Is Aeromonas hydrophila the dominant motile Aeromonas species that causes disease outbreaks in aquaculture production in the Zhejiang Province of China?

Abstract

The significance of Aeromonas hydrophila in association with disease outbreaks in aquaculture production in the Zhejiang province of China was investigated. Bacteriological examination of moribund fish and crabs resulted in 95 bacterial isolates: 88 bacterial isolates from fish and 7 isolates from crabs. PCR and traditional biochemical methods were used for identification of A. hydrophila. Out of 69 motile aeromonads, 35 isolates were identified as A. hydrophila by biochemical tests. However, 6 of those were not identified as A. hydrophila by a species specific PCR method. Serotyping revealed 2 dominant serotypes (O9 and O97) among A. hydrophila isolates. The data presented show that approximately 42% of the motile aeromonads isolated from disease outbreaks among various fish species were A. hydrophila. It is noteworthy that A. hydrophila accounted for more than 50% of the isolated aeromonands isolated from crucian carp Carassius carassius and Wuchang bream Megalobrama amblycephala with haemorrhagic septicaemia. Although this species was the most frequently isolated organism from internal organs of diseased fish and crabs in the present study, other motile Aeromonas spp. were also found. The PCR assay was useful in preventing misidentification of A. hydrophila, which may occur when only phenotypic tests are employed. KEY WORDS: Aeromonas hydrophila · PCR · China · Haemorrhagic septicaemia · Fish diseases Resale or republication not permitted without written consent of the publisherDis Aquat Org 46: [23][24][25][26][27][28][29] 2001 primary pathogen of freshwater fish or a secondary opportunistic pathogen of compromised or stressed hosts (Jeney & Jeney 1995). A. hydrophila has been associated with tail and fin rot, haemorrhagic septicaemia and epizootic ulcerative syndrome (EUS) (Austin & Adams 1996, Roberts 1997. A. hydrophila has also been described as the dominant infectious agent of 'fish-bacterial-septicaemia' in freshwater cultured cyprinid fishes, mainly crucian carp Carassius carassius, Wuchang bream Megalobrama amblycephala and silver carp Hypophthalmichthys molitrix in the Zhejiang province and other provinces in the Southeast of China between 1989to 1993(Qian et al. 1997. 'Fish-bacterial-septicaemia' occurs each summer in the Zhejiang province and results in significant losses for the fish farmers of the region; from 1989 to 1991 the losses were estimated to have been approximately 2200 tons of fish per year (D. Qian pers. comm.).The taxonomy of the genus Aeromonas has been revised, and new motile, mesophilic species have been identified: A. allosaccharophila, A. veronii biogroups sobria and veronii and A. encheleia have been reported as fish pathogens (Toranzo et al. 1989, Paniagua et al. 1990, Joseph & Carnahan 1994, Esteve et al. 1995. Still, A. hydrophila is regarded as the predominant fish pathogen within the mesophilic aeromonads, although its importance may have been overestimated in the past.Thus, the purpose of the present study was to estimate the actual significance of Aeromonas...

Multilocus sequence typing revealed a clonal lineage of Aeromonas hydrophila caused motile Aeromonas septicemia outbreaks in pond-cultured cyprinid fish in an epidemic area in central China

“…Aeromonas hydrophila and other motile aeromonads are among the most common bacteria in freshwater habitats, and these bacteria frequently cause diseases among cultured and feral fishes worldwide (Akinbowale et al, 2007;Cipriano, 2001;da Silva et al, 2012;Gopalakannan and Arul, 2006;Nielsen et al, 2001). During the past 30 years, the aquaculture industry in China has evolved dramatically, and the capital-intensive production has become the main culture mode (Hishamunda and Subasinghe, 2003;Nielsen et al, 2001;Zhang and Jostein, 2004).…”

“…During the past 30 years, the aquaculture industry in China has evolved dramatically, and the capital-intensive production has become the main culture mode (Hishamunda and Subasinghe, 2003;Nielsen et al, 2001;Zhang and Jostein, 2004). The total area devoted to aquaculture increased from 2.86 million hectares in 1979 to 5.63 million hectares in 2008 in China.…”

“…Meanwhile, total production rose from 1.23 to 34.13 million tons, garnering a 69.7% share of the total aquatic production, making China the only country in the world where aquaculture production exceeds the wild catch (Li et al, 2011;National Bureau of Statistics of China, 2009). With the rapid development of the aquaculture industry, motile aeromonad infections caused by A. hydrophila have become an increasingly prominent problem (Xiao et al, 2011;Nielsen et al, 2001;Xu et al, 1993). Based on different clinical symptoms, A. hydrophila can cause several diseases in fish, which include motile Aeromonas septicemia (MAS) or hemorrhagic septicemia (da Silva et al, 2012;Nielsen et al, 2001;Xu et al, 1993), hemolytic ascitesosis (Sun et al, 1991), intussusception (Liu et al, 2008), tail or fin rot (Liu et al, 1993;Rahman et al, 2001), stigmatosis (Xu et al, 1980), and epizootic ulcerative syndrome (Austin and Adams, 1996;Roberts, 1997).…”

“…With the rapid development of the aquaculture industry, motile aeromonad infections caused by A. hydrophila have become an increasingly prominent problem (Xiao et al, 2011;Nielsen et al, 2001;Xu et al, 1993). Based on different clinical symptoms, A. hydrophila can cause several diseases in fish, which include motile Aeromonas septicemia (MAS) or hemorrhagic septicemia (da Silva et al, 2012;Nielsen et al, 2001;Xu et al, 1993), hemolytic ascitesosis (Sun et al, 1991), intussusception (Liu et al, 2008), tail or fin rot (Liu et al, 1993;Rahman et al, 2001), stigmatosis (Xu et al, 1980), and epizootic ulcerative syndrome (Austin and Adams, 1996;Roberts, 1997). MAS is the most serious disease and has frequently caused huge economic losses in the cyprinid fish industry throughout China since 1989 (Lu, 1992;Nielsen et al, 2001;Qian et al, 1997).…”

“…All these studies revealed a high intra-specific genetic diversity within A. hydrophila, and no dominant clones were found. As an etiological agent in fish and shellfish diseases, A. hydrophila is widely identified and characterized at the species level (da Silva et al, 2012;Nielsen et al, 2001;Xu et al, 1993). However, studies concerning the genetic diversity of this widespread fish pathogen are scarce.…”