Food-borne disease outbreaks due to bacteria in Taiwan, 1986 to 1995

Virulence phenotypes differ between toxigenic Vibrio parahaemolyticus isolated from western coasts of Europe

Vibrio parahaemolyticus is the leading bacterial cause of gastroenteritis associated with seafood consumption worldwide. Not all members of the species are thought to be pathogenic, thus identification of virulent organisms is essential to protect public health and the seafood industry. Correlations of human disease and known genetic markers (e.g. thermostable direct hemolysin (TDH), TDH-related hemolysin (TRH)) appear complex. Some isolates recovered from patients lack these factors, while their presence has become increasingly noted in isolates recovered from the environment. Here, we used whole-genome sequencing in combination with mammalian and insect models of infection to assess the pathogenic potential of V. parahaemolyticus isolated from European Atlantic shellfish production areas. We found environmental V. parahaemolyticus isolates harboured multiple virulence-associated genes, including TDH and/or TRH. However, carriage of these factors did not necessarily reflect virulence in the mammalian intestine, as an isolate containing TDH and the genes coding for a type 3 secretion system (T3SS) 2α virulence determinant, appeared avirulent. Moreover, environmental V. parahaemolyticus lacking TDH or TRH could be assigned to groups causing low and high levels of mortality in insect larvae, with experiments using defined bacterial mutants showing that a functional T3SS1 contributed to larval death. When taken together, our findings highlight the genetic diversity of V. parahaemolyticus isolates found in the environment, their potential to cause disease and the need for a more systematic evaluation of virulence in diverse V. parahaemolyticus to allow better genetic markers.

Surveillance of foodborne diseases in Taiwan: A retrospective study

ABSTRACT

Foodborne pathogens cause diseases and death, increasing the economic burden. It needs to identify incident places, media food and pathgens. Our aim is to survey empirical data that provide a retrospective historical perspective on foodborne diseases and explore the causes and trends of outbreaks.We examined publicly available annual summary data on reported foodborne disease outbreaks in Taiwan from 2014 to 2018. We calculated the percentage of places, media food, bacteria and natural toxin sources in foodborne diseases and performed a chi-square test for difference evaluation. The higher risk of places and causes in 2018 compared with 2014 was empolyzed with univariate logistic regression.There were 26847 patients with foodborne diseases during the period from 2014 to 2018. The top 2 primary source locations of the foodborne diseases were schools and restaurants. The top 2 primary food media classifications of the foodborne diseases were boxed meals and compounded foods. The top 2 primary incident bacterial classifications of the observed foodborne diseases were Bacillus cereus and Staphylococcus aureus. The top 2 primary natural toxin classifications of the foodborne diseases were plants and histamines. The incidence of foodborne disease in military facilities, fruits and vegetables, and Staphylococcus aureus was increased in our study.Our study confirmed the high risk and increased incidence of foodborne diseases, food media classifications, bacterial classifications, and natural toxins in Taiwan. It is worthy of attention for the government health department-designed policy to promote disease prevention.

The Bacillus cereus Food Infection as Multifactorial Process

The ubiquitous soil bacterium Bacillus cereus presents major challenges to food safety. It is responsible for two types of food poisoning, the emetic form due to food intoxication and the diarrheal form emerging from food infections with enteropathogenic strains, also known as toxico-infections, which are the subject of this review. The diarrheal type of food poisoning emerges after production of enterotoxins by viable bacteria in the human intestine. Basically, the manifestation of the disease is, however, the result of a multifactorial process, including B. cereus prevalence and survival in different foods, survival of the stomach passage, spore germination, motility, adhesion, and finally enterotoxin production in the intestine. Moreover, all of these processes are influenced by the consumed foodstuffs as well as the intestinal microbiota which have, therefore, to be considered for a reliable prediction of the hazardous potential of contaminated foods. Current knowledge regarding these single aspects is summarized in this review aiming for risk-oriented diagnostics for enteropathogenic B. cereus.

Detection of chicken carcasses contaminated with Salmonella enterica serovar in the abattoir environment of Taiwan

Although a nation-wide microbiological screening program of chicken carcasses after chilling in Taiwanese chicken abattoirs has been undertaken since 2006, little is known regarding the potential sources of the Salmonella during the slaughter process. The present study provides data on the detection and serotypes of Salmonella isolated from broilers during processing and from the environment in six abattoirs in Taiwan. Overall, Salmonella were detected in 156 of 622 samples (25.1%; 95% CI: 21.7-28.7) collected. The prevalence of Salmonella varied between sampling sites with 5.8, 17.6, 31.3 and 35.5% of cloacal swabs, environmental samples prior to processing, environmental samples during processing and carcass rinse fluid, respectively, being positive (χ² = 51.3, p < 0.0001). A total of 15 serotypes were identified from the 156 Salmonella isolates with S. Albany (41.7%) S. Schwarzengrund (20.5%), S. Kentucky (12.8%) and S. Tennessee (5.1%) being the most commonly isolated serotypes. Characterization of 156 isolates by Pulse Field Gel Electrophoresis (PFGE) identified 50 PFGE types. Typing confirmed the presence of the same PFGE type at multiple stages during processing including plucking, evisceration, chilling and post-chilling. The abattoir environment and intestinal contents of chickens are important sources of Salmonella in broiler chicken abattoirs, with the same PFGE types detected at different stages of processing both before and during slaughtering. It is concluded that Salmonella isolates present in the environment and intestinal contents of processed birds survived in the abattoir environment resulting in subsequent carcass contamination along the processing chain including plucking, evisceration, chilling and post-chilling.

Efficacy of chemical sanitizers against Bacillus cereus on food contact surfaces with scratch and biofilm

This study was performed to investigate the efficacy of chemical sanitizers (viz., chlorine, chlorine dioxide, alcohol, and quaternary ammonium compound) against Bacillus cereus on five food contact materials under different conditions (smooth vs. scratched and with vs. without biofilms). After incubating materials in B. cereus suspension, cell adhesion on a smooth surface (10 cm2) was in the following ascending order: stainless steel (7.36 ± 0.08 log CFU), glass (7.51 ± 0.26 log CFU), polyethylene (7.66 ± 0.30 log CFU), polypropylene (7.76 ± 0.30 log CFU), and wood (8.02 ± 0.33 log CFU). The efficacy of sanitizers was dramatically reduced in the presence of a biofilm on all materials. Among four different chemical sanitizers, chlorine showed the best bactericidal activity against B. cereus on the surface with scratch and biofilm. Selection of adequate materials, maintenance of a smooth surface, and inhibition of biofilm formation are good practices for food safety.

Efficacy of chemical sanitizers against Bacillus cereus on food contact surfaces with scratch and biofilm

This study was performed to investigate the efficacy of chemical sanitizers (viz., chlorine, chlorine dioxide, alcohol, and quaternary ammonium compound) against Bacillus cereus on five food contact materials under different conditions (smooth vs. scratched and with vs. without biofilms). After incubating materials in B. cereus suspension, cell adhesion on a smooth surface (10 cm²) was in the following ascending order: stainless steel (7.36 ± 0.08 log CFU), glass (7.51 ± 0.26 log CFU), polyethylene (7.66 ± 0.30 log CFU), polypropylene (7.76 ± 0.30 log CFU), and wood (8.02 ± 0.33 log CFU). The efficacy of sanitizers was dramatically reduced in the presence of a biofilm on all materials. Among four different chemical sanitizers, chlorine showed the best bactericidal activity against B. cereus on the surface with scratch and biofilm. Selection of adequate materials, maintenance of a smooth surface, and inhibition of biofilm formation are good practices for food safety.

Detection of Total and Pathogenic Vibrio parahaemolyticus in Shellfish Growing along the South Yellow Sea and the East China Sea

This study was conducted to monitor the densities of total and pathogenic Vibrio parahaemolyticus in 300 samples of nine shellfish species harvested from the coasts of the South Yellow Sea and the East China Sea (N 23° to 34°, E 116° to 124°), People's Republic of China, between May and October 2015. Total V. parahaemolyticus densities were measured, and V. parahaemolyticus isolates were biochemically identified with probes for the thermostable direct hemolysin gene (tdh) and the thermostable direct hemolysin-related hemolysin gene (trh). We found that 202 of the 300 samples were positive for V. parahaemolyticus from all the sites: 58 of the 100 samples from the Fujian province, 71 of the 100 samples from the Zhejiang province, and 73 of the 100 samples from the Jiangsu province. In most (170) of the 300 samples, V. parahaemolyticus densities were 0.3 to 10 most probable number (MPN)/g; five lots exceeded 110 MPN/g, and two lots were estimated at 110 MPN/g. Among the 202 V. parahaemolyticus strains, only one was trh positive. Densities of V. parahaemolyticus in these shellfish were temperature dependent, with highest densities in June and July. Among the nine mollusk species, V. parahaemolyticus was most abundant in the agemaki clam (Sinonovacula constricta). The highest and lowest V. parahaemolyticus prevalences were found in oriental cyclina (Cyclina sinensis, 93.8%) and mussels (Mytilus edulis, 28.1%), respectively. Overall, although V. parahaemolyticus is widely distributed in marine environments, the density of V. parahaemolyticus was low and the prevalence of the main virulence factor was very low in shellfish along the coasts of the South Yellow Sea and East China Sea, which is important from a public health perspective. Data presented here will be useful for correlational research and can be utilized for developing risk management plans that establish food safety guidelines for V. parahaemolyticus in Chinese shellfish.

Effects of varying concentrations of sodium chloride and acidic conditions on the behavior of Vibrio parahaemolyticus and Vibrio vulnificus cold-starved in artificial sea water microcosms

There has been limited information available on the behavior of Vibrio parahaemolyticus and Vibrio vulnificus as a function of higher levels of NaCl in combination with acidic pH. In the present study, bacterial suspensions were transferred into artificial seawater (pH 4-7) microcosms containing 0.75% NaCl and supplemented with 5, 10, and 30% NaCl, respectively. Each of V. parahaemolyticus and V. vulnificus was inoculated in these microcosms and fermented seafood, and then stored at 4 °C until the microbial populations reached below the detectable levels on agar plates (thiosulphate-citrate-bile salts-sucrose agar and tryptic soy agar amended with 3% NaCl). Consequently, V. parahaemolyticus ATCC 27969, V. parahaemolyticus ATCC 33844, and V. vulnificus ATCC 33815 rapidly reached the viable-but-nonculturable (VBNC) state with increasing levels (≤30%) of NaCl at 4 °C. Within seven days, these pathogens in seafood appeared to enter the VBNC state at 4 °C, as shown by the fluorescence microscopic assay.

Vibrio parahaemolyticus Strains of Pandemic Serotypes Identified from Clinical and Environmental Samples from Jiangsu, China

Vibrio parahaemolyticus has emerged as a major foodborne pathogen in China, Japan, Thailand, and other Asian countries. In this study, 72 strains of V. parahaemolyticus were isolated from clinical and environmental samples between 2006 and 2014 in Jiangsu, China. The serotypes and six virulence genes including thermostable direct hemolysin (TDR) and TDR-related hemolysin (TRH) genes were assessed among the isolates. Twenty five serotypes were identified and O3:K6 was one of the dominant serotypes. The genetic diversity was assessed by multilocus sequence typing (MLST) analysis, and 48 sequence types (STs) were found, suggesting this V. parahaemolyticus group is widely dispersed and undergoing rapid evolution. A total of 25 strains of pandemic serotypes such as O3:K6, O5:K17, and O1:KUT were identified. It is worth noting that the pandemic serotypes were not exclusively identified from clinical samples, rather, nine strains were also isolated from environmental samples; and some of these strains harbored several virulence genes, which may render those strains pathogenicity potential. Therefore, the emergence of these "environmental" pandemic V. parahaemolyticus strains may poses a new threat to the public health in China. Furthermore, six novel serotypes and 34 novel STs were identified among the 72 isolates, indicating that V. parahaemolyticus were widely distributed and fast evolving in the environment in Jiangsu, China. The findings of this study provide new insight into the phylogenic relationship between V. parahaemolyticus strains of pandemic serotypes from clinical and environmental sources and enhance the MLST database; and our proposed possible O- and K- antigen evolving paths of V. parahaemolyticus may help understand how the serotypes of this dispersed bacterial population evolve.

Prevalence, characterization, and antibiotic susceptibility of Vibrio parahaemolyticus isolated from retail aquatic products in North China

Background

Vibrio parahaemolyticus is a major foodborne pathogen, particularly in Asian countries. Increased occurrence of outbreaks of V. parahaemolyticus gastroenteritis in China indicates the need to evaluation of the prevalence of this pathogenic species. V. parahaemolyticus distribution in shellfish from the eastern coast of China has been reported previously. However, to date, the prevalence of V. parahaemolyticus in retail aquatic products in North China has not been determined. To investigate the prevalence of V. parahaemolyticus in aquatic products in North China, 260 aquatic product samples were obtained from retail markets in 6 provinces of North China from November to December in 2012 and July to August in 2013.

Results

V. parahaemolyticus was detected in 94 (36.2 %) of the samples by the most probable number method. The density of V. parahaemolyticus ranged from 1.50 to 1100 MPN/g. V. parahaemolyticus was detected at a rate of 50.0 % and 22.7 % in summer and in winter, respectively. The density of V. parahaemolyticus was significantly higher in summer than in winter, with mean levels of 16.5 MPN/g and 5.0 MPN/g, respectively. Among 145 V. parahaemolyticus isolates examined, none of the isolates possessed tdh and trh. In multiplex PCR-based O-antigen serotyping of these 145 isolates, all serotypes, other than O6, O7, and O9, were detected, and serotype O2 was found to be the most prevalent (detected in 54 isolates). The 145 isolates were grouped into 7 clusters by enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) at a similarity coefficient of 0.66. The antimicrobial resistance patterns of these 145 isolates to 12 antimicrobial agents revealed that most of the isolates were resistant to streptomycin (86.2 %), while fewer were resistant to ampicillin (49.6 %), cefazolin (43.5 %), cephalothin (35.9 %), and kanamycin (22.1 %). All of the examined isolates were susceptible to azithromycin and chloramphenicol.

Conclusions

The findings of this study will help in defining appropriate monitoring programs, understanding of the dissemination of antibiotic resistant strains, and providing information for the assessment of exposure to this microorganism at the consumption level.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0650-6) contains supplementary material, which is available to authorized users.

Isolation and molecular identification of Vibrio spp. by sequencing of 16S rDNA from seafood, meat and meat products in Libya

The genus Vibrio includes several food-borne pathogens that cause a spectrum of clinical conditions including septicemia, cholera and milder forms of gastroenteritis. Several Vibrio spp. are commonly associated with food-borne transmission including Vibrio cholerae, Vibrio parahemolyticus, and Vibrio vulnificus. Microbiological analysis for enumeration and isolation of Vibrio spp. were carried out for a total of 93 samples of seafood, meat and meat products from different geographic localities in Libya (Tripoli, Regdalin, Janzour and Tobruk). Vibrio spp. were detected by conventional cultural and molecular method using PCR and sequencing of 16S rDNA. Out of the 93 cultured samples only 48 (51.6%) yielded colonies on Thiosulfate Citrate Bile Salt agar (TCBS) with culture characteristics of Vibrio spp. More than half (n=27) of processed seafood samples (n=46) yielded colonies on TCBS, while only 44.6 % of samples of meat and meat products showed colonies on TCBS. Among cultured seafood samples, the highest bacterial count was recorded in clam with a count of 3.8 ×10⁴ CFU\g. Chicken burger samples showed the highest bacterial count with 6.5 ×10⁴ CFU\g. Molecular analysis of the isolates obtained in this study, showed that 11 samples out of 48 (22.9%) were Vibrio spp. Vibrio parahemolyticus was isolated from camel meat for the first time. This study is an initial step to provide a baseline for future molecular research targeting Vibrio spp. foodborne illnesses. This data will be used to provide information on the magnitude of such pathogens in Libyan seafood, meat and meat products.

Microbiological Quality of Seafood Marketed in Taiwan

Seafood is often associated with foodborne illnesses, and Vibrio parahaemolyticus is the most common pathogen implicated in outbreaks in Taiwan. In this study, the microbiological quality of 300 raw or mixed ready-to-eat (RTE) and other cooking-needed seafood samples was examined. The total aerobic and coliform counts of the RTE samples were significantly higher than those of other cooking-needed samples. On average, 55.8 and 29.7% of the RTE samples failed to meet the local microbiological standards for total aerobic (5 log CFU/g) and coliform (3 log most probable number [MPN] per g), counts respectively; the corresponding percentages for the RTE samples from Taipei City were 9.1 and 18.2%, respectively. The total aerobic and coliform counts in the RTE samples from supermarkets and chain restaurants were significantly lower than those from traditional restaurants. The Vibrio species were more frequently identified in the cooking-needed samples than in RTE samples. Low incidences of V. parahaemolyticus (1.4%), V. vulnificus (1.9%), and V. cholerae (0%) were detected in most RTE samples. High densities of V. parahaemolyticus and V. vulnificus (1,200 MPN/g) were detected in a few RTE samples, only one of which contained toxigenic (tdh(+)) V. parahaemolyticus. The results of this investigation reveal that better hygiene of seafood providers such as chain restaurants, supermarkets, and traditional restaurants in Taipei City would effectively improve the microbiological quality of the seafood. The results will facilitate the establishment of measures for controlling the risks associated with seafood in Taiwan.

A Foodborne Outbreak of Gastroenteritis Caused by Vibrio parahaemolyticus and Norovirus through Non-Seafood Vehicle

Foodborne outbreaks caused by a mixed infection of Vibrio parahaemolyticus and norovirus have rarely been described. We reported a mixed outbreak of Vibrio parahaemolyticus and norovirus causing acute gastroenteritis in 99 staff members of a company in Guangdong, China, in May 2013, following consumption of roasted duck, an uncommon non-seafood vehicle for such mixed infection, in one meal served in the company's catering service. Epidemiological and laboratory findings indicated that a single asymptomatic food handler was the source of both pathogens, and the high rate of infection of both pathogens was exacerbated by the setting's suboptimal food hygiene practice.

Bacillus cereus food poisoning: international and Indian perspective

Food borne illnesses result from eating food or drinking beverages that are contaminated with chemical matter, heavy metals, parasites, fungi, viruses and Bacteria. Bacillus cereus is one of the food-borne disease causing Bacteria. Species of Bacillus and related genera have long been troublesome to food producers on account of their resistant endospores. Their spores may be present on various types of raw and cooked foods, and their ability to survive high cooking temperatures requires that cooked foods be served hot or cooled rapidly to prevent the growth of this bacteria. Bacillus cereus is well known as a cause of food poisoning, and much more is now known about the toxins produced by various strains of this species, so that its significance in such episodes are clearer. However, it is still unclear why such cases are so rarely reported worldwide.

Association of a D-alanyl-D-alanine carboxypeptidase gene with the formation of aberrantly shaped cells during the induction of viable but nonculturable Vibrio parahaemolyticus

Vibrio parahaemolyticus is a halophilic Gram-negative bacterium that causes human gastroenteritis. When the viable but nonculturable (VBNC) state of this bacterium was induced by incubation at 4°C in Morita minimal salt solution containing 0.5% NaCl, the rod-shaped cells became coccoid, and various aberrantly shaped intermediates were formed in the initial stage. This study examined the factors that influence the formation of these aberrantly shaped cells. The proportion of aberrantly shaped cells was not affected in a medium containing D-cycloserine (50 μg/ml) but was lower in a medium containing cephalosporin C (10 μg/ml) than in the control medium without antibiotics. The proportion of aberrantly shaped cells was higher in a culture medium that contained 0.5% NaCl than in culture media containing 1.0 or 1.5% NaCl. The expression of 15 of 17 selected genes associated with cell wall synthesis was enhanced, and the expression of VP2468 (dacB), which encodes D-alanyl-D-alanine carboxypeptidase, was enhanced the most. The proportion of aberrantly shaped cells was significantly lower in the dacB mutant strain than in the parent strain, but the proportion was restored in the presence of the complementary dacB gene. This study suggests that disturbance of the dynamics of cell wall synthesis by enhanced expression of the VP2468 gene is associated with the formation of aberrantly shaped cells in the initial stage of induction of VBNC V. parahaemolyticus cells under specific conditions.

Antibacterial hybrid materials fabricated by nanocoating of microfibril bundles of cellulose substance with titania/chitosan/silver-nanoparticle composite films

Uniform ultrathin titania/chitosan composite films were coated on the cellulose microfibril bundles of natural cellulose substance (common commercial filter paper) by a layer-by-layer self-assembly process. Relying on the strong chelating ability of chitosan for metal ions, silver ions were abundantly adsorbed on the titania/chitosan composite film coated cellulose substance and were thereafter in situ reduced to silver nanoparticles (Ag-NPs) under UV irradiation. As such, hybrid cellulose/titania/chitosan/Ag-NP composite materials were obtained, which feature the same hierarchically fibrous structure as the initial cellulose substance. Meanwhile, the hybrid fibres in the composite materials exhibit a cable-like core-shell structure, displaying a cellulose microfibril bundle core as well as a nanometer-thick titania/chitosan/Ag-NP composite film shell with Ag-NPs (4-20 nm in diameter) well distributed. The antibacterial activities of the titania/chitosan/Ag-NP composite film coated cellulose materials were evaluated against both Gram-positive and Gram-negative bacteria, and the materials as such disinfected almost all the inoculated bacteria due to the intrinsic biocidal effect of titania composition, positively charged chitosan component and high loading content of Ag-NPs with small sizes, showing excellent antibacterial activities.

Development of a sensitive rRNA-targeted reverse transcription-quantitative polymerase chain reaction for detection of Vibrio cholerae/mimicus, V. parahaemolyticus/alginolyticus and Campylobacter jejuni/coli

A sensitive rRNA-targeted reverse transcription-quantitative polymerase chain reaction (RT-qPCR) method was developed for detection of Vibrio cholerae/mimicus, V. parahaemolyticus/alginolyticus and Campylobacter jejuni/coli by using specific primers. Counts of the enteric pathogens spiked in human stools were quantified at the lower detection limit of 10(3) cells/g stool by RT-qPCR, in marked contrast with conventional quantitative polymerase chain reaction (qPCR) at the detection limit of 10(5) to 10(6) cells/g stool. The bacterial counts determined by RT-qPCR were almost equivalent to those determined by the culture method and fluorescence in situ hybridization (FISH) during the course of in vitro culture. Bacterial rRNA in the stools was stable for at least 4 weeks when the stools were kept as the suspensions in RNA-stabilizing agent, RNAlater®, even at 37(o) C. These data suggested that the rapid and high sensitive rRNA-targeted RT-qPCR was applicable for the accurate quantification of viable enteric pathogens, such as V. cholerae/mimicus, V. parahaemolyticus/alginolyticus and C. jejuni/coli.

Molecular typing of Vibrio parahaemolyticus isolates from the middle-east coastline of China

The occurrence of outbreaks of Vibrio parahaemolyticus gastroenteritis in China highlights the need for strain characterization and subtyping of this pathogenic species. A total of 56 epidemiologically-unrelated strains of V. parahaemolyticus were isolated from clinical samples, seafood and various environmental sites in the middle-east coastline of China from 2006 to 2008. The isolates were characterized using four molecular typing methods, including ribotyping, enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR), pulsed-field gel electrophoresis (PFGE), and sequence analysis of the gyrB gene. Genetic profiles of cluster analysis from these molecular typing tests clearly showed that there were differences in potential pathogenicity among isolates from seafood and its environments. Genetic characterization of two isolates (F13 and QS2) that originated from seafood demonstrated that they were potentially pathogenic. Discriminatory indices of four typing methods for the 56 V. parahaemolyticus isolates were differentiated by Simpson's Index of Diversity. The discriminatory index of ERIC-PCR typing was maximal (D=0.942), while that of sequence analysis of the gyrB gene was minimal (D=0.702). The discriminatory ability was greatly enhanced (D=0.966) when ERIC-PCR was coupled with sequence analysis of the gyrB gene. These results suggest that ERIC-PCR combined with sequence analysis of gyrB gene may be a reliable, rapid typing strategy for V. parahaemolyticus strains.

Occurrence of Vibrio parahaemolyticus and its specific phages from shrimp ponds in east coast of India

Vibrio parahaemolyticus is a natural microflora of marine and coastal water bodies and associated with mortality of larval shrimp in penaeid shrimp in ponds. Bacteriophages occur virtually in all places where their hosts exist. In this study, total distribution of V. parahaemolyticus and its phages were examined in shrimp ponds, seawater, estuary, animal surface, and tissues. Total vibrio count in sediments of two ponds was found to be 2.6 × 10(3) and 5.6 × 10(3) cfu/g. Incidence of V. parahaemolyticus in the ponds was close, while it was markedly higher in the animal surface and tissue samples. Biochemically identified eight strains of V. parahaemolyticus (V1, V3-V6, V9, V11, and V12) were taken for further infection studies with bacteriophage. Totally five bacteriophages capable of infecting V. parahaemolyticus MTCC-451 strain were isolated from all the samples. One of the isolated bacteriophage Vp1 from estuary was able to lyse all the isolated V. parahaemolyticus strains we used. Therefore, the morphology of Vp1 was estimated in TEM. Vp1 phage head measuring approximately about 50-60 nm diameter with icosahedral outline and a contractile tails of diameter 7 nm and length 100 nm and it was identified as Myoviridae. Therefore, the phages have the potential application in destroying bacterial pathogens.

Correlation between environmental factors and prevalence of Vibrio parahaemolyticus in oysters harvested in the southern coastal area of Sao Paulo State, Brazil

The presence of Vibrio parahaemolyticus in 123 oyster samples collected from an estuary on the southern coast of Sao Paulo state, Brazil, was investigated. Of the 123 samples, 99.2% were positive with densities ranging from < 3 to 10(5) most probable number (MPN)/g. Densities correlated significantly with water temperature (r = 0.48; P < 0.001) but not with salinity (r = -0.09; P = 0.34). The effect of harvest site on counts was not significant (P > 0.05). These data provide information for the assessment of exposure of V. parahaemolyticus in oysters at harvest.

Antibacterial effects of roselle calyx extracts and protocatechuic acid in ground beef and apple juice

The antibacterial effects of roselle calyx aqueous and ethanol extracts and protocatechuic acid against food spoilage bacteria Salmonella typhimurium DT104, Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus, and Bacillus cereus were examined. Minimal inhibitory concentrations of roselle calyx aqueous and ethanol extracts and protocatechuic acid against these bacteria were in the range of 112-144, 72-96, and 24-44 microg/mL, respectively. Protocatechuic acid content in roselle calyx aqueous and ethanol extracts was 2.8 +/- 0.7 and 11.9 +/- 1.2 mg/g, respectively. Antibacterial activity of roselle calyx ethanol extract and protocatechuic acid was not affected by heat treatments from 25 degrees to 75 degrees C and 25 degrees to 100 degrees C, respectively. After 3 days storage at 25 degrees C, the addition of roselle calyx extracts and protocatechuic acid exhibited dose-dependent inhibitory effects against test bacteria in ground beef and apple juice, in which the roselle calyx ethanol extract showed greater antibacterial effects than the aqueous extract. These data suggest that roselle calyx ethanol extract and protocatechuic acid might be potent agents as food additives to prevent contamination from these bacteria.

Molecular analysis of the emergence of pandemic Vibrio parahaemolyticus

Background

Vibrio parahaemolyticus is abundant in the aquatic environment particularly in warmer waters and is the leading cause of seafood borne gastroenteritis worldwide. Prior to 1995, numerous V. parahaemolyticus serogroups were associated with disease, however, in that year an O3:K6 serogroup emerged in Southeast Asia causing large outbreaks and rapid hospitalizations. This new highly virulent strain is now globally disseminated.

Results

We performed a four-way BLAST analysis on the genome sequence of V. parahaemolyticus RIMD2210633, an O3:K6 isolate from Japan recovered in 1996, versus the genomes of four published Vibrio species and constructed genome BLAST atlases. We identified 24 regions, gaps in the genome atlas, of greater than 10 kb that were unique to RIMD2210633. These 24 regions included an integron, f237 phage, 2 type III secretion systems (T3SS), a type VI secretion system (T6SS) and 7 Vibrio parahaemolyticus genomic islands (VPaI-1 to VPaI-7). Comparative genomic analysis of our fifth genome, V. parahaemolyticus AQ3810, an O3:K6 isolate recovered in 1983, identified four regions unique to each V. parahaemolyticus strain. Interestingly, AQ3810 did not encode 8 of the 24 regions unique to RMID, including a T6SS, which suggests an additional virulence mechanism in RIMD2210633. The distribution of only the VPaI regions was highly variable among a collection of 42 isolates and phylogenetic analysis of these isolates show that these regions are confined to a pathogenic clade.

Conclusion

Our data show that there is considerable genomic flux in this species and that the new highly virulent clone arose from an O3:K6 isolate that acquired at least seven novel regions, which included both a T3SS and a T6SS.

Optimization of inactivation of endospores of Bacillus cereus by antimicrobial lipopeptides from Bacillus subtilis fmbj strains using a response surface method

Bacillus subtilis fmbj can produce a lipopeptide antimicrobial substance, the main components of which are surfactin and fengycin. In this paper, the sensitivity of Bacillus cereus to antimicrobial lipopeptides from B. subtilis fmbj was observed, and the effect of the microstructure of antimicrobial lipopeptide on spores of B. cereus was investigated. At the same time, the optimization of the inactivation of antimicrobial lipopeptides to spores of B. cereus by a response surface methodology was studied. Results showed that B. cereus had high sensitivity to it, whose minimal inhibitory concentration was 156.25 microg/ml. It could result in the death of spores by destroying the structure of resting spores and sprouting spores, as was observed by transmission electron microscopy. The optimization result indicated that spores of B. cereus could be inactivated by 2 orders of magnitude when the temperature was 29.6 degrees C, the action time was 7.6 h, and the concentration was 3.46 mg.ml(-1).

A pulsed field gel electrophoresis (PFGE) study that suggests a major world-wide clone of Salmonella enterica serovar Enteritidis

Since human infections by Salmonella enterica serovar Enteritidis (Salmonella Enteritidis) have been increasing world-wide over the past years and epidemiological studies have implicated the consumption of meat, poultry, eggs and egg products, elucidation of the predominant subtypes for this Salmonella spp. is important. In this study, 107 poultry and food isolates of Salmonella Enteritidis obtained from Germany were analyzed by pulsed field gel electrophoresis (PFGE), and the subtypes were compared with those of the 124 human isolates obtained in Taiwan. Results showed that for these 107 poultry and food isolates, when XbaI, SpeI and NotI were used for chromosomal DNA digestion followed by PFGE analysis, a total of 19, 20 and 19 PFGE patterns, respectively, were identified. Of them, 51 (47.7%), 52 (48.6%) and 42 (39.3%) strains belong to a single pattern of X3, S3 and N3, respectively, and 34 strains belong to a pattern combination of X3S3N3, which was the major subtype. When PFGE patterns of these 107 German isolates were compared with those of the 124 human isolates obtained in Taiwan, pattern combination of X3S3N3 was found as the most common pattern shared by isolates from both areas. PT4 is a major phage type for German and Taiwan isolates. Although most of the X3S3N3 strains are of this phage type, some strains of other PFGE patterns are also of this phage type. Since strains used in this study were unrelated, i.e., they were isolated from different origins in areas geographically far apart from each other, the PFGE study suggests a major world-wide clone of S. enterica serovar Enteritidis.

Detection of viable enterohemorrhagic Escherichia coli O157 using the combination of immunomagnetic separation with the reverse transcription multiplex TaqMan PCR system in food and stool samples

Enterohemorrhagic Escherichia coli O157:H7 is an infectious pathogen and outbreaks have been reported all over the world, specifically in Australia, Canada, Japan, the United States, and in various countries in Europe and South Africa. Therefore, it is necessary to develop rapid methods to determine the target pathogens for food sanitation and disease. Three combinations of primers and probes were designed to detect and identify E. coli O157 using the TaqMan detection system which focuses on the specific genes eae, rfb(O157, and stxII. Reverse transcription (RT) multiplex TaqMan PCR was carried out to accurately detect viable target cells correctly. Furthermore, the acidic pretreatment and immunomagnetic separation (IMS) of food and stool samples also improved the specificity and accuracy of the RT multiplex TaqMan PCR. The developed multiplex TaqMan PCR was effective in differentiating E. coli O157, enterovirulent E. coli, and non-E. coli pathogens from 100 strains which were isolated from clinical patients and the environment. Viable and nonviable cells were also distinguished by this assay. The pretreatment protocol, which included IMS to concentrate and purify the E. coli O157, was developed and the sensitivity of the assay was improved to 10(0) CFU/ml in pure culture, food, and stool samples. The TaqMan PCR assay is a rapid test for the detection of E. coli O157 in food and stool matrices. It shortens the process time and increases the specificity of the pathogens detected. This is critical for improving the safety and sanitation of our food supply.

Efficacy of amphoteric surfactant- and peracetic acid-based disinfectants on spores of bacillus cereus in vitro and on food premises of the German armed forces

In mass catering facilities of the German Armed Forces, foodborne outbreaks are commonly attributed to Bacillus cereus, and spores of this organism are regularly found on equipment surfaces. B. cereus is the causative agent of foodborne emetic or diarrheic disease. Hence, the use of sporicidal disinfectants may provide a starting point for successful risk mitigation of diseases associated with B. cereus. In this study, the amphoteric surfactant-based disinfectant (product A) that has been routinely used in catering facilities of the German Armed Forces and a peracetic acid-based disinfectant (product B) were compared for their efficacy against B. cereus spores in laboratory tests and under field conditions. In a carrier test for B. cereus spores, product A displayed no efficacy against spores of the test strain. In contrast, a substantial reduction in spore concentration (>5-log reduction) was achieved with product B. In a controlled trial conducted in seven Army catering facilities, the reduction in the number of B. cereus-positive samples was significantly greater (P < 0.001) for product B (from 28% initial contamination to 3% after application) than for product A (from 33 to 21%). Product B was estimated to be 6.25 times more efficacious than product A. Field trials confirmed the higher efficacy of the peracetic acid-based disinfectant to reduce B. cereus contamination on surfaces as found for the in vitro experiments. The tests used to assess the sporicidal effects of disinfectants were adequate under practice conditions and could be used for sporicidal testing of disinfectants for catering and food production establishments.

Four genomic islands that mark post-1995 pandemic Vibrio parahaemolyticus isolates

Background

Vibrio parahaemolyticus is an aquatic, halophilic, Gram-negative bacterium, first discovered in 1950 in Japan during a food-poisoning outbreak. Infections resulting from consumption of V. parahaemolyticus have increased globally in the last 10 years leading to the bacterium's classification as a newly emerging pathogen. In 1996 the first appearance of a pandemic V. parahaemolyticus clone occurred, a new O3:K6 serotype strain that has now been identified worldwide as a major cause of seafood-borne gastroenteritis.

Results

We examined the sequenced genome of V. parahaemolyticus RIMD2210633, an O3:K6 serotype strain isolated in Japan in 1996, by bioinformatic analyses to uncover genomic islands (GIs) that may play a role in the emergence and pathogenesis of pandemic strains. We identified 7 regions ranging in size from 10 kb to 81 kb that had the characteristics of GIs such as aberrant base composition compared to the core genome, presence of phage-like integrases, flanked by direct repeats and the absence of these regions from closely related species. Molecular analysis of worldwide clinical isolates of V. parahaemolyticus recovered over the last 33 years demonstrated that a 24 kb region named V. parahaemolyticus island-1 (VPaI-1) encompassing ORFs VP0380 to VP0403 is only present in new O3:K6 and related strains recovered after 1995. We investigated the presence of 3 additional regions, VPaI-4 (VP2131 to VP2144), VPaI-5 (VP2900 to VP2910) and VPaI-6 (VPA1254 to VPA1270) by PCR assays and Southern blot analyses among the same set of V. parahaemolyticus isolates. These 3 VPaI regions also gave similar distribution patterns amongst the 41 strains examined.

Conclusion

The 4 VPaI regions examined may represent DNA acquired by the pandemic group of V. parahaemolyticus isolates that increased their fitness either in the aquatic environment or in their ability to infect humans.

Pulsed-field gel electrophoresis, plasmid profiles and phage types for the human isolates of Salmonella enterica serovar Enteritidis obtained over 13 years in Taiwan

AIMS

Plasmid profile, phage typing, and pulsed-field gel electrophoresis (PFGE) patterns of 124 Salmonella Enteritidis strains isolated in 1998-2002 in Taiwan were analysed and the results were compared with those of the 63 strains obtained in 1991-1997, so that molecular subtypes and epidemic strains for Salmonella Enteritidis over a 13-year period (1991-2002) could be elucidated.

METHODS AND RESULTS

A total of 124 strains of Salmonella Enteritidis isolated from human in Taiwan between 1998 and 2002 were analysed by PFGE, plasmid analysis and phage typing. The results obtained were compared with those of the 63 strains obtained in 1991-1997, so that the clonal relationships for a total of 187 strains obtained over 13 years could be elucidated. For PFGE, restriction enzymes XbaI, SpeI and NotI were used for chromosomal DNA digestion. Results showed 28 PFGE pattern combinations for the 187 Salmonella strains. Of them, pattern X3S3N3 was the major subtype as 130 strains isolated from different locations during 1991-2002 showed this PFGE pattern. For all these 187 strains, the genetic similarity was higher than 80%. Plasmid analysis showed 17 distinct types, which consist of one to four plasmids and the predominant phage type of those strains was PT4 (71.6%) and PT6a (13.4%). The three methods identified different degrees of polymorphism in the following order: plasmid profile (18 types, D = 0.659) > PFGE (28 types, D = 0.512) > phage typing (13 types, D = 0.438). As PFGE patterns, phage type and plasmid profile were combined for subtyping, the 187 strains could be grouped into 46 subtypes and the discriminatory index was raised to 0.795. For these 46 subtypes, the predominant one was X3S3N3/P1/PT4, which contained 77 (41%) isolates.

CONCLUSIONS

Most of the Salmonella Enteritidis strains from sporadic cases were with pattern X3S3N3. They were the prevalent and may be the epidemic strains found in Taiwan during 1991-2002. The present study suggested that the several variants were derived from a single clonal line and the genome for strains of Salmonella Enteritidis are highly conserved over a 13-year period (1991-2002).

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained here are useful for epidemiolgical study of salmonellosis caused by Salmonella Enteritidis in Taiwan. Comparing the data of the present study with those obtained for strains from other countries, the major subtypes for Salmonella Enteritidis infection in the world can be elucidated.

Molecular subtyping for Escherichia coli O157: H7 isolated in Taiwan

Enterohaemorrhagic Escherichia coli O157: H7 is an important pathogen these days. Outbreaks of its infection have been reported all over the world, in Australia, Canada, Japan, the United States, south Africa, and various countries in Europe. In the summer of 2001, the first clinical infection by E. coli O157: H7 was identified in Taiwan. In this study, the standard procedures for molecular subtyping were applied to several strains collected in Taiwan as well as from elsewhere. The two molecular subtyping methods we used are pulsed-field gel electrophoresis (PFGE) and amplified fragment length polymorphism (AFLP). The isolates from the U.S.A., Canada, Japan, and Taiwan each showed a unique molecular fingerprinting pattern. The environmental strains isolated in Taiwan showed closer relationships with each other, and their similarity was in the range of 75-85%. The first clinical strain isolated in Taiwan in 2001 was similar to the strains from North America but not closely related to the Taiwanese environmental strains. Our surveys showed that some local E. coli O157: H7 strains did exist in Taiwan, but there had been only one official case report of the infection by local E. coli O157: H7. The eating habits of the people and the geographic distribution of the pathogen are considered crucial risk factors in Taiwan. The establishment of a database of our own and joining the global network database are important tasks if we want to control such agricultural and food-borne pathogens, and reduce the number of victims and amount sufferings, as well as the economic losses due to the infection.

Bacterial food-borne illness outbreaks in northern Taiwan, 1995-2001

How to reduce the occurrence of food-borne illness has always been one issue of great importance in Taiwan's disease prevention and control efforts, and it is important to determine, from survey results, whether the pathogens in Taiwan are the same or different from those in other countries. Accordingly, data on 1171 food-borne illness outbreaks were collected from the Center for Disease Control (CDC) of the Department of Health in Taiwan. The patients and the cases were numbered according to the guidelines and definition of food poisoning given by the Department of Health in Taiwan. All rectal swabs for culture were collected from the CDC. During 1995 to 2001, 1171 outbreaks of food-borne illness, including 109,884 cases, were reported in northern Taiwan, of which 735 (62.8%) were caused by bacterial infection. Bacterial pathogens, particularly Vibrio parahaemolyticus (86.0%), Staphylococcus aureus (7.6%), and Salmonella spp. (4.9%) were the main etiologic agents. The responsible pathogens in Taiwan appeared to be quite different from those in Europe and the United States. It is important to establish a unique surveillance net of our own to prevent and control our situation of food-borne disease outbreaks effectively.

Epidemiology, pathogenesis, and prevention of foodborne Vibrio parahaemolyticus infections

Since its discovery about 50 years ago, Vibrio parahaemolyticus has been implicated as a major cause of foodborne illness around the globe. V. parahaemolyticus is a natural inhabitant of marine waters. Human infections are most commonly associated with the consumption of raw, undercooked or contaminated shellfish. A few individual V. parahaemolyticus virulence factors, including the thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH), have been investigated in depth, yet a comprehensive understanding of this organism's ability to cause disease remains unclear. Since 1996, serotype O3:K6 strains have been associated with an increased incidence of gastroenteritis in India and in Southeast Asia, and with large-scale foodborne outbreaks in the United States (US). In light of the emerging status of pathogenic V. parahaemolyticus, the US Food and Drug Administration conducted a microbial risk assessment to characterize the risk of contracting V. parahaemolyticus infections from consuming raw oysters. This review summarizes epidemiological findings, discusses recognized and putative V. parahaemolyticus virulence factors and pathogenicity mechanisms, and describes strategies for preventing V. parahaemolyticus infections.

Characterization of new O3:K6 strains and phylogenetically related strains of Vibrio parahaemolyticus isolated in Taiwan and other countries

AIMS

We analysed the genetic divergence in the pandemic new O3:K6 and phylogenetically related (new O3:K6-like) strains and compare these two groups in terms of virulence and other biological traits.

METHODS AND RESULTS

A total of 160 new O3:K6, new O3:K6-like and other strains of Vibrio parahaemolyticus isolated in Taiwan and other countries were collected and their clonal relationships analysed using SfiI-pulsed-field gel electrophoresis. All of the new O3:K6 and new O3:K6-like strains were grouped in cluster I with five new patterns identified. A O6:K18 strain was identified as a new member of the new O3:K6-like strains in addition to O4:K68, O1:KUT and O1:K25 strains. All of the lipopolysaccharide preparations of the selected strains exhibited closely spaced quadruplet banding patterns with similar mobility. The two groups of strains exhibited 100% sequence identity in the internal sequences of the toxR and laf genes, and also displayed similar virulence properties as determined with a suckling mouse model.

CONCLUSIONS

The new O3:K6 and new O3:K6-like strains were highly similar in virulence and in several other phenotypical and genotypical traits.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work demonstrated the spread and divergence of the pandemic and related clone of V. parahaemolyticus with similar virulence.

Bacillus cereus food poisoning and its toxins

The genus Bacillus includes members that demonstrate a wide range of diversity from physiology and ecological niche to DNA sequence and gene regulation. The species of most interest tend to be known for their pathogenicity and are closely linked genetically. Bacillus anthracis causes anthrax, and Bacillus thuringiensis is widely used for its insecticidal properties but has also been associated with foodborne disease. Bacillus cereus causes two types of food poisoning, the emetic and diarrheal syndromes, and a variety of local and systemic infections. Although in this review we provide information on the genus and a variety of species, the primary focus is on the B. cereus strains and toxins that are involved in foodborne illness. B. cereus produces a large number of potential virulence factors, but for the majority of these factors their roles in specific infections have not been established. To date, only cereulide and the tripartite hemolysin BL have been identified specifically as emetic and diarrheal toxins, respectively. Nonhemolytic enterotoxin, a homolog of hemolysin BL, also has been associated with the diarrheal syndrome. Recent findings regarding these and other putative enterotoxins are discussed.

Hydrophobicity, cell adherence, cytotoxicity, and enterotoxigenicity of starved Vibrio parahaemolyticus

Vibrio parahaemolyticus is a ubiquitous gram-negative enteropathogenic bacterium that may encounter starvation or other environmental stresses during food processing or human infection. Pathogenic V. parahaemolyticus ST550 cultures starved in modified Morita mineral salt solution with 3 or 0.5% NaCl exhibited similar resistance against challenges of environmental stresses. Changes in virulence of the starved V. parahaemolyticus was determined using HEp-2 cell culture and suckling mouse assay. The starved cells exhibited greater cell adherence and hydrophobicity than did the cells in exponential growth phase. Expression of virulence in terms of cytotoxicity and mouse lethality was lower in the starved cells than in the exponential-phase cells at the same postinfection time. An additional 1 h of in vitro or in vivo incubation was required to enable these starved cells to reach the same cytotoxicity and mouse lethality levels as exhibited by the exponential-phase cells.

Detection of pathogenic Vibrio spp. in shellfish by using multiplex PCR and DNA microarrays

This study describes the development of a gene-specific DNA microarray coupled with multiplex PCR for the comprehensive detection of pathogenic vibrios that are natural inhabitants of warm coastal waters and shellfish. Multiplex PCR with vvh and viuB for Vibrio vulnificus, with ompU, toxR, tcpI, and hlyA for V. cholerae, and with tlh, tdh, trh, and open reading frame 8 for V. parahaemolyticus helped to ensure that total and pathogenic strains, including subtypes of the three Vibrio spp., could be detected and discriminated. For DNA microarrays, oligonucleotide probes for these targeted genes were deposited onto epoxysilane-derivatized, 12-well, Teflon-masked slides by using a MicroGrid II arrayer. Amplified PCR products were hybridized to arrays at 50 degrees C and detected by using tyramide signal amplification with Alexa Fluor 546 fluorescent dye. Slides were imaged by using an arrayWoRx scanner. The detection sensitivity for pure cultures without enrichment was 10(2) to 10(3) CFU/ml, and the specificity was 100%. However, 5 h of sample enrichment followed by DNA extraction with Instagene matrix and multiplex PCR with microarray hybridization resulted in the detection of 1 CFU in 1 g of oyster tissue homogenate. Thus, enrichment of the bacterial pathogens permitted higher sensitivity in compliance with the Interstate Shellfish Sanitation Conference guideline. Application of the DNA microarray methodology to natural oysters revealed the presence of V. vulnificus (100%) and V. parahaemolyticus (83%). However, V. cholerae was not detected in natural oysters. An assay involving a combination of multiplex PCR and DNA microarray hybridization would help to ensure rapid and accurate detection of pathogenic vibrios in shellfish, thereby improving the microbiological safety of shellfish for consumers.

Molecular and epidemiologic analysis of a county-wide outbreak caused by Salmonella enterica subsp. enterica serovar Enteritidis traced to a bakery

Background

An increase in the number of attendees due to acute gastroenteritis and fever was noted at one hospital emergency room in Taiwan over a seven-day period from July to August, 2001. Molecular and epidemiological surveys were performed to trace the possible source of infection.

Methods

An epidemiological investigation was undertaken to determine the cause of the outbreak. Stool and blood samples were collected according to standard protocols per Center for Disease Control, Taiwan. Typing of the Salmonella isolates from stool, blood, and food samples was performed with serotyping, antibiotypes, and pulsed field gel electrophoresis (PFGE) following XbaI restriction enzyme digestion.

Results

Comparison of the number of patients with and without acute gastroenteritis (506 and 4467, respectively) during the six weeks before the outbreak week revealed a significant increase in the number of patients during the outbreak week (162 and 942, respectively) (relative risk (RR): 1.44, 95% confidence interval (CI): 1.22–1.70, P value < 0.001). During the week of the outbreak, 34 of 162 patients with gastroenteritis were positive for Salmonella, and 28 of these 34 cases reported eating the same kind of bread. In total, 28 of 34 patients who ate this bread were positive for salmonella compared to only 6 of 128 people who did not eat this bread (RR: 17.6, 95%CI 7.9–39.0, P < 0.001). These breads were produced by the same bakery and were distributed to six different traditional Chinese markets., Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis) was isolated from the stool samples of 28 of 32 individuals and from a recalled bread sample. All S. Enteritidis isolates were of the same antibiogram. PFGE typing revealed that all except two of the clinical isolates and the bread isolates were of the same DNA macrorestriction pattern.

Conclusions

The egg-covered bread contaminated with S. Enteritidis was confirmed as the vehicle of infection. Alertness in the emergency room, surveillance by the microbiology laboratory, prompt and thorough investigation to trace the source of outbreaks, and institution of appropriate control measures provide effective control of community outbreaks.

Effects of heat, acid, and freeze-thaw challenges on survival of starved Vibrio parahaemolyticus in minimal salt medium, tryptic soy broth, and filtered oyster homogenate medium

Vibrio parahaemolyticus is a ubiquitous gram-negative enteropathogenic bacterium. To evaluate the risk of stress-adapted V. parahaemolyticus cells in food, we investigated the survivability of starvation-adapted and starvation-low salinity-adapted cells of this pathogen in different media against different stresses. Logarithmically grown bacterial cells were starved at 25 degrees C in a minimal salt medium with 0.5 or 3.0% NaCl for 24 h. Resistances against challenges of heat, acid, and freeze-thaw treatment exhibited by the starvation-adapted cells were similar to those exhibited by the starvation-low salinity-adapted cells but substantially higher than those of the unadapted control cells. The increased stress resistance of the adapted cells against freeze-thaw challenge was lower in tryptic soy broth than in the starving medium. Resistance of the adapted bacteria against heat and freeze-thaw treatment was completely eliminated in filter-sterilized oyster homogenate medium. Practically, these results help to assess the risk of stress-adapted V. parahaemolyticus in food.