Identification of Salmonella serovars isolated from live molluscan shellfish and their significance in the marine environment

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.

Genome Analysis Identifies a Novel Type III Secretion System (T3SS) Category in Vibrio Species

The nanomachine referred to as the type III secretion system (T3SS) is used by many Gram-negative pathogens or symbionts to inject their effector proteins into host cells to promote their infections or symbioses. Among the genera possessing T3SS is Vibrio, which consists of diverse species of Gammaproteobacteria including human pathogenic species and inhabits aquatic environments. We describe the genetic overview of the T3SS gene clusters in Vibrio through a phylogenetic analysis from 48 bacterial strains and a gene order analysis of the two previously known categories in Vibrio (T3SS1 and T3SS2). Through this analysis we identified a new T3SS category (named T3SS3) that shares similar core and related proteins (effectors, translocons, and chaperones) with the Ssa-Esc family of T3SSs in Salmonella, Shewanella, and Sodalis. The high similarity between T3SS3 and the Ssa-Esc family suggests a possibility of genetic exchange among marine bacteria with similar habitats.

Prevalence, distribution and environmental effects on faecal indicator bacteria and pathogens of concern in commercial shellfish production areas in a subtropical region of a developing country (Santa Catarina, Brazil)

This paper reviews recent literature on the abundance and distribution of faecal indicator bacteria and pathogens in shellfish production areas in the state of Santa Catarina, on the subtropical coast of Brazil. This state supplies > 95% of the national production of shellfish. Microbiological monitoring data were mapped using GIS and the results compared with those from other countries. Coastal human population is the main predictive parameter for faecal bacteria in the production areas. Temporal variations of the bacteria can also be predicted by solar radiation and rainfall. The prevalence of pathogens such as hepatitis A virus, human norovirus, Salmonella spp. and Vibrio spp. does not differ substantially from that in developed countries. The information reported here can be used to inform development of microbiological risk profiles for shellfish production areas.

An Evaluation of the Pathogenic Potential, and the Antimicrobial Resistance, of Salmonella Strains Isolated from Mussels

Salmonella spp. and antimicrobial resistant microorganisms are two of the most important health issues worldwide. In the present study, strains naturally isolated from mussels harvested in Galicia (one of the main production areas in the world), were genetically characterized attending to the presence of virulence and antimicrobial resistance genes. Additionally, the antimicrobial profile was also determined phenotypically. Strains presenting several virulence genes were isolated but lacked all the antimicrobial resistance genes analyzed. The fact that some of these strains presented multidrug resistance, highlighted the possibility of bearing different genes than those analyzed, or resistance based on completely different mechanisms. The current study highlights the importance of constant surveillance in order to improve the safety of foods.

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.

Changing Patterns of Salmonella enterica Serovar Rissen From Humans, Food Animals, and Animal-Derived Foods in China, 1995-2019

Salmonellosis represents a growing threat to global public health. Salmonella enterica remains the leading cause of bacterial foodborne diseases in China. Salmonella enterica serovar Rissen (S. Rissen) has been recognized as one of the emerging serovars among humans in different countries worldwide. However, knowledge on the prevalence of S. Rissen in China is largely lacking. To address essential epidemiological information for S. Rissen in China, a total of 1,182 S. Rissen isolates recovered from samples across the food chain were collected from 16 provinces or province-level cities between 1995 and 2019. Risk factors due to the consumption of animal-derived food products were also analyzed. We found S. Rissen is widely distributed, especially in the Eastern and Southern parts of China, and there is an increasing frequency in recent years as evidenced by the greater number of isolates recovered in 2016, 2017, and 2018. Interestingly, the majority of S. Rissen isolates recovered in this study were from human samples (63.4%; 749/1182), remarkably, 58.4% (438/749) were from asymptomatic carriers. We obtained most of the S. Rissen isolates from humans from Guangxi (59.5%; 446/749) and Shanghai (29.5%; 221/749). Among 302 human diarrheal isolates (40.3%; 302/749), we found 44.6% (139/311) of S. Rissen in children with diarrhea (age below 10 years old). This is of clinical significance as diarrhea is one of the crucial causes of child mortality globally and our findings here highlighted the importance of Salmonella infections in Chinese children. Additionally, S. Rissen isolates were also found to be associated with pork and poultry products in China. This study projected the most updated national-wide study of S. Rissen isolates obtained from different sources in China over the past two decades. Continued surveillance is warranted to further monitor this emerging serovar in China and elsewhere over the world.

Detection of colistin resistance mcr-1 gene in Salmonella enterica serovar Rissen isolated from mussels, Spain, 2012- to 2016

Nineteen Salmonella strains were isolated from 5,907 randomly selected mussel samples during a monitoring programme for the presence of Salmonella in shellfish in Galicia, north-west Spain (2012–16). Serovars, sequence type and antimicrobial resistance genes were determined through genome sequencing. Presence of the mcr-1 gene in one strain belonging to serovar Rissen and ST-469 was identified. The mcr-1 gene had not been isolated previously in environmental Salmonella isolated from mussels in Spain.

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.

A novel host-adapted strain of Salmonella Typhimurium causes renal disease in olive ridley turtles (Lepidochelys olivacea) in the Pacific

Salmonella spp. are frequently shed by wildlife including turtles, but S. enterica subsp. enterica serovar Typhimurium or lesions associated with Salmonella are rare in turtles. Between 1996 and 2016, we necropsied 127 apparently healthy pelagic olive ridley turtles (Lepidochelys olivacea) that died from drowning bycatch in fisheries and 44 live or freshly dead stranded turtles from the west coast of North and Central America and Hawaii. Seven percent (9/127) of pelagic and 47% (21/44) of stranded turtles had renal granulomas associated with S. Typhimurium. Stranded animals were 12 times more likely than pelagic animals to have Salmonella-induced nephritis suggesting that Salmonella may have been a contributing cause of stranding. S. Typhimurium was the only Salmonella serovar detected in L. olivacea, and phylogenetic analysis from whole genome sequencing showed that the isolates from L. olivacea formed a single clade distinct from other S. Typhimurium. Molecular clock analysis revealed that this novel clade may have originated as recently as a few decades ago. The phylogenetic lineage leading to this group is enriched for non-synonymous changes within the genomic area of Salmonella pathogenicity island 1 suggesting that these genes are important for host adaptation.

Assessing microbial contamination and antibiotic resistant bacteria using zebra mussels (Dreissena polymorpha)

Aquatic pollution with faecal bacteria and subsequent consumption of contaminated water or food is a worldwide issue that causes severe health effects (e.g. meningitis, salmonellosis, dysentery). In addition, the excessive use of antibiotics in animal husbandry and human medicine has enhanced the selective pressure on pathogenic bacteria, further increasing human health risks and detrimental effects on natural microbial communities. This urges the need to monitor faecal contamination using a time-integrated approach, as grab water samples can miss pathogen peaks. We tested the ability of zebra mussels (Dreissena polymorpha) to take up and depurate faecal indicator bacteria such as Escherichia coli and intestinal enterococci. Furthermore, we quantified the frequency of antibiotic resistant bacteria in water and mussels both in controlled laboratory tests and under in situ conditions downstream of a sewage treatment plant (STP). Laboratory results show that bacterial indicators in mussels were 132 times higher than their concentration in water, and that mussels retained bacteria up to 2 days after pulse exposure. Field results show decreasing bacterial concentrations in both water and mussels downstream the STP, with maximum E. coli concentrations ranging 173-9 cfu mL^-1 in water and 2970-330 cfu g^-1 in mussels. Similarly, enterococci ranged 59-4 cfu mL^-1 and 1450-240 cfu g^-1 in water and mussels, respectively. High proportions of antibiotic resistant E. coli were found in mussels (72%) and water (65%), and slightly lower proportion of resistant enterococci was found in mussels (47%) and in water (34%). Moreover, 33% of the bacteria isolated from mussels were resistant to multiple antibiotics, which emphasizes that resistance is a common feature in surface waters and highlights the need for safe water management. Our results show that zebra mussels provide an efficient, time-integrating tool for quantifying faecal indicators, including resistant and multidrug resistant bacteria.

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.

Multiple approaches to assess the safety of artisanal marine food in a tropical estuary

In this study, metal and metalloid concentrations and pathogens were measured in shellfish at different locations in a tropical estuary, including sites impacted by sewage and industry. Oyster, mangrove snails and mud snails did not exceed Australian and New Zealand Food Standards maximum levels for copper, lead or estimated inorganic arsenic at any site although copper concentrations in oysters and mud snails exceeded generally expected levels at some locations. Bacterial community composition in shellfish was species-specific regardless of location and different to the surrounding water and sediment. In the snails Telescopium telescopium, Terebralia palustris and Nerita balteata, some bacterial taxa differed between sites, but not in Saccostrea cucullata oysters. The abundance of potential human pathogens was very low and pathogen abundance or diversity was not associated with site classification, i.e. sewage impact, industry impact and reference.

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.

Heterogeneity of persistence of Salmonella enterica serotype Senftenberg strains could explain the emergence of this serotype in poultry flocks

Salmonella enterica serotype Senftenberg (S. Senftenberg) has recently become more frequent in poultry flocks. Moreover some strains have been implicated in severe clinical cases. To explain the causes of this emergence in farm animals, 134 S. Senftenberg isolates from hatcheries, poultry farms and human clinical cases were analyzed. Persistent and non-persistent strains were identified in chicks. The non-persistent strains disappeared from ceca a few weeks post inoculation. This lack of persistence could be related to the disappearance of this serotype from poultry farms in the past. In contrast, persistent S. Senftenberg strains induced an intestinal asymptomatic carrier state in chicks similar to S. Enteritidis, but a weaker systemic infection than S. Enteritidis in chicks and mice. An in vitro analysis showed that the low infectivity of S. Senftenberg is in part related to its low capacity to invade enterocytes and thus to translocate the intestinal barrier. The higher capacity of persistent than non-persistent strains to colonize and persist in the ceca of chickens could explain the increased persistence of S. Senftenberg in poultry flocks. This trait might thus present a human health risk as these bacteria could be present in animals before slaughter and during food processing.

Prevalence and characterization of Salmonella serovars isolated from oysters served raw in restaurants

To determine if Salmonella-contaminated oysters are reaching consumer tables, a survey of raw oysters served in eight Tucson restaurants was performed from October 2007 to September 2008. Salmonella spp. were isolated during 7 of the 8 months surveyed and were present in 1.2% of 2,281 oysters tested. This observed prevalence is lower than that seen in a previous study in which U.S. market oysters were purchased from producers at bays where oysters are harvested. To test whether the process of refrigerating oysters in restaurants for several days reduces Salmonella levels, oysters were artificially infected with Salmonella and kept at 4°C for up to 13 days. Direct plate counts of oyster homogenate showed that Salmonella levels within oysters did not decrease during refrigeration. Six different serovars of Salmonella enterica were found in the restaurant oysters, indicating multiple incidences of Salmonella contamination of U.S. oyster stocks. Of the 28 contaminated oysters, 12 (43%) contained a strain of S. enterica serovar Newport that matched by pulsed-field gel electrophoresis a serovar Newport strain seen predominantly in the study of bay oysters performed in 2002. The repeated occurrence of this strain in oyster surveys is concerning, since the strain was resistant to seven antimicrobials tested and thus presents a possible health risk to consumers of raw oysters.

Distribution and genotypic characterization of Salmonella serovars isolated from tropical seafood of Cochin, India

AIMS

To determine the distribution of Salmonella serovars in seafood and to examine the intraserovar genetic variations in Salmonella enterica subsp. enterica serovar Rissen and Salmonella Weltevreden by polymerase chain reaction (PCR)-ribotyping and enterobacterial repetitive intergenic consensus (ERIC)-PCR methods.

METHOD AND RESULTS

A total of 417 seafood samples collected over 2003-2006 from fishing harbours and fish markets of Cochin (India) was studied for presence of Salmonella serovars. Seafood samples were analysed for the presence of Salmonella by Bacteriological Analytical Manual (BAM), U.S. Food & Drug Administration (USFDA) method. The study indicated that 23.2% of the seafood samples were positive for Salmonella and a total of 241 Salmonella isolates comprising of 27 different serovars were isolated from seafood. S. Weltevreden, Salmonella Rissen, Salmonella Typhimurium and Salmonella Derby were found to be the most predominant serovars in seafood. PCR-ribotypes and ERIC-PCR profiles showed multiple genotypic profiles for S. Rissen and S. Weltevreden in seafood and the level of discrimination indices obtained was at 0.974 for S. Rissen and 0.988 for S. Weltevreden, respectively.

CONCLUSION

The study highlighted the major Salmonella serovars in the seafood of Cochin (India) and molecular fingerprinting pattern revealed genetic variation among S. Rissen and S. Weltevreden.

SIGNIFICANCE AND IMPACT OF THE STUDY

Widespread occurrence of Salmonella contamination in seafood and multiple clones of S. Rissen and S. Weltevreden detected in seafood, thus, indicated the diverse routes of Salmonella contamination in seafood.

Characteristics and dynamics of Salmonella contamination along the coast of Agadir, Morocco

The occurrence of Salmonella enterica in the environment of tropical and desert regions has remained largely uninvestigated in many areas of the world, including Africa. In the present study, we investigated the presence of Salmonella spp. along 122 km of the coastline of Agadir (southern Morocco) in relation to environmental parameters. A total of 801 samples of seawater (243), marine sediment (279), and mussels (279) were collected from six sites between July 2004 and May 2008. The overall prevalence of Salmonella spp. was 7.1%, with the highest occurrence in mussels (10%), followed by sediment (6.8%) and seawater (4.1%). Only three serotypes were identified among the 57 Salmonella sp. strains isolated. S. enterica serotype Blockley represented 43.8% of all Salmonella strains and was identified in mussel and sediment samples. S. enterica serotype Kentucky (29.8%) was found almost exclusively in mussels, whereas S. enterica serotype Senftenberg (26.3%) was detected in sediment and seawater. Statistical analysis using generalized additive models identified seawater temperature, environmental temperature, rainfall, and solar radiation as significant factors associated with the presence of Salmonella. Rainfall was the only variable showing a linear positive effect on the presence of Salmonella in the sea, whereas the remaining variables showed more complex nonlinear effects. Twenty-eight (49.1%) Salmonella isolates displayed resistance to ampicillin (22 isolates), nalidixic acid (9 isolates), sulfonamide compounds (2 isolates), and tetracycline (1 isolate), with six of these isolates displaying multiple resistance to two of these antimicrobial agents. Pulsed-field gel electrophoresis analysis revealed homogenous restriction patterns within each serotype that were uncorrelated with the resistance pattern profiles.

Climate patterns governing the presence and permanence of salmonellae in coastal areas of Bahia de Todos Santos, Mexico

Despite the importance of salmonellae as one of the major causes of food-borne infections worldwide, data regarding the presence of these organisms in the environment are limited. We investigated the presence of Salmonella spp. in Bahia de Todos Santos (Baja California, Mexico) and evaluated the environmental factors that affect the occurrence of Salmonella spp. in this arid region. A total of 1,331 samples collected from 21 sites along the coast during a period of 3 years were analyzed for Salmonella spp. Geographical and seasonal distribution of Salmonella spp. was evaluated in association with environmental parameters and with human infections in the area. The incidence of Salmonella bacteria throughout the study was 4.8%, with the highest incidence detected in wastewater (16.2%), followed by stream water (10.6%), mollusks (7.4%), and seawater (2.3%). Twenty different serotypes were identified among the 64 Salmonella isolates. The dominant serotype was Typhimurium (23.4%), followed by Vejle (6.2%). The presence of Salmonella spp. in coastal areas was mostly confined to rainy periods and areas of stream discharges, and runoff was identified as the predominant factor influencing the transport of Salmonella bacteria from source points to the sea via streams. Isolation of Salmonella spp. was negatively and significantly associated with temperature, probably because of the effect of solar radiation in the decline of permanence of Salmonella bacteria. Conversely, human infections prevailed during the warmest months and were negatively correlated with the presence of Salmonella spp. in the marine environment.

Pathogenic bacteria associated with oysters (Crassostrea brasiliana) and estuarine water along the south coast of Brazil

Oysters and estuarine water samples were collected monthly, from June 1998 to March 1999, in the Cananéia estuary, on the south coast of São Paulo, Brazil, and analyzed for bacterial hazards with and without depuration in filtered estuarine water. Aeromonas spp., Plesiomonas shigelloides, Vibrio cholerae O1, Vibrio parahaemolyticus, and Vibrio vulnificus were counted in oyster samples using the most probable number (MPN) and their presence verified in the surrounding estuarine water samples. The presence of Salmonella, Shigella, Escherichia coli O157:H7, and fecal coliforms counts were determined in oysters and in water samples too. Sixty percent of water samples contained fecal coliforms ranging from <1 to >200 CFU/100 ml and 100%, 30%, 20% and 10% were positive for V. parahaemolyticus, Salmonella, Aeromonas, and V. vulnificus in 5 l of water samples, respectively. In oyster samples, the fecal coliforms concentration ranged from <3.0 to > or =2.4 x 10(3) MPN/g in 40% of untreated and from <3.0 to 1.1 x 10(3) MPN/g in 40% of treated samples. Vibrio parahaemolyticus Kanagawa-negative was detected in all oyster samples and their concentration varied from 3.6 to > or =2.4 x 10(3) MPN/g. For the untreated oyster samples 80%, 70%, and 10% were positive for V. vulnificus (<3 - 11.0 MPN/g), Aeromonas (<3-15 MPN/g), and Salmonella (presence in 25 g), respectively. However, for treated oyster samples 60%, 30%, and 0% of them contained the same bacteria, respectively. Escherichia coli O157:H7, Shigella spp., P. shigelloides, and V. cholerae O1 were not detected in any of the samples. Fecal indicators did not correlate with Vibrio presence (p>0.05), although the isolation of Aeromonas species had a positive correlation (p = 0.017). The results showed no correlation between temperature, salinity, and bacteria (p > 0.05). The comparison between bacterial concentration in treated and untreated oyster samples, showed that only Aeromonas was higher in untreated oyster samples (p = 0.039). This study contributes toward creating a more global understanding of food-borne bacterial pathogens. The presence and concentration of viable bacterial hazards in oysters and water surrounding areas was determined for the first time on the south coast of São Paulo and it helps to define better the true microbial hazard in the aquatic environment and oysters.

Detection and characterization of Salmonella associated with tropical seafood

The prevalence of Salmonella in seafood samples collected from the southwest coast of India was studied by conventional culture and by a DNA based molecular technique, polymerase chain reaction (PCR). While conventional culture techniques detected Salmonella in only 20 out of the 100 samples analyzed, direct enrichment lysate PCR detected 52 as positive for Salmonella. A set of three different PCR primers viz., hns, invA and invE were used. It was observed that hns primer detected Salmonella in a significantly higher number of samples. Fourteen out of nineteen isolates belonged to serovar S. enterica Weltevreden. S. Weltevreden isolates were genotyped yielding 4 different patterns both by RAPD and ERIC-PCR but when combined, the overall results discriminated the isolates of S. Weltevreden into 6 different types. This suggests that genetically diverse Salmonella Weltevreden are prevalent in seafood.

Étude de la contamination microbienne des myes (Mya arenaria) de la rive nord de l'estuaire maritime du fleuve Saint-Laurent (Québec, Canada)

The aims of the present study were to assess the microbial quality of Mya arenaria clams from the north shore of the St. Lawrence River estuary and to validate various microbial indicator microorganisms of bivalve mollusks contamination. Clams were collected from nine sites, including four harvesting sites closed by virtue of the Canadian Shellfish Sanitation Program (CSSP). Six contamination indicators (fecal coliforms, somatic coliphages, F-specific coliphages, fecal streptococci, Clostridium perfringens, and Escherichia coli) and four pathogens (Campylobacter sp., Cryptosporidium parvum, Giardia sp., and Salmonella sp.) were identified in the clams. Indicators sensibility, specificity and predictive values with respect to the presence of pathogens were calculated. Pathogenic microorganisms detection frequency in clams was important (92%). Globally, pathogens tend to be less frequently detected in opened harvesting sites (p = 0.086). Although the assessed indicators were not perfect, when F-specific coliphages are associated with E. coli or fecal coliforms, a good sensibility (62%–64%) and good positive predictive value (88%) with respect to the investigated pathogens are obtained.Key words: mollusks, coliforms, Giardia, Cryptosporidium, Campylobacter.[Journal translation]

Phenotypic and genotypic characterization of Salmonella enterica serotype paratyphi B isolates from environmental and human sources in Galicia, Spain

Salmonella serotype Paratyphi B isolates obtained from shellfish and human infections in Galicia (northwest Spain) from 1998 were investigated by different phenotypic and genetic methods to evaluate their systemic or enteric nature. Isolates were investigated for D-tartrate fermentation, presence of genes encoding the effector proteins sopE1 and avrA, pulsed-field gel electrophoresis profile, and antimicrobial susceptibility. Systemic variant strains (dT-) were the dominant among the marine environment isolates. All dT- isolates were sopE1 positive and avrA negative, presented an indistinguishable electrophoresis profile, and were grouped in a single cluster. More electrophoresis heterogeneity was observed among dT+ isolates. Only two isolates showed resistance to any of the 16 antibiotics included in our panel. The present study identified the marine environment as a potential natural source of systemic variant isolates of Salmonella Paratyphi B. The presence of systemic variant isolates of Salmonella Paratyphi B in the marine environment is of notable public health significance as a result of the potential risk of acquiring enteric fever linked to the consumption of raw shellfish.

Eight-hour PCR-based procedure for the detection ofSalmonellain raw oysters

The aim of this study was to evaluate the ability of a nested PCR system to detect Salmonella senftenberg in raw oysters. The specific primers of the PCR were derived from the invA gene sequence, essential for Salmonella invasiveness into epithelial cells. First, for the extraction of DNA, four methods (guanidine isothiocyanate, E.Z.N.A. Mollusc Kit, Chelex-100, and lysis with detergents) were compared. A nested PCR method combined with 3.5 h pre-enrichment in buffered peptone water (BPW) and DNA extraction by the resin Chelex-100 is proposed for the detection of S. senftenberg in oyster samples. The detection limit of the method is less than 0.1 CFU/ml (<1 CFU/g of oyster). This procedure is shown to be an excellent tool for the sensitive detection of S. senftenberg from naturally contaminated oysters, with results being obtained within 8 h.

Prevalence of Salmonella spp. in oysters in the United States

Food-borne diseases such as salmonellosis can be attributed, in part, to the consumption of raw oysters. To determine the prevalence of Salmonella spp. in oysters, oysters harvested from 36 U.S. bays (12 each from the West, East, and Gulf coasts in the summer of 2002, and 12 bays, four per coast, in the winter of 2002-2003) were tested. Salmonella was isolated from oysters from each coast of the United States, and 7.4% of all oysters tested contained Salmonella. Isolation tended to be bay specific, with some bays having a high prevalence of Salmonella, while other bays had none. Differences in the percentage of oysters from which Salmonella was isolated were observed between the summer and winter months, with winter numbers much lower probably due to a variety of weather-related events. The vast majority (78/101) of Salmonella isolates from oysters were Salmonella enterica serovar Newport, a major human pathogen, confirming the human health hazard of raw oyster consumption. Contrary to previous findings, no relationship was found between the isolation of fecal coliforms and Salmonella from oysters, indicating a necessity for specific monitoring for Salmonella and other pathogens rather than the current reliance on fecal coliform testing.

Investigation of clonal distribution and persistence of Salmonella Senftenberg in the marine environment and identification of potential sources of contamination

Salmonella Senftenberg was detected in the coastal areas of Galicia (NW Spain) in 1998, where it remained the predominant serovar for the next four years. Although the overall incidence of this serovar in the zone was lower than 1%, contamination by Salmonella serovar Senftenberg was located in very specific areas of the Ría de Arousa, where it persisted for more than five years. A total of 60 Salmonella serovar Senftenberg isolates, originating from surveillance activities in marine environments, was subjected to molecular characterization by pulsed-field gel electrophoresis (PFGE). PFGE analysis of the marine isolates allowed the differentiation of three main PFGE types, which contained the majority of the isolates, each type showing a specific spatial distribution in the coastal waters. The most prevalent pulse types persisted for more than four years, emphasizing their capacity to adapt and survive in marine environments. Using PFGE analysis, marine isolates were compared with Salmonella serovar Senftenberg isolates from neighbouring mussel-processing facilities and to other epidemiologically unrelated isolates from human, animal and feed sources. Comparison of the restriction patterns showed that indistinguishable PFGE types were present in the isolates from mussel-processing facilities and their surrounding marine areas, suggesting that the mussel processing is the main source for contamination with Salmonella Senftenberg in these marine environments. A molecular fingerprinting relationship was established between three shellfish isolates and a human isolate, which could be considered as preliminary evidence of infection caused by Salmonella Senftenberg associated with molluscan consumption.

Application of antimicrobial ice for reduction of foodborne pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes) on the surface of fish

AIMS

The efficacy of antimicrobial ice was evaluated for the reduction of foodborne pathogens on the surface of fish.

METHODS AND RESULTS

Antimicrobial ice containing chlorine dioxide (ClO2) was utilized to control foodborne pathogens in laboratory media and on fish skin. Escherichia coli O157:H7, Salmonella serotype Typhimurium and Listeria monocytogenes strains were treated with antimicrobial ice for 30 min on plates of selective agar and for 120 min on fish skin at room temperature, and then incubated for enumeration. After treatment with 100 ppm ClO2 for 30 min, 5.4, 4.4 and 3.2 log10 reduction was obtained with E. coli O157:H7, Salm. Typhimurium and L. monocytogenes on laboratory media, respectively. When antimicrobial ice (100 ppm ClO2) was applied to fish skin for 120 min, total reduction of E. coli O157:H7, Salm. Typhimurium and L. monocytogenes was 4.8, 2.6 and 3.3 log10, respectively.

CONCLUSION

The initial load of foodborne pathogens was reduced by antimicrobial ice and the lowered microbial level was maintained during treatment.

SIGNIFICANCE AND IMPACT OF THE STUDY

The application of antimicrobial ice is a simple and effective method for the safe preservation of fish.

Characterization of Salmonella enterica serovar typhimurium from marine environments in coastal waters of Galicia (Spain)

Twenty-three Salmonella enterica serovar Typhimurium isolates from marine environments were characterized by phage typing, pulsed-field gel electrophoresis (PFGE) analysis, plasmid analysis, and antibiotic resistance, and the distribution of the different types in the coastal waters were subsequently analyzed. Five phage types were identified among the isolates (PT41, PT135, PT99, DT104, and DT193). PT135 isolates were exclusively detected during the winter months from 1998 to 2000, whereas DT104 and PT41 isolates were detected exclusively in the summer months from 2000 to 2002. XbaI PFGE analysis revealed 9 PFGE types, and plasmid profiling identified 8 plasmid types (with 1 to 6 plasmids) among the isolates. Only three isolates presented multidrug resistance to antibiotics. Two DT104 isolates were resistant to 8 and 7 antibiotics (profiles ACCeFNaSSuT and ACeFNeSSuT), whereas a PT193 isolate presented resistance to 6 antibiotics (profile ACFSSu). In addition, four PT41 isolates were resistant to a single antibiotic. The detection of multidrug-resistant phage types DT104 and DT193 in shellfish emphasizes the importance of monitoring the presence of Salmonella in routine surveillance of live bivalve molluscs.

Influence of environmental factors and human activity on the presence of Salmonella serovars in a marine environment

The temporal and spatial distribution of Salmonella contamination in the coastal waters of Galicia (northwestern Spain) relative to contamination events with different environmental factors (temperature, wind, hours of sunlight, rainfall, and river flow) were investigated over a 4-year period. Salmonellae were isolated from 127 of 5,384 samples of molluscs and seawater (2.4%), and no significant differences (P < 0.05) between isolates obtained in different years were observed. The incidence of salmonellae was significantly higher in water column samples (2.9%) than in those taken from the marine benthos (0.7%). Of the 127 strains of Salmonella isolated, 20 different serovars were identified. Salmonella enterica serovar Senftenberg was the predominant serovar, being represented by 54 isolates (42.5%), followed by serovar Typhimurium (19 isolates [15%]) and serovar Agona (12 isolates [9.4%]). Serovar Senftenberg was detected at specific points on the coast and could not be related to any of the environmental parameters analyzed. All serovars except Salmonella serovar Senftenberg were found principally in the southern coastal areas close to the mouths of rivers, and their incidence was associated with high southwestern wind and rainfall. Using multiple logistic regression analysis models, the prevalence of salmonellae was best explained by environmental parameters on the day prior to sampling. Understanding this relationship may be useful for the control of molluscan shellfish harvests, with wind and rainfall serving as triggers for closure.

Detection of Salmonella Senftenberg associated with high saline environments in mussel processing facilities

A contamination by Salmonella Senftenberg in frozen mussels was detected in 1998 during a routine analytical surveillance. From June 1998 to December 2001, a total of 3,410 samples of steamed frozen mussels and items related to their manufacture were analyzed for the presence of Salmonella. Salmonella Senftenberg was isolated in 573 (16.8%) samples, and no other serovar was detected. The contamination episodes extended for several months. Salmonella Senftenberg colonies from the first contamination events showed a rugose morphology on agar with a shiny crystalline layer and limited colony formation on microbiological media. These contaminations were mainly associated with brine (300 g of NaCl per liter), while the live molluscs that were being processed were free of Salmonella. When the brine contaminations were nearly controlled, new episodes were detected that were associated with live mussels. In the new episodes, colonies showed the typical characteristics of Salmonella and normal growth on agar. Salmonella Senftenberg presented a high resistance to unfavorable environments and showed a preference for clean environments. While Salmonella Senftenberg could be isolated from mussels after steam treatment, it could not survive after immersion in water at 80 degrees C for 1 min. This fact was used to develop a process to remove contamination from products, minimizing the health risk associated with frozen mussel consumption. The general incidence of Salmonella Senftenberg in facilities and mussels was reduced from 31.2% in 1998 to 2.5% in 2001. During this study, no cases of illness from consumption of frozen mussels were reported, indicating a possible lack of virulence of Salmonella Senftenberg in these contamination events.