Prevalence and antimicrobial susceptibility of Vibrio parahaemolyticus isolated from retail shellfish in Shanghai
Introduction
Seafood is recognized as a nutritious food choice, and is liked by increasing numbers of consumers worldwide (Hellberg, DeWitt, & Morrissey, 2012). For the last two decades, there has been a four-fold growth in commercial aquaculture worldwide (Cabello, 2006). However, the main obstacles in the consumption of seafood are their high perishability and health risk due to contamination by pathogens (Reyhanath & Kutty, 2014). Vibrio parahaemolyticus is a halophilic bacterium, which is ubiquitous in marine and coastal environments. Some V. parahaemolyticus strains are pathogenic to human, and responsible for most seafood-related human illness (Yano et al., 2014). Potentially virulent V. parahaemolyticus strains are usually differentiated from avirulent strains by the presence of thermostable direct hemoylsin (tdh) and/or thermostable direct hemolysin-related hemolysin (trh) genes (Bej et al., 1999). According to the official surveillance system of China, V. parahaemolyticus is the leading cause of foodborne bacterial poisoning in China (Liu, Chen, Guo, & Wang, 2008). This bacterium is frequently isolated from a variety of raw seafood, particularly in shellfish (Su & Liu, 2007). Consumption of raw or undercooked seafood contaminated with pathogenic V. parahaemolyticus may lead to acute gastroenteritis (Su & Liu, 2007). Although only a portion of V. parahaemolyticus strains is pathogenic for humans, the time-temperature abuse in markets provides ample scope for these strains to multiply to dangerous levels (Sudha, Divya, Francis, & Hatha, 2012). After harvest, V. parahaemolyticus showed an average of 790-fold increase in live oysters when they were kept at 26 °C for 24 h during April to December (Gooch, DePaola, Bowers, & Marshall, 2002). Therefore, failure to immediately maintain the temperature of freshly harvested shellfish at sufficiently low level will ensure that V. parahaemolyticus population easily surpass the FDA recommended maximum level of 1.0 × 104 organisms/mL, leading to V. parahaemolyticus infection associated with raw shellfish consumption (FDA, 2001, Yeung and Boor, 2004).
Large-scale aquaculture is characterized by intensive cultivation methods with high stocking density that leads to poor hygienic conditions (Diana et al., 2013). As a consequence, the incidence of foodborne outbreaks caused by bacterial infection is increasing in shellfish (Wang, Duan, Zhang, & Li, 2007). Antibiotics are largely used for therapeutic and prophylactic purposes on aquaculture (Hirsch et al., 1999, Jerbi et al., 2011). The widely use of antibiotics has helped selection for resistant bacterial strains, and increased antibiotic resistance among the environmental bacteria, including potentially pathogenic Vibrio species (Tendencia & de la Peña, 2001). Antibiotic-resistant bacteria may represent a potential threat to human health due to direct transmission through the food chain (DuráN & Marshall, 2005) or by transferring the antimicrobial resistance genes to human pathogens by mobile genetic elements (Guglielmetti et al., 2009, Serrano, 2005).
As one of the major pathogens in seafood, V. parahaemolyticus has been reported to be resistant to a number of antibiotics including ampicillin, ciprofloxacin, cephazolin, streptomycin, cefuroxime sodium (Al-Othrubi et al., 2014, Jiang et al., 2014, Yano et al., 2014). Notably, some isolates even have resistant to chloramphenicol which has been banned for many years (Jiang et al., 2014, Wong et al., 2012). Due to their detrimental effects on the environment, quinolones have been totally restricted in aquaculture in industrialized countries (Cabello, 2004, Gorbach, 2001, Sørum, 2006). However, the use of quinolones and many other antibiotics remains unrestricted in aquaculture in countries with growing aquaculture industries such as China and Chile (Cabello, 2004, Jacoby, 2005).
Shanghai is one of the largest import cities in China with overwhelming amounts of shellfish transported from other cities or countries. The prevalence of foodborne V. parahaemolyticus is more diverse and complex according to our previous reports (Chen et al., 2012, Dai et al., 2013). To our knowledge, there has been little research focus on the comprehensive reports of the isolation, identification, enumeration of V. parahaemolyticus, and analysis the antibiotic resistant patterns of these isolates in Shanghai. In this context, it is critical to gain a better understanding of the contamination and antimicrobial susceptibility patterns of V. parahaemolyticus isolated from local markets in Shanghai. Therefore, we made an attempt to isolate, identify and enumerate V. parahaemolyticus from various shellfish in local markets in Shanghai and to analyze the antibiotic resistant patterns of those isolates. These data can serve as a benchmark to monitor the prevalence and antimicrobial susceptibility of V. parahaemolyticus, and provide insight for the use of antibiotics in clinical treatments.
Section snippets
Sample collection and processing
In this study, 140 shellfish samples were collected between February 2014 and February 2015 in retail market A and B, whose seafood are both from the biggest aquatic wholesale market in Shanghai. The samples include clam (Meretrix meretrix; N = 43), oyster (Crassostrea ariakensis; N = 38), razor clam (Sinonovacula constricta; N = 35), and scallop (Chlamys nobilis; N = 24). Before being sold, these shellfish were stored in ice box. After collection, all samples were placed on ice, immediately
Prevalence and identification of V. parahaemolyticus
Ninety-six V. parahaemolyticus isolates were isolated from 140 shellfish samples collected from Shanghai aquatic retail markets. The isolates from 48 samples were confirmed as positive based on the standard biochemical tests and species-specific PCR assays. The isolation rate of V. parahaemolyticus in collected shellfish is shown in Table 2. The positive rate of V. parahaemolyticus in shellfish was 34.3% (48/140). The positive rate of V. parahaemolyticus was 60.5% (23/38) in oysters, 28.6%
Discussion
Molluscan shellfish are filter feeders that filter large volumes of seawater to obtain food. During the process of filter-feeding, shellfish may also concentrate and retain human pathogens derived from sewage contamination (Lees, 2000). Unfortunately, little information on the contamination of V. parahaemolyticus among shellfish in Chinese retail markets is available.
Shanghai is located in the Yangtze River estuary. The salinity of seawater is too low to raise shellfish. Almost all shellfish
Conflict interest
None declared.
Acknowledgments
This work was jointly supported by the grant No. 2012AA101601 from the Ministry of Science and Technology of China and the grant No. 31000063 from the National Natural Science Foundation of China.
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2020, Fish and Shellfish ImmunologyCitation Excerpt :In the fields of aquaculture, antibiotics are commonly used as prophylactic or therapeutic agents to manage outbreaks and reduce mortality [7]. Recently, antibiotic resistant V. parahaemolyticus has been widely isolated from farmed scallops in China [8], Korea [9] and Poland [5]. The development of sustainable alternatives to antibiotics are urgently required and several recent reports have provided evidence of promise in the use of antimicrobial peptides (AMPs) [10].