Isolation and characterization of Aeromonas schubertii from diseased snakehead, Channa maculata (Lacepède)

Abstract

Pure bacterial cultures were isolated from diseased snakeheads, Channa maculata (Lacepède), suffering high mortality in a farm in Zhongshan, southern China. Three isolates, namely ZS20100725, ZS20100725-1 and ZS20100725-2, were identified as Aeromonas schubertii. All the isolates showed high 16S rRNA sequence similarities with A. schubertii. The isolates exhibited strong virulence to snakeheads in experimental challenges with LD(50) ranging between 1.4 × 10(4) and 6.4 × 10(6) CFU g(-1). Two of the isolates were positive for haemolysin, elastase, lipase and lecithinase by phenotypic determination, which was further confirmed by PCR amplification of the haemolysin and elastase genes. In sterile liquid medium, the best growth conditions of strain ZS20100725 were 30 °C, pH 7 and 0.5% salinity (w/v). Antibiotic susceptibility tests showed that strain ZS20100725 was susceptible to cefoxitin, cefoperazone and chloramphenicol. Furthermore, histopathology of diseased snakeheads infected with A. schubertii showed necrosis and congestion in liver, kidney and spleen and also damage to the cardiac muscle, intestine and gills.

Aeromonas shuberti as a cause of multi‐organ necrosis in internal organs of Nile tilapia, Oreochromis niloticus

“…The strain LF1708 possesses susceptibility to a wide spectrum of antibiotics including broad‐spectrum sulphonamides, quinolones, chloramphenicols, cephalosporins, aminoglycosides and tetracycline, and resistant to penicillin,ampicillin and lincolmensin. The results are inconsistent with the results obtained from other A. schubertii strains (Chen et al., ; Liu & Li, ). This antibiogram probably demonstrated that the abuse of antimicrobial agents did not occur in the fish farming areas of this outbreak.…”

“…In the present study, the white spot disease in tilapia typically presents with the similar signs as the disease of snakehead fish caused by A. schubertii in 2012 (Chen et al., ; Liu & Li, ; Liu et al., ), including white nodules in the liver, spleen and kidney. In an interesting manner, it is easy to replicate these typical white nodule signs of naturally occurring disease in experimental challenge but rarely reported on other Aeromonas species infection.…”

“…The effect of pH on LF1708 showed the isolated strain grows at pH from 3 to 11, and the optimal pH for growth ranged from 6 to 10. In an interesting manner, it was found that LF1708 strain possessed more tolerance to pH compared with other reported A. schubertii such as strains ZS20100725 (suitable pH range of 6–8) and WL‐4 (grow well within the pH ranges from 7 to 9) (Chen et al., ; Mo et al., ).…”

“…The common signs of the diseases are manifested clinically with ulcerations, anaemia, ascitic fluid, septicaemia, failure of osmoregulatory balance and even death. However, since 2012, another specie of Aeromonas called A. schubertii caused high mortality has been reported in Channa argus (Liu & Li, ) and Channa maculate (Chen, Liang, Zhuo, Wu, & Zou, ) associated with typical signs of white nodules in internal organs which was seldom reported in other infected fish. In October 2017, diseased tilapia with similar white nodules in internal organs were found in earth ponds in Zhanjiang, Guangdong Province, south of China.…”

Detection and quantification of Aeromonas schubertii in Channa maculata by TaqMan MGB probe fluorescence real‐time quantitative PCR

“…In 2009, A. schubertii was reported to be an aquacultural pathogen causing internal nodular diseases in the family Channidae and has since spread rapidly throughout China. The pathogen infects the main snakehead species, C. maculata and C. argus , as well as the hybrid cross of C. maculata females × C. argus males, causing high mortality (45%) and becomes one of the most severe diseases in China's snakehead farming industry (Chen, Liang, Zhuo, Wu, & Zou, ; Liu & Li, ; Liu et al., ). This species is also frequently found in other aquatic organisms, including frogs (Pearson, Hirono, Aoki, Miranda, & Inglis, ), shrimp (Yano et al., ), mussels (Latif‐Eugenin, Beaz‐Hidalgo, & Figueras, ) and tilapia (Liu et al., ).…”