Occurrence of Pandemic Clones ofVibrio parahaemolyticusIsolates from Seafood and Clinical Samples in a Chinese Coastal Province

Molecular characterization of Vibrio species isolated from dairy and water samples

Vibrio species can cause foodborne infections and lead to serious gastrointestinal illnesses. The purpose of this research was to detect the Vibrio cholerae and Vibrio parahaemolyticus in raw milk, dairy products, and water samples. Also, it investigated the virulence factors, antibiotic resistance and biofilm formation in isolated bacteria. Conventional and molecular approaches were used to identify the isolates in this study. Vibrio species were detected in 5% of the samples. Vibrio cholerae and Vibrio parahaemolyticus were isolated from 1.25 and 1.5%, respectively, of the total samples. Penicillin resistance was detected in all strains of Vibrio cholerae and Vibrio parahaemolyticus, with a MAR index ranging from 0.16 to 0.5. Four isolates were moderate biofilm producer and three of them were MDR. When Vibrio cholerae was screened for virulence genes, ctxAB, hlyA, and tcpA were found in 80, 60, and 80% of isolates, respectively. However, tdh + /trh + associated-virulence genes were found in 33.3% of Vibrio parahaemolyticus isolates.

Challenges in Vibrio parahaemolyticus infections caused by the pandemic clone

Vibrio Parahaemolyticus infections caused by the pandemic clone have become a global public health issue. The pandemic clone includes over ten sequence types and 49 serotypes. Several markers such as toxRS/new, orf8 and genomic islands were considered specific for pandemic strains, but subsequent studies later confirmed a lack of specificity. Thus, identifying stable indicators for the pandemic clone is still an open question. In recent years, several environmental pandemic strains are growing, constituting a new threat to seafood safety and human health. Traditional methods show limited discrimination in studying the microevolution of pandemic strains. For example, multilocus sequence typing divides many pandemic strains into ST3 type, making it difficult to further distinguish the variability within ST3 strains from different contexts. When using a whole genome sequencing-based technique, strains including those with the same sequence type, could be well separated. Whole genome sequencing-based technology also played important roles in dissecting the evolution process and revealing the mechanism underlying rapid serotype conversion within pandemic strains. In addition, the emergence of multiple-antibiotic resistant pandemic strains needs attention. Altogether, we are facing many challenges posed by pandemic V. parahaemolyticus strains, which need to be resolved in future studies.

Characterization of clinical Vibrio parahaemolyticus strains in Zhoushan, China, from 2013 to 2014

Vibrio parahaemolyticus is recognized as major cause of foodborne illness of global public health concern. This study collected 107 strains of V. parahaemolyticus during active surveillance of diarrheal diseases in hospitals in Zhoushan during 2013 to 2014 and investigated their serotypes, virulence genes (tdh, trh, and orf8), antimicrobial resistance, and genotypes. The dominant serotypes of the 107 clinical strains were O3:K6, O4:K8, and O4:KUT with 87.9% and 3.7% of the strains carrying the virulence genes tdh and trh, respectively. Molecular typing by pulsed-field gel electrophoresis indicated divergence among the clinical strains. Most isolates were sensitive to the common antimicrobial agents used against the Vibrio species except ampicillin. We conclude that continuous surveillance of V. parahaemolyticus in diarrhea patients is a public health priority and is useful for conducting risk assessment of foodborne illnesses caused by V. parahaemolyticus.

Spreading of Pandemic Vibrio parahaemolyticus O3:K6 and Its Serovariants: A Re-analysis of Strains Isolated from Multiple Studies

In China, V. parahaemolyticus has been a leading cause of foodborne outbreaks and bacterial infectious diarrhea since the 1990s, and most infections have been associated with the pandemic V. parahaemolyticus O3:K6 and its serovariants. However, a comprehensive overview of the sero-prevalence and genetic diversity of the pandemic V. parahaemolyticus clone in China is lacking. To compensate for this deficiency, pandemic isolates in both clinical and environmental Chinese samples collected from multiple studies were analyzed in this study. Surprisingly, as many as 27 clinical pandemic serovariants were identified and were widely distributed across nine coastal provinces and two inland provinces (Beijing and Sichuan). O3:K6, O4:K68, and O1:KUT represented the predominant clinical serovars. Only four environmental pandemic serovariants had previously been reported, and they were spread throughout Shanghai (O1:KUT, O3:K6), Jiangsu (O3:K6, O4:K48), Zhejiang (O3:K6), and Guangdong (O4:K9). Notably, 24 pandemic serovariants were detected within a short time frame (from 2006 to 2012). The pandemic isolates were divided into 15 sequence types (STs), 10 of which fell within clonal complex (CC) 3. Only three STs (ST3, ST192, and ST305) were identified in environmental isolates. Substantial serotypic diversity was mainly observed among isolates within pandemic ST3, which comprised 21 combinations of O/K antigens. The pandemic O3:K6 serotype showed a high level of sequence diversity, which was shared by eight different STs (ST3, ST227, ST431, ST435, ST487, ST489, ST526, and ST672). Antimicrobial susceptibility testing revealed that most isolates shared similar antibiotic susceptibility profiles. They were resistant to ampicillin but sensitive to most other drugs that were tested. In conclusion, the high levels of serotypic and genetic diversity of the pandemic clone suggest that the involved regions are becoming important reservoirs for the emergence of novel pandemic strains. We underscore the need for routine monitoring to prevent pandemic V. parahaemolyticus infection, which includes monitoring antimicrobial responses to avoid excessive misuse of antibiotics. Further investigations are also needed to delineate the specific mechanisms underlying the possible seroconversion of pandemic isolates.

Strategies of Vibrio parahaemolyticus to acquire nutritional iron during host colonization

Iron is an essential element for the growth and development of virtually all living organisms. As iron acquisition is critical for the pathogenesis, a host defense strategy during infection is to sequester iron to restrict the growth of invading pathogens. To counteract this strategy, bacteria such as Vibrio parahaemolyticus have adapted to such an environment by developing mechanisms to obtain iron from human hosts. This review focuses on the multiple strategies employed by V. parahaemolyticus to obtain nutritional iron from host sources. In these strategies are included the use of siderophores and xenosiderophores, proteases and iron-protein receptor. The host sources used by V. parahaemolyticus are the iron-containing proteins transferrin, hemoglobin, and hemin. The implications of iron acquisition systems in the virulence of V. parahaemolyticus are also discussed.

Phenotypic and phylogenetic analysis of Vibrio parahaemolyticus isolates recovered from diarrhea cases in Guangdong Province, China

Vibrio parahaemolyticus has emerged as a common foodborne pathogen of global concern. In this study, 108 V. parahaemolyticus isolates that recovered from diarrhea cases (n=96) and seafood products (n=12) in Guangdong Province from 2007 to 2011 were characterized by serotyping, tdh and trh toxin gene detection and multilocus sequence typing (MLST). The dominant serotypes from the cases were O3:K6, O4:K8 and O1: KUT (untyped). However, most isolates recovered from seafood products belonged to other serotypes. None of the isolates carried the trh gene, while the major isolates from the cases were tdh positive. MLST analysis revealed 31 sequence types (STs); 17 STs were unique in this study. eBURST analysis revealed four clonal complexes (CC), The majority of the isolates (n=58, all from cases and tdh+) were grouped into the CC3, which included O3:K6, O4:K68 and O1:KUT isolates. The CC3 was the most prevalent clonal complex, and all of the CC3 isolates were recovered from clinical cases of geographically diverse origin. As to the CC345, which was completely constituted by O4:K8, was another important clonal complex affecting Guangdong Province. Ongoing surveillance of V. parahaemolyticus in diarrhea patients and seafood products remains a public health priority for Guangdong Province, China.

Vibrio parahaemolyticus, Southern Coastal Region of China, 2007-2012

We analyzed the prevalence and characteristics of Vibrio parahaemolyticus among patients with acute infectious diarrhea in the southern coastal region of China. V. parahaemolyticus was the leading cause of bacterial infectious diarrhea in this region during 2007–2012. Serotype O3:K6 strains were most common, followed by serotypes O4:K8 and O3:K29.

Vibrio parahaemolyticus isolates from southeastern Chinese coast are genetically diverse with circulation of clonal complex 3 strains since 2002

Multilocus sequence typing (MLST) was used to examine the clonal relationship and genetic diversity of 71 Vibrio parahaemolyticus isolates from clinical and seafood-related sources in southeastern Chinese coast between 2002 and 2009. The tested isolates fell into 61 sequence types (STs). Of 17 clinical isolates, 7 belonged to ST3 of the pandemic clonal complex 3, with 3 strains isolated in 2002. Although there was no apparent clonal relationship found between clinical strains and those from seafood-related sources positive with pathogenic markers, there were clonal relationships between clinical strains from this study and those from environmental sources in other parts of China. Phylogenetic analysis showed that strains of 112 STs (61 STs from this study and 51 retrieved from PUBMLST database covering different continents) could be divided into four branches. The vast majority of our isolates and those from other countries were genetically diverse and clustered into two major branches of mixed distribution (of geographic origins and sample sources), whereas five STs representing six isolates split as two minor branches because of divergence of their recA genes, which had 80%-82% nucleotide identity to typical V. parahaemolyticus strains and 73.3%-76.9% identity to the CDS24 of a Vibrio sp. plasmid p23023, indicating that the recA gene might have recombined by lateral gene transfer. This was further supported by a high ratio of recombination to mutation (3.038) for recA. In conclusion, MLST with fully extractable database is a powerful system for analysis of clonal relationship for strains of a particular region in a national or global scale as well as between clinical and environmental or food-related strains.

Insufficiency of the Kanagawa hemolytic test for detecting pathogenic Vibrio parahaemolyticus in Shanghai, China

We evaluated the Kanagawa hemolytic test and tdh gene test for accuracy in identifying pathogenic Vibrio parahaemolyticus isolates in Shanghai. One hundred and seventy-two V. parahaemolyticus isolates were collected from diarrhea patients, freshly harvested sea fish, or fresh water samples. Statistical data for the Kanagawa hemolytic test and tdh gene test were compared. There were 83.51% isolates (81/97) from patients and 22.22% isolates (10/45) from sea-fish positive for the tdh gene. However, none of 30 isolates from fresh water samples were tdh-positive. Positive Kanagawa hemolytic tests were obtained in 88.66%, 46.67%, and 76.67% of isolates, which were from patients, sea fish, and fresh water samples, respectively. Positive rates of the Kanagawa hemolytic tests and the tdh gene tests were significantly different in isolates from those 3 sources (P < 0.001). The tdh gene test showed higher specificity than the Kanagawa hemolytic test on identifying pathogenic V. parahaemolyticus isolates in Shanghai, China.