Virulence, resistance, and genetic diversity of Vibrio parahaemolyticus recovered from commonly consumed aquatic products in Shanghai, China

Antibiotic susceptibility of Vibrio parahaemolyticus isolated from prawns and oysters marketed in Zhanjiang, China

To evaluate the antibiotic susceptibility of Vibrio parahaemolyticus from prawns and oysters marketed in Zhanjiang, Guangdong, China. 84 strains of V. parahaemolyticus were isolated from prawns and oysters sampled from 9 major markets. The results showed that 84 V. parahaemolyticus strains had the highest rate of antibiotic resistance to oxytetracycline (69.05 %, 58/84) and the lowest rate of antibiotic resistance to enrofloxacin (1.19 %, 1/84), ciprofloxacin (4.76 %, 4/84) and norfloxacin (7.14 %, 6/84) in quinolone. Meanwhile, 96.42 % of the strains showed multiple antibiotic resistance (MAR). PCR results showed that the resistance phenotype was closely related to the antibiotic resistance genes and efflux pump genes (p < 0.01), and the efflux pump gene was the key causing MAR. The combination of antibiotics significantly eliminated multidrug resistance. In addition, efflux pump inhibitors also reduce MAR. This study may provide information on antibiotic susceptibility, antibiotic resistance and strategies for the control of V. parahaemolyticus.

Comprehensive analysis of predominant pathogenic bacteria and viruses in seafood products

Given the growing global demand for seafood, it is imperative to conduct a comprehensive study on the prevalence and persistence patterns of pathogenic bacteria and viruses associated with specific seafood varieties. This assessment thoroughly examines the safety of seafood products, considering the diverse processing methods employed in the industry. The importance of understanding the behavior of foodborne pathogens, such as Salmonella typhimurium, Vibrio parahaemolyticus, Clostridium botulinum, Listeria monocytogenes, human norovirus, and hepatitis A virus, is emphasized by recent cases of gastroenteritis outbreaks linked to contaminated seafood. This analysis examines outbreaks linked to seafood in the United States and globally, with a particular emphasis on the health concerns posed by pathogenic bacteria and viruses to consumers. Ensuring the safety of seafood is crucial since it directly relates to consumer preferences on sustainability, food safety, provenance, and availability. The review focuses on assessing the frequency, growth, and durability of infections that arise during the processing of seafood. It utilizes next-generation sequencing to identify the bacteria responsible for these illnesses. Additionally, it analyzes methods for preventing and intervening of infections while also considering the forthcoming challenges in ensuring the microbiological safety of seafood products. This evaluation emphasizes the significance of the seafood processing industry in promptly responding to evolving consumer preferences by offering current information on seafood hazards and future consumption patterns. To ensure the continuous safety and sustainable future of seafood products, it is crucial to identify and address possible threats.

Genomic and Transcriptomic Analyses Reveal Multiple Strategies for Vibrio parahaemolyticus to Tolerate Sub-Lethal Concentrations of Three Antibiotics

Vibrio parahaemolyticus can cause acute gastroenteritis, wound infections, and septicemia in humans. The overuse of antibiotics in aquaculture may lead to a high incidence of the multidrug-resistant (MDR) pathogen. Nevertheless, the genome evolution of V. parahaemolyticus in aquatic animals and the mechanism of its antibiotic tolerance remain to be further deciphered. Here, we investigated the molecular basis of the antibiotic tolerance of V. parahaemolyticus isolates (n = 3) originated from shellfish and crustaceans using comparative genomic and transcriptomic analyses. The genome sequences of the V. parahaemolyticus isolates were determined (5.0-5.3 Mb), and they contained 4709-5610 predicted protein-encoding genes, of which 823-1099 genes were of unknown functions. Comparative genomic analyses revealed a number of mobile genetic elements (MGEs, n = 69), antibiotic resistance-related genes (n = 7-9), and heavy metal tolerance-related genes (n = 2-4). The V. parahaemolyticus isolates were resistant to sub-lethal concentrations (sub-LCs) of ampicillin (AMP, 512 μg/mL), kanamycin (KAN, 64 μg/mL), and streptomycin (STR, 16 μg/mL) (p < 0.05). Comparative transcriptomic analyses revealed that there were significantly altered metabolic pathways elicited by the sub-LCs of the antibiotics (p < 0.05), suggesting the existence of multiple strategies for antibiotic tolerance in V. parahaemolyticus. The results of this study enriched the V. parahaemolyticus genome database and should be useful for controlling the MDR pathogen worldwide.

Meta-Analysis and Systematic Review of Phenotypic and Genotypic Antimicrobial Resistance and Virulence Factors in Vibrio parahaemolyticus Isolated from Shrimp

This systematic review and meta-analysis investigates the prevalence of Vibrio parahaemolyticus, its virulence factors, antimicrobial resistance (AMR), and its resistance determinants in shrimp. This study was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, to identify and select relevant peer-reviewed articles published between January 2020 and December 2022. The search strategy involved multiple online databases, including Google Scholar, PubMed, ScienceDirect, and Scopus. The inclusion criteria focused on studies that examined V. parahaemolyticus prevalence, virulence factors, and AMR in shrimp from farms to retail outlets. A total of 32 studies were analyzed, revealing a pooled estimate prevalence of V. parahaemolyticus in shrimp at 46.0%, with significant heterogeneity observed. Subgroup analysis highlighted varying prevalence rates across continents, emphasizing the need for further investigation. Virulence factor analysis identified thermostable direct hemolysin (tdh) and tdh-related hemolysin (trh) as the most common. Phenotypic AMR analysis indicated notable resistance to glycopeptides, nitrofurans, and beta-lactams. However, the correlation between antimicrobial usage in shrimp farming and observed resistance patterns was inconclusive. Funnel plots suggested potential publication bias, indicating a need for cautious interpretation of findings. This study underscores the urgency of coordinated efforts to address AMR in V. parahaemolyticus to safeguard public health and to ensure sustainable aquaculture practices.

Antibacterial efficiency of the curcumin-mediated photodynamic inactivation coupled with L-arginine against Vibrio parahaemolyticus and its application on shrimp

The aim of this study was to investigate the antibacterial potency of a novel photodynamic inactivation (PDI) system with an enhanced bactericidal ability against Vibrio parahaemolyticus in vitro and in vivo. The synergistically bactericidal action of curcumin (Cur) and L-arginine (L-Arg) was firstly investigated, and then a novel curcumin-mediated PDI coupled with L-Arg was developed. Meanwhile, its potent inactivation mechanism against V. parahaemolyticus and preservation effects on shrimp were explored. Results showed that L-Arg disrupted the cell membrane by binding to membrane phospholipids and disrupting iron homeostasis, which helped curcumin to damage DNA and interrupt protein synthesis. Once irradiated by blue LED, the curcumin-mediated PDI produced the reactive oxygen species (ROS) which reacted with L-Arg to generate NO, and the NO was converted to reactive nitrogen species (RNS) with a strong bactericidal ability by consuming ROS. On this basis, the curcumin-mediated PDI coupled with L-Arg potently killed >8.0 Log CFU/mL with 8 μM curcumin, 0.5 mg/mL L-Arg and 1.2 J/cm2 irradiation. Meanwhile, this PDI also effectively inhibited the colour and pH changes, lipids oxidation and protein degradation of shrimp. Therefore, this study proposes a new potent PDI system to control microbial contamination in the food industry.

Biological Function of Prophage-Related Gene Cluster ΔVpaChn25_RS25055~ΔVpaChn25_0714 of Vibrio parahaemolyticus CHN25

Vibrio parahaemolyticus is the primary foodborne pathogen known to cause gastrointestinal infections in humans. Nevertheless, the molecular mechanisms of V. parahaemolyticus pathogenicity are not fully understood. Prophages carry virulence and antibiotic resistance genes commonly found in Vibrio populations, and they facilitate the spread of virulence and the emergence of pathogenic Vibrio strains. In this study, we characterized three such genes, VpaChn25_0713, VpaChn25_0714, and VpaChn25_RS25055, within the largest prophage gene cluster in V. parahaemolyticus CHN25. The deletion mutants ΔVpaChn25_RS25055, ΔVpaChn25_0713, ΔVpaChn25_0714, and ΔVpaChn25_RS25055-0713-0714 were derived with homologous recombination, and the complementary mutants ΔVpaChn25_0713-com, ΔVpaChn25_0714-com, ΔVpaChn25_RS25055-com, ΔVpaChn25_RS25055-0713-0714-com were also constructed. In the absence of the VpaChn25_RS25055, VpaChn25_0713, VpaChn25_0714, and VpaChn25_RS25055-0713-0714 genes, the mutants showed significant reductions in low-temperature survivability and biofilm formation (p < 0.001). The ΔVpaChn25_0713, ΔVpaChn25_RS25055, and ΔVpaChn25_RS25055-0713-0714 mutants were also significantly defective in swimming motility (p < 0.001). In the Caco-2 model, the above four mutants attenuated the cytotoxic effects of V. parahaemolyticus CHN25 on human intestinal epithelial cells (p < 0.01), especially the ΔVpaChn25_RS25055 and ΔVpaChn25_RS25055-0713-0714 mutants. Transcriptomic analysis showed that 15, 14, 8, and 11 metabolic pathways were changed in the ΔVpaChn25_RS25055, ΔVpaChn25_0713, ΔVpaChn25_0714, and ΔVpaChn25_RS25055-0713-0714 mutants, respectively. We labeled the VpaChn25_RS25055 gene with superfolder green fluorescent protein (sfGFP) and found it localized at both poles of the bacteria cell. In addition, we analyzed the evolutionary origins of the above genes. In summary, the prophage genes VpaChn25_0713, VpaChn25_0714, and VpaChn25_RS25055 enhance V. parahaemolyticus CHN25's survival in the environment and host. Our work improves the comprehension of the synergy between prophage-associated genes and the evolutionary process of V. parahaemolyticus.

Prevalence, virulence characteristics, and antimicrobial resistance of Vibrio parahaemolyticus isolates from raw seafood in a province in Northern Thailand

Vibrio parahaemolyticus (V. parahaemolyticus) is commonly found in seawater and seafood products, but evidence is limited of its presence in seafood marketed in locations very distant from coastal sources. This study determined the prevalence and characterization of V. parahaemolyticus in seafood from markets in landlocked Phayao province, Northern Thailand. Among 120 samples, 26 (21.7%) were positive for V. parahaemolyticus, being highest in shrimp (43.3%), followed by shellfish (36.7%), and squid (6.7%), but was not found in fish. V. parahaemolyticus comprised 33 isolates that were non-pathogenic and non-pandemic. Almost all isolates from shrimp and shellfish samples were positive for T3SS1. Only five isolates (15.2%) showed two antimicrobial resistance patterns, namely, kanamycin-streptomycin (1) carrying sul2 and ampicillin-kanamycin-streptomycin (4) that carried tetA (2), tetA-sul2 (1), as well as one negative. Antimicrobial susceptible V. parahaemolyticus isolates possessing tetA (67.9%) and sul2 (3.5%) were also found. Six isolates positive for integron class 1 and/or class 2 were detected in 4 antimicrobial susceptible and 2 resistant isolates. While pathogenic V. parahaemolyticus was not detected, contamination of antimicrobial resistance V. parahaemolyticus in seafood in locations distant from coastal areas requires ongoing monitoring to improve food safety in the seafood supply chain.

Field Efficacy of a Feed-Based Inactivated Vaccine against Vibriosis in Cage-Cultured Asian Seabass, Lates calcarifer, in Malaysia

Vibrio spp. are important aquaculture pathogens that cause vibriosis, affecting large numbers of marine fish species. This study determines the field efficacy of a feed-based inactivated vaccine against vibriosis in cage-cultured Asian seabass. A total of 4800 Asian seabass, kept in a field environment, were separated equally into two groups (vaccinated and non-vaccinated) in duplicate. Fish of Group 1 were orally administered the feed-based vaccine on weeks 0 (prime vaccination), 2 (booster), and 6 (second booster) at 4% body weight, while the non-vaccinated fish of Group 2 were fed with a commercial formulated pellet without the vaccine. Fish gut, mucus, and serum were collected, the length and weight of the fish were noted, while the mortality was recorded at 2-week intervals for a period of 16 weeks. The non-specific lysozyme activities were significantly (p < 0.05) higher in the fish of Group 1 than the non-vaccinated fish of Group 2. Similarly, the specific IgM antibody levels in serum and mucus were significantly (p < 0.05) higher in Group 1 than in Group 2, as seen in the second week, with the highest level 8 weeks after primary immunization. At week 16, the growth performance was significantly (p < 0.05) better in Group 1 and showed lower bacterial isolation in the gut than Group 2. Despite the statistical insignificance (p > 0.05), the survival rate was slightly higher in Group 1 (71.3%) than Group 2 (67.7%). This study revealed that feed-based vaccination improves growth performance, stimulates innate and adaptive immune responses, and increases protection of cultured Asian seabass, L. calcarifer, against vibriosis.

Genomic and Transcriptomic Analysis Reveal Multiple Strategies for the Cadmium Tolerance in Vibrio parahaemolyticus N10-18 Isolated from Aquatic Animal Ostrea gigas Thunberg

The waterborne Vibrio parahaemolyticus can cause acute gastroenteritis, wound infection, and septicemia in humans. Pollution of heavy metals in aquatic environments is proposed to link high incidence of the multidrug-resistant (MDR) pathogen. Nevertheless, the genome evolution and heavy metal tolerance mechanism of V. parahaemolyticus in aquatic animals remain to be largely unveiled. Here, we overcome the limitation by characterizing an MDR V. parahaemolyticus N10-18 isolate with high cadmium (Cd) tolerance using genomic and transcriptomic techniques. The draft genome sequence (4,910,080 bp) of V. parahaemolyticus N10-18 recovered from Ostrea gigas Thunberg was determined, and 722 of 4653 predicted genes had unknown function. Comparative genomic analysis revealed mobile genetic elements (n = 11) and heavy metal and antibiotic-resistance genes (n = 38 and 7). The bacterium significantly changed cell membrane structure to resist the Cd2+ (50 μg/mL) stress (p < 0.05). Comparative transcriptomic analysis revealed seven significantly altered metabolic pathways elicited by the stress. The zinc/Cd/mercury/lead transportation and efflux and the zinc ATP-binding cassette (ABC) transportation were greatly enhanced; metal and iron ABC transportation and thiamine metabolism were also up-regulated; conversely, propanoate metabolism and ribose and maltose ABC transportation were inhibited (p < 0.05). The results of this study demonstrate multiple strategies for the Cd tolerance in V. parahaemolyticus.

Analysis of Pathogenic Vibrio Contamination in Marine Products along China Based on Fluorescence Quantitative PCR

At present, aquatic product pollution has become the main root of frequent food safety problems and causes economic losses. Vibrio is one of the main pathogens causing foodborne diseases. In this study, in order to uncover the pollution status of pathogenic Vibrio in the marine products of China, a total of 646 aquatic products were collected and analyzed from 10 coastal cities in China. Five kinds of pathogenic Vibrio were separated from these samples and monitored to explore the relationship between pollution and the pathogen. Real-time fluorescence quantitative PCR was adopted to detect foodborne Vibrio quantitatively in marine aquatic products. Aquatic pathogenic Vibrio was collected in different regions, different types of aquatic products, and different sampling places, and the difference in detection rate was statistically significant through statistical analysis. This study made a frame for the pollution degree of pathogenic Vibrio in marine products in China and established the dominant flora of pathogenic Vibrio in different types of aquatic products, which provides a theoretical basis for food safety supervision departments to take targeted prevention and control measures.

Characterization of Vibrio parahaemolyticus isolated from stool specimens of diarrhea patients in Nantong, Jiangsu, China during 2018–2020

Vibrio parahaemolyticus is the leading cause of acute seafood-associated gastroenteritis worldwide. The aim of this study was to investigate the presence of virulence genes, biofilm formation, motor capacities and antimicrobial resistance profile of V. parahaemolyticus isolates isolated from clinical samples in Nantong during 2018–2020. Sixty-six V. parahaemolyticus strains isolated from stool specimens of diarrheal patients were examined. The PCR results showed that there were two tdh+trh+ isolates, four tdh-trh- isolates and sixty tdh+trh- isolates, accounting for 3.0%, 6.1% and 90.9%, respectively. All the tdh carrying isolates manifested the positive reactions for the Kanagawa phenomenon (KP) test. Most of the isolates harbored at least one of the specific DNA markers of ‘pandemic group’ strains, suggesting that the dominant isolates of V. parahaemolyticus in Nantong might belong to the new O3: K6 or its serovariants. All tdh+ isolates possessed the Vp-PAI genes, but no tdh-trh- isolates carried the T3SS2 genes. All isolates were biofilm producers and had relatively strong motor capacities. In addition, the V. parahaemolyticus isolates were resistant to ampicillin (98.5%), cefuroxime (75.6%), cefepime (66.7%), piperacillin (59.1%) and ampicillin/sulbactam (50.0%), but sensitive to ciprofloxacin (100.0%), levofloxacin (100.0%), trimethoprim-sulfamethoxazole (98.5%), gentamicin (98.5%), amikacin (97%), meropenem (71.2%), and ceftazidime (56.1%). Multidrug-resistant isolates in clinical might be related to the inappropriate use of antimicrobials in aquaculture.

Diverse Aquatic Animal Matrices Play a Key Role in Survival and Potential Virulence of Non-O1/O139 Vibrio cholerae Isolates

Vibrio cholerae can cause pandemic cholera in humans. The waterborne bacterium is frequently isolated from aquatic products worldwide. However, current literature on the impact of aquatic product matrices on the survival and pathogenicity of cholerae is rare. In this study, the growth of eleven non-O1/0O139 V. cholerae isolates recovered from eight species of commonly consumed fish and shellfish was for the first time determined in the eight aquatic animal matrices, most of which highly increased the bacterial biomass when compared with routine trypsin soybean broth (TSB) medium. Secretomes of the V. cholerae isolates (draft genome size: 3,852,021–4,144,013 bp) were determined using two-dimensional gel electrophoresis (2DE-GE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques. Comparative secretomic analyses revealed 74 differential extracellular proteins, including several virulence- and resistance-associated proteins secreted by the V. cholerae isolates when grown in the eight matrices. Meanwhile, a total of 8,119 intracellular proteins were identified, including 83 virulence- and 8 resistance-associated proteins, of which 61 virulence-associated proteins were absent from proteomes of these isolates when grown in the TSB medium. Additionally, comparative genomic and proteomic analyses also revealed several strain-specific proteins with unknown functions in the V. cholerae isolates. Taken, the results in this study demonstrate that distinct secretomes and proteomes induced by the aquatic animal matrices facilitate V. cholerae resistance in the edible aquatic animals and enhance the pathogenicity of the leading waterborne pathogen worldwide.

Prophage-encoded gene VpaChn25_0734 amplifies ecological persistence of Vibrio parahaemolyticus CHN25

Vibrio parahaemolyticus is a waterborne pathogen that can cause acute gastroenteritis, wound infection, and septicemia in humans. The molecular basis of its pathogenicity is not yet fully understood. Phages are found most abundantly in aquatic environments and play a critical role in horizontal gene transfer. Nevertheless, current literature on biological roles of prophage-encoded genes remaining in V. parahaemolyticus is rare. In this study, we characterized one such gene VpaChn25_0734 (543-bp) in V. parahaemolyticus CHN25 genome. A deletion mutant ΔVpaChn25_0734 (543-bp) was obtained by homologous recombination, and a revertant ΔVpaChn25_0734-com (543-bp) was also constructed. The ΔVpaChn25_0734 (543-bp) mutant was defective in growth and swimming mobility particularly at lower temperatures and/or pH 7.0–8.5. Cell surface hydrophobicity and biofilm formation were significantly decreased in the ΔVpaChn25_0734 (543-bp) mutant (p < 0.05). Based on the in vitro Caco-2 cell model, the deletion of VpaChn25_0734 (543-bp) gene significantly reduced the cytotoxicity of V. parahaemolyticus CHN25 to human intestinal epithelial cells (p < 0.05). Comparative secretomic and transcriptomic analyses revealed a slightly increased extracellular proteins, and thirteen significantly changed metabolic pathways in the ΔVpaChn25_0734 (543-bp) mutant, showing down-regulated carbon source transport and utilization, biofilm formation, and type II secretion system (p < 0.05), consistent with the observed defective phenotypes. Taken, the prophage-encoded gene VpaChn25_0734 (543-bp) enhanced V. parahaemolyticus CHN25 fitness for survival in the environment and the host. The results in this study facilitate better understanding of pathogenesis and genome evolution of V. parahaemolyticus, the leading sea foodborne pathogen worldwide.

Qualitative and Quantitative Detection of Potentially Virulent Vibrio parahaemolyticus in Drinking Water and Commonly Consumed Aquatic Products by Loop-Mediated Isothermal Amplification

Vibrio parahaemolyticus can cause acute gastroenteritis, wound infection, and septicemia in humans. In this study, a simple, specific, and user-friendly diagnostic tool was developed for the first time for the qualitative and quantitative detection of toxins and infection process-associated genes opaR, vpadF, tlh, and ureC in V. parahaemolyticus using the loop-mediated isothermal amplification (LAMP) technique. Three pairs of specific inner, outer, and loop primers were designed for targeting each of these genes, and the results showed no cross-reaction with the other common Vibrios and non-Vibrios pathogenic bacteria. Positive results in the one-step LAMP reaction (at 65 °C for 45 min) were identified by a change to light green and the emission of bright green fluorescence under visible light and UV light (302 nm), respectively. The lowest limit of detection (LOD) for the target genes ranged from 1.46 × 10-5 to 1.85 × 10-3 ng/reaction (25 µL) for the genomic DNA, and from 1.03 × 10-2 to 1.73 × 100 CFU/reaction (25 µL) for the cell culture of V. parahaemolyticus. The usefulness of the developed method was demonstrated by the fact that the bacterium could be detected in water from various sources and commonly consumed aquatic product samples. The presence of opaR and tlh genes in the Parabramis pekinensis intestine indicated a risk of potentially virulent V. parahaemolyticus in the fish.

Increased incidence and antimicrobial resistance among Vibrio parahaemolyticus in shellfishes from major fish markets in Cochin, South India: Seafood risk assessment

India remains as a top supplier of value-added seafoods to the global markets. Cochin is one of the leading fishing ports in India contributing to country’s major seafood export. As part of risk assessment, we analyzed the prevalence of multi-drug resistant Vibrio parahaemolyticus; seafood borne gastroenteritis-causing pathogen, in shellfishes collected from major fish markets in Cochin. This bacterial species was initially isolated on Thiosulfate-citrate-bile salts-sucrose agar and HiCrome™ Vibrio agar, further confirmed by detection of V. parahaemolyticus species-specific toxR gene and by 16S r RNA sequencing. A total of 113 confirmed V. parahaemolyticus were recovered. Almost all the strains exhibited resistance towards three or more antibiotics (multiple-drug resistant) and harbored virulence related exoenzymes especially hemolysin (Kanagawa phenomenon); which is indeed a matter of concern. The multiple antibiotic resistance (MAR) index of the isolates ranged from 0.21 to 0.57. Furthermore, our results also indicate a substantial increase in the incidence of the pathogen in seafood from the area compared to previous years. This may pose a risk to the local and international consumers of the seafood. Practicing complete hygiene and adequate cooking is strongly recommended. Regular monitoring of aquaculture areas and fish markets is urged to reduce dissemination of pathogenic V. parahaemolyticus in seafood and to prevent fatal cases of human infection induced by this species in the country.

Antimicrobial Drug-resistance Profile of Vibrio Parahaemolyticus isolated from Japanese Horse Mackerel (Trachurus Japonicus)

This study aimed at investigating antimicrobial resistance (AMR) profile of Vibrio parahaemolyticus (V. parahaemolyticus). The bacteria were isolated from wild-caught and farmed Japanese horse mackerel (Trachurus japonicus), and examined for the antimicrobial drug resistance. Furthermore, the serotype, and the genes of thermostable direct hemolysin (tdh) and cholera toxin transcriptional activator (toxR) of the isolates were investigated by using a serotype testing kit and PCR method. Eighty-eight and 126 V. parahaemolyticus strains were isolated from wild-caught and farmed Japanese horse mackerel, respectively. Ten and 18 distinct serotypes were detected from wild-caught and farmed Japanese horse mackerel. All strains were negative for tdh genes but positive for toxR genes. Resistances to ampicillin (ABP) and to both ABP and fosfomycin (FOM) were observed in 54 and 23 strains from the wild-caught fish, while those resistant strains from farm fish were 112 and 7 strains. Multidrug-resistance to three or four drugs including ABP was observed in one or two strains from the wild-caught fish.

These results strongly suggest that the environmental exposure of antimicrobial drugs results in the spread of resistant genes in Japanese horse mackerel. This study highlights the need for monitoring the spread of resistance genes to the human intestinal flora as well as to other bacteria in the environment.

First Experimental Evidence for the Presence of Potentially Virulent Klebsiella oxytoca in 14 Species of Commonly Consumed Aquatic Animals, and Phenotyping and Genotyping of K. oxytoca Isolates

Klebsiella oxytoca is a recently emerging pathogen that can cause necrotizing enterocolitis, hemorrhagic colitis, sepsis-associated purpura fulminans, and infective endocarditis in humans. The bacterium is ubiquitous in water and soil environments. Nevertheless, current literature on K. oxytoca in aquatic products is rare. In this study, we surveyed K. oxytoca contamination in 41 species of consumable aquatic animals sold in July, August, and September of 2018 and 2019 in Shanghai, China, 40 of which had no history of carrying this bacterium. K. oxytoca was for the first time isolated from 14 species with high abundance in benthic animals. None of the K. oxytoca isolates (n = 125) harbored toxin genes mviM, tisB, and yqgB. However, a high occurrence of virulence-associated genes was observed, including brkB (73.6%), cdcB (66.4%), pduV (64.8%), and virk (63.2%). Resistance to sulphamethoxazole-trimethoprim (56.0%) was the most predominant among the isolates, followed by chloramphenicol (6.4%), tetracycline (5.6%), and kanamycin (3.2%). Approximately 8.0% of the isolates displayed multidrug resistant phenotypes. Meanwhile, high percentages of the isolates tolerated the heavy metals Cu²⁺ (84.8%), Pb²⁺ (80.8%), Cr³⁺ (66.4%), Zn²⁺ (66.4%), and Hg²⁺ (49.6%). Different virulence and resistance profiles were observed among K. oxytoca isolates in 3 types and 14 species of aquatic animals. The ERIC-PCR-based genome fingerprinting of the 125 K. oxytoca isolates revealed 108 ERIC genotypes with 79 singletons, which demonstrated the genetic diversity of the isolates. The results of this study fill gaps for policy and research in the risk assessment of K. oxytoca in consumable aquatic animals.

Presence, Seasonal Distribution, and Biomolecular Characterization of Vibrio parahaemolyticus and Vibrio vulnificus in Shellfish Harvested and Marketed in Sardinia (Italy) between 2017 and 2018

ABSTRACT

In the present study, we investigated the presence, seasonal distribution, and biomolecular characteristics of Vibrio parahaemolyticus and Vibrio vulnificus in samples of bivalve mollusks (Mytilus galloprovincialis, Crassostrea gigas, and Ruditapes decussatus) harvested and marketed in Sardinia (Italy) between 2017 and 2018. A total of 435 samples were submitted for qualitative determination of Vibrio spp., V. parahaemolyticus, and V. vulnificus. Potentially enteropathogenic isolates were detected with biomolecular methods. The overall prevalence of Vibrio spp. was 7.6%. The highest Vibrio prevalence was found in R. decussatus (8.3%). The prevalences of V. parahaemolyticus and V. vulnificus were 2.7 and 4.8%, respectively. Higher prevalences of V. parahaemolyticus and V. vulnificus were found in R. decussatus (4.2%) and C. gigas (6.2%), respectively. Only two pathogenic V. parahaemolyticus strains were recovered (genotypes: tdh- and trh+; tdh+ and trh-), both from M. galloprovincialis. None of the isolates were tdh+ and trh+. Pathogenic Vibrio infections are often underestimated, and human infections are increasing in Europe. European data on the true distribution of Vibrionaceae are scarce, and the results of the present study highlight the need of constant monitoring to update the distribution of pathogenic vibrios.

HIGHLIGHTS

Vibrio parahaemolyticus CadC regulates acid tolerance response to enhance bacterial motility and cytotoxicity

Pathogens adapted to sub-lethal acidic conditions could increase the virulence and survival ability under lethal conditions. In the aquaculture industry, feed acidifiers have been used to increase the growth of aquatic animals. However, there is limited study on the effects of acidic condition on the virulence and survival of pathogens in aquaculture. In this study, we investigated the survival ability of Vibrio parahaemolyticus at lethal acidic pH (4.0) after adapted the bacteria to sub-lethal acidic pH (5.5) for 1 hr. Our results indicated that the adapted strain increased the survival ability at lethal acidic pH invoked by an inorganic (HCl) or organic (citric) acid. RNA-sequencing (RNA-seq) results revealed that 321 genes were differentially expressed at the sub-lethal acidic pH including cadC, cadBA and groES/groEL relating to acid tolerance response (ATR), as well as genes relating to outer membrane, heat-shock proteins, phosphotransferase system and flagella system. Quantitative real-time polymerase chain reaction (qRT-PCR) confirmed that cadC and cadBA were upregulated under sub-lethal acidic conditions. The CadC protein could directly regulate the expression of cadBA to modulate the ATR in V. parahaemolyticus. RNA-seq data also indicated that 113 genes in the CadC-dependent way and 208 genes in the CadC-independent way were differentially expressed, which were related to the regulation of ATR. Finally, the motility and cytotoxicity of the sub-lethal acidic adapted wild type (WT) were significantly increased compared with the unadapted strain. Our results demonstrated that the dietary acidifiers may increase the virulence and survival of V. parahaemolyticus in aquaculture.

Prevalence and Antibiogram of Vibrio parahaemolyticus and Aeromonas hydrophila in the Flesh of Nile Tilapia, with Special Reference to Their Virulence Genes Detected Using Multiplex PCR Technique

Vibrio parahaemolyticus and Aeromonas hydrophila are major public health problems and the main cause of bacterial disease in Nile tilapia (Oreochromis niloticus). This study was conducted to determine the prevalence, antibiotic resistance and some virulence genes of both V. parahaemolyticus and A. hydrophila isolates from Nile tilapia. From Manzala Farm at Dakahlia governorate, 250 freshwater fish samples were collected. The confirmed bacterial isolates from the examined Nile tilapia samples in the study were 24.8% (62/250) for V. parahaemolyticus and 19.2% (48/250) for A. hydrophila. multiplex PCR, revealing that the tlh gene was found in 46.7% (29/62) of V. parahaemolyticus isolates, while the tdh and trh virulence genes were found in 17.2% (5/29). Meanwhile, 39.5% (19/48) of A. hydrophila isolates had the 16s rRNA gene and 10.5% (2/19) had the aerA and ahh1 virulence genes. The Multiple Antibiotic Resistance indices of V. parahaemolyticus and A. hydrophila were 0.587 and 0.586, respectively. In conclusion, alternative non-antibiotic control strategies for bacterial infections in farmed fish should be promoted to avoid multidrug-resistant bacteria. Therefore, it is suggested that farmers should be skilled in basic fish health control and that molecular detection methods are more rapid and cost-effective than bacteriological methods.