Prevalence of Salmonella spp. in oysters in the United States

Investigation of the presence and persistence of bacteria in seawater and oysters from an aquaculture farm in Rehoboth Bay, Delaware

The filter-feeding nature of oysters, anthropogenic activities, and increasing agriculture in Delaware compromise the microbial safety of Eastern oysters from local aquaculture farms. From July to October 2023, we evaluated the presence and persistence of eight bacteria in seawater and oysters produced from off-bottom and bottom cultures at Sally Cove, an aquaculture farm within Rehoboth Bay in Delaware. A control site within Sally Cove, which was without oyster cultures, was also included in the study. Seawater temperature, salinity, pH, and dissolved oxygen were measured in situ during sampling. Molecular confirmation with PCR and qPCR showed that Vibrio parahaemolyticus, Shiga-toxin-producing Escherichia coli, Salmonella enterica, Staphylococcus aureus, Pseudomonas aeruginosa, and Clostridium spp. were present and persisted in seawater and oyster samples from both cultures at Sally Cove and in off-bottom and bottom seawater samples from the control site throughout the study. Shigella spp. and Listeria monocytogenes were consistently found in seawater and oyster samples from July to September. However, Shigella spp. was only detected in samples from the bottom cultures, whereas L. monocytogenes was undetectable in all samples from both cultures in October. The observed temperature, salinity, pH, and dissolved oxygen levels across the study period were in the range of 15.30-29.67°C, 29.33-31.87 ppt, 7.25-7.95, and 3.79-8.10 mg/L, respectively, and comparable with the conditions suitable for the growth and survival of these bacteria. These findings suggest that consuming raw oysters from Sally Cove poses contamination risks from several bacteria, especially in the summer months.IMPORTANCEAlthough studies have evaluated bacterial contamination in seawater and oysters within the Delaware Inland Bays and nearby areas, the focus has primarily been on Vibrio species. However, other bacteria have been found in seawater and seafood at various locations and could potentially occur in oysters produced from aquaculture farms within the Delaware Inland Bays. Sally Cove is an oyster aquaculture farm that produces Eastern oysters (Crassostrea virginica) for consumption in Delaware using both off-bottom and bottom culturing methods. The risk of bacterial contamination from consuming raw oysters from this farm is unknown. This paper shows the presence and persistence of several bacteria, including those associated with waste, in seawater and oysters at the farm. The findings can inform consumers about the contamination risks from consuming raw oysters produced at the farm.

Evaluation of Multidrug Resistance of Salmonella Isolated from Pork Meat Obtained from Traditional Slaughter Systems in Romania

Antibiotic resistance among pathogenic bacteria in humans and animals poses a critical public health challenge, leading to diminished effectiveness of existing antimicrobial treatments. Notably, animal-derived food products are significant vectors for the transmission of resistant bacteria to humans, with Salmonella species being predominant culprits in foodborne illnesses. This study investigates the prevalence and antibiotic resistance patterns of Salmonella serovars isolated from traditionally sourced pork meat in Romania. Over a four-year period, 208 pork samples were collected using standardized protocols during traditional slaughtering practices. Salmonella spp. were isolated following ISO 6579:2002 guidelines and confirmed using biochemical assays and PCR. Serotyping was performed using specific antisera, and antimicrobial susceptibility testing was conducted through the standard disk diffusion method, assessing 11 antibiotics. Results indicated a 23.07% prevalence of Salmonella, with 48 isolates categorized into eight serovars, primarily S. Infantis (n = 15), S. Typhimurium (n = 15), and S. Derby (n = 11). PCR results confirmed the presence of Salmonella by detecting the hilA and ompC genes, with 31.25% of isolates being positive for the Typhimurium-specific sequence. Notably, 93.75% of the isolates were multidrug-resistant (MDR), exhibiting high resistance rates against streptomycin (91.66%) (>10 µg), tetracycline (83.33%) (>30 µg), and sulfamethoxazole (68.75%) (>300 µg). More than 60% of MDR isolates displayed resistance to five or more antibiotics. These findings underscore the need for coordinated control measures in the pork production chain to combat the spread of Salmonella and protect public health. Enhanced surveillance and intervention strategies are crucial for addressing antibiotic resistance and reducing the risk of foodborne illnesses linked to contaminated animal products.

Characteristics of Nontyphoid Salmonella Isolated from Human, Environmental, Animal, and Food Samples in Burkina Faso: A Systematic Review and Meta-Analysis

Salmonella is one of the world's leading causes of zoonotic and foodborne illnesses. Recently, antimicrobial resistance (AMR) has become one of the most critical challenges to public health and food safety. Herein, we employed a meta-analysis to determine the pooled prevalence and spatiotemporal distribution of serovars and antimicrobial resistance in NTS in Burkina Faso. To find eligible articles, a comprehensive literature search of PubMed, African Journals Online, ScienceDirect, Google Scholar, and the gray literature (university libraries) in Burkina was conducted for the period from 2008 to 2020. Studies meeting the inclusion criteria were selected and assessed for risk of bias. To assess the temporal and spatial relationships between serotypes and resistant strains from humans, animals, food, and the environment, a random-effects statistical model meta-analysis was carried out using the Comprehensive Meta-Analysis Version 3.0 program. The NTS prevalence rates were 4.6% (95% CI: 3-7) and 20.1% (95% CI: 6.6-47.4) in humans and animals, respectively, and 16.8% (95% CI: 10.5-25.8) and 15.6% (95% CI: 8.2-27.5) in food and the environment, respectively. Most NTS serovars were S. Derby, reported both in food and animals, and S. Typhimurium, reported in humans, while S. Croft II, S. Jodpur II, and S. Kentucky were the most prevalent in the environment. NTS isolates were highly resistant to erythromycin, amoxicillin, cefixime, and cephalothin, with a pooled prevalence of multidrug resistance of 29% (95% CI: 14.5-49.5). The results of this review show a high diversity of Salmonella serotypes, as well as high antibiotic resistance in Salmonella isolates from animal, human, food, and environmental samples in Burkina, calling for a consolidated "One Health" approach to better understand the drivers of pathogen emergence, spread, and antimicrobial resistance, as well as the formulation of intervention measures needed to limit the risk associated with the disease.

A Comprehensive Review for the Surveillance of Human Pathogenic Microorganisms in Shellfish

Bivalve molluscan shellfish have been consumed for centuries. Being filter feeders, they may bioaccumulate some microorganisms present in coastal water, either naturally or through the discharge of human or animal sewage. Despite regulations set up to avoid microbiological contamination in shellfish, human outbreaks still occur. After providing an overview showing their implication in disease, this review aims to highlight the diversity of the bacteria or enteric viruses detected in shellfish species, including emerging pathogens. After a critical discussion of the available methods and their limitations, we address the interest of technological developments using genomics to anticipate the emergence of pathogens. In the coming years, further research needs to be performed and methods need to be developed in order to design the future of surveillance and to help risk assessment studies, with the ultimate objective of protecting consumers and enhancing the microbial safety of bivalve molluscan shellfish as a healthy food.

Microbiological Quality and Heavy Metal Concentrations in Slipper Oyster (Crassostrea iredalei) Cultured in Major Growing Areas in Capiz Province, Western Visayas, Philippines: Compliance with International Shellfish Safety and Sanitation Standards

ABSTRACT

The increasing demand for slipper oyster (Crassostrea iredalei) has propelled farmers to expand oyster cultivation areas in the Philippines, chiefly for local consumption and feasibly for export overseas. As filter feeders, oysters can accumulate pathogens from the surrounding waters, and these pathogens can cause foodborne diseases in consumers. Therefore, oyster farming areas must be monitored for microbiological quality and heavy metal concentrations. In the present study, the microbiological quality of oysters and their growing waters in the major oyster farming areas of the Cogon and Palina Rivers and Cabugao Bay (in Roxas City and the Municipality of Ivisan, respectively, Capiz Province, Western Visayas, Philippines) were examined monthly during the wet (May to October) and dry (November to April) seasons over 12 months. Regardless of the sampling period, high levels of fecal coliforms in the water and Escherichia coli in oysters were found, clearly illustrating that these oyster growing areas would meet only the class B standard under the European Union classification system and would be considered "prohibited" for growing oysters under the U.S. classification system. Although Salmonella was occasionally detected in oysters, Vibrio cholerae was not detected and Vibrio parahaemolyticus was within acceptable limits. The heavy metal concentrations in oyster meat were also determined during the wet (July) and dry (March) seasons. Zinc and copper were the most abundant metals detected, and concentrations of lead, cadmium, mercury, and chromium were below the regulatory limits set by the European Union and the U.S. Food and Drug Administration. These oyster culture areas should be rehabilitated immediately to improve the microbiological quality of the oysters. Oysters harvested from these sites must be depurated or relayed to ensure quality and safety.

HIGHLIGHTS

Bacterial diversity and potential risk factors associated with Salmonella contamination of seafood products sold in retail markets in Bangkok, Thailand

Consumption of contaminated food causes 600 million cases, including 420,000 of fatal infections every year. Estimated cost from food-borne illnesses is USD 110 billion per year, which is an economic burden to low- and middle-income countries. Thailand is a leading producer and consumer of seafood, but little is known about bacterial contamination in seafood. In particular, public health agencies need to know the relationship between Salmonella contamination in seafood and risk factors, as assessed with readily available culture-dependent and bacterial phenotyping methods. To address this, levels of indicator bacteria, Salmonella and Vibrio in various seafood products were determined to identify risk factors associated with Salmonella contamination. A total of 335 samples were collected from October 2018 to July 2019 at seafood markets throughout Bangkok, Thailand; overall sample composition was Pacific white shrimp (n = 85), oysters (n = 82), blood cockles (n = 84), and Asian seabass (n = 84). Prevalence was 100% for fecal coliforms and 85% for E. coli. In contrast, prevalence was 59% for V. parahaemolyticus, 49% for V. cholerae, 19% for V. alginolyticus, 18% for V. vulnificus, and 36% for Salmonella. Highest concentrations of fecal coliforms and E. coli were in oysters. Highest concentrations of Salmonella with Matopeni (31%) being the predominant serotype were in shrimp. Salmonella contamination was significantly associated with type of seafood, sampling location, retail conditions, and the presence of E. coli, V. alginolyticus and V. vulnificus. A cutoff value for E. coli concentration of 1.3 × 104 MPN/g predicted contamination of Salmonella, with a sensitivity of 84% and specificity of 61%. Displaying seafood products on ice, presence of E. coli and Vibrio, and seafood derived from Eastern Thailand were associated with an increased risk of Salmonella contamination.

Atypical Salmonella Typhimurium persistence in the pacific oyster, Crassostrea gigas, and its effect on the variation of gene expression involved in the oyster's immune system

Salmonella is one of the most important pathogens involved in food intoxication outbreaks, and in many cases, the intoxication has been linked to shellfish which is typically consumed raw. While much is understood about the interactions between Salmonella and vertebrates, much less is known about its relationships with invertebrates, which could be an overlooked and important aspect to better understand the Salmonella interaction with its diversified hosts. The aim of this study was to investigate the effect of preadaptation in seawater microcosms during 12 months on Salmonella Typhimurium by determining its survival capacity within this mollusk over a period of 30 days. The results showed that the stressed bacteria are able to survive in this mollusk at a higher concentration even after thirty days of infection compared to bacteria in the normal state. In order to minimize the effect of an experimental device for one month on the survival of Salmonella, we carried out an in vitro study to determine the number of viable Salmonella in the hemocytes of oysters. Interestingly, we evaluated the effect of the antibacterial activity of different extracts of C. gigas using the solvents (Methanol, Ethanol and acetic acid) specifically against stressed and unstressed Salmonella. Furthermore, we compared the expression of three genes in the oyster Cg-big-def1, timp and sod in response to experimental infections of this mollusk with Vibrio splendidus kb133 and S. Typhimurium LT2DT104 in normal and stressed states. These findings are very important to contribute to explaining several questions about the persistence of S. Typhimurium for a long time in C. gigas and the host's immune response to this microorganism which is considered to be non-virulent for molluscs.

Prevalence, typing and antimicrobial resistance of Salmonella isolates from commercial shellfish in the North coast of Morocco

Salmonellosis is one of the most common foodborne illnesses in the world. The irrational use of antibiotics in medicine and in animal nutrition has greatly favored the emergence and spread of resistant strains of non-typhoid Salmonella. This study aims the determination of the prevalence of Salmonella in bivalve mollusks in Northern Morocco, as well as the molecular typing and antibiotic susceptibility testing of the strains isolated from positive samples. In total, 150 samples from shellfish composed of mussels (Mytilus galloprovincialis), clams (Callista chione and Ruditapes descussatus) and oysters (Magallana gigas). Isolated Salmonella were characterized by Molecular techniques PCR, MLST and MLVA, phylogenetically grouped by MLSA, and susceptibilities were determined for 30 antimicrobial drugs using microdilution method by the BD Phoenix Automated Microbiology System. Prevalence of Salmonella enterica subsp. enterica was 12.67%, grouped in four serovars identified as Chester, Hadar, Typhimurium and Kentucky. Five different MLST STs (sequence types) were detected, ST1954 being the most common, which was mostly found in Chester isolates. Forty-two percent of the isolates showed resistance to more than one antibiotic, especially trimethoprim, sulfa drugs, quinolones and β-lactam. There was a marked change in the serovars and antimicrobial resistance profiles of the Salmonella isolates in this study compared to those in previous studies.

Innovative Seafood Preservation Technologies: Recent Developments

Fish and fishery products are among the food commodities of high commercial value, high-quality protein content, vitamins, minerals and unsaturated fatty acids, which are beneficial to health. However, seafood products are highly perishable and thus require proper processing to maintain their quality and safety. On the other hand, consumers, nowadays, demand fresh or fresh-like, minimally processed fishery products that do not alter their natural quality attributes. The present article reviews the results of studies published over the last 15 years in the literature on: (i) the main spoilage mechanisms of seafood including contamination with pathogens and (ii) innovative processing technologies applied for the preservation and shelf life extension of seafood products. These primarily include: high hydrostatic pressure, natural preservatives, ozonation, irradiation, pulse light technology and retort pouch processing.

Phage therapy as a potential approach in the biocontrol of pathogenic bacteria associated with shellfish consumption

Infectious human diseases acquired from bivalve shellfish consumption constitute a public health threat. These health threats are largely related to the filter-feeding phenomenon, by which bivalve organisms retain and concentrate pathogenic bacteria from their surrounding waters. Even after depuration, bivalve shellfish are still involved in outbreaks caused by pathogenic bacteria, which increases the demand for new and efficient strategies to control transmission of shellfish infection. Bacteriophage (or phage) therapy represents a promising, tailor-made approach to control human pathogens in bivalves, but its success depends on a deep understanding of several factors that include the bacterial communities present in the harvesting waters, the appropriate selection of phage particles, the multiplicity of infection that produces the best bacterial inactivation, chemical and physical factors, the emergence of phage-resistant bacterial mutants and the life cycle of bivalves. This review discusses the need to advance phage therapy research for bivalve decontamination, highlighting their efficiency as an antimicrobial strategy and identifying critical aspects to successfully apply this therapy to control human pathogens associated with bivalve consumption.

Prevalence, Distribution, and Diversity of Salmonella Strains Isolated From a Subtropical Lake

This study investigated the prevalence, serovar distribution, antimicrobial resistance, and pulsed field gel electrophoresis (PFGE) typing of Salmonella enterica isolated from Lake Zapotlán, Jalisco, Mexico. Additionally, the association of the presence of Salmonella with physicochemical and environmental parameters was analyzed using Pearson correlation analysis and principal component analysis (PCA). Salmonella spp. were identified in 19 of 63 (30.15%) samples. The prevalence of Salmonella was positively correlated with air temperature, electrical conductivity, pH, and dissolved oxygen and negatively correlated with relative humidity, water temperature, turbidity, and precipitation. The predominant serotype identified was Agona (68.48%), followed by Weltevreden (5.26%), Typhimurium (5.26%), and serogroup B (21.05%). Overall, the highest detected antimicrobial resistance was toward colistin (73.68%), followed by sulfamethoxazole (63.15%), tetracycline (57.89%), nalidixic acid (52.63%), and trimethoprim (52.63%). All Salmonella strains were genetically diverse, with a total of 11 XbaI and four BlnI profiles on PFGE. The use of these two enzymes allowed differentiate strains of Salmonella of the same serotype. The results obtained in this study contribute to a better understanding of the Salmonella spp. ecology in an endorheic subtropical lake and provide information for decision makers to propose and implement effective strategies to control point and non-point sources of pathogen contamination.

Enumeration and Survival of Salmonella enterica in Live Oyster Shellstock Harvested from Canadian Waters

Since 2015, 11 recalls of live oyster shellstock have been issued in Canada due to the presence of Salmonella enterica. Six of those recalls took place in 2018. To understand this increase, fundamental information is needed on the relationship between S. enterica and oysters. The aims of this study were to address important data gaps concerning the levels of Salmonella in naturally contaminated oysters and the ability of this pathogen to survive in live oyster shellstock. Enumeration data were evaluated for five oyster and clam samples collected from the east coast of Canada from 2015 to 2018. The reported levels were <0.0015 to 0.064 most probable number per g of oyster tissue. The S. enterica isolates recovered from these animals belonged to serovars Typhimurium, Infantis, Enteritidis, and I 4,5:i:-. Filter feeding by the oysters was exploited to assess the Salmonella accumulation that would occur following a natural contamination event. Detectable levels of the pathogen were observed after 30 min of exposure and began to plateau at 60 min. A survival study in live oyster shellstock indicated that after 4 days of storage at ambient temperatures, the Salmonella level declined slightly from 4.3 to 3.7 log CFU/g. These data indicate that the levels of Salmonella found in naturally contaminated oysters are low and are not expected to increase between the point of harvest and the point of consumption. The changing ecology of shellfish environments requires continued monitoring and testing to safeguard public health. The data presented here will be useful for the evaluation and design of sampling plans and risk management approaches for the control of Salmonella in live oyster shellstock.

Worldwide Epidemiology of Salmonella Serovars in Animal-Based Foods: a Meta-analysis

Salmonella spp. are among the most important foodborne pathogens and the third leading cause of human death among diarrheal diseases worldwide. Animals are the primary source of this pathogen, and animal-based foods are the main transmission route to humans. Thus, understanding the global epidemiology of Salmonella serovars is key to controlling and monitoring this bacterium. In this context, this study aimed to evaluate the prevalence and diversity of Salmonella enterica serovars in animal-based foods (beef, pork, poultry, and seafood) throughout the five continents (Africa, the Americas [North and Latin America], Asia, Europe, and Oceania). The meta-analysis consisted of a chemometric assessment (hierarchical cluster analysis and principal component analysis) to identify the main epidemiological findings, including the prevalence and diversity of the Salmonella serovars in each matrix. Regarding the serovar distribution, S Typhimurium presented a cosmopolitan distribution, reported in all four assessed matrices and continents; poultry continues to play a central role in the dissemination of the Enteritidis serovar to humans, and Anatum and Weltevreden were the most frequently found in beef and seafood, respectively. Additionally, we recommended careful monitoring of certain serovars, such as Derby, Agona, Infantis, and Kentucky. Finally, given the scientific data regarding the most frequently reported serovars and which matrices constitute the main vehicles for the transmission of this pathogen, control programs may be improved, and specific interventions may be implemented in an attempt to reduce the risk of this pathogen reaching humans.IMPORTANCE Salmonellosis is caused by Salmonella spp. and is the third leading cause of death among food-transmitted diseases. This pathogen is commonly disseminated in domestic and wild animals, and the infection's symptoms are characterized by acute fever, nausea, abdominal pain, and diarrhea. The animals are the primary source of salmonellae, and animal-based foods are the main transmission route to humans. Therefore, data collected from these sources could contribute to future global interventions for effective control and surveillance of Salmonella along the food chain. In light of this, the importance of our research is in identifying the prevalence of Salmonella serovars in four animal-based food matrices (pork, poultry, beef, and seafood) and to evaluate the importance that each matrix has as the primary source of this pathogen to humans.

Prevalence of Antimicrobial Resistance and Virulence Gene Elements of Salmonella Serovars From Ready-to-Eat (RTE) Shrimps

Gastrointestinal illnesses continue to be a global public health risk. Exposure to foodborne Salmonella directly or indirectly through consumption of ready-to-eat seafood can be an important route of infection to humans. This study was designed to estimate the population cell density, prevalence, virulence gene signatures, and antibiotic resistance of Salmonella serovars from ready-to-eat shrimps. Ready-to-eat (RTE) shrimp samples were obtained from different open markets in Delta and Edo States, Nigeria from November 2016 to October 2017. We employed classical and polymerase chain reaction (PCR) approaches. The mean Salmonella species enumerated from the RTE shrimps ranged from -0.301 to 5.434 log10 cfu/g with 210/1440 (14.58%) of the RTE shrimp samples harbored Salmonella species. After biochemical and PCR approach, the identified isolates were Salmonella Enteritidis 11(24.4%), Salmonella Typhimurium 14 (31.1%) and other Salmonella spp. 20 (44.4%). All Salmonella species recovered were resistant to penicillin and erythromycin with 100% sensitivity to cefotaxime, cephalothin, colistin, and polymyxin B. Findings on the multidrug-resistant (MDR) profile showed that a total of 9/14 (64.3%) of Salmonella Enteritidis were resistant to 5 antibiotics which belongs to 3 different groups of antimicrobials with a multiple antibiotic-resistant (MAR) index of 0.21; while 3/11 (27.3%) of Salmonella Typhimurium were resistant to 11 antibiotics which belongs to 7 different groups of antimicrobials with a MAR index of 0.46. Virulence genes (spiA, sipB, invA, sif A, fljB, and sefA) and resistance genes (class 1 and II integrase, sul2, catB3, flor, tmp, bla TEM, strB, dfr1, and tetC) were also detected in some of the Salmonella species with variable percentage. This study indicates that ready-to-eat shrimps are probable reservoirs harboring Salmonella strains. The identified Salmonella isolates which exhibited virulence determinants and antibiotic-resistant coupled with high MAR index constitute a consumer health risk to the communities.

Modelling of Indicator Escherichia coli Contamination in Sentinel Oysters and Estuarine Water

This study was performed to improve the ability to predict the concentrations of Escherichia coli in oyster meat and estuarine waters by using environmental parameters, and microbiological and heavy metal contamination from shellfish growing area in southern Thailand. Oyster meat (n = 144) and estuarine waters (n = 96) were tested for microbiological and heavy metal contamination from March 2016 to February 2017. Prevalence and mean concentrations of E. coli were 93.1% and 4.6 × 10³ most probable number (MPN)/g in oyster meat, and 78.1% and 2.2 × 10² MPN/100 mL in estuarine water. Average 7-day precipitation, ambient air temperature, and the presence of Salmonella were associated with the concentrations of E. coli in oyster meat (p < 0.05). Raw data (MPN/g of oyster meat and MPN/100 mL of estuarine water) and log-transformed data (logMPN/g of oyster meat and logMPN/100 mL of estuarine water) of E. coli concentrations were examined within two contrasting regression models. However, the more valid predictions were conducted using non-log transformed values. These findings indicate that non-log transformed data can be used for building more accurate statistical models in microbiological food safety, and that significant environmental parameters can be used as a part of a rapid warning system to predict levels of E. coli before harvesting oysters.

W. Vieira C, Parveen S. Genotypic and phenotypic characterization of Escherichia coli isolated from mollusks in Brazil and the United States

The aim of this study was to determine the serogroups, antimicrobial resistance and genetic diversity of Escherichia coli isolates from samples of bivalve mollusks collected along Santa Catarina coast, Brazil, and from the Chesapeake Bay, Maryland, USA. One hundred forty-one E. coli isolates were characterized for serogroups with 181 specific O antisera and antimicrobial susceptibility using the disk diffusion method. The genetic diversity was assessed using pulsed-field gel electrophoresis (PFGE). The results showed that among the isolates, 19.9% were classified as multi-drug resistant (MDR) and resistance was most frequently observed to cephalothin, nitrofurantoin, and ampicillin. The predominant serogroups were O6, O8, and O38. Some serogroups were recognized as pathogenic E. coli. PFGE dendrograms indicated extensive genetic diversity among the isolates. Although characteristics of the E. coli isolates were highly variable, it is important to note that E. coli belonging to pathogenic serogroups and MDR isolates are present in mollusks of both study areas. This is the first report on the phenotypic and genotypic characterization of E. coli from mollusks from Santa Catarina and the Chesapeake Bay that should encourage studies focusing on comparison of isolates across countries.

A review of Salmonella enterica with particular focus on the pathogenicity and virulence factors, host specificity and antimicrobial resistance including multidrug resistance

Salmonella genus represents the most common foodborne pathogens frequently isolated from food-producing animals that is responsible for zoonotic infections in humans and animal species including birds. Thus, Salmonella infections represent a major concern to public health, animals, and food industry worldwide. Salmonella enterica represents the most pathogenic specie and includes > 2600 serovars characterized thus far. Salmonella can be transmitted to humans along the farm-to-fork continuum, commonly through contaminated foods of animal origin, namely poultry and poultry-related products (eggs), pork, fish etc. Some Salmonella serovars are restricted to one specific host commonly referred to as "host-restricted" whereas others have broad host spectrum known as "host-adapted" serovars. For Salmonella to colonize its hosts through invading, attaching, and bypassing the host's intestinal defense mechanisms such as the gastric acid, many virulence markers and determinants have been demonstrated to play crucial role in its pathogenesis; and these factors included flagella, capsule, plasmids, adhesion systems, and type 3 secretion systems encoded on the Salmonella pathogenicity island (SPI)-1 and SPI-2, and other SPIs. The epidemiologically important non-typhoidal Salmonella (NTS) serovars linked with a high burden of foodborne Salmonella outbreaks in humans worldwide included Typhimurium, Enteritidis, Heidelberg, and Newport. The increased number of NTS cases reported through surveillance in recent years from the United States, Europe and low- and middle-income countries of the world suggested that the control programs targeted at reducing the contamination of food animals along the food chain have largely not been successful. Furthermore, the emergence of several clones of Salmonella resistant to multiple antimicrobials worldwide underscores a significant food safety hazard. In this review, we discussed on the historical background, nomenclature and taxonomy, morphological features, physical and biochemical characteristics of NTS with a particular focus on the pathogenicity and virulence factors, host specificity, transmission, and antimicrobial resistance including multidrug resistance and its surveillance.

Diversified sources for human infections by Salmonella enterica serovar newport

Salmonella enterica Newport (S. Newport), with phylogenetic diversity feature, contributes to significant public health concerns. Our previous study suggested that S. Newport from multiple animal-borne routes, with distinct antibiotic resistant pattern, might transmit to human. However, their genetic information was lacking. As a complement to the earlier finding, we investigate the relationship between each other among the hosts, sources, genotype and antibiotic resistance in S. Newport. We used the multilocus sequence typing (MLST) in conjunction with minimum inhibitory concentration of 16 antibiotics of globally sampled 1842 S. Newport strains, including 282 newly contributed Chinese strains, to evaluate this association. Our analysis reveals that sequence types (STs) are significantly associated with different host sources, including livestock (ST45), birds (ST5), contaminated water and soil (ST118), reptiles (ST46) and seafood (ST31). Importantly, ST45 contained most of (344/553) the multi-drug resistance (MDR) strains, which were believed to be responsible for human MDR bacterial infections. Chinese isolates were detected to form two unique lineages of avian (ST808 group) and freshwater animal (ST2364 group) origin. Taken together, genotyping information of S. Newport could serve to improve Salmonella source-originated diagnostics and guide better selection of antibiotic therapy against Salmonella infections.

Rotavirus analyses by SYBR Green real-time PCR and microbiological contamination in bivalves cultivated in coastal water of Amazonian Brazil

The contamination of mussels and oysters by viruses and bacteria is often associated with water contamination and gastroenteritis in humans. The present study evaluated viral and bacterial contamination in 380 samples, from nine mollusk-producing regions in coastal water north of the Brazilian Amazon. Rotavirus contamination was studied for groups A to H, using a two-step SYBR Green RT-qPCR (quantitative reverse transcription polymerase chain reaction), and bacterial families Enterobacteriaceae, Vibrionaceae, and Aeromonadaceae by classical and molecular methods. From the 19 pools analyzed, 26.3% (5/19) were positive for group A Rotavirus, I2 genotype for VP6 region, without amplifications for groups B-H. Bacteriological analysis identified Escherichia coli isolates in 89.5% (17/19) with identification of atypical enteropathogenic E. coli aEPEC in 10.5% (2/19), Salmonella (Groups C1 and G) (10.5%, 2/19), Vibrio alginolyticus (57.9%, 11/19) V. parahaemolyticus (63.2%, 12/19), V. fluvialis (42.1%, 8/19), V. vulnificus (10.5%, 2/19), V. cholerae non-O1, non O139(10.5%, 2/19) and Aeromonas salmonicida (52.6%, 10/19). All the samples investigated presented some level of contamination by enterobacteria, rotavirus, or both, and these results may reflect the level of contamination in the Northern Amazon Region, due to the natural maintenance of some of these agents or by the proximity with human populations and their sewer.

Occurrence of Bacterial Pathogens and Human Noroviruses in Shellfish-Harvesting Areas and Their Catchments in France

During a 2-year study, the presence of human pathogenic bacteria and noroviruses was investigated in shellfish, seawater and/or surface sediments collected from three French coastal shellfish-harvesting areas as well as in freshwaters from the corresponding upstream catchments. Bacteria isolated from these samples were further analyzed. Escherichia coli isolates classified into the phylogenetic groups B2, or D and enterococci from Enterococcus faecalis and E. faecium species were tested for the presence of virulence genes and for antimicrobial susceptibility. Salmonella members were serotyped and the most abundant serovars (Typhimurium and its monophasic variants and Mbandaka) were genetically characterized by high discriminative subtyping methods. Campylobacter and Vibrio were identified at the species level, and haemolysin-producing Vibrio parahaemolyticus were searched by tdh- and trh- gene detection. Main results showed a low prevalence of Salmonella in shellfish samples where only members of S. Mbandaka were found. Campylobacter were more frequently isolated than Salmonella and a different distribution of Campylobacter species was observed in shellfish compared to rivers, strongly suggesting possible additional inputs of bacteria. Statistical associations between enteric bacteria, human noroviruses (HuNoVs) and concentration of fecal indicator bacteria revealed that the presence of Salmonella was correlated with that of Campylobacter jejuni and/or C. coli as well as to E. coli concentration. A positive correlation was also found between the presence of C. lari and the detection of HuNoVs. This study highlights the importance of simultaneous detection and characterization of enteric and marine pathogenic bacteria and human noroviruses not only in shellfish but also in catchment waters for a hazard assessment associated with microbial contamination of shellfish.

Assessment of Bacterial Accumulation and Environmental Factors in Sentinel Oysters and Estuarine Water Quality from the Phang Nga Estuary Area in Thailand

This study characterized microbiological and chemical contamination of oyster meat and estuarine water in Phang Nga, Thailand. Pooled oyster meats (n = 144), estuarine waters (n = 96) and environmental parameters were collected from March, 2016 to February, 2017, and assessed for levels of total coliforms (TC), fecal coliforms (FC), Escherichia coli (EC), and Vibrio parahaemolyticus (VP), presence of Salmonella and Shigella and levels of heavy metals (Mn, Pb and Cd). The prevalence of TC, FC and EC were in 99.3%, 94.4% and 93.1% of oyster meat and 94.8%, 79.2%, and 78.1% of water, respectively. The average VP levels was 8.5 × 10⁷ most probable number (MPN)/g oyster. Prevalence of Shigella and Salmonella in the pooled oysters were 7.6% and 30.6%, respectively. The dominant Salmonella serovars were Paratyphi B followed by Seremban, and Kentucky. In contrast, the prevalence of Shigella were 27.1%, but Salmonella was not detected in estuarine water. Factors statistically associated with EC accumulation in oyster were level of FC, 7-day average precipitation, temperature, relative humidity, and presence of Salmonella in the sample. The optimal cutoff value of EC to predict Salmonella in oyster was 420 MPN/g. Results indicate this area has relatively safe levels of heavy metals, whereas bacterial contamination was very high for oysters.

Salmonella Cold Stress Response: Mechanisms and Occurrence in Foods

Since bacteria in foods often encounter various cold environments during food processing, such as chilling, cold chain distribution, and cold storage, lower temperatures can become a major stress environment for foodborne pathogens. Bacterial responses in stressful environments have been considered in the past, but now the importance of stress responses at the molecular level is becoming recognized. Documenting how bacterial changes occur at the molecular level may help to achieve the in-depth understanding of stress responses, to predict microbial fate when they encounter cold temperatures, and to design and develop more effective strategies to control pathogens in food for ensuring food safety. Microorganisms differ in responding to a sudden downshift in temperature and this, in turn, impacts their metabolic processes and can cause various structural modifications. In this review, the fundamental aspects of bacterial cold stress responses focused on cell membrane modification, DNA supercoiling modification, transcriptional and translational responses, cold-induced protein synthesis including CspA, CsdA, NusA, DnaA, RecA, RbfA, PNPase, KsgA, SrmB, trigger factors, and initiation factors are discussed. In this context, specific Salmonella responses to cold temperature including growth, injury, and survival and their physiological and genetic responses to cold environments with a focus on cross-protection, different gene expression levels, and virulence factors will be discussed.

Comparative Study on Antibiotic Resistance and DNA Profiles of Salmonella enterica Serovar Typhimurium Isolated from Humans, Retail Foods, and the Environment in Shanghai, China

We characterized antibiotic resistance profiles, antibiotic resistance-associated genes, and pulsed-field gel electrophoresis (PFGE) patterns of 145 Salmonella enterica serotype Typhimurium isolates from human infections and retail foods that were possibly responsible for salmonellosis outbreaks from 2008 to 2012 in Shanghai, China. Resistance to at least three antibiotics was found in 66.7% of chicken isolates, 76.5% of duck isolates, 77.8% of pork isolates, and 80.5% of human isolates. Seven antibiotic resistance phenotypes were detected in chicken isolates, 16 in pork isolates, 17 in duck isolates, and 50 in human isolates. No significant difference (p > 0.05) was found between Salmonella isolates derived from human salmonellosis and from retail foods in terms of the percent resistance of ampicillin, amoxicillin/clavulanic acid, ceftiofur, ceftriaxone, nalidixic acid, chloramphenicol, gentamicin, kanamycin, streptomycin, tetracycline, sulfisoxazole, and sulfamethoxazole/trimethoprim. PFGE using XbaI and BlnI showed that some Salmonella isolates recovered from human infections and retail foods had same or highly similar genetic profile. Same or similar antibiotic resistance profiles, antibiotic resistance associated genes (i.e., qnrA, qnrB, qnrS, aac(6')-Ib, and oqxAB), gene cassettes (i.e., aadA2, dfrA12-aadA2, and aadA1), and mutations were detected in those isolates that exhibited high genetic similarities. These findings highlighted the frequent presence of Salmonella Typhimurium in retail chicken, pork, duck, and humans.

Multiple Food-Animal-Borne Route in Transmission of Antibiotic-Resistant Salmonella Newport to Humans

Characterization of transmission routes of Salmonella among various food-animal reservoirs and their antibiogram is crucial for appropriate intervention and medical treatment. Here, we analyzed 3728 Salmonella enterica serovar Newport (S. Newport) isolates collected from various food-animals, retail meats and humans in the United States between 1996 and 2015, based on their minimum inhibitory concentration (MIC) toward 27 antibiotics. Random Forest and Hierarchical Clustering statistic was used to group the isolates according to their MICs. Classification and Regression Tree (CART) analysis was used to identify the appropriate antibiotic and its cut-off value between human- and animal-population. Two distinct populations were revealed based on the MICs of individual strain by both methods, with the animal population having significantly higher MICs which correlates to antibiotic-resistance (AR) phenotype. Only ∼9.7% (267/2763) human isolates could be attributed to food-animal origins. Furthermore, the isolates of animal origin had less diverse antibiogram than human isolates (P < 0.001), suggesting multiple sources involved in human infections. CART identified trimethoprim-sulfamethoxazole to be the best classifier for differentiating the animal and human isolates. Additionally, two typical AR patterns, MDR-Amp and Tet-SDR dominant in bovine- or turkey-population, were identified, indicating that distinct food-animal sources could be involved in human infections. The AR analysis suggested fluoroquinolones (i.e., ciprofloxacin), but not extended-spectrum cephalosporins (i.e., ceftriaxone, cefoxitin), is the adaptive choice for empirical therapy. Antibiotic-resistant S. Newport from humans has multiple origins, with distinct food-animal-borne route contributing to a significant proportion of heterogeneous isolates.

Heterogeneity of Multidrug-Resistant Salmonella enterica Isolates with Increasing Frequency of Resistance to Ciprofloxacin During a 4-Year Period in Iran

BACKGROUND

The study was conducted to assess the trend of antimicrobial resistance among Salmonella enterica strains during a period of 4 years and to compare the effectiveness of three genotyping methods, including flagellin polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP), enterobacterial repetitive intergenic consensus (ERIC)-PCR, and pulsed-field gel electrophoresis (PFGE), and to determine the most efficient method for S. enterica genotyping.

METHODS AND RESULTS

About 50 S. enterica isolates were isolated from 5,064 stool samples. All of the isolates harbored fliC gene, 29 of which (58%) showed diphasic characteristic with a fliC⁺/fljB⁺ genotype. Simpson diversity index (Di) for RFLP analysis of fliC and fljB genes was calculated as 0.71 and 0.82, respectively. Strains were differentiated into 40 ERIC genotypes and 27 pulsotypes. All isolates with identical pulsotypes belonged to common serogroups which depict their correlation in a good manner. The Di calculated for ERIC-PCR and PFGE analysis was 0.99 and 0.94, respectively. The frequency of multidrug resistance (MDR) was dramatically increased from 25% in 2009-2010 to 63% in 2011-2012 with the emergence of 10% ciprofloxacin resistance in the latter period.

CONCLUSION

About 44% increase in MDR phenotype among S. enterica isolates during a 4-year period and concomitant appearance of ciprofloxacin resistance is a traumatic situation for health professionals in Iran. PFGE profiles offered a satisfactory discriminatory power, which was positively correlated with S. enterica serogrouping. The current study marks the superiority of PFGE method over other conventional molecular techniques in epidemiological investigations; however, their limitations need to be addressed for further refinement.

Prevalence and Antimicrobial Resistance of Salmonella in Market Raw Oysters in Taiwan

We tested 137 samples of domestic shucked oysters and 114 samples of imported oysters collected from traditional retail markets and supermarkets during 2010 and 2011 in Taiwan for the presence of Salmonella. We obtained a total of 91 Salmonella isolates, representing nine serotypes, from 80 of the domestic samples. We did not find any Salmonella in the imported oysters. The presence of Salmonella contamination tended to be specific to the area from which the oysters were harvested: the Dongshih area had a significantly higher contamination rate (68.8%) than the Budai (20.0%) and Wanggong (9.1%) areas. In addition, the rate of Salmonella contamination was higher in oysters that were packed or sold with water (P < 0.05). The most commonly identified Salmonella serotypes were Saintpaul (26.4%), Newport (22.0%), and Infantis (13.2%). We screened the isolates for susceptibility to nine antimicrobials and compared them genetically by using PCR for the class 1 integron (int1), tetA, tetB, and blaPSE-1 genes. Eighteen isolates (19.8%) were resistant to at least one antimicrobial agent, and the most frequent resistances were those to tetracycline and oxytetracycline (n = 12, 14.3%).We detected the antimicrobial resistance genes int1, tetA, tetB, and blaPSE-1 in 16.5, 26.4, 6.6, and 22.0% of the isolates, respectively. Eleven of the 18 antimicrobial-resistant isolates contained one or two int1 cassettes, suggesting that the presence of int1 is highly correlated with antimicrobial resistance in Salmonella isolates from oysters. The consumption of oysters is increasing in Taiwan, and information related to Salmonella contamination in oysters is rather limited. Our results indicate that raw oyster consumption from retail markets in Taiwan is associated with a human health hazard owing to Salmonella, including multidrug-resistant Salmonella strains.

Evaluation of the microbiological quality of jacopevers and plaices in Korea, 2015-2016

In Southeast Asian countries, including Korea, China, and Japan, the considerable amounts of raw fish have been annually consumed in the manner of live fish fillets without minimally thermal processing, increasing the risks of causing food-borne diseases. This study investigated the occurrence of total aerobic bacteria (TAB), coliform, Vibrio parahaemolyticus, Salmonella enterica serovar spp., Listeria monocytogenes, and Staphylococcus aureus in jacopevers and plaices. Total 200 live fishes were collected from randomly selected restaurants located in Anseong-si, and then they were microbiologically monitored. TAB ranged from 3.09 to 3.21 Log10 CFU/g in jacopever and plaice. Coliform in the levels of 1.54 Log10 CFU/g were detected in samples. Out of 100 jacopevers, a single jacopever (1%) exhibited the prevalence of S. aureus in the edible part, though none of pathogenic bacteria were detected. These results will be useful for understanding the microbial prevalence in the domestic living jacopevers and plaices.

Characterization and in vitro evaluation of new bacteriophages for the biocontrol of Escherichia coli

In the present study two new phages (phT4A and ECA2) were characterized and their efficacy was evaluated separately and in cocktail (phT4A/ECA2) to control Escherichia coli. The isolated phages, phT4A and ECA2, belonged to the Myoviridae and Podoviridae family, respectively and both are safe (no integrase and toxin codifying genes) to be used in bacterial control. In general, the increase of multiplicity of infection (MOI) from 1 to 100 promoted a significant increase in the efficiency of phage phT4A and phage cocktail phT4A/ECA2. Both phages were effective against E. coli, but phage phT4A (reduction of 5.8 log CFU/mL after 8h treatment) was more effective than phage ECA2 phage (reduction of 4.7 log CFU/mL after 8h treatment). The use of a cocktail phT4A/ECA2 was significantly more effective (reductions of 6.2 log CFU/mL after 6h treatment) than the use single phage suspensions of phT4A and ECA2 (reductions 5.3 log CFU/mL and 4.9 log CFU/mL, respectively, after 6h treatment). The rate of emergence of phage-resistant mutants was lower for phage phT4A when compared with phage ECA2 and phage cocktail phT4A/ECA2.The results indicate that in addition to the efficacy, the potential development of phage-resistant mutants must also be considered in the design of phage cocktails.

Draft Genome Sequence of Salmonella enterica subsp. enterica Serovar Bardo Strain CRJJGF_00099 (Phylum Gammaproteobacteria)

Here, we report a 4.87-Mbp draft genome sequence of the multidrug-resistant (MDR) Salmonella enterica subsp. enterica serovar Bardo strain CRJJGF_00099, isolated from dairy cattle in 2005.

Turtles as a Possible Reservoir of Nontyphoidal Salmonella in Shanghai, China

Terrapins and turtles are known to transmit Salmonella to humans. However, little was known about the occurrence of this pathogen in soft-shelled terrapin that is a popular delicacy in Chinese and other East Asian cuisines. We isolated and characterized 82 (24.4%) isolates of Salmonella from 336 fecal samples of soft-shelled terrapins (51 of 172; 29.7%) and pet turtles (31 of 164; 18.9%) in Shanghai. Salmonella Thompson was the most common serotype (17.1%) among others. Many isolates (84.1%) were resistant to multiple antimicrobials (≥3). Molecular analysis of Salmonella Thompson and Salmonella Typhimurium using pulsed-field gel electrophoresis unveiled a close genetic relationship between several human and terrapin isolates. Our results highlight the risk associated with the handling and consumption of turtles and their role in the spread of Salmonella in the human salmonellosis.

Bacteriophages with potential to inactivate Salmonella Typhimurium: Use of single phage suspensions and phage cocktails

The aim of this study was to compare the dynamics of three previously isolated bacteriophages (or phages) individually (phSE-1, phSE-2 and phSE-5) or combined in cocktails of two or three phages (phSE-1/phSE-2, phSE-1/phSE-5, phSE-2/phSE-5 and phSE-1/phSE-2/phSE-5) to control Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) in order to evaluate their potential application during depuration. Phages were assigned to the family Siphoviridae and revealed identical restriction digest profiles, although they showed a different phage adsorption, host range, burst size, explosion time and survival in seawater. The three phages were effective against S. Typhimurium (reduction of ∼2.0 log CFU/mL after 4h treatment). The use of cocktails was not significantly more effective than the use of single phages. A big fraction of the remained bacteria are phage-resistant mutants (frequency of phage-resistant mutants 9.19×10(-5)-5.11×10(-4)) but phage- resistant bacterial mutants was lower for the cocktail phages than for the single phage suspensions and the phage phSE-1 presented the highest rate of resistance and phage phSE-5 the lowest one. The spectral changes of S. Typhimurium resistant and phage-sensitive cells were compared and revealed relevant differences for peaks associated to amide I (1620cm(-1)) and amide II (1515cm(-1)) from proteins and from carbohydrates and phosphates region (1080-1000cm(-1)). Despite the similar efficiency of individual phages, the development of lower resistance indicates that phage cocktails might be the most promising choice to be used during the bivalve depuration to control the transmission of salmonellosis.

Food Safety Impacts from Post-Harvest Processing Procedures of Molluscan Shellfish

Post-harvest Processing (PHP) methods are viable food processing methods employed to reduce human pathogens in molluscan shellfish that would normally be consumed raw, such as raw oysters on the half-shell. Efficacy of human pathogen reduction associated with PHP varies with respect to time, temperature, salinity, pressure, and process exposure. Regulatory requirements and PHP molluscan shellfish quality implications are major considerations for PHP usage. Food safety impacts associated with PHP of molluscan shellfish vary in their efficacy and may have synergistic outcomes when combined. Further research for many PHP methods are necessary and emerging PHP methods that result in minimal quality loss and effective human pathogen reduction should be explored.

Salmonella grows vigorously on seafood and expresses its virulence and stress genes at different temperature exposure

Background

Seafood is not considered the natural habitat of Salmonella except the river fish, but still, the incidence of Salmonella in seafood is in a steady rise. By extending our understanding of Salmonella growth dynamics and pathogenomics in seafood, we may able to improve seafood safety and offer better strategies to protect the public health. The current study was thus aimed to assess the growth and multiplication of non-typhoidal and typhoidal Salmonella serovars on seafood and further sought to evaluate their virulence and stress genes expression while in contact with seafood at varying temperature exposure.

Results

Salmonella enterica Weltevreden and Salmonella enterica Typhi were left to grow on fish fillets at −20, 4, room temperature (RT) and 45 °C for a period of one week. Total RNA from both Salmonella serovars were extracted and qRT-PCR based relative gene expression approach was used to detect the expression of rpoE, invA, stn and fimA genes at four different temperature conditions studied on incubation days 0, 1, 3, 5 and 7. Salmonella Weltevreden growth on seafood was increased ~4 log₁₀ at RT and 45 °C, nevertheless, nearly 2 and >4 log ₁₀ reduction was observed in cell count stored at 4 and −20 °C on seafood, respectively. Growth pattern of Salmonella Typhi in seafood has shown identical pattern at RT and 45 °C, however, growth was sharply reduced at 4 and −20 °C as compared to the Salmonella Weltevreden. Total RNA of Salmonella Weltevreden was in the range from 1.3 to 17.6 μg/μl and maximum concentration was obtained at 45 °C on day 3. Similarly, RNA concentration of Salmonella Typhi was ranged from 1.2 to 11.8 μg/μl and maximum concentration was obtained at 45 °C on day 3. The study highlighted that expression of invA and stn genes of Salmonella Weltevreden was >8-fold upregulated at RT, whereas, fimA gene was increasingly down regulated at room temperature. Storage of Salmonella Weltevreden at 45 °C on seafood resulted in an increased expression (>13 -fold) of stn genes on day 1 followed by down regulation on days 3, 5, and 7. Nevertheless, other genes i.e. fimA, invA and rpo remained downregulated throughout the storage period. More intense upregulation was observed for invA and stn genes of Salmonella Typhi at RT and 45 °C. Further, incubating Salmonella Weltevreden at 4 °C resulted in down regulation in the expression of rpoE, invA and stn genes. Regarding Salmonella Typhi, fimA and stn genes were upregulated on day one, in addition, an increased expression of fimA was noted on day 3. At −20 °C, there was no obvious expression of target genes of Salmonella Weltevreden and Salmonella Typhi when stored along with seafood.

Conclusion

Here we demonstrate that nutritional constituents and water content available in seafood has become useful growth ingredients for the proliferation of Salmonella in a temperature dependent manner. Although, it was absence of serovar specific growth pattern of non-typhoidal and typhoidal Salmonella in seafood, there was observation of diverse expression profile of stress and virulent genes in non-typhoidal and typhoidal Salmonella serovars. In presence of seafood, the induced expression of Salmonella virulent genes at ambient temperature is most likely to be impacted by increased risk of seafood borne illness associated with Salmonella.

Influence of Salmonella enterica Serovar Typhimurium ssrB on Colonization of Eastern Oysters (Crassostrea virginica) as Revealed by a Promoter Probe Screen

Although Salmonella has been isolated from 7.4 to 8.6% of domestic raw oysters, representing a significant risk for food-borne illness, little is known about the factors that influence their initial colonization by Salmonella. This study tested the hypothesis that specific regulatory changes enable a portion of the invading Salmonella population to colonize oysters. An in vivo promoter probe library screen identified 19 unique regions as regulated during colonization. The mutants in the nearest corresponding downstream genes were tested for colonization defects in oysters. Only one mutation, in ssrB, resulted in a significantly reduced ability to colonize oysters compared to that of wild-type Salmonella. Because ssrB regulates Salmonella pathogenicity island 2 (SPI-2)-dependent infections in vertebrate macrophages, the possibility that ssrB mediated colonization of oyster hemocytes in a similar manner was examined. However, no difference in hemocyte colonization was observed. The complementary hypothesis that signal exchange between Salmonella and the oyster's native microbial community aids colonization was also tested. Signals that triggered responses in quorum sensing (QS) reporters were shown to be produced by oyster-associated bacteria and present in oyster tissue. However, no evidence for signal exchange was observed in vivo. The sdiA reporter responded to salinity, suggesting that SdiA may also have a role in environmental sensing. Overall, this study suggests the initial colonization of live oysters by Salmonella is controlled by a limited number of regulators, including ssrB.

Diversity and Persistence of Salmonella enterica Strains in Rural Landscapes in the Southeastern United States

Salmonellosis cases in the in the United States show distinct geographical trends, with the southeast reporting among the highest rates of illness. In the state of Georgia, USA, non-outbreak associated salmonellosis is especially high in the southern low-lying coastal plain. Here we examined the distribution of Salmonella enterica in environmental waters and associated wildlife in two distinct watersheds, one in the Atlantic Coastal Plain (a high case rate rural area) physiographic province and one in the Piedmont (a lower case rate rural area). Salmonella were isolated from the two regions and compared for serovar and strain diversity, as well as distribution, between the two study areas, using both a retrospective and prospective design. Thirty-seven unique serovars and 204 unique strain types were identified by pulsed-field gel electrophoresis (PFGE). Salmonella serovars Braenderup, Give, Hartford, and Muenchen were dominant in both watersheds. Two serovars, specifically S. Muenchen and S. Rubislaw, were consistently isolated from both systems, including water and small mammals. Conversely, 24 serovars tended to be site-specific (64.8%, n = 37). Compared to the other Salmonella serovars isolated from these sites, S. Muenchen and S. Rubislaw exhibited significant genetic diversity. Among a subset of PFGE patterns, approximately half of the environmental strain types matched entries in the USA PulseNet database of human cases. Ninety percent of S. Muenchen strains from the Little River basin (the high case rate area) matched PFGE entries in PulseNet compared to 33.33% of S. Muenchen strains from the North Oconee River region (the lower case rate area). Underlying the diversity and turnover of Salmonella strains observed for these two watersheds is the persistence of specific Salmonella serovars and strain types that may be adapted to these watersheds and landscapes.

Prevalence of antimicrobial resistance of non-typhoidal Salmonella serovars in retail aquaculture products

Aquaculture products can become sources of Salmonella by exposure to contaminated water or through processing practices, thus representing a public health hazard. A study was conducted on Salmonella contamination in aquaculture products sampled from marketplaces and retailers in Shanghai, China. A total of 730 samples (including fish, shellfish, bullfrog, clam, shrimp and others) were obtained from 2006 to 2011. Among them, 217 (29.7%) were positive for Salmonella. Thirty-eight serovars were identified in the 217 Salmonella isolates. The most prevalent were Salmonella Aberdeen (18.4%), S. Wandsworth (12.0%), S. Thompson (9.2%), S. Singapore (5.5%), S. Stanley (4.6%), S. Schwarzengrund (4.6%), S. Hvittingfoss (4.1%) and S. Typhimurium (4.1%). Many resistant isolates were detected, with 69.6% resistant to at least one antimicrobial drug. We observed high resistance to sulfonamides (56.5%), tetracycline (34.1%), streptomycin (28.6%), ampicillin (23.5%) and nalidixic acid (21.2%). Lower levels of resistance were found for gentamicin (3.2%), ciprofloxacin (2.3%), ceftiofur (1.3%), cefotaxime (0.9%), ceftazidime (0.5%) and cefepime (0.5%). A total of 43.3% of the Salmonella isolates were multidrug-resistant and 44 different resistance patterns were found. This study provided data on the prevalence, serovars and antimicrobial resistance of Salmonella from retail aquaculture products in Shanghai, and indicated the need for monitoring programs for microbiologic safety in such projects and for more prudent drug use in aquaculture production in order to reduce the risk of development and spread of antimicrobial resistance.

Coliform risk assessment through use of the clam Anomalocardia brasiliana as animal sentinel for shellfish harvesting areas in Brazil's northeast

Outbreaks of food-borne diseases related to consumption of contaminated shellfish have been reported in many countries, but not in Brazil, possibly due to deficient reporting. Here we investigated the suitability of the clam Anomalocardia brasiliana as an animal sentinel for coliform monitoring in shellfish harvesting areas of Brazil's northeast. Samples of shellfish meats (40 clams per sample; n = 8 per collection) were collected at random from April 2009 through March 2010 in the bay area of Mangue Seco (state of Pernambuco). The numbers of thermotolerant coliforms were analyzed through the most probable number technique, and these contamination levels were tentatively correlated with the precipitation recorded on the day of sampling or 24 to 48 h beforehand. A. brasiliana shellfish meats from local retail shops (250 g per sample/ n = 3 per market) sold frozen were also investigated from August 2010 through June 2011. We found that the highest coliform contamination levels were correlated with recent rainfall events, limited to 24 h before sampling. However, irrespective of the rainfall level, the mean contamination above the Brazilian legal threshold of < 3 × 10(2) MPN/ 100 g for shellfish harvesting areas ranged from 18.7 to 93.7 % of samples analyzed monthly. Additionally, a large number of samples obtained from retail shops were also highly contaminated by coliforms during rainy periods, and therefore were not proper for human consumption. We conclude that A. brasiliana can be successfully used to monitor the contamination levels of coliforms in shellfish harvesting areas in Brazil's northeast coast.

Effects of climate change on the persistence and dispersal of foodborne bacterial pathogens in the outdoor environment: A review

According to the Intergovernmental Panel on Climate Change (IPCC), warming of the climate system is unequivocal. Over the coming century, warming trends such as increased duration and frequency of heat waves and hot extremes are expected in some areas, as well as increased intensity of some storm systems. Climate-induced trends will impact the persistence and dispersal of foodborne pathogens in myriad ways, especially for environmentally ubiquitous and/or zoonotic microorganisms. Animal hosts of foodborne pathogens are also expected to be impacted by climate change through the introduction of increased physiological stress and, in some cases, altered geographic ranges and seasonality. This review article examines the effects of climatic factors, such as temperature, rainfall, drought and wind, on the environmental dispersal and persistence of bacterial foodborne pathogens, namely, Bacillus cereus, Brucella, Campylobacter, Clostridium, Escherichia coli, Listeria monocytogenes, Salmonella, Staphylococcus aureus, Vibrio and Yersinia enterocolitica. These relationships are then used to predict how future climatic changes will impact the activity of these microorganisms in the outdoor environment and associated food safety issues. The development of predictive models that quantify these complex relationships will also be discussed, as well as the potential impacts of climate change on transmission of foodborne disease from animal hosts.

Assessment of Nutrient Value and Microbiological Safety of Pomacea lineata

Pomacea lineata is a fresh water shellfish that is utilized as food, medicinal portions, or licking remedies. The objective of this study was to evaluate the nutritional and microbiological aspects of P. lineata and spawning. The samples were collected in the Jaguaribe River (Paraíba, Brazil) during the rainy and dry seasons. The biochemical composition, mineral composition, total mesophilic bacteria (TMB), total coliforms (TC), fecal coliforms (FC), Salmonella sp., Staphylococcus aureus, and Vibrio presence were determined. Each 100 g of P. lineata presented 3.1 g of ashes; 9.4 g of proteins; 2.7 g of lipids; 0.6 g of carbohydrates; 1800.0 mg of calcium; 78.0 mg of phosphorus, and 58.4 mg of iron. Each 100 g of spawning presented 10.4 g of ashes; 4.5 g of proteins; 2.8 g of lipids; 1.3 g of carbohydrates; 3633.0 mg of calcium; 39.4 mg of phosphorus; and 4.6 mg of iron. Each 100 g of P. lineata provided 65.7 kcal and spawning 48.3 kcal. In the dry season P. lineata and spawning showed no TMB and TC, FC, S. aureus, Salmonella, or Vibrio. In the rainy season P. lineata and spawning presented increase in TMB and TC, FC, S. aureus, and Salmonella. The presence of Vibrio was not detected. P. lineata presented proteins, low lipid, and carbohydrate content, energy values close to those of lean meats, high contents of calcium and iron, and presented low contamination level with pathogenic bacteria. Since P. lineata substances may be useful in the treatment of respiratory and gastrointestinal diseases without presenting toxic or cytotoxic effects already described in the literature, it may be considered as a potential functional food.

Seasonal variation of bacterial communities in shellfish harvesting waters: preliminary study before applying phage therapy

The recurrent emergence of infections outbreaks associated with shellfish consumption is an important health problem, which results in substantial economic losses to the seafood industry. Even after depuration, shellfish is still involved in outbreaks caused by pathogenic bacteria, which increases the demand for new efficient strategies to control the shellfish infection transmission. Phage therapy during the shellfish depuration is a promising approach, but its success depends on a detailed understanding of the dynamics of bacterial communities in the harvesting waters. This study intends to evaluate the seasonal dynamics of the overall bacterial communities, disease-causing bacterial populations and bacterial sanitary quality indicators in two authorized harvesting-zones at Ria de Aveiro. During the hot season, the total bacterial community presented high complexity and new prevalent populations of the main shellfish pathogenic bacteria emerged. These results indicate that the spring/summer season is a critical period during which phage therapy should be applied.

High Pressure Processing of Bivalve Shellfish and HPP's Use as a Virus Intervention

Bivalve shellfish readily bioconcentrate pathogenic microbes and substance, such as algal and dinoflagulate toxins, fecal viruses and bacteria, and naturally present vibrio bacteria. High pressure processing (HPP) is currently used as an intervention for Vibrio vulnificus bacteria within molluscan shellfish and its potential to inactivate food-borne viruses and bacteria are discussed. Mechanisms of action of high pressure against bacteria and viruses, as well as how time of pressure application, pressure levels, and pre-pressurization temperature influence inactivation are described. Matrix influences such as ionic strength are noted as important additional considerations. The potential of HPP to influence spoilage and enhance shelf-life of shucked shellfish is also discussed.

Occurrence of Vibrio and Salmonella species in mussels (Mytilus galloprovincialis) collected along the Moroccan Atlantic coast

This study reports the occurrence of different Vibrio and Salmonella species in 52 samples of Mytilus galloprovincialis collected from four sites along the Atlantic coast between Agadir and Essaouira (Anza, Cap Ghir, Imssouane and Essaouira). The level of Escherichia coli (E. coli) was also determined to evaluate the degree of microbial pollution in the investigated areas. In this study three methods were used : AFNOR NF EN ISO 6579 V08-013 for Salmonella spp., the provisional method routinely used by several laboratories (Institut Pasteur, Paris,…) for Vibrio cholerae and Vibrio parahaemolyticus in the seafood, and the most probable number method (MPN) using Norm ISO/TS 16649–3 (2005) for E. coli. The most frequently isolated Vibrios were Vibrio alginolyticus (90.4% of samples), followed by V. cholerae non O1 non O139 (15.4%) and V. parahaemolyticus (7.7%). Salmonella spp. was found in 15% of the samples. The number of E. coli ranged between 0.2/100 g and 1.8 10³ /100 g of mussel soft tissues. This study indicates the potential sanitary risk associated with the presence of pathogenic bacteria in cultivated mussels in the two populous regions of southern Morocco, where shellfish production and maritime tourism are important to the local economy.

Antimicrobial activity of oregano oil against antibiotic-resistant Salmonella enterica on organic leafy greens at varying exposure times and storage temperatures

The objective of this study was to evaluate the effectiveness of oregano oil on four organic leafy greens (Iceberg and Romaine lettuces and mature and baby spinaches) inoculated with Salmonella Newport as a function of treatment exposure times as well as storage temperatures. Leaf samples were washed, dip inoculated with S. Newport (6-log CFU/ml) and dried. Oregano oil was prepared at 0.1, 0.3, and 0.5% concentrations in sterile phosphate buffered saline (PBS). Inoculated leaves were immersed in the treatment solution for 1 or 2 min, and individually incubated at 4 or 8 °C. Samples were taken at day 0, 1, and 3 for enumeration of survivors. The results showed that oregano oil was effective against S. Newport at all concentrations. S. Newport showed reductions from the PBS control of 0.7-4.8 log CFU/g (Romaine lettuce), 0.8-4.8 log CFU/g (Iceberg lettuce), 0.8-4.9 log CFU/g (mature spinach), and 0.5-4.7 log CFU/g (baby spinach), respectively. The antibacterial activity also increased with exposure time. Leaf samples treated for 2 min generally showed greater reductions (by 1.4-3.2 log CFU/g), than those samples treated for 1 min; however, there was minimal difference in antimicrobial activity among samples stored under refrigeration and abuse temperatures. This study demonstrates the potential of oregano oil to inactivate S. Newport on organic leafy greens.