Streptococcus agalactiae, an Emerging Pathogen for Cultured Ya-Fish, Schizothorax prenanti, in China

Abstract

Streptococcus agalactiae (Group B streptococcus) has emerged as an important pathogen that affects humans and animals, including aquatic species. S. agalactiae infections are becoming an increasing problem in aquaculture and have been reported worldwide in a variety of fish species, especially those living in warm water. Recently, a very serious infectious disease of unknown aetiology broke out in ya-fish (Schizothorax prenanti) farms in Sichuan Province. A Gram-positive, chain-forming coccus was isolated from moribund cultured ya-fish. The goals of this study were to identify the bacterial strains isolated from diseased fish between 2009 and 2011 in Sichuan Province, China, to evaluate the pathogenicity of the pathogen in ya-fish, crucian carp (Carassius carassius) and the Nile tilapia (Oreochromis niloticus); and to determine the susceptibility of the pathogen strains to many currently available anti-microbial agents. The virulence tests were conducted by intraperitoneal injection of bacterial suspensions. In this study, four strains of a Gram-positive, chain-forming coccus were isolated from moribund cultured ya-fish (S. prenanti). The coccoid microorganism was identified as S. agalactiae using a commercial streptococcal grouping kit and 16S rDNA sequencing analysis. Susceptibility of the isolates to 22 antibiotics was tested using the disc diffusion method. All isolates showed a similar antibiotic susceptibility, which were sensitive to amoxicillin, ciprofloxacin, lomefloxacin, chloramphenicol, rifampin, vancomycin, azithromycin, florfenicol, cefalexin, cefradine and deoxycycline and resistant to gentamicin, sinomin (SMZ/TMP), penicillin, tenemycin, fradiomycin and streptomycin. Furthermore, the virulence tests were conducted by intraperitoneal injection of the isolated strain GY101 in ya-fish, crucian carp and the Nile tilapia. This coccus was lethal to ya-fish, Nile tilapia and crucian carp. The mortality rates of infected ya-fish were 100%, 100%, 60% and 20% at doses of 1.0 × 10⁷, 1.0 × 10⁶, 1.0 × 10⁵ and 1.0 × 10⁴ CFU/fish, respectively. The values were 100%, 80%, 60% and 30% for Nile tilapia and 100%, 60%, 10% and 0% for crucian carp. To our knowledge, this is the first report of S. agalactiae as a pathogen of ya-fish.

Isolation and molecular identification of the etiological agents of streptococcosis in Nile tilapia (Oreochromis niloticus) cultured in net cages in Lake Sentani, Papua, Indonesia

“…Transmission of bacteria from wild fish to cultured fish is also possible (Zlotkin et al 1998; Evans et al 2002). S. agalactiae isolated from diseased ya-fish ( Schizothorax prenanti ) could be experimentally transmitted to crucian carp ( Carassius carassius ) and Nile tilapia (Geng et al 2012) suggesting potential horizontal transmission (e.g. fish to fish) among cultured species in the area.…”

Molecular characterization of Streptococcus agalactiae in diseased farmed tilapia in China

“…agalactiae was identified as the causative agent of severe endemic diseases that has caused heavy tilapia mortality in China over the past years (Geng et al, 2012;Ye et al, 2011). Moreover, the said pathogen has been associated with the deaths in many other fish species worldwide (Geng et al, 2012).…”

“…agalactiae was identified as the causative agent of severe endemic diseases that has caused heavy tilapia mortality in China over the past years (Geng et al, 2012;Ye et al, 2011). Moreover, the said pathogen has been associated with the deaths in many other fish species worldwide (Geng et al, 2012). Most studies have focused on S. agalactiae of human and mammalian origin, whereas only sporadic information is known about the genetic features of fish S. agalactiae isolates as well as their genetic relatedness to the GBS strains of hosts other than fish (Delannoy et al, 2013;Evans et al, 2008;Suanyuk et al, 2008;Ye et al, 2011).…”

On the origin of Group B Streptococcus from disease outbreaks in wild marine fish in Australia

“…These findings have raised public and industry concern over threats to human health from potential transmission between fish and humans, over environmental impacts on other aquatic animals, and over the potential threat posed to the growing Australian aquaculture industry in which, to date, there have been no reported cases of this disease in spite of the devastation caused to the industry overseas (Abuseliana et al, 2010;Geng et al, 2012;Najiah et al, 2012;Pridgeon, 2012). Therefore, my thesis set out to determine whether GBS isolated from dead wild fish in Australia is indeed virulent in…”

“…), red hybrid and Nile tilapia (Oreochromis niloticus) grown in Thailand, Malaysia and Columbia (Abuseliana et al, 2010;Chen et al, 2007;Hernández et al, 2009;Musa et al, 2009;Suanyuk et al, 2008;Zamri-Saad et al, 2010), and Gilthead seabream (Sparus aurata) in Kuwait (Glibert et al, 2002). The bacterium has recently been isolated in China affecting Barcoo grunter (Scortum barcoo) and Ya-fish (Schizothorax prenanti) (Geng et al, 2012;Liu et al, 2013c).…”