Contamination Status and Risk Assessment of Paralytic Shellfish Toxins in Shellfish along the Coastal Areas of China.

Paralytic shellfish toxins (PSTs) are widely distributed in shellfish along the coast of China, causing a serious threat to consumer health; however, there is still a lack of large-scale systematic investigations and risk assessments. Herein, 641 shellfish samples were collected from March to November 2020, and the PSTs' toxicity was detected via liquid chromatography-tandem mass spectrometry. Furthermore, the contamination status and potential dietary risks of PSTs were discussed. PSTs were detected in 241 shellfish samples with a detection rate of 37.60%. The average PST toxicities in mussels and ark shells were considerably higher than those in other shellfish. The PSTs mainly included N-sulfonylcarbamoyl toxins (class C) and carbamoyl toxins (class GTX), and the highest PST toxicity was 546.09 µg STX eq. kg-1. The PST toxicity in spring was significantly higher than those in summer and autumn (p < 0.05). Hebei Province had the highest average PST toxicity in spring. An acute exposure assessment showed that consumers in Hebei Province had a higher dietary risk, with mussels posing a significantly higher dietary risk to consumers. This research provides reference for the green and sustainable development of the shellfish industry and the establishment of a shellfish toxin prevention and control system.

Optimization of Physical Refining Process of Camellia Oil for Reduction of 3-Monochloropropane-1,2-Diol (3-MCPD) Ester Formation Using Response Surface Methodology on a Laboratory Scale.

Refined and deodorized camellia oil has been reported to contain a high amount of 3-monochloropropane-1,2-diol esters (3-MCPDE) due to the high-temperature deodorization step. To reduce 3-MCPDE in camellia oil, the physical refining process of camellia oil was simulated on a laboratory scale. Response surface methodology (RSM) was designed to modify and optimize the refining process with five processing parameters (water degumming dosage, degumming temperature, activated clay dosage, deodorization temperature and deodorization time). The optimized new refining approach achieved a 76.9% reduction in 3-MCPDE contents, in which the degumming moisture was 2.97%, the degumming temperature was 50.5 °C, the activated clay dosage was 2.69%, the deodorizing temperature was 230 °C, and the deodorizing time was 90 min. A significance test and analysis of variance results demonstrated that the deodorization temperature and deodorization time contributed significantly to the reduction of 3-MCPD ester. The joint interaction effects of activated clay dosage and deodorization temperature were significant for 3-MCPD ester formation.

Correlation Analysis of Microbial Contamination and Alkaline Phosphatase Activity in Raw Milk and Dairy Products.

Microbial contamination in raw milk and dairy products can detrimentally affect product quality and human health. In this study, the aerobic plate count, aerobic Bacillus abundance, thermophilic aerobic Bacillus abundance, and alkaline phosphatase activity were determined in 435 raw milk, 451 pasteurized milk, and 617 sterilized milk samples collected from 13 Chinese provinces (or municipalities). Approximately 9.89% and 2.22% of raw milk and pasteurized milk samples exceeded the threshold values for the aerobic plate count, respectively. The proportions of aerobic Bacillus in raw milk, pasteurized milk, and sterilized milk were 54.02%, 14.41%, and 1.30%, respectively. The proportions of thermophilic aerobic Bacillus species were 7.36% in raw milk and 4.88% in pasteurized milk samples, and no bacteria were counted in sterilized milk. Approximately 36.18% of raw milk samples contained >500,000 mU/L of alkaline phosphatase activity, while 9.71% of pasteurized milk samples contained >350 mU/L. For raw milk, there was a positive correlation between the aerobic plate count, the aerobic Bacillus abundance, and the alkaline phosphatase activity, and there was a positive correlation between the aerobic Bacillus abundance, the thermophilic aerobic Bacillus count, and the alkaline phosphatase activity. For pasteurized milk, there was a positive correlation between the aerobic plate count, the aerobic Bacillus abundance, and the thermophilic aerobic Bacillus count; however, the alkaline phosphatase activity had a negative correlation with the aerobic plate count, the aerobic Bacillus abundance, and the thermophilic aerobic Bacillus abundance. These results facilitate the awareness of public health safety issues and the involvement of dairy product regulatory agencies in China.

Dietary Exposure Assessment of Rare Earth Elements in the Chinese Population.

Rare earth elements (REEs) are widely found in foods. A high intake of REEs may have associations with adverse effects on human health. This study aimed to investigate the concentrations of REEs in foods in China and to assess the risk of dietary REEs exposure in the Chinese population. The mean concentrations of the total REEs in 27,457 food samples from 11 food categories ranged from 0.04 to 1.41 mg/kg. The daily mean dietary exposure of the total REEs was 1.62 µg/kg BW in the general Chinese population and ranged from 1.61 to 2.80 µg/kg BW in different sex-age groups. The high consumer exposure (95th percentile, P95) was 4.83 µg/kg BW, 9.38% of the temporary ADI (tADI) of REEs (51.5 µg/kg BW). None of the P95 exposure exceeded the tADI in all of the sub-groups. Lanthanum, cerium, and yttrium accounted for approximately 63% of the total exposure of the 16 REEs. The hazard index of 16 REEs was far below 1. Therefore, the health risk of dietary REEs exposure in the general Chinese population was low. No cumulative risk was found for the 16 REEs in China. The results indicate there was no need to stipulate the limits of REEs in foods.

Occurrence and Risk Assessment of Fluoroquinolone Residues in Chicken and Pork in China.

Antibiotics, especially fluoroquinolones, have been exhaustively used in animal husbandry. However, very limited information on the occurrence and exposure assessment of fluoroquinolone residues in chicken and pork in China is available to date. Thus, a total of 1754 chicken samples and 1712 pork samples were collected from 25 provinces in China and tested by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for residual determination of six common fluoroquinolones. The results revealed that the detection frequencies of fluoroquinolone residues were 3.99% and 1.69% in chicken and pork samples. The overall violation frequencies were 0.68% and 0.41% for chicken and pork. Enrofloxacin and its metabolite ciprofloxacin were found to be the most predominant fluoroquinolones. The occurrence of these antibiotics in different sampling regions and market types was analyzed. The %ADI values of enrofloxacin and ciprofloxacin were far less than 100, indicating the health risk associated with the exposure to these aforementioned fluoroquinolone residues via chicken and pork for Chinese children, adolescents, and adults was acceptable. The results provided useful references for Chinese consumers, and helped to appropriately use these antibiotics in poultry and livestock industry.

Antimicrobial-Resistant Evolution and Global Spread of Enterococcus faecium Clonal Complex (CC) 17: Progressive Change from Gut Colonization to Hospital-Adapted Pathogen.

For a long time, Enterococcus faecium (E. faecium) was thought to be a commensal strain in human and animal digestive tracts. However, over the past three decades, some unique E. faecium clones rapidly acquired multiple antimicrobial resistance (AMR), which led these clones to survive hospital environments and become a hospital-adapted E. faecium clonal complex (CC) 17. Since the adaptation of these clones to changes in habitat, vancomycin-resistant E. faecium CC17 has emerged as the leading cause of hospital-acquired infections worldwide. This epidemic hospital-adapted lineage has diverged from other populations approximately 75 years ago. The CC17 lineage originated from animal strains, but not human commensal lines. We reviewed the evolutionary progress and the molecular mechanisms of E. faecium CC17 from a gut commensal to a multi-antimicrobial resistant nosocomial pathogen.

[Microbial contamination in dried fruit products in China in 2019].

OBJECTIVE: To investigate the microbial contamination in dried fruit products in China. METHODS: In 2019, 2917 samples of dried fruit products on the market were collected, and examined for aerobic bacterial count, coliforms, molds, yeasts, Salmonella and Listeria monocytogenes according to the method specified in GB 4789. RESULTS: A total of 34.42%(1004/2917)of the samples had molds above 50 CFU/g and 9.46%(276/2917)of the samples had yeast above 50 CFU/g. The occurrence of aerobic plate count above 10~4 CFU/g and coliforms above 10~2 CFU/g was 5.01%(146/2917)and 2.98%(87/2917), respectively. The detection rate of Salmonella and Listeria monocytogenes were 0.14%(4/2917) and 0.03%(1/2917), respectively. Microbial contamination in different kinds of dried fruit products varied widely, with dried wolfberries and dried durian having the worst overall hygiene. There were differences in microbial contamination of dried fruit products in different regions. In general, samples collected in South China, Southwest China and Central China had more serious microbial contamination. There was no significant difference in microbial contamination between dried fruit products with different packaging and sampling places. CONCLUSION: The hygienic condition of dried fruit products is generally poor in 2019.

The contamination and estimation of dietary intake for perchlorate and chlorate in infant formulas in China.

The contents of perchlorate and chlorate were determined in a total of 278 samples of infant formulas marketed in China. The associated health risk via infant and young child formulas consumption for 0-36 month old children in China was also assessed. The contents of perchlorate and chlorate were measured by a validated method with LC-MS and the limit of detection (LOD) was 1.5 µg kg-1 and 3.0 µg kg-1 for perchlorate and chlorate, respectively. Perchlorate and chlorate were detected in about 85.8% (median 6.92 µg kg-1, maximum 74.20 µg kg-1) and 99.3% (median 52.80 µg kg-1, maximum 2780 µg/kg) of the samples. The exposures of infant and young children to perchlorate from formulas were lower than the provisional maximum tolerable daily intake (PMTDI, 0.7 µg/kg bw/day), which was established by U.S. Environmental Protection Agency (EPA). The European Food Safety Authority (EFSA) in 2015 also proposed a tolerable daily intake (TDI) of 3 µg/kg bw/day for chlorate based on the mean and average concentrations. Only for infants 0-6 month at the 95th percentile did exposures exceed the TDI of 3 µg/day for chlorate. Therefore, the safety of infant and young child formulas is excellent. To our knowledge, this is the first report to assess the exposure of infant and young child formulas in China to perchlorate and chlorate.

Occurrence of 3- and 2-monochloropropanediol esters in infant formulas in China and exposure assessment.

The presence of 3-monochloropropane-1,2-diol (3-MCPD) esters and 2-MCPD esters in infant formulas have raised a number of food safety concerns. Here, a dietary exposure assessment was conducted for 3-and 2-MCPD esters in infant formulas available for consumption in Chinese infant and toddlers aged 0-3 years old. This work presents the occurrence data for 3-and 2-MCPD ester in 874 infant formulas purchased in China between 2015 and 2017. The concentrations of 3-MCPD esters ranged from ND to 1.469 mg/kg, with concentrations of 2-MCPD esters ranging from ND to 0.218 mg/kg. The LODs of 3-and 2-MCPD esters were 0.027-0.074 mg/kg. The mean exposures of infants and toddlers to 3-MCPD esters from formulas were lower than the tolerable daily intake (TDI, 2 µg/kg bw/day, established by EFSA), while high exposures (95th percentile) to 3-MCPD esters ranged from 0.907 to 2.520 µg/kg bw/day. On the whole, the health risk of Chinese infant and toddlers exposed to 3-MCPD esters was low, but the health risk of some infants aged 0-6 months with high formula consumption (95th percentile) raises some concern.

The China National Foodborne Pathogen Surveillance System: Twenty Years of Experience and Achievements.

National foodborne pathogen surveillance is a system that collects data regarding food contamination by pathogenic bacteria, viruses, parasites, and other harmful microbial factors. The surveillance data are used to understand the potential microbial risks in different categories of food and to provide science-based data for risk assessment and development of reference standards in the form of maximum limits. This review introduces stepwise expansion of the foodborne pathogen surveillance in China, relevant policies, function and duties of different organizations and institutions, surveillance plans, and quality control. Achievements of the surveillance system and future challenges are also presented.

Whole-Genome Sequencing and Machine Learning Analysis of Staphylococcus aureus from Multiple Heterogeneous Sources in China Reveals Common Genetic Traits of Antimicrobial Resistance.

Staphylococcus aureus is a worldwide leading cause of numerous diseases ranging from food-poisoning to lethal infections. Methicillin-resistant S. aureus (MRSA) has been found capable of acquiring resistance to most antimicrobials. MRSA is ubiquitous and diverse even in terms of antimicrobial resistance (AMR) profiles, posing a challenge for treatment. Here, we present a comprehensive study of S. aureus in China, addressing epidemiology, phylogenetic reconstruction, genomic characterization, and identification of AMR profiles. The study analyzes 673 S. aureus isolates from food as well as from hospitalized and healthy individuals. The isolates have been collected over a 9-year period, between 2010 and 2018, from 27 provinces across China. By whole-genome sequencing, Bayesian divergence analysis, and supervised machine learning, we reconstructed the phylogeny of the isolates and compared them to references from other countries. We identified 72 sequence types (STs), of which, 29 were novel. We found 81 MRSA lineages by multilocus sequence type (MLST), spa, staphylococcal cassette chromosome mec element (SCCmec), and Panton-Valentine leukocidin (PVL) typing. In addition, novel variants of SCCmec type IV hosting extra metal and antimicrobial resistance genes, as well as a new SCCmec type, were found. New Bayesian dating of the split times of major clades showed that ST9, ST59, and ST239 in China and European countries fell in different branches, whereas this pattern was not observed for the ST398 clone. On the contrary, the clonal transmission of ST398 was more intermixed in regard to geographic origin. Finally, we identified genetic determinants of resistance to 10 antimicrobials, discriminating drug-resistant bacteria from susceptible strains in the cohort. Our results reveal the emergence of Chinese MRSA lineages enriched of AMR determinants that share similar genetic traits of antimicrobial resistance across human and food, hinting at a complex scenario of evolving transmission routes. IMPORTANCE Little information is available on the epidemiology and characterization of Staphylococcus aureus in China. The role of food is a cause of major concern: staphylococcal foodborne diseases affect thousands every year, and the presence of resistant Staphylococcus strains on raw retail meat products is well documented. We studied a large heterogeneous data set of S. aureus isolates from many provinces of China, isolated from food as well as from individuals. Our large whole-genome collection represents a unique catalogue that can be easily meta-analyzed and integrated with further studies and adds to the library of S. aureus sequences in the public domain in a currently underrepresented geographical region. The new Bayesian dating of the split times of major drug-resistant enriched clones is relevant in showing that Chinese and European methicillin-resistant S. aureus (MRSA) have evolved differently. Our machine learning approach, across a large number of antibiotics, shows novel determinants underlying resistance and reveals frequent resistant traits in specific clonal complexes, highlighting the importance of particular clonal complexes in China. Our findings substantially expand what is known of the evolution and genetic determinants of resistance in food-associated S. aureus in China and add crucial information for whole-genome sequencing (WGS)-based surveillance of S. aureus.

Spatial analysis of dietary exposure of aflatoxins in peanuts and peanut oil in different areas of China.

Peanuts in China are heavily contaminated with aflatoxin, which pose a threaten to human health. To compare the dietary exposure risk of aflatoxins (AFT) in peanuts and peanut oil in different areas of China, the spatial distribution of AFT contamination levels in peanuts and peanut oil from different areas was analyzed. The dietary exposure was calculated by simple distributed risk assessment method before characterizing the health risk using both the margin of exposure (MOE) approach proposed by the European Food Safety Authority (EFSA) and the quantitative liver cancer risk approach proposed by the Joint Food and Agricultural Organization/World Health Organization (FAO/WHO) Expert Committee on Food Additives (JECFA). The results showed that the AFT content in peanuts and peanut oil was high with agglomeration in several provinces of East and South China under a subtropical temperate monsoon climate, and the AFT contamination in peanut oil was more substantial than peanuts. On average, the estimated dietary exposure to AFT from the total of peanuts and peanut oil for Chinese general population ranged from 1.776 to 1.940 ng/kg bw/day (LB-UB), from which the MOE values of 88-96 (UB-LB) and liver cancer risk of 0.055-0.060 cases/100,000 persons/year (LB-UB) were calculated. As for different areas in China, the mean AFT exposure ranged between 0.000 and 17.270 ng/kg bw/day. Moreover, the corresponding health risk was estimated at 10-868759 MOE values and 0.000-0.851 liver cancer cases/100,000 persons/year. Guangdong, Fujian and Jiangxi provinces were at a higher risk rank. The liver cancer risk of AFT exposure from peanuts and peanut oil was far below all-cause liver cancer incidence (18.0 cases/100,000 persons/year) in China, but several areas with relatively high risk should be of concern. Compared with other age groups, children aged 2-6 years should be paid more attention because they have the highest AFT exposure level.

[Chloropropanol and glycidyl esters content in edible vegetable oils in China in 2015-2017].

OBJECTIVE: To investigate the occurrence data for fatty acid esters of chloropropanol and glycidyl in edible vegetable oils purchased in China. METHODS: The 1309 samples of edible vegetable oil were collected and the data of chloropropanol and glycidyl were detected by the gas chromatography-mass spectrometry from 2015 to 2017. RESULTS: The detection rate of 3-monochloropropanediol esters in vegetable oils was 81. 83% with the mean level of 1. 21 mg/kg. The mean content of tea-seed oil was significantly higher than that of other varieties, followed by peanut oil(1. 36 mg/kg), rapeseed oil(1. 12 mg/kg). The sunflower seed oil has the lowest mean content(0. 54 mg/kg). The detection rate of 2-monochloropropanediol esters in vegetable oils was 82. 84% with the mean level of 0. 39 mg/kg. The content of peanut oil was significantly higher than that of other varieties, followed by blended oil(0. 30 mg/kg) and soybean oil(0. 25 mg/kg). There was no significant difference with rapeseed oil(0. 66 mg/kg). The exceeding rate of glycidyl ester was 19. 90% with the mean level of 0. 68 mg/kg. The average content of glycidyl ester in blended oil(0. 78 mg/kg) was significantly higher than that in peanut oil(0. 54 mg/kg). There was no significant difference among other varieties. CONCLUSION: The pollution of chloropropanol esters is common in edible vegetable oils in China. The contamination is different in kinds of edible oils.

Development and application of a comparative risk assessment method for ranking chemical hazards in food.

The aim of this study was to develop a comparative risk assessment method to prioritise the public health risks posed by chemical hazards in food. Through a literature review, and in light of expert opinions, a bottom-up, semi-quantitative scoring method was applied to screen the ranking metrics and assign a score. In addition, a metrics system and a ranking model were constructed. The fuzzy comprehensive analysis model was used to assess typical chemical hazards in a specific food, as well as to rank risks in many foods. Data were collected from the National Food Surveillance System in China, the Food Consumption of Chinese Residents Database, government reports, public websites and databases of authoritative organisations. The comparative risk assessment method was applied to case studies on ranking chemical hazards in different kinds of food. According to application testing, the method truly reflects the overall risk and ranking of chemical hazards in food.

Dietary exposure of general Chinese population to fatty acid esters of 3-monochloropropane-1, 2-diol (3-MCPD) from edible oils and oil-containing foods.

Edible oils and oil-containing foods have been regarded as the main source of 3-monochloropropane-1, 2-diol (3-MCPD) esters. A total of 3,847 individual food samples were collected in China to carry out 3-MCPD fatty acid esters analysis. The samples comprising edible oils, fried foods and bakery foods from 31 Chinese provinces, municipalities and autonomous regions were obtained from the national food contaminant information system during 2015-2017. The dietary exposure and potential risks associated with the consumption of 3-MPCD esters from edible oils and oil-containing foods were estimated using a semi-probabilistic assessment model. Concentrations of 3-MCPD fatty acid esters in food samples were detected by gas chromatography-mass spectrometry (GC-MS). The mean levels of 3-MCPD fatty acid esters in edible oils, fried foods and bakery foods were 0.862, 0.249 and 0.145 mg/kg, respectively. The range of mean dietary intakes of 3-MCPD esters in different subpopulation groups (classified by gender and age) was from 0.586 to 1.539 µg/kg bw/day, which were all lower than 2 µg/kg bw/day - the tolerable daily intake (TDI) established by the European Food Safety Authority (EFSA). The range of dietary intake of 3-MCPD esters in high consumers (95th percentile) in each group was from 1.511 to 4.027 µg/kg bw/day, which accounted for 75.6% to 201.4% of the TDI. The 3-MCPD esters exposure level of 3.5% of the total Chinese population exceeded the TDI. The findings indicate that the potential health risks caused by dietary 3-MCPD esters from edible oils and oil-containing foods were of low concern for most of the Chinese population. However, the exposure risk of the consumers with excessive edible oil consumption calls for attention.

Risk assessment and spatial analysis of deoxynivalenol exposure in Chinese population.

Deoxynivalenol (DON) is one of the most commonly found mycotoxins across the world, and it mainly contaminates staple food crops. This study aims to evaluate the dietary exposure of DON and to provide a geographical profile of DON exposure in China. The concentrations of DON and its acetylated derivatives in 15,004 cereal samples (10,192 wheat flour, 1750 maize meal, 892 oat flakes, and 2170 polished rice) were collected from 30 provinces, autonomous regions, or municipalities across China during 2010-2017, through a national food safety risk surveillance system. The consumption data for cereals were obtained from China National Nutrition and Health Survey in 2002, and 67,923 respondents from the same 30 regions were included in the analysis. Among all the cereals considered, the concentration was the highest in wheat flour, with the mean concentration of 250.8 µg/kg. Applying a worst-case scenario, some individuals were possibly at risk, but the probability of acute effects was low. The mean and median exposure for the entire population was 0.61 and 0.36 µg/kg bw/day, respectively, below the (PM) TDI, indicating an acceptable overall health risk in Chinese population. Wheat contributed to 86% of the total DON exposure. Significant discrepancy was observed between the exposure and the contamination of DON. The high-exposure cluster area was in northern China, whilst the most seriously contaminated regions were all located in the southeast, which formed a seriously contaminated area.

[Sodium nitrite in cooked meat during 2012-2015 in China].

OBJECTIVE: To investigate the contamination levels of sodium nitrite in cooked meat from parts of China during 2012-2015. METHODS: The samples were detected in accordance with the national standardization method, and were determined by the GB 2760-2014. RESULTS: The average sodium nitrite in cooked meat was 9. 7 mg/kg with the content range from not detected to 85. 3 mg/kg, and its exceeding standard rate was 4. 8%(922/19360). The average sodium nitrite in visceral products was 16. 6 mg/kg, which was the highest in all kinds of cooked meat. The exceeding standard rate of farmers' market was significantly higher than that of other sampling links. The exceeding standard rate of bulk samples was 5. 8 times of the stereotyped packaging. The exceeding standard rate was downgrade year by year. The main problem was the bulk sauce-stewed meat product in the farm product market which the exceeding standard rate was 9. 5%(327/3461). CONCLUSION: A four-year successive observation shows that the quality of cooked meat with sodium nitrite is improved. But the problem is focused on the bulk. The risk of nitrite in cooked meat is lower.

Prevalence and antimicrobial susceptibility of Salmonella in the commercial eggs in China.

Salmonellosis is a challenge to public health globally, and many infections have been principally linked to the consumption of contaminated eggs. The objective of this study is to estimate the prevalence of Salmonella in commercial eggs and susceptibilities of isolates to a panel of 14 antimicrobial agents which were determined according to Clinical and Laboratory Standards Institute (CSLI) procedures. A total of 33,288 eggs (5548 pooled samples of six eggs) were collected across China in 2016 and the prevalence of Salmonella was 0.5% (27/5548). The most predominant serotype was S. enteritidis. No significant differences were observed on the basis of the egg component tested, shell condition, packaging type, sampling site or sampling season. However, there were significant differences among provincial regions. About 64.3% (n = 18) isolates were resistant to nalidixic acid, followed by ampicillin (39.3%) and ampicillin/sulbactam (39.3%). All isolates were susceptible to ceftazidime, cefalothin, ciprofloxacin, cefepime, cefotaxime, imipenem and meropenem. Three Salmonella isolates exhibited resistance to multiple antibiotics. This study provides valuable baseline data of the occurrence of Salmonella in eggs, which will be used for risk assessments of possible human foodborne infections associated with the consumption of contaminated eggs.

[Application of isotope dilution-liquid chromatography-tandem mass spectrometry in the preparation and certification of reference material of tenuazonic acid and tentoxin in wheat flour].

A method for the preparation and certification of the reference material of tenuazonic acid (TeA) and tentoxin (TEN) in wheat flour was developed. This method provided methodological references to develop of standard material for analyzing alternaria toxins in grains. The wheat flour reference materials were based on wheat grains which were naturally contaminated with alternaria toxins. The certified values for TeA and TEN were determined by isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) and cooperated certification of multiple laboratories. The wheat flour reference materials were stored at room temperature, protected from light and characterized by low uncertainty. The wheat flour reference materials are currently the only wheat flour reference materials that naturally contaminate TeA and TEN, and it can be used in the evaluating related analytical methods involved in food safety risk monitoring, product quality testing and quality control measurements.

Recent mixing of Vibrio parahaemolyticus populations.

Humans have profoundly affected the ocean environment but little is known about anthropogenic effects on the distribution of microbes. Vibrio parahaemolyticus is found in warm coastal waters and causes gastroenteritis in humans and economically significant disease in shrimps. Based on data from 1103 genomes of environmental and clinical isolates, we show that V. parahaemolyticus is divided into four diverse populations, VppUS1, VppUS2, VppX and VppAsia. The first two are largely restricted to the US and Northern Europe, while the others are found worldwide, with VppAsia making up the great majority of isolates in the seas around Asia. Patterns of diversity within and between the populations are consistent with them having arisen by progressive divergence via genetic drift during geographical isolation. However, we find that there is substantial overlap in their current distribution. These observations can be reconciled without requiring genetic barriers to exchange between populations if long-range dispersal has increased dramatically in the recent past. We found that VppAsia isolates from the US have an average of 1.01% more shared ancestry with VppUS1 and VppUS2 isolates than VppAsia isolates from Asia itself. Based on time calibrated trees of divergence within epidemic lineages, we estimate that recombination affects about 0.017% of the genome per year, implying that the genetic mixture has taken place within the last few decades. These results suggest that human activity, such as shipping, aquatic products trade and increased human migration between continents, are responsible for the change of distribution pattern of this species.