Salmonella Weltevreden in integrated and non-integrated tilapia aquaculture systems in Guangdong, China

Managing the microbiological safety of tilapia from farm to consumer

Tilapia stands out as one of the most extensively farmed and consumed fish species globally, valued for its ease of preparation and relative affordability. Although tilapia is a valuable protein source, it can also function as a vector for foodborne pathogens. This literature review reveals that tilapia could carry a variety of contamination with various foodborne pathogens, including Plesiomonas shigelloides, diarrheagenic Escherichia coli, Vibrio parahaemolyticus, Salmonella Weltevreden, Salmonella enterica, Shigella, Staphylococcus aureus, Campylobacter jejuni, Clostridium botulinum, and Listeria monocytogenes. Although guidelines from entities, such as the Global Seafood Alliance, Aquaculture Stewardship Council, and International Organization for Standardization, have been established to ensure the microbiological safety of tilapia, the unique challenges posed by pathogens in tilapia farming call for a more nuanced and targeted approach. Recognizing that contaminants could emerge at various stages of the tilapia supply chain, there is a crucial need for enhanced detection and monitoring of pathogens associated with this fish and its culturing environment. Additionally, it is essential to acknowledge the potential impact of climate change on the safety of tilapia, which may elevate the prevalence and contamination levels of pathogens in this fish. Proactive measures are essential to understand and mitigate the effects of climate change on tilapia production, ensuring the sustainability and safety of this seafood product for both present and future generations.

Foodborne Outbreak by Salmonella enterica Serovar Weltevreden in West Bengal, India

Foodborne gastroenteritis outbreaks owing to Salmonella enterica serovar Weltevreden (Salmonella Weltevreden) represent a significant global public health problem. In the past two decades, Salmonella Weltevreden has emerged as a dominant foodborne pathogen, especially in South-East Asian countries. This report describes a community foodborne outbreak of gastroenteritis caused by Salmonella Weltevreden in August 2022 following consumption of panipuri from a street vendor in the Polba block in Hooghly district, West Bengal, India. This food item was consumed by 185 people, of whom 129 had acute watery diarrhea with other clinical symptoms and 65 of them were admitted to different District hospitals for treatment. Stool specimens collected from hospitalized cases were positive for S. enterica, and further serotyped as Salmonella Weltevreden. All the Salmonella Weltevreden strains possessed the Salmonella pathogenicity islands associated genes (invA/E, orgA, ttrc, ssaQ, mgtC, misL, spi4D), the enterotoxin (stn), and hyperinvasive locus gene (hilA). Except erythromycin, all the strains were susceptible for commonly used antimicrobials in the treatment of diarrhea. The XbaI-based pulsed-field gel electrophoresis analysis indicated that all the isolates responsible for the recent outbreak were similar, but diverged from other Salmonella Weltevreden that were previously reported in West Bengal. This report indicates that foodborne infection is a major public health concern in India and demands to strengthen capacity-building measures at the local health care levels for linking causative agents of outbreaks.

SW16-7, a Novel Ackermannviridae Bacteriophage with Highly Effective Lytic Activity Targets Salmonella enterica Serovar Weltevreden

Salmonella enterica serovar Weltevreden is a foodborne pathogen commonly transmitted through fresh vegetables and seafood. In this study, a lytic phage, SW16-7, was isolated from medical sewage, demonstrating high infectivity against S. Weltevreden, S. London, S. Meleagridis, and S. Give of Group O:3. In vitro inhibition assays revealed its effective antibacterial effect for up to 12 h. Moreover, analysis using the Comprehensive Antibiotic Resistance Database (CARD) and the Virulence Factor Database (VFDB) showed that SW16-7's genome does not contain any virulence factors or antibiotic resistance genes, indicating its potential as a promising biocontrol agent against S. Weltevreden. Additionally, a TSP gene cluster was identified in SW16-7's genome, with TSP1 and TSP2 showing a high similarity to lysogenic phages ε15 and ε34, respectively, in the C-terminal region. The whole-genome phylogenetic analysis classified SW16-7 within the Ackermannviridae family and indicated a close relationship with Agtrevirus, which is consistent with the ANI results.

Salmonella spp. in Aquaculture: An Exploratory Analysis (Integrative Review) of Microbiological Diagnoses between 2000 and 2020

The present study aimed to characterize, through descriptive statistics, data from scientific articles selected in a systematic integrative review that performed a microbiological diagnosis of Salmonella spp. in aquaculture. Data were obtained from research articles published in the BVS, Scielo, Science Direct, Scopus and Web of Science databases. The selected studies were published between 2000 and 2020 on samples of aquaculture animal production (fish, shrimp, bivalve mollusks, and other crustaceans) and environmental samples of aquaculture activity (farming water, soil, and sediments). After applying the exclusion criteria, 80 articles were selected. Data such as country of origin, categories of fish investigated, methods of microbiological diagnosis of Salmonella spp., sample units analyzed and most reported serovars were mined. A textual analysis of the word cloud and by similarity and descending hierarchical classification with the application of Reinert's algorithm was performed using R® and Iramuteq® software. The results showed that a higher percentage of the selected articles came from Asian countries (38.75%). Fish was the most sampled category, and the units of analysis of the culture water, muscle and intestine were more positive. The culture isolation method is the most widespread, supported by more accurate techniques such as PCR. The most prevalent Salmonella serovars reported were S. Typhimurium, S. Weltevreden and S. Newport. The textual analysis showed a strong association of the terms "Salmonella", "fish" and "water", and the highest hierarchical class grouped 25.4% of the associated text segments, such as "aquaculture", "food" and "public health". The information produced characterizes the occurrence of Salmonella spp. in the aquaculture sector, providing an overview of recent years. Future research focusing on strategies for the control and prevention of Salmonella spp. in fish production are necessary and should be encouraged.

Integration assay of bacteriological risks in marine environment using salmonella spp and multimarker response in the bivalve Donax trunculus: Novel biomonitoring approach

Microbiological contamination is one of the riskiest forms of human contamination in seawater, which threaten the stability of ecosystems and human health. In this study, we study the accumulation of a pathogenic bacteria Salmonella spp; isolated from the marine environment, in the soft tissue of Donax trunculus (Mollusca, Bivalvia), a commonly used as a bioindicators species for aquatic ecosystems monitoring, under laboratory conditions during both exposure and recovery periods. These bacteria were added in seawater at three concentrations previously determined against sentinel specie at three exposure periods (24, 48 and 96 h). In a second series of experiments, exposed specimens were afterward transplanted to clean water to assess the recovery pattern. The mortality rate of bivalves was determined as biomarker of general stress. Our findings suggest that microbiological contamination by Salmonella spp was gradually incorporated into the body of D. trunculus causing a significant induction of enzymatic activity of acetylcholinesterase (AChE), Catalase (CAT), glutathione-S-transferase (GST) and malondialdehyde (MDA) levels, as a function of time and concentration. Exposure to a bacterial concentration of 5.10⁴ bacteria/liter resulted in the mortality of more than 80% of the specimens. This study is to test the pathogenicity of Salmonella strains at concentrations close to those of the marine environment, and their effects on biomarkers, thus deducing the existence of an exponential relationship between bacterial concentrations and enzymatic response. The principal component analysis shows that the four biomarkers had similar variation with bacterial concentrations, while two groups were obtained to change following the exposure time (CAT-GST and AChE-MDA). This study provides new findings on the potential accumulation of pathogenic bacteria associated with neurotoxicity and oxidative stress in the wedge clam Donax trunculus.

Molecular Characteristics and Zoonotic Potential of Salmonella Weltevreden From Cultured Shrimp and Tilapia in Vietnam and China

Salmonella Weltevreden is increasingly reported from aquatic environments, seafood, and patients in several Southeast Asian countries. Using genome-wide analysis, we characterized S. Weltevreden isolated from cultured shrimp and tilapia from Vietnam and China to study their genetic characteristics and relatedness to clinical isolates of S. Weltevreden ST-365. The phylogenetic analysis revealed up to 312 single-nucleotide polymorphism (SNP) difference between tilapia isolates, whereas isolates from shrimp were genetically more closely related. Epidemiologically unrelated isolates from Vietnam were closely related to isolates from China, e.g., 20 SNPs differences between strains 28V and 75C. In comparison with strains from other parts of the world, our environmental isolates predominantly clustered within the continental South Asia lineage, constituted mostly of strains from human stool with as low as seven SNPs difference, e.g., 30V versus Cont_ERR495254. All sequenced isolates were MLST type ST-365 and contained the major virulence-related genes encoded by the Salmonella Pathogenicity Islands 1–5. Ten of the isolates harbored the IncFII(S) plasmid similar to the virulence genes-mediated plasmid pSPCV of S. Paratyphi C, and one isolate had the IncQ1 plasmid on the same contig with strA/B, sul2, and tetA resistance genes similar to the IncQ1 type, pNUC of S. Typhimurium. A pangenomic analysis yielded 7891 genes including a core genome of 4892 genes, with a closely related accessory genome content between clinical and environmental isolates (Benjamini p > 0.05). In a search for differences that could explain the higher prevalence of S. Weltevreden in aquatic samples, genomes were compared with those of other Salmonella enterica serovars. S. Weltevreden revealed specific regions harboring glpX (Fructose-1;6-bisphosphatase; class II), rfbC (dTDP-4-dehydrorhamnose 3;5-epimerase), and cmtB (PTS Mannitol-specific cryptic phosphotransferase enzyme IIA component) involved in carbohydrate biosynthesis pathways. Our study builds grounds for future experiments to determine genes or pathways that are essential when S. Weltevreden are in aquatic environments and microbial interactions providing survival advantages to S. Weltevreden in such environments.

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.

Endocrine disruption in western mosquitofish from open and closed aquatic ecosystems polluted by swine farm wastewaters

Swine farm wastewaters (SFWs) are generally discharged either directly into nearby rivers or into fish ponds as a source of fertilizer/food for aquaculture in China. SFWs contain various contaminants including steroid hormones. However, there is an extreme paucity of data on their effects in fish populations. Here we investigated the endocrine disrupting effects of SFWs in G. affinis from 2 rivers (7 sites) and 2 fish ponds (2 sites) receiving SFWs and a reference site in Guangdong Province, China. In this study, a total number of 3078 adult western mosquitofish (Gambusia affinis) were collected and the sex ratio was determined. In addition, secondary sexual characteristics were examined and the transcriptional levels of target genes were analyzed. The results showed the mosquitofish populations had a significant increase in male-to-female ratio from 7 sites (including 2 fish ponds) among the 9 sampling sites. The hemal spines of females were masculinized at most sites while the hemal spines of males were feminized at approximately half of the sites (including 2 fish ponds). Significant reduction in vitellogenin (Vtg) mRNA expression was observed in females from 2 sites (including RS7) while elevated Vtg mRNA expression was noticed in males from 2 sites along the rivers (including RS7). Redundancy analysis showed that androgens in the water samples were closely related with male-to-female ratio in the mosquitofish populations and the masculinized hemal spines of females. The findings from this study demonstrated that discharge of SFWs could result in occurrence of both masculinized females and feminized males in mosquitofish population.

Food-to-Humans Bacterial Transmission

Microorganisms vehiculated by food might benefit health, cause minimal change within the equilibrium of the host microbial community or be associated with foodborne diseases. In this chapter we will focus on human pathogenic bacteria for which food is conclusively demonstrated as their transmission mode to human. We will describe the impact of foodborne diseases in public health, the reservoirs of foodborne pathogens (the environment, human and animals), the main bacterial pathogens and food vehicles causing human diseases, and the drivers for the transmission of foodborne diseases related to the food-chain, host or bacteria features. The implication of food-chain (foodborne pathogens and commensals) in the transmission of resistance to antibiotics relevant to the treatment of human infections is also evidenced. The multiplicity and interplay of drivers related to intensification, diversification and globalization of food production, consumer health status, preferences, lifestyles or behaviors, and bacteria adaptation to different challenges (stress tolerance and antimicrobial resistance) from farm to human, make the prevention of bacteria-food-human transmission a modern and continuous challenge. A global One Health approach is mandatory to better understand and minimize the transmission pathways of human pathogens, including multidrug-resistant pathogens and commensals, through food-chain.

Scanning electron microscopy of Salmonella biofilms on various food-contact surfaces in catfish mucus

The objective of this study was to determine the growth and survival of Salmonella enterica in the presence of high and low concentrations (375 μg/ml and 15 μg/ml) of catfish mucus extract at 10 °C and 22 °C for 63 days. The second objective of this study was to investigate the biofilm formation of Salmonella enterica serovar Blockley (7175) in catfish mucus extract for 48 h at 22 °C on four food-contact surfaces and to observe the biofilm populations using Scanning Electron Microscopy (SEM). The surface properties, surface roughness and surface energies were determined using contact angle measurement and atomic force microscopy. In 375 μg/ml of catfish mucus extract that was inoculated with 3 log CFU/ml, the growth of Salmonella counts were increased to a maximum of 6-7 log CFU/ml at 10 °C and 7-8 log CFU/ml at 22 °C in 7-14 d and decreased by 1-2 log CFU/ml from these peak levels at both 10 °C and 22 °C from 21 to 63 d. In 15 μg/ml of catfish mucus extract, Salmonella counts were in the range of 4-5 log CFU/ml at 10 °C and 5-6 log CFU/ml at 22 °C over 7-63 d of storage. By contrast, Salmonella counts were non-detectable in the absence of catfish mucus by 21-28 d of storage at 10 °C or 22 °C. The biofilm counts of S. Blockley (7175) on a stainless steel surface were 4 log CFU/cm² and 5.5 log CFU/cm² in 15 μg/ml and 375 μg/ml of catfish mucus extract respectively after 48 h incubation at 22 °C. SEM revelead that biofilm formation by S. Blockley (7175) was less in 15 μg/ml than 375 μg/ml of catfish mucus extract on stainless steel. In addition, SEM indicated that the visible biofilms were least on buna-N rubber as compared to stainless steel, polyethylene and polyurethane surfaces. Contact angle and atomic force microscopy confirmed that buna-N rubber was highly hydrophobic with low surface energy and low roughness when compared to other three surfaces. These findings indicate that Salmonella can utilize catfish mucus as a nutrient source to survive for longer periods and promote biofilm formation for its persistence on different food-contact surfaces.

Application of molecular tools to elucidate the microbiota of seafood

The aim of this review is to present the methodologies currently applied to identify microbiota and pathogens transmitted to humans through seafood consumption, focusing on molecular techniques and pointing out their importance, advantages, disadvantages and applicability. Knowledge of available techniques allows researchers to identify which technique best fits their expectations. With such discernment, it will be possible to infer which disadvantages will be present and, therefore, not interfering with the final result. Two methodologies can be employed for this purpose, dependent and independent cultures. However, the dependent culture has certain limitations that can be solved through the independent cultivation techniques, such as PCR, PFGE and NGS, especially through the sequencing of the 16S rRNA region, providing a complete view of microbial diversity. These have revolutionized microbiological knowledge, mainly because they allow for the identification of uncultivable micro-organisms, which represent a substantial portion of total micro-organisms, making it possible to elucidate not yet described taxa which may display pathogenic potential, besides quantifying microbial communities, microbiota genetics, translated proteins and produced metabolites. In addition, transcriptomic and metabolomic techniques also allow for the evaluation of possible impacts that microbial communities may create in their environment, as well as the determination of potential pathogenicity to humans.