Salmonella occurrence and Enterobacteriaceae counts in pig feed ingredients and compound feed from feed mills in Ireland

Search for carbapenem-resistant bacteria and carbapenem resistance genes along swine food chains in Central Italy

The presence of carbapenem-resistant bacteria and carbapenem resistance genes (CRGs) in livestock is increasing. To evaluate the presence of carbapenemase-producing Enterobacteriaceae (CPE) and the main CRGs along swine food chains of the Marche Region (Central Italy), samples of faeces, feed, and animal-food derived products were collected from seven small/medium, medium, and large-scale pig farms. A total of 191 samples were analysed using a culture-dependent method, with the aim of isolating CPE. Isolates were analysed for their resistance to carbapenems using a modified Hodge test and the microdilution method for the minimum inhibitory concentration (MIC) determination. Moreover, the extraction of microbial DNA from each sample was performed to directly detect selected CRGs via qPCR. Among the 164 presumptive resistant isolates, only one strain from a liver sample, identified as Aeromonas veronii, had an ertapenem MIC of 256 μg/mL and carried a carbapenemase- (cphA) and a β-lactamase- (blaOXA-12) encoding genes. A low incidence of CRGs was found; only nine and four faecal samples tested positive for blaNDM-1 and blaOXA-48, respectively. Overall, the importance of monitoring CPE and CRGs in livestock and their food chains should be stressed to control all potential non-human CPE and CRGs reservoirs and to determine safety levels for human health.

Effectiveness of the Organic Acid-Based Antimicrobial Agent to Prevent Bacterial Contamination in Fish Meal

Animal feed production is an important step of the food animal production chain in a farm-to-table model. The contamination of raw ingredients with foodborne pathogens in feed production remains as an important safety issue where pathogens may spread into food animals to cause illnesses in humans when affected food animals are consumed. In the present study, we aimed to examine the quality and microbial contamination of fish meal and to investigate the effectiveness of the organic acid-based antimicrobial agent SALTEC 514^TM against Salmonella to prevent bacterial contamination in fish meal. Fish meal samples (n = 4) collected from feed mills at different locations were analyzed for protein and total volatile basic nitrogen (TVBN) content to assess their nutritional value and freshness, and its microbiological quality. The protein and TVBN content ranged from 53.2 ± 3.1 to 67.5 ± 2.3 g/100 g and 73.8 ± 4.5 to 100.4 ± 11.2 mg/100 g meal, respectively. Total plate count of the fish meal samples ranged from 2.0 ± 0.3 to 4.5 ± 0.5 log units, whereas suspected foodborne bacteria, Escherichia coli and Salmonella, were not detected in all samples. Fish meal samples were artificially contaminated (day 0) and re-challenged (day 30 and 90) with Salmonella Enteritidis (3 log CFU/g) to test for the effectiveness of SALTEC 514^TM, an organic acid-based antimicrobial formulation, in preventing Salmonella contamination and recontamination during storage. SALTEC 514^TM, when applied at three different doses, was found to reduce the number of Salmonella in monitored samples after one day of storage. A low dose of 0.5 kg/ton SALTEC 514^TM prevented Salmonella recontamination from occurring in fish meal samples stored for 37 days. In medium (1.0 kg/ton) and high doses (3.0 kg/ton), applications of SALTEC 514^TM prevented the Salmonella recontamination for a maximum storage duration of 97 days. The application of SALTEC 514^TM in fish meal and/or other feed ingredients may prove to be a safe alternative to reduce the microbial load, especially of foodborne-related microorganisms, to contribute to feed and food safety.

Feed safety evaluation for prevalence of zoonotic Salmonella spp. in animal feed

Owing to the zoonotic nature of Salmonella, its transmission from feed-to-food is quite feasible and considered as one of the prime factors for the transmission and spread of virulent and drug-resistant strains in humans. Therefore, the present study was designed to investigate the prevalence of Salmonella in animal feed pellets from different feed mills in Jaipur and its nearby areas. For this, isolation of Salmonella was performed as per standard ISO methods and the presumable strains were further confirmed and characterized into different species by molecular methods. The confirmed strains were analyzed for virulence genes by PCR. Finally, the strains were analyzed for antimicrobial drug resistance by the standard disk diffusion method. The study revealed that the prevalence of Salmonella in feed pellets was moderate and Salmonella enteritidis and Salmonella typhimurium were the two dominated species. Strikingly, the majority of strains were found to possess the virulence genes and resistant to analyzed clinical antimicrobials. Results inferred that contaminated animal feeds may act as a potential source for the dissemination of virulent and drug-resistant Salmonella spp in animals as well as human beings. The present study implicated the need for more focused and extensive investigations from different parts of the country and the world for strict regulation of animal feed safety to assure one health concept.

Salmonella enterica in soybean production chain: Occurrence, characterization, and survival during soybean storage

This study aimed to determine Salmonella enterica occurrence along the soybean meal production chain (raw material, in-processing samples, final products, and in the environment of five processing plants), characterize the isolates, and assess the survival of Salmonella Senftenberg 775W in soybeans stored under different temperature conditions. Among 713 samples analyzed, 12.9% (n = 92) were positive for Salmonella enterica. Dust collected inside and outside processing plants (n = 148) comprised the samples with the highest positivity for Salmonella enterica, 47.3%. The occurrence of Salmonella enterica varied among the different processing plants. Twenty-nine (n = 29) Salmonella serotypes were isolated, with S. Mbandaka as the most frequent serotype, whereas S. Typhimurium was mainly linked to final product samples (soybean meal). S. Senftenberg 775W did not survive for a long time in soybean stored at 20-37 °C, but at 20 °C, cells were viable for more than 60 days. This study suggests that soybean meal may harbor Salmonella serotypes related to foodborne disease outbreaks in humans and can be responsible for Salmonella introduction into livestock and, consequently, in foods of animal origin. This study provides crucial data on contamination pathways of Salmonella in the soybean production chain, contributing to the understanding of Salmonella epidemiology which is strategic for the development of preventive and control measures to reduce the burden of salmonellosis linked to products of animal origin.

Salmonella enterica 4,[5],12:i:-, an Emerging Threat for the Swine Feed and Pork Production Industry

ABSTRACT

Salmonella continues to be a significant cause of foodborne illnesses in human medicine. The Centers for Disease Control and Prevention reported Salmonella as the second leading cause of foodborne illness in the United States and the leading cause of both hospitalizations and deaths. Salmonella enterica 4,[5],12:i:- (STM) is a monophasic variant of Salmonella Typhimurium, and it is an emerging threat to both human and animal health. STM was first identified in the 1980s from poultry products and has become increasingly prevalent in meat products including pork. STM has also been identified in swine farms as well as in feed manufacturing environments and feed itself. Similar pulse-field gel electrophoresis profiles have been observed between human clinical cases and the STM samples originating from swine feed. These related profiles suggest a link between ingestion of contaminated feed by swine and the source of foodborne illness in human. The objective of this article was to better understand the history of STM and the possible pathway from swine feed to table. Continued research is necessary to better understand how STM can enter both the feed supply chain and the pork production chain to avoid contamination of pork products destined for human consumption.

HIGHLIGHTS

Antimicrobial-resistant Salmonella is detected more frequently in feed milling equipment than in raw feed components or processed animal feed

Food for human and animal consumption can provide a vehicle for the transfer of pathogenic and antimicrobial‐resistant bacteria into the food chain. We investigated the antimicrobial susceptibility of 453 Salmonella isolates collected from raw feed components, equipment and finished feed from 17 commercial feed mills in Australia between 2012 and 2021. Previous studies have found Salmonella prevalence and the diversity of Salmonella serotypes are greatest in the raw feed components. We, therefore, hypothesised that we would find a greater proportion of antimicrobial‐resistant Salmonella isolates in the raw feed components compared to other sample types. We found that of 453 isolates tested, 356 (0.80) were susceptible to all antimicrobials tested, 49 (0.11) were nonsusceptible to streptomycin only and 48 (0.11) were resistant to two or more antimicrobials. Of the 48 antimicrobial‐resistant isolates, 44 were found in feed milling equipment, two in raw feed components and two in finished feed. Statistical analysis, using a logistic regression with random effects model, found that the population‐adjusted mean probability of detecting antimicrobial‐resistant Salmonella isolates from feed milling equipment of 0.39, was larger than the probability of detecting resistant isolates in raw feed components 0.01, (P < 0.001) and in finished feed, 0.11, (P = 0.006). This propensity for antimicrobial‐resistant bacteria to colonise feed milling equipment has not been previously reported. Further studies are required to understand the ecology of antimicrobial‐resistant Salmonella in the feed milling environment.

Salmonella detection in commercially prepared livestock feed and the raw ingredients and equipment used to manufacture the feed: A systematic review and meta-analysis

Salmonella contamination of livestock feed is a serious veterinary and public health issue. In this study we used a systematic review to assess the prevalence and characterization of Salmonella isolates detected in raw feed components, feed milling equipment and finished feed from 97 studies published from 1955 to 2020 across seven global regions. Eighty-five studies were included in a meta-analyses to estimate the combined prevalence of Salmonella detection and to compare the risk of contamination associated with different sample types. We found the overall combined prevalence estimate of Salmonella detection was 0.14 with a prevalence of 0.18 in raw feed components, 0.09 in finished feed and 0.08 in feed milling equipment. Animal based raw feed components were 3.9 times more likely to be contaminated with Salmonella than plant based raw feed components. Differences between studies accounted for 99 % of the variance in the prevalence estimate for all sample types and there was no effect of region on the prevalence estimates. The combined prevalence of Salmonella detection in raw feed components decreased from 0.25 in 1955 to 0.11 in 2019. The proportion of Salmonella isolates that were resistant to antimicrobials was largest for amikacin (0.20), tetracycline (0.18) streptomycin (0.17), cefotaxime (0.14) and sulfisoxazole (0.11). The prevalence of Salmonella contamination of animal feed varies widely between individual studies and is an ongoing challenge for the commercial feed industry. Control relies on the vigilant monitoring and control of Salmonella in each individual mill.

Microbial Quality of Liquid Feed for Pigs and Its Impact on the Porcine Gut Microbiome

Simple Summary

Liquid feed is produced by mixing dry feed ingredients with water, and sometimes liquid co-products from the food and beverage industry, at a defined ratio. Liquid feeding of pigs is popular, particularly in parts of northern and western Europe, and can be associated with lower feed costs, improved dry matter intake, growth rate and gut health, compared to dry feeding. However, spontaneous/uncontrolled fermentation upon mixing of feed with water or co-products can decrease the microbial and nutritional quality of the feed, resulting in poorer pig health and growth. For this reason, strategies aimed at optimising liquid feed microbial quality are frequently employed. These include: deliberate fermentation with/without the use of lactic acid bacteria starter cultures that produce lactic acid and lower the feed pH, thereby preventing growth of pathogens. Fermenting only the cereal component of the diet is preferred to whole diet fermentation to minimise loss of free amino acids from the diet during fermentation. This review examines the microbiome of liquid feed and explores how optimisation strategies impact both feed microbial quality and the gut microbiota and growth of liquid-fed pigs. It also covers cleaning and disinfection of liquid feeding systems and how this might impact liquid feed microbial quality.

Abstract

There is evidence that spontaneous fermentation frequently occurs in liquid pig feed that is intended to be delivered as fresh liquid feed, often with a resultant deterioration in the microbial and nutritional quality of the feed, which can negatively affect pig health and growth. Strategies including controlled fermentation with microbial inoculants, pre-fermentation or soaking of the cereal fraction of the diet, enzyme supplementation and dietary acidification have been employed to inhibit pathogens and prevent deterioration of feed nutritional quality, with promising results obtained in many cases. This review evaluates the impact of these strategies on the microbial quality of liquid feed and discusses how they can be further improved. It also investigates if/how these strategies impact the pig gut microbiota and growth performance of liquid-fed pigs. Finally, we review liquid feed system sanitisation practices, which are highly variable from farm to farm and discuss the impact of these practices and whether they are beneficial or detrimental to liquid feed microbial quality. Overall, we provide a comprehensive review of the current state of knowledge on liquid feed for pigs, focusing on factors affecting microbial quality and strategies for its optimisation, as well as its impact on the pig gut microbiome.

Using environmental sampling to evaluate the effectiveness of decontamination methods to reduce detection of porcine epidemic diarrhea virus RNA on feed manufacturing surfaces

Porcine epidemic diarrhea virus (PEDV) is a possible biological hazard in feed mills. If the virus enters a feed mill, it becomes widely distributed and is difficult to decontaminate from both feed contact and non-feed contact surfaces. The objective of this study was to evaluate a variety of liquid and dry decontamination treatments that could be used to reduce the amount of PEDV found on feed manufacturing surfaces. This experiment was designed as a 5 × 10 factorial with five different feed manufacturing surfaces and 10 decontamination treatments with three replicates of each combination. Surfaces included stainless steel, solid polyethylene, woven polypropylene tote bag, rubber, and sealed concrete coupons. One mL (1×10⁵ TCID₅₀/mL) of stock PEDV was applied to each surface and allowed to dry completely for 60 min. Next, for decontamination requiring surface application, the application was performed and allowed 15 min contact time. The quantity of PEDV RNA was determined using quantitative reverse transcription PCR. A decontamination treatment × surface interaction was observed (P < 0.0001), indicating the efficacy of treatment is dependent upon the surface in which it is applied. Within the cement surfaces, the sodium hypochlorite resulted in the greatest (P < 0.05) cycle threshold (Ct) value, followed by formaldehyde which had a greater (P < 0.05) Ct value compared to remaining treatments. Within polyethylene, rubber, and stainless steel surfaces, the formaldehyde treated surfaces had the greatest Ct values (P < 0.05), followed by the sodium hypochlorite treatment, with other treatments all having lower Ct values (P < 0.05). For the woven polyethylene surfaces, the formaldehyde and sodium hypochlorite treatments had greater Ct values compared to all other treatments (P < 0.05). Additional research is necessary to identify the role of decontamination treatment on PEDV infectivity and develop methods for decontamination of feed manufacturing facilities.

Role played by the environment in the emergence and spread of antimicrobial resistance (AMR) through the food chain

The role of food-producing environments in the emergence and spread of antimicrobial resistance (AMR) in EU plant-based food production, terrestrial animals (poultry, cattle and pigs) and aquaculture was assessed. Among the various sources and transmission routes identified, fertilisers of faecal origin, irrigation and surface water for plant-based food and water for aquaculture were considered of major importance. For terrestrial animal production, potential sources consist of feed, humans, water, air/dust, soil, wildlife, rodents, arthropods and equipment. Among those, evidence was found for introduction with feed and humans, for the other sources, the importance could not be assessed. Several ARB of highest priority for public health, such as carbapenem or extended-spectrum cephalosporin and/or fluoroquinolone-resistant Enterobacterales (including Salmonella enterica), fluoroquinolone-resistant Campylobacter spp., methicillin-resistant Staphylococcus aureus and glycopeptide-resistant Enterococcus faecium and E. faecalis were identified. Among highest priority ARGs bla CTX -M, bla VIM, bla NDM, bla OXA -48-like, bla OXA -23, mcr, armA, vanA, cfr and optrA were reported. These highest priority bacteria and genes were identified in different sources, at primary and post-harvest level, particularly faeces/manure, soil and water. For all sectors, reducing the occurrence of faecal microbial contamination of fertilisers, water, feed and the production environment and minimising persistence/recycling of ARB within animal production facilities is a priority. Proper implementation of good hygiene practices, biosecurity and food safety management systems is very important. Potential AMR-specific interventions are in the early stages of development. Many data gaps relating to sources and relevance of transmission routes, diversity of ARB and ARGs, effectiveness of mitigation measures were identified. Representative epidemiological and attribution studies on AMR and its effective control in food production environments at EU level, linked to One Health and environmental initiatives, are urgently required.

Expert Elicitation To Estimate the Feed Safety Impact of Criteria Included in the Canadian Food Inspection Agency Risk Assessment Model for Feed Mills

ABSTRACT

The Canadian Food Inspection Agency is developing an Establishment-based Risk Assessment (ERA) model for commercial and on-farm mills involved in the manufacture, storage, packaging, labeling, or distribution of livestock feed (ERA-Feed Mill model). This model will help inform the allocation of inspection resources on the basis of feed safety risk, including animal health and food safety risk. In a previous study, 34 risk factors, grouped into inherent, mitigation, and compliance clusters, along with assessment criteria were selected. The objective of this current study was to estimate the relative risk (RR) of the 203 assessment criteria on the basis of the impact on feed safety to design an ERA-Feed Mill model algorithm. Furthermore, the intent of this study was to assess the maximum increase or decrease of risk obtained when multiple criteria belonging to a same cluster were identified in a specific feed mill. To do so, a two-round face-to-face expert elicitation was conducted with 28 Canadian feed experts. Results showed no significant association between respondent profiles (years of experience and work sector) and estimated RR. Uniformity of answers between experts improved between rounds. Criteria having the highest increase in risk (median RR ≥ 4) included the presence of materials prohibited to be fed to ruminants in a facility that produces ruminant feed, the presence of multiple livestock species on-site, and historical noncompliances related to the inspection of the feed mill's process control and end-product control programs. Risk mitigation criteria having the highest impact on decreasing the risk were the implementation of feed safety certifications, the use of dedicated manufacturing lines (prohibited materials or medications), and having a hazard sampling plan in place for finished feed. The median RR assigned to each criterion and cluster will be used to build an algorithm of the Canadian Food Inspection Agency's ERA-Feed Mill model.

HIGHLIGHTS

Antimicrobial resistance in commensal Escherichia coli and Enterococcus spp. is influenced by production system, antimicrobial use, and biosecurity measures on Spanish pig farms

Background

Antimicrobial resistance (AMR) is a global public health threat consequence of antimicrobial use (AMU) in human and animal medicine. In food-producing animals factors such as management, husbandry or biosecurity may impact AMU. Organic and extensive Iberian swine productions are based on a more sustainable and eco-friendly management system, providing an excellent opportunity to evaluate how sustained differences in AMU impact the AMR in indicator bacteria. Here, we evaluate the usefulness of commensal Escherichia coli and Enterococcus spp. isolates as AMR bioindicators when comparing 37 Spanish pig farms from both intensive and organic-extensive production systems, considering the effect of AMU and biosecurity measures, the last only on intensive farms.

Results

The production system was the main factor contributing to explain the AMR differences in E. coli and Enterococcus spp. In both bacteria, the pansusceptible phenotype was more common (p < 0.001) on organic-extensive farms when compared to intensive herds. The microbiological resistance in commensal E. coli was, for most of the antimicrobials evaluated, significantly higher (p < 0.05) on intensive farms. In enterococci, the lincosamides usage revealed the association between AMR and AMU, with an increase in the AMR for erythromycin (p < 0.01), quinupristin-dalfopristin (p < 0.01) and the multidrug-resistant (MDR) phenotype (p < 0.05). The biosecurity measures implemented on intensive farms influenced the AMR of these bioindicators, with a slightly lower resistance to sulfamethoxazole (p < 0.01) and the MDR phenotype (p < 0.05) in E. coli isolated from farms with better cleaning and disinfection protocols. On these intensive farms, we also observed that larger herds had a higher biosecurity when compared to smaller farms (p < 0.01), with no significant associations between AMU and the biosecurity scores.

Conclusions

Overall, this study evidences that the production system and, to a lesser extent, the biosecurity measures, contribute to the AMR development in commensal E. coli and Enterococcus spp., with antimicrobial usage as the main differential factor, and demonstrates the potential value of these bacteria as bioindicators on pig farms in AMR surveillance programs.

The effect of feed form and delivery method on feed microbiology and growth performance in grow-finisher pigs

There is no generally accepted optimal feed form and delivery method for feeding finisher pigs. The objective of this study was to compare the effect of feed form (meal and pellet) and delivery method (liquid, dry, and wet/dry) on feed microbiology and growth, gain-to-feed ratio (G:F), and carcass quality of finisher pigs. Two batches of pigs were used, each with six pen replicates per treatment. In each batch 216 pigs (32.7 kg; ± 0.48 SE) housed in same-sex (entire male or female) pens of six pigs per pen were on treatment for ~62 d prior to slaughter. The experiment was a 2 × 3 factorial arrangement with two factors for diet form (meal and pellets) and three factors for feed delivery (dry, wet/dry, liquid). The treatments were 1) meal from dry feeder, 2) meal from wet/dry feeder, 3) meal from liquid system, 4) pellet from dry feeder, 5) pellet from wet/dry feeder, and 6) pellet from liquid system. Pig growth performance was determined, blood samples collected at slaughter for hematological analysis and microbiological and proximate analysis of feed performed. A significant feed form × delivery interaction was found for G:F. During the overall period G:F was 0.446, 0.433, 0.423, 0.474, 0.459, and 0.418 g/g (SE = 0.0080; P < 0.01) for treatments 1 through 6, respectively. When feed was pelleted, G:F was improved when feed delivery was dry or wet/dry compared to meal but when the delivery was liquid, pelleting did not affect G:F. There were no interactive effects for overall average daily gain (ADG). Overall ADG was 1,114 and 1,156 g/d (SE = 16.9; P < 0.01) for pigs fed diets in meal and pellet form, respectively and 1,080, 1,114, and 1,210 g/d (SE = 18.4; P < 0.001) for dry-, wet/dry-, and liquid-fed pigs, respectively. Carcass weight was 76.6 and 79.0 kg (SE = 0.55; P < 0.001) for pigs fed in meal and pellet form, respectively, while it was 74.7, 77.3, and 81.5 kg (SE = 0.60; P < 0.001) for pigs delivered dry, wet/dry, and liquid diets, respectively. Lactic acid bacteria (P < 0.05) and yeast (P < 0.01) counts in troughs were greater for the liquid than the dry diet in both meal and pelleted form. There was also evidence of lysine degradation in the liquid diet but this did not impact pig growth. Feeding the diet in pelleted vs. meal form led to lower hemoglobin and greater white blood cell and neutrophil counts (P < 0.05). To conclude, wet/dry feeding of a pelleted diet is recommended to maximize growth rate while optimizing G:F in grow-finisher pigs.

Prevalence and genomic characterization of Salmonella Weltevreden in commercial pig feed

Viet Nam is the world's fifth largest producer of pork meat. Salmonella is frequently found at farm level; however, risk factors for Salmonella infection in pigs have not been thoroughly investigated in the production system. In the current study, 123 commercial feed samples were obtained from 103 small, medium and large-scale pig farms in Viet Nam and investigated for the presence of Salmonella in 25 g of feed using the ISO 6579:2002/Cor 1:2004 method. Salmonella was detected in five samples (4.1%; 95% CI 1.75-9.16%). All five samples were found to contain S. Weltevreden as the only serovar. The isolates were subjected to phenotypic and whole genome sequencing analysis for further characterization. They all belonged to ST365 and were sensitive to the 14 antimicrobials tested. Four strains were found to belong to the continental lineage of S. Weltevreden, while one isolate was of the island type. This isolate, contrary to the remaining four isolates contained a prophage homolog to the Vibrio prophage X-29. The findings of only S. Weltevreden, which is often isolated from fish and aquatic samples, suggests that fishmeal used in the feed preparation was a likely source of contamination.

Addition of Olive Pomace to Feeding Substrate Affects Growth Performance and Nutritional Value of Mealworm (Tenebrio Molitor L.) Larvae

The well-recognized efficiency of Tenebrio molitor larvae to convert low quality organic matter into a nutritionally valuable biomass was exploited to manage solid wastes coming from the olive oil industry, which represent a severe environmental challenge in the Mediterranean area. Three organic pomace-enriched substrates (mixtures middlings/pomace 3:1, 1:1, and 1:3) were assessed, together with 100% organic wheat flour and 100% organic middlings as control feeds. A feeding substrate made up of 25% olive pomace and 75% wheat middlings appeared to be the best compromise between growth performance (larval and pupal weights, survival rate, development time) and nutritional properties of mealworm larvae. In fact, larvae fed the 3:1 feed showed the highest dry matter (DM) yield (38.05%), protein content (47.58% DM), and essential/non-essential amino acids ratio (1.16). Fat content (32.14% DM) and fatty acid composition were not significantly different than those of larvae fed more pomace-enriched feeds.

Microevolution of antimicrobial resistance and biofilm formation of Salmonella Typhimurium during persistence on pig farms

Salmonella Typhimurium and its monophasic variant S. 4,[5],12:i:- are the dominant serotypes associated with pigs in many countries. We investigated their population structure on nine farms using whole genome sequencing, and their genotypic and phenotypic variation. The population structure revealed the presence of phylogenetically distinct clades consisting of closely related clones of S. Typhimurium or S. 4,[5],12:i:- on each pig farm, that persisted between production cycles. All the S. 4,[5],12:i:- strains carried the Salmonella genomic island-4 (SGI-4), which confers resistance to heavy metals, and half of the strains contained the mTmV prophage, harbouring the sopE virulence gene. Most clonal groups were highly drug resistant due to the presence of multiple antimicrobial resistance (AMR) genes, and two clades exhibited evidence of recent on-farm plasmid-mediated acquisition of additional AMR genes, including an IncHI2 plasmid. Biofilm formation was highly variable but had a strong phylogenetic signature. Strains capable of forming biofilm with the greatest biomass were from the S. 4,[5],12:i:- and S. Typhimurium DT104 clades, the two dominant pandemic clones found over the last 25 years. On-farm microevolution resulted in enhanced biofilm formation in subsequent production cycle.

Evaluation of Antimicrobial Activity of Four Organic Acids Used in Chicks Feed to Control Salmonella typhimurium: Suggestion of Amendment in the Search Standard

Today, the general public has become increasingly aware of salmonellosis problems. Organic acids are known by their antimicrobial potential and commonly used for improving the quality of poultry feed. In this context, the present work evaluated the inhibitory effect of four organic acids, namely, acetic acid, citric acid, lactic acid, and tartaric acid, at different levels of contamination by Salmonella typhimurium. The neutralization of these organic acids in vitro and in the presence of one-day-old chick's organs was also investigated during the search for Salmonella serovars in birds as described in the Moroccan standard "NM 08.0.550." The effect of four organic acids on Salmonella typhimurium was tested in vitro and in the presence of chick's organs at different concentrations set of strain and organic acids tested. The MIC results demonstrated that tartaric acid, citric acid, and acetic acid inhibited Salmonella typhimurium at concentrations of 0.312%, 0.625%, and 0.512% for the three levels of strain: 10, 100, and 103 CFU/ml, respectively, while lactic acid and depending on the amount of the strain introduced acts differently: 0.078% for 10 CFU/ml and 0.156% for 100 and 103 CFU/ml. The concentration of 0.04M of Na2HPO4 solution has proved, in vitro, in caecums and organs of chicks (in presence of organic acids) that strain introduced, even at low concentrations, can be recovered. The use of additives has beneficial effects in Salmonella control program. However, the present results recommend the amendment of Salmonella research standard, taking into account the probable presence of organic acids in digestive content of one-day-old chicks.

Evaluation of Salmonella presence in selected United States feed mills

Salmonella is a pathogen of public health concern. Each year, Salmonella infections cost to the food industry approximately $2.3 billion and 33% of the reported cases are associated with beef, poultry, or pork. Pathogen presence in feed mills can represent one of the many potential routes for entry and transmission into the food production chain. Nevertheless, little is known about Salmonella incidence and association with these types of environments. The objective of this study was to investigate Salmonella presence in different feed mills across the United States. Eleven facilities were selected in eight states and 12 sites were sampled within each feed mill. Samples were analyzed following the FSIS guidelines for isolation and identification of Salmonella. Positive isolates were further investigated by a PCR analysis targeting the invA gene to differentiate for Salmonella enterica. The total number of environmental samples collected was 237: 66% resulted culture positive and 13.1% were PCR positive. All sampled feed mills had at least one culture positive site and following production flow the number of positive samples decreased from ingredient receiving to final product. These preliminary results demonstrate the presence of Salmonella in selected United States feed mills and suggest their potential role as vehicle for pathogen transmission and spread into the food production chain.

The bacterial biota of laboratory-reared edible mealworms (Tenebrio molitor L.): From feed to frass

Tenebrio molitor represents one of the most popular species used for the large-scale conversion of plant biomass into protein and is characterized by high nutritional value. In the present laboratory study, the bacterial biota characterizing a pilot production chain of fresh T. molitor larvae was investigated. To this end, different batches of fresh mealworm larvae, their feeding substrate (wheatmeal) and frass were analyzed by viable microbial counts, PCR-DGGE and Illumina sequencing. Moreover, the occurrence of Coxiella burnetii, Pseudomonas aeruginosa and Shiga toxin-producing E. coli (STEC) was assessed through qualitative real-time PCR assays. Microbial viable counts highlighted low microbial contamination of the wheatmeal, whereas larvae and frass were characterized by high loads of Enterobacteriaceae, lactic acid bacteria, and several species of mesophilic aerobes. Spore-forming bacteria were detected to a lesser extent in all the samples. The combined molecular approach used to profile the microbiota confirmed the low microbial contamination of wheatmeal and allowed the detection of Enterobacter spp., Erwinia spp., Enterococcus spp. and Lactococcus spp. as dominant genera in both larvae and frass. Moreover, Klebsiella spp., Pantoea spp., and Xenorhabdus spp. were found to be in the minority. Entomoplasmatales (including Spiroplasma spp.) constituted a major fraction of the microbiota of one batch of larvae. From the real-time PCR assays, no sample was positive for either C. burnetii or STEC, whereas P. aeruginosa was detected in one sample of frass. Based on the overall results, two sources of microbial contamination were hypothesized, namely feeding with wheatmeal and vertical transmission of microorganisms from mother to offspring. Since mealworms are expected to be eaten as a whole, the overall outcomes collected in this laboratory study discourage the consumption of fresh mealworm larvae. Moreover, microbial loads and the absence of potential pathogens known to be associated with this insect species should be carefully assessed in order to reduce the minimum risk for consumers, by identifying the most opportune processing methods (e.g., boiling, frying, drying, etc.).

Surveillance Data Highlights Feed Form, Biosecurity, and Disease Control as Significant Factors Associated with Salmonella Infection on Farrow-to-Finish Pig Farms

Among the zoonotic pathogens affecting pigs, Salmonella stands out due to the high number of human cases linked to pork consumption. In the last two decades many countries have put considerable effort into the control of the infection by surveillance and control strategies on farm. Despite this effort, many herds still have a high Salmonella prevalence and they require guidance to address this problem. The present study, using the serological surveillance data of finishing pigs from the Irish National pig Salmonella Control Programme, aimed to highlight factors associated with increased risk or that might mitigate Salmonella occurrence on farm. A questionnaire with 33 questions regarding herd characteristics, management, feeding, biosecurity, and health was completed for 61 individual herds. After the multivariate analysis by linear regression, nine variables were retained in the final model and linked to herd seroprevalence. Home produced-feed linked to the use of meal showed an eight points reduction in Salmonella prevalence compared to purchased feed (p = 0.042). Different biosecurity measures were associated to lower seroprevalence. Changing of footwear from outside to inside the farm decreased seroprevalence nearly 20 units (p = 0.014) and policies not permitting access to the farmyard to feed trucks (p = 0.048) or avoiding the presence of cats on the farm (p = 0.05) were estimated in 10 units less of seroprevalence. In contrast, the lack of perimeter fence increased the chance to have higher seroprevalence in five units (p = 0.05). Finally, intestinal diseases such as swine dysentery (p = 0.044) and E. coli diarrhea (p = 0.1) were estimated to increase Salmonella prevalence in ~20 and 10 units, respectively, demonstrating the importance of controlling other enteric pathogens in an on-farm Salmonella control programme. These results show the usefulness of surveillance data to improve on-farm control and confirm that Salmonella infection in pigs is multi-factorial and the approach to its control should be multifaceted.

Bayesian model for tracing Salmonella contamination in the pig feed chain

Salmonella infections in pigs are in most cases asymptomatic, posing a risk of salmonellosis for pork consumers. Salmonella can transmit to pigs from various sources, including contaminated feed. We present an approach for quantifying the risk to pigs from contaminations in the feed chain, based on a Bayesian model. The model relies on Salmonella surveillance data and other information from surveys, reports, registries, statistics, legislation and literature regarding feed production and pig farming. Uncertainties were probabilistically quantified by synthesizing evidence from the available information over a categorically structured flow chain of ingredients mixed for feeds served to pigs. Model based probability for infection from feeds together with Salmonella subtyping data, were used to estimate the proportion of Salmonella infections in pigs attributable to feed. The results can be further used in assessments considering the human health risk linked to animal feed via livestock. The presented methods can be used to predict the effect of changes in the feed chain, and they are generally applicable to other animals and pathogens.

The invasome of Salmonella Dublin as revealed by whole genome sequencing

Background

Salmonella enterica serovar Dublin is a zoonotic infection that can be transmitted from cattle to humans through consumption of contaminated milk and milk products. Outbreaks of human infections by S. Dublin have been reported in several countries including high-income countries. A high proportion of S. Dublin cases in humans are associated with invasive disease and systemic illness. The genetic basis of virulence in S. Dublin is not well characterized.

Methods

Whole genome sequencing was applied to a set of clinical invasive and non-invasive S. Dublin isolates from different countries in order to characterize the putative genetic determinants involved in the virulence and invasiveness of S. Dublin in humans.

Results

We identified several virulence factors that form the bacterial invasome and may contribute to increasing bacterial virulence and pathogenicity including mainly Gifsy-2 prophage, two different type 6 secretion systems (T6SSs) harbored by Salmonella pathogenicity islands; SPI-6 and SPI-19 respectively and virulence genes; ggt and PagN. Although Vi antigen and the virulence plasmid have been reported previously to contribute to the virulence of S. Dublin we did not detect them in all invasive isolates indicating that they are not the main virulence determinants in S. Dublin.

Conclusion

Several virulence factors within the genome of S. Dublin might contribute to the ability of S. Dublin to invade humans’ blood but there were no genomic markers that differentiate invasive from non-invasive isolates suggesting that host immune response play a crucial role in the clinical outcome of S. Dublin infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-017-2628-x) contains supplementary material, which is available to authorized users.

Review on the effects of potential prebiotics on controlling intestinal enteropathogens Salmonella and Escherichia coli in pig production

Salmonella enterica serotypes (Salmonella sp.) are the second cause of bacterial foodborne zoonoses in humans after campylobacteriosis. Pork is the third most important cause for outbreak-associated salmonellosis, and colibacillosis is the most important disease in piglets and swine. Attachment to host cells, translocation of effector proteins into host cells, invasion and replication in tissues are the vital virulence steps of these pathogens that help them to thrive in the intestinal environment and invade tissues. Feed contamination is an important source for Salmonella infection in pig production. Many on-farm feeding strategies intervene to avoid the introduction of pathogens onto the farm by contaminated feeds or to reduce infection pressure when pathogens are present. Among the latter, prebiotics could be effective at protecting against these enteric bacterial pathogens. Nowadays, a wide range of molecules can potentially serve as prebiotics. Here, we summarize the prevalence of Salmonella sp. and Escherichia coli in pigs, understanding of the mechanisms by which pathogens can cause disease, the feed related to pathogen contamination in pigs and detail the mechanisms on which prebiotics are likely to act in order to fulfil their protective action against these pathogens in pig production. Many different mechanisms involve the inhibition of Salmonella and E. coli by prebiotics such as coating the host surface, modulation of intestinal ecology, downregulating the expression of adhesin factors or virulence genes, reinforcing the host immune system.