A Nonluminescent and Highly Virulent Vibrio harveyi Strain Is Associated with “Bacterial White Tail Disease” of Litopenaeus vannamei Shrimp

Recurrent outbreaks of a disease in pond-cultured juvenile and subadult Litopenaeus vannamei shrimp in several districts in China remain an important problem in recent years. The disease was characterized by “white tail” and generally accompanied by mass mortalities. Based on data from the microscopical analyses, PCR detection and 16S rRNA sequencing, a new Vibrio harveyi strain (designated as strain HLB0905) was identified as the etiologic pathogen. The bacterial isolation and challenge tests demonstrated that the HLB0905 strain was nonluminescent but highly virulent. It could cause mass mortality in affected shrimp during a short time period with a low dose of infection. Meanwhile, the histopathological and electron microscopical analysis both showed that the HLB0905 strain could cause severe fiber cell damages and striated muscle necrosis by accumulating in the tail muscle of L. vannamei shrimp, which led the affected shrimp to exhibit white or opaque lesions in the tail. The typical sign was closely similar to that caused by infectious myonecrosis (IMN), white tail disease (WTD) or penaeid white tail disease (PWTD). To differentiate from such diseases as with a sign of “white tail” but of non-bacterial origin, the present disease was named as “bacterial white tail disease (BWTD)”. Present study revealed that, just like IMN and WTD, BWTD could also cause mass mortalities in pond-cultured shrimp. These results suggested that some bacterial strains are changing themselves from secondary to primary pathogens by enhancing their virulence in current shrimp aquaculture system

Shewanella putrefaciens: an emerging pathogen for farmed yellow catfish Pelteobagrus fulvidraco

Bacteriosis has caused significant economic losses in farmed yellow catfish Pelteobagrus fulvidraco. Information is limited on Shewanella putrefaciens as a pathogen for yellow catfish. In this study, a virulent strain, temporarily named Y2, was isolated from diseased yellow catfish, identified phenotypically and molecularly as S. putrefaciens. A phylogenetic tree was constructed to examine isolate Y2 and compare it to other known isolates. In addition, isolate Y2 is apparently susceptible to aminoglycosides and tetracycline drugs for veterinary use in aquaculture as revealed when screened against a range of common antibiotics. To the best of our knowledge, this is the first report of S. putrefaciens as an emerging pathogen for cultured yellow catfish

Control by Herbal Extract of Serratia marcescens from Cultured Siberian Sturgeon Acipenser baerii Brandt

A virulent strain of Serratia marcescens, provisionally named SFY, was isolated from farmed Siberian sturgeon Acipenser baerii Brandt suffering from mouth-swelling disease and identified using the ATB 32GN system. Its taxonomic position was determined by phylogenetic analysis. A phylogenetic tree constructed using the neighbor-joining method showed that the SFY isolate was the S. marcescens strain (GenBank accession no. FJ530951). The strain was resistant to chloramphenicol, erythromycin, furazolidone, sulfamethoxydiazine, tetracycline, and trimethoprim-sulfamethoxazole, and susceptible to ciprofloxacin, enrofloxacin, gentamicin, neomycin, norfloxacin, ofloxacin, and streptomycin. Extracts from 30 Chinese herbs were screened as possible agents for control of the disease. Fructus mume extract was the most efficacious agent against the SFY isolate and control bacteria, indicated by its low minimum inhibitory concentration ≤21 mg/ml. At concentrations of 10 and 15 g/kg feed, protective efficacy was 42.68% and 64.64%

Providencia rettgeri: an Emerging Pathogen for Freshwater Cultured Whiteleg Shrimp (Penaeus vannamei)

Bacteriosis is a major economic problem affecting the farming industry of whiteleg shrimp Penaeus vannamei. Little information is available on Providencia rettgeri as a possible pathogen for P. vannamei. In this study, a virulent strain, here named S6, was isolated from diseased P. vannamei, identified phenotypically, and molecularly, as P. rettgeri. A phylogenetic tree was constructed to examine the taxonomic position and relatedness of isolate S6 to other P. rettgeri isolates. When screened against a range of common veterinary antibiotics, isolate S6 exhibited resistance to aminoglycosides and sulfonamides antibiotics in aquaculture. To the best of our knowledge, this is the first report of P. rettgeri as a causal agent of bacteriosis in freshwater farmed P. vannamei

Citrobacter freundii: a Causative Agent for Tail Rot Disease in Freshwater Cultured Japanese Eel Anguilla japonica

Tail rot disease causes significant economic damage in freshwater farmed Japanese eel Anguilla japonica, yet information on Citrobacter freundii as a possible causal agent for this disease is scarce. In this study, a virulent strain, temporarily named MINA, was isolated from diseased A. japonica suffering from tail rot disease. It was identified through phylogenetic analysis and phenotypic characteristics and thus compared to other known isolates. Isolate MINA has developed multiple resistances to penicillin, quinolones and sulfonamide antibiotics as well as to amide alcohols, cephalosporin, glycopeptide and macrolide drugs used in aquaculture when screened against a range of common antibiotics. To the best of our knowledge, this is the first report of tail rot disease caused by C. freundii in freshwater farmed A. japonica

Aeromonas schubertii: a Potential Pathogen for Freshwater Cultured Whiteleg Shrimp, Penaeus vannamei

Bacteriosis has become a major global economic problem in freshwater farmed whiteleg shrimp Penaeus vannamei. However, limited information is available on the incidence of Aeromonas schubertii infections in freshwater cultured P. vannamei. Red body disease, an epidemic frequently associated with P. vannamei freshwater farming, occurred in a P. vannamei farm in Shanghai China in June 2013. A pathogenic strain of A. schubertii (isolate HS1) was isolated from diseased freshwater cultured P. vannamei suffering from red body disease, and identified through phylogenetic analysis and phenotypic characteristics. A phylogenetic tree was constructed to examine the relatedness of isolate HS1 with other A. schubertii isolates. In addition, isolate HS1 showed no signs developing antibiotic resistance when screened against a range of common antibiotics used in aquaculture. To the best of our knowledge, this is the first report of A. schubertii infection in freshwater farmed P. vannamei

Penaeus vannamei, white feces syndrome, Vibrio cholerae, pathogenicity, antibiotic susceptibility

Whiteleg shrimp Penaeus vannamei is an important commercial shrimp species cultivated in China and many other countries worldwide. Bacteriosis is a major economic problem that inhibits the farming of this species in fresh water. White feces syndrome is an emerging epidemic in freshwater cultured P. vannamei and has caused significant economic damage. Only scarce information is available on Vibrio cholerae as a possible causal agent for this disease. In this study, a virulent strain BB31 was isolated from diseased P. vannamei suffering from white feces syndrome, and identified as a V. cholerae isolate through phylogenetic analysis and phenotypic characteristics. A phylogenetic tree was constructed to examine the relationship of isolate BB31 to other V. cholerae isolates. Three genes encoding hemolysin, outer membrane protein, and cholera toxin transcriptional activator were present in the BB31 isolate confirming its potential pathogenicity. In addition, isolate BB31 is known to have developed resistance to penicillin, sulfonamides and cephalosporin antibiotics. This was demonstrated when screened against a range of common antibiotics for aquaculture and veterinary use. To the best of our knowledge, this is the first report of white feces syndrome caused by V. cholerae in freshwater farmed P. vannamei

Aeromonas hydrophila: a Causative Agent for Tail Rot Disease in Freshwater Cultured Murray Cod Maccullochella peelii

Tail rot disease is the cause of significant economic damage in freshwater farmed Murray cod Maccullochella peelii. Only scarce information is available on Aeromonas hydrophila as a possible causal agent for this disease. In this study, a virulent strain, temporarily named XY3, was isolated from diseased codfish suffering from tail rot disease, and identified as A. hydrophila through phylogenetic analysis and phenotypic characteristics. A. hydrophila possesses multiple virulence genes including aerA, ahpA, alt, ast and hlyA genes. In addition, it appears that isolate XY3 has developed multiple resistances to cephalosporin, chloromycetin, glycopeptides, macrolides, nitrofuran, and penicillin drugs, as well as to aminoglycosides, sulfonamides, and tetracyclines antibiotics for veterinary uses in aquaculture as revealed when screened against a range of common antibiotics. To the best of our knowledge, this is the first report of tail rot disease caused by A. hydrophila in freshwater farmed codfish

Effect of Dietary Supplementation of Lactobacillus Casei YYL3 and L. Plantarum YYL5 on Growth, Immune Response and Intestinal Microbiota in Channel Catfish

The purpose of this study is to investigate the effect of probiotics L. casei YYL3 (Lc) and L. plantarum YYL5 (Lp) on growth performance, innate immunity, disease resistance and intestinal microbiota of channel catfish. A total of 252 catfish (67.20 ± 1.46 g) were randomly divided into 3 groups which were fed with basal diet, Lc-added (3.0 × 108 cfu/g) or Lp-added (3.0 × 108 cfu/g) diets, respectively. After 4 weeks of feeding, Lc significantly enhanced the growth and feed utilization of channel catfish compared with the control group (CG). Following that, the catfish were challenged with an intraperitoneal injection of 200 μL of the pathogenic E.ictaluri (2.0 × 106 cfu/mL), the relative percent survival of Lc and Lp were 38.28% and 12.76%, respectively. High-throughput sequencing indicated Lc and Lp reduced the alpha diversity of the intestinal microbiota in channel catfish. Lactobacillus were overwhelming in the guts during probiotics treatment, but almost vanished away after 2 weeks post-cessation of probiotics administration. Compared to CG, Lc and Lp resulted in an increased abundance of Pseudomonas and decreased amount of Aeromonas. Functional analysis revealed that Lc treatment upregulated the relative abundance of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways including lipid metabolism, metabolism of other amino acids, metabolism of terpenoids and polyketides, xenobiotics biodegradation and metabolism, and nucleotide metabolism. Combined, our data revealed that Lc, as a feed additive at 3.0 × 108 cfu/g, could promote the growth performance, disease resistance and dramatically change the composition of intestinal microbiota of channel catfish