Field investigations of multidrug-resistant Salmonella Infantis epidemic strain incursions into broiler flocks in England and Wales.

Salmonella Infantis is a major public health concern and has become established in the broiler sector in some European countries, as well as globally, and is frequently multidrug resistant (MDR). Three broiler farms in England and Wales, which had incursions of MDR S. Infantis between 2013 and 2017, were investigated longitudinally. The company feed mill and two associated hatcheries were intensively sampled. Following each visit, advice on cleaning, disinfection and other control measures for Salmonella was given to help eliminate S. Infantis from the premises. Four samples collected from inside the broiler houses after cleaning and disinfection were Salmonella-positive, indicating cleaning and disinfection within houses was generally effective. However, the exterior of persistently infected houses remained substantially contaminated and feeding systems could not be sampled. Clearance of S. Infantis from affected houses requires additional attention to decontamination of these aspects. Sixty S. Infantis isolates were tested for antimicrobial susceptibility by disk diffusion tests. All isolates were MDR, with resistance to at least nalidixic acid (Na), tetracycline (T), compound sulphonamide (Su), streptomycin (S) and furazolidone. This is a similar resistance pattern to the previously identified MDR (NaSSuT) clone in some European countries. The study shows that to remove S. Infantis from premises effectively, a combined approach to poultry houses and the surrounding farm environment is necessary. A revised cleaning and disinfection programme was developed that was associated with the clearance of MDR S. Infantis from persistently infected and newly infected broiler flocks, and UK livestock remains free of MDR S. Infantis. RESEARCH HIGHLIGHTS Standard cleaning and disinfection protocols did not completely eliminate infection. A revised cleaning and disinfection programme was developed. Disinfecting feeder lines and external areas was key to eliminating S. Infantis. Identified similar antimicrobial resistance pattern to MDR epidemic S. Infantis.

Role of wild birds and environmental contamination in the epidemiology of Salmonella infection in an outdoor pig farm.

Foodborne outbreaks caused by Salmonella are often attributed to the pork consumption. Salmonella contamination of retail pork is directly linked to the Salmonella prevalence on farm. In UK, approximately 40% of breeding pigs are kept outdoors. Aim of this study was to investigate the role of wild birds in the epidemiology of Salmonella in one outdoor pig farm. Three sampling visits were carried out at monthly intervals to an outdoor farm consisting of two fields, one left empty of pigs for more than 2 years (field A) while the second (field B) was occupied by pigs during the first visit only. Faeces from wild bird droppings, environmental samples and pig faeces were tested for Salmonella. Salmonella spp. was isolated from environmental samples also in field A that had not been occupied by pigs more than 2 years. Interestingly, the wild bird population accessing the fields increased considerably once the pigs had left the farm and the proportion of Salmonella positive wild bird droppings increased over time with 7.4%, 15.8% and 44.3% at the first, second and third visit, respectively. The levels of Salmonella identified in some of the wild bird droppings were unusually high (105-106 CFU/g) suggesting that Salmonella was actively replicating in the gastrointestinal tract of these birds. Monophasic Salmonella Typhimurium DT193 was the predominant serotype isolated in pigs as well as in wild bird droppings and the environment, suggesting that the pigs were the original source of infection, as this serovar is typically associated with pigs.

Observations on the distribution and persistence of monophasic Salmonella Typhimurium on infected pig and cattle farms.

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.

Commercial Frozen Mice Used by Owners to Feed Reptiles are Highly Externally Contaminated with Salmonella Enteritidis PT8.

Salmonella remains one of the most prevalent zoonoses worldwide. Although salmonellosis is commonly associated with the consumption of contaminated food, it has been estimated that up to 11% of Salmonella infections overall are acquired from direct or indirect contact with animals, including reptiles. In 2016, an outbreak of Salmonella Enteritidis involving multiple cases, especially children, associated with reptile contact and contaminated feeder mice was reported in the United Kingdom. The aim of this study was to investigate Salmonella external and internal contamination of stored commercial frozen feeder mice used to feed reptiles and obtained from the same supplier involved in the outbreak. In this study a total of 295 mice were tested (60 pinkies, 60 fuzzies, 60 small, 60 large, and 55 extra large). In this study, both external (integument) and internal (selected organs) contamination were evaluated. Salmonella Enteritidis PT8 and PT13 were isolated from 28.8% (n = 17) of the 59 batches tested, with the exception of the large mice category. Positive mice were mostly contaminated externally (92.3% vs. 26.9% for carcass wash and viscera, respectively). All isolates were sensitive to all 16 antimicrobials tested. The high level of external contamination of the rodent carcasses might have played a role in the human outbreak in 2016. Reptile owner management of the rodent carcasses at home could be an important source of salmonellosis outbreaks. Collaboration among public health officials, pet industry, veterinarians, and reptile owners is needed to help prevent the risk of salmonellosis associated with animal-based food intended for reptiles.

Evaluation of an enhanced cleaning and disinfection protocol in Salmonella contaminated pig holdings in the United Kingdom.

Salmonella is the second most commonly reported zoonotic gastrointestinal pathogen in the European Union, and a significant proportion of the cases are linked to the consumption of contaminated pork. Reduction of Salmonella at the farm level helps to mininimise the contamination pressure at the slaughterhouse, and therefore the number of Salmonella bacteria entering the food chain. Cleaning and disinfection (C&D) between batches of pigs is an intervention measure that has potential to reduce the transmission of Salmonella contamination within farms. In this study, two pig finisher buildings in each of 10 Salmonella positive farms were sampled pre-C&D, post-C&D, post-restocking with the following batch of pigs, and shortly before these pigs were sent to slaughter. The incoming batch of pigs was also sampled before it reached the study building (pre-restocking). At each visit, pooled and individual faecal samples were collected and Salmonella isolation was carried out according to an ISO 6579:2002 Annex D-based method. One building on each farm (intervention) was cleaned and disinfected according to a rigorous protocol consisting of several steps and a Defra-approved disinfectant used at the General Orders concentration, whilst the other building (control) was cleaned and disinfected as per normal farm routine. At the post-C&D visit, Enterobacteriaceae and total bacterial counts were determined to evaluate residual faecal contamination and general hygiene levels. Rodent specialists visited the farms before and after C&D and rodent carcasses were collected for Salmonella testing. The intervention buildings were significantly less likely (p = 0.004) to be positive for Salmonella after C&D. The pre-restocking pigs had the highest likelihood (p<0.001) of being Salmonella positive (often with multiple serovars) and there was no significant difference between intervention and control buildings in Salmonella prevalence at the post-restocking visit (p = 0.199). However, the pigs housed in the intervention buildings were significantly less likely (p = 0.004) to be positive for Salmonella at slaughter age. Multivariable analysis suggested that cleaning all fixtures of buildings, leaving the pens empty for 2-3 days and using an effective disinfectant are factors significantly improving the likelihood of removing Salmonella contamination during C&D. Signs of rodents were recorded in all farms, but rodent activity and harbourage availability decreased between visits. All the rats tested were Salmonella negative. S. Typhimurium or its monophasic variants were isolated from 6 mouse carcasses in 3 farms where the same serovars were isolated from pigs. This study demonstrates that an appropriate C&D programme significantly reduces the likelihood of residual contamination in Salmonella positive pig buildings, and suggests a significant reduction in the prevalence of Salmonella in the pigs in appropriately cleaned and disinfected buildings when sampled before slaughter. Due to a high prevalence of infection in replacement pigs, control of Salmonella in pig farms is challenging. Rodents may also contribute to the carry-over of infection between batches. C&D is a useful measure to help reduce the number of infected pigs going to the slaughterhouse, but should be supplemented by other control measures along the pig breeding and production chain.

Assessment of anti-Salmonella activity of boot dip samples.

The introduction of pathogens from the external environment into poultry houses via the boots of farm workers and visitors presents a significant risk. The use of boot dips containing disinfectant to help prevent this from happening is common practice, but the effectiveness of these boot dips as a preventive measure can vary. The aim of this study was to assess the anti-Salmonella activity of boot dips that are being used on poultry farms. Boot dip samples were collected from commercial laying hen farms in the UK and tested within 24 hours of receipt at the laboratory to assess their anti-Salmonella activity. All boot dip samples were tested against a field strain of Salmonella enterica serovar Enteritidis using three test models: pure culture, paper disc surface matrix and yeast suspension model. Of the 112 boot dip samples tested 83.6% were effective against Salmonella in pure culture, 37.3% in paper disc surface matrix and 44.5% in yeast suspension model. Numerous factors may influence the efficacy of the disinfectants. Disinfectants used in the dips may not always be fully active against surface or organic matter contamination; they may be inaccurately measured or diluted to a concentration other than that specified or recommended; dips may not be changed regularly or may have been exposed to rain and other environmental elements. This study showed that boot dips in use on poultry farms are frequently ineffective.

Characterization of the invasiveness of monophasic and aphasic Salmonella Typhimurium strains in 1-day-old and point-of-lay chickens.

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.

Assessment of the anti-Salmonella activity of commercial formulations of organic acid products.

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.