Bacillus cereus, a potential pathogen of snakehead fish Ophiocephalus argus

Abstract

Bacillus cereus is an emerging pathogen that has caused high mortalities in aquaculture animals. Yet the pathogenicity of B. cereus in snakehead fish Ophiocephalus argus is still unclear. In this study, a virulent strain (CA4) was isolated from diseased snakehead fish suffering from a typical symptom of hepatic hemorrhage with blood vessel congestion and macrophage infiltration, and was identified molecularly and phenotypically as B. cereus. It was β-hemolytic, showed an LD50 value of 2.57×106 CFU mL-1 for snakehead fish, and developed multiple resistances to cotrimoxazole, doxycycline, florfenicol, neomycin, sulfisoxazole, and tetracycline in aquaculture use. To the best of our knowledge, this is the first report of snakehead fish- pathogenic B. cereus. The findings of this study provide new insights into the potential threat of pathogenic B. cereus to snakehead fish.

Haemolytic Bacillus subtilis, a potential pathogen of hemorrhage disease in farmed yellow catfish Pelteobagrus fulvidraco

“…23 Isolate CA4 of B. cereus has been confirmed to cause hepatic hemorrhage of snakehead fish. 14 However, there is limited information on B. subtilis as a causative pathogen of yellow catfish. In the present study, we characterized the phenotype, taxonomic position, virulence, and antimicrobial susceptibility of B. subtilis HS5.…”

“…Haemolysin is a primary virulence factor of pathogenic Bacillus species, 26 and the haemolysin-producing Bacillus strains have been found to cause bacterial diseases in aquaculture animals. 14,27 Several haemolytic strains of B. subtilis have been found to be pathogenic to S. maximus and C. semilaevis. 10 In the present study, isolate HS5 of *B. subtilis *was demonstrated to produce beta-haemolysins.…”

“…13 The challenge strain was re-isolated from freshly dead fish to confirm the cause of death. Meanwhile, careful examinations of parasites and pathogenic viruses were also carried out as described by Wang et al 14…”

“…The haemolysis production of the pathogenic isolate was tested with rabbit blood agar (RBA) plates (Guangdong Huankai Microbial Science and Technology Co. Ltd., China), and was observed for the presence of zones around the colony after 24h of growth on RBA plates at 28 0 C. 14 In addition, the virulence genes of the pathogenic isolate were also detected by PCR according to Yu et al 20 and Owusu-Kwarteng et al 21 Briefly, the genomic DNA was extracted from the pathogenic isolate using a DNA extraction kit (Tiangen Biotech (Beijing) Co., Ltd., China). The virulent genes encoding enterotoxins (entFM, nheA, nheB, and nheC) were amplified from the genomic DNA by PCR according to Yu et al 20 and Owusu-Kwarteng et al 21 using specific primers listed in Table 1 .…”

“…The PCR products were electrophoresed on 1% (w/v) agarose gel and visualized under ultraviolet illumination. The virulent B. cereus strain CA4, previously isolated from diseased snakehead fish Ophiocephalus argus, 14 was used as the control.…”