the anti-Salmonella effect of the various products in tests that reflect field application. The present studies examined the effects of 13 commercial blends (four water products and nine feed products) on Salmonella Enteritidis and Typhimurium strains. Initial screening, in nutrient broth, of all products with all strains revealed little variation between strains in respect of maximum inhibitory and bactericidal dilutions of each product. However, between the products there was wide and significant variation in the maximum inhibitory and bactericidal dilutions, spanning a 700-fold range in the case of bactericidal dilutions for feed-associated products. Further tests were performed, examining reductions in inoculated Salmonella numbers in various matrices (water, feed, soiled litter, crop and caecal contents) following the addition of the products at recommended inclusion rates. One product, incorporating formaldehyde in addition to organic acid, was consistently most active in all matrices, exceeding reductions associated with other products by 1 to 3 log units at most time points. Many products showed only modest anti-Salmonella activity, amounting to 0 or 1 log unit above negative controls at many time points, and the most active products were not the same in all matrices. Tap water appeared to enhance the ability of products to reduce Salmonella, in comparison with bottled mineral or river water.