**Abstract**

*Vibrio* is a rod-shaped Gram-negative bacteria, which is widely distributed in marine and estuarine environments worldwide. It is an important component of the aquatic ecosystem and plays an important role in biogeochemical cycle. Its population dynamics are usually affected by climate and seasonal factors. Most of the *Vibrios* in the environment are not pathogenic, but some of them are pathogenic bacteria for human and animal, such as *Vibrio* cholerae, *Vibrio* vulnificus, *Vibrio parahaemolyticus*, and *Vibrio* anguillarum, etc., which are generally reported to be related to aquatic animal diseases and human food-borne diseases. Over the last couple of years, due to the influence of the rising seawater temperature and climate change, the incidence of diseases caused by *Vibrio* infection has increased significantly, which poses a great threat to human health and aquaculture. The research on pathogenic *Vibrio* has attracted more and more attention. The abundance and community changes of *Vibrio* in the environment are usually controlled by many biological and abiotic factors. The *Vibrio* pathogenicity is related to the virulence factors encoded by virulence genes. The process of *Vibrio* infecting the host and causing host disease is determined by multiple virulence factors acting together, instead of being determined by a single virulence factor. In this chapter, community changes of *Vibrio*, as well as the virulence factors of *Vibrio* and the related virulence genes of Vibiro are summarized, and their important roles in *Vibrio* infection are also discussed.

**Keywords:** *Vibrio*, community change, foodborne diseases, pathogenicity, virulence factors

### **1. Introduction**

The *Vibrio* belongs to the *Vibrionaceae* family of the *Gammaproteobacteria*, is a thermophilic, rod-shaped, heterotrophic Gram-negative bacterium [1]. *Vibrio* has genetic and metabolic diversity, and there are great phenotypic and genotypic differences among different species. It widely exists in estuaries and marine habitats all over the world and is an important part of aquatic ecosystems [2].

*Vibrio* usually has chemotaxis and motility, which can quickly respond to fluctuations of nutrient concentration and make use of nutrients in the environment to grow rapidly [3, 4]. In addition, *Vibrio* has the ability to degrade the common carbon substrates. It can decompose and utilize a variety of substrates by producing chitinase, protease, lipase and other extracellular proteases. The production and secretion of

these enzymes can provide *Vibrio* rich nutrients unavailable for other organisms, enabling *Vibrio* to quickly transform from a relatively small part to a dominant bacteria in response to environmental and climate changes [5]. *Vibrio* plays an important role in the biogeochemical cycle, which regulates inorganic nutrients and carbon flux by fixing and re-mineralize nutrients [6].

Most *Vibrio* are not pathogenic, but there are several *Vibrio* that are pathogens of humans, fish, shellfish, or other species and can cause a range of clinical manifestations including gastroenteritis, acute diarrhea, sepsis, narcotizing soft tissue infection, high mortality in cultured aquatic animals, and, in some reported cases, human death [7–10]. Vibriosis usually occurs by eating raw or under cooked seafood products, drinking contaminated water, or by direct contact with the contaminated environment through wounds [11, 12]. In the United States, the most common cause of gastroenteritis is the consumption of oysters infected or under cooked with *V. parahaemolyticus* [13]. According to the report of the Centers for Disease Control and Prevention (CDC) in 2006, *V. parahaemolyticus* is a major food-borne pathogen in the United States, and there are about 34,664 food-borne cases every year [14]. In another report, 80,000 people were infected with food-borne *Vibrio* annually in the United States in 2016, resulting in more than 500 hospitalizations and 100 deaths, the vast majority of which were *V. vulnificus* and *V. parahaemolyticus* [15]. Moreover, *V.parahaemolyticus* is a common source of food borne disease in Asian countries such as China, Japan and South Koala [7].

Aquaculture is a fast growing sector and continues to grow to meet the increasing global demand for seafood. From 2000 to 2017, aquaculture business grew by approximately 150%. China is the world's largest aquaculture producer (accounting for 58% of global production) producing 46.8 million tons of aquaculture animals per year [9]. In order to further meet the needs of the national economy and food security, the mariculture industry in southern China has gradually developed into intensive and industrialized [16]. However, high-density farming, severe human activities and global climate change have led to frequent Vibriosis, which has posed a huge threat to human health and social and economic development [17]. Vibriosis is one of the most common bacterial diseases affecting a variety of marine fish and shellfish [18, 19]. Studies have demonstrated that the content of *Vibrio* in aquaculture facilities is very high, especially during the outbreak of disease. The culturable *Vibrio* community in the affected facilities is composed of single or few *Vibrio* species, including *V. alginolyticus*, *V. parahaemolyticus*, *V. vulnificus* and *Vibrio harveyi*. These species include human and animal pathogens, which can lead to high mortality of aquatic animals [20]. For example, from May 2000 to November 2003, the mortality rate of large yellow croakers reared in marine cages due to infection with *V. alginolyticus* and *V. harveyi* ranged from 30% to 40% and even as high as 80% in Zhejiang province, China [21]. In addition, wastewater from aquaculture farms is often released to the environment without treatment, potentially causing large quantities of pathogenic *Vibrio* to enter the environment, posing a potential threat to human health. Therefore, understanding the dynamic changes of *Vibrio* community and the pathogenicity of *Vibrio* is of great significance for the healthy development of aquaculture and reducing the impact on human public health [22, 23].

#### **2. Dynamic changes of** *Vibrio* **community**

#### **2.1 Abundance of** *Vibrio*

*Vibrio* are widely distributed in estuaries and marine environments, and mainly in nearshore areas. *Vibrio* generally exhibit two different growth strategies, either

*Community Change and Pathogenicity of* Vibrio *DOI: http://dx.doi.org/10.5772/intechopen.96515*

as a free-living form or attached to biological or non-biological surfaces, where they can co-exist with the host or cause host disease [24]. For example, some *Vibrio* living in squid or other organisms can be used as the source of luminescence of light-emitting organs and also an important part of the combination of biofilm and macroalgae [25].

*Vibrio* easily grow on conventional medium (such as seawater 2216E agar medium) and selective medium (such as thiosulfate citrate bile salt sucrose agar medium, TCBS) and can carry out a variety of metabolic activities [26]. In some studies based on culture, *Vibrio* can account for 10% of culturable marine bacteria [27], and the average abundance in estuaries and nearshore waters is 103 ~ 106 CFU L−1. However, in studies using non-culture methods, *Vibrio* population only accounts for about 1% of the total plankton bacteria in nearshore waters, and the average abundance in estuaries and nearshore waters is 104 ~ 108 16 s rRNA copies L−1 [28]. Their *Vibrio* abundance was found to be between 15 and 2395 CFU mL−1 in a study of tropical estuaries and coastal water in Malaysia [29]. In addition, studies have shown a high density of *Vibrio* on the surface and in the body of marine animals such as fish, shrimp, mollusks, corals, sponges, zooplankton, algae and seaweed [30]. For example, in a study examining the effects of aquaculture on *Vibrio* communities, the relative abundance of the 16SrRNA gene sequence reads 16 from seaweed samples were the highest by sequencing water, sediment, seaweed and tissue samples obtained in the aquaculture area of Hainan [9]. This is also consistent with studies describing *Vibrio* communities as important components of seagrass bacterial communities. These bacteria account for 25% of the culturable bacteria in seaweed off the coast of Hainan province [31].

#### **2.2 Diversity of** *Vibrio*

At least 110 *Vibrios* have been found and reported, and more may be found in the future. Among the *Vibrios* that have been described, several are commonly associated with human diseases, among which *V. cholerae*, *V. parahaemolyticus*, and *V. vulnificus* are recognized as human pathogenic bacteria, while *Vibrio alginolyticus*, *V. anguillarum*, *V. harveyi*, *Vibrio* fluvialis, *Vibrio* furniss, *Vibrio* metschnikovii, and *Vibrio* mimicus are primarily marine animal pathogenic bacteria but occasionally associated with human infections [32–36].

*Vibrio* usually has species-specific salinity and temperature preferences, and different kinds of *Vibrio* may exist in different environments. They exit from deepsea hydrothermal vents and sediment are more than 6, 000 meters deep to seawater 10, 500 meters deep in the mariana trench [37, 38]. For example, the optimal growth temperature and salinity for *Vibrio devil*, first isolated from deep-sea hydrothermal vents, is 30 ~ 45 °C and 20 ~ 50 ppt, respectively [39]. The salinity-dependent *Vibrio* carinii is mainly present in seawater in the range of salinity from the Baltic Sea to the Mediterranean Sea [40]. *Vibrio pacinii*, *Vibrio cyclotrophicus*, *Vibrio lentus*, and some unnamed *Vibrio* have also been found at low temperatures [32].

At present, studies on the diversity of *Vibrio* communities in marine environments are mainly based on *Vibrio* isolated and cultured [41]. However, due to the low interspecific resolution of the 16S rRNA gene, the use of 16S rRNA gene similarity as a major interspecific marker for the phylogenetic relationships of *Vibrios* appears to have lost its effect. Multiple-locus sequence analysis (MLSA) and other novel phylogenetic markers such as the iron absorption regulatory gene *fur* have been used as alternative approaches [42, 43]. In order to study the diversity of environmental *Vibrio*, Siboni et al. first extracted DNA from seawater, and then used 16S rRNA gene primers specific to *Vibrio* to conduct high-throughput sequencing, thus making it possible to more intuitively and effectively explore the

diversity of *Vibrio* communities [44]. In another study by Bei et al., the abundance and community structure of *Vibrio* species at different depths was studied using *Vibrio-specific* 16S rRNA gene high-throughput sequencing and quantitative PCR (qPCR) techniques as well as traditional culture methods [5].
