Vaccination of sex reversed hybrid tilapia (Oreochromis niloticus × O. aureus) with an inactivated Vibrio vulnificus vaccine

Vibrio vulnificus causes disease in economically important aquaculture raised fish and is an opportunistic human pathogen. This study reports on the isolation of V. vulnificus from diseased hybrid tilapia (Oreochromis niloticus × O. aureus) cultured in a North American water reuse facility. Our objectives were to characterize the isolate using biochemical and molecular methods, develop a disease challenge model, and determine the ability of a formalin inactivated whole-cell vaccine to protect against V. vulnificus. The V. vulnificus isolate recovered was biotype 1, 16S rRNA type B, vcg type C, and vvhA type 2 and caused disease in tilapia held in static salt water (1.5 g/l sea salt). Fish vaccinated with the formalin inactivated whole-cell vaccine responded to vaccination with titers from vaccinated fish ranging from 32 to 64 and titers from non-vaccinated fish ranging from 4 to 8. In two trials, vaccinated tilapia exhibited relative percent survival (RPS) of 73 and 60% following homologous isolate challenge. In two additional trials, vaccinated tilapia exhibited RPS values of up to 88% following challenge with a heterologous isolate; the use of a mineral oil adjuvant enhanced protection. This vaccine may provide an effective means of preventing infections caused by biochemically and genetically diverse V. vulnificus.     

Competitive exclusion as a mode of action of a novel Bacillus cereus aquaculture biological agent

Aims: To determine the contribution of potential modes of action of a Bacillus cereus aquaculture biological control agent in inhibition of the fish pathogen, Aeromonas hydrophila. Methods and Results: When B. cereus was tested in plate well inhibition studies, no production of antimicrobial compounds was detected. Bacillus cereus had a high growth rate (0·96 h^?1), whereas Aer. hydrophila concentration decreased by c. 70% in co‐culture experiments. In nutrient limitation studies, B. cereus had a significantly higher growth rate when cultured under glucose (P < 0·05) and iron (P < 0·01) limitation in comparison with Aer. hydrophila. Bacillus cereus glucose (0·30 g l^?1 h^?1) and iron (0·60 mg l^?1 h^?1) uptake rates were also significantly higher (P < 0·01) than the Aer. hydrophila glucose (0·14 g l^?1 h^?1) and iron (0·43 mg l^?1 h^?1) uptake rates. Iron uptake was facilitated by siderophore production shown in time profile studies where relative siderophore production was c. 60% through the late exponential and sporulation phases. Conclusions: Competitive exclusion by higher growth rate, competition for organic carbon and iron, facilitated by siderophore production, could be identified as mechanisms of pathogen growth inhibition by B. cereus. Significance and Impact of the Study: This study is the first elucidation of the mechanism of action of our novel B. cereus biological agent in growth attenuation of pathogenic Aer. hydrophila. This study enhances the application knowledge and attractiveness for adoption of B. cereus NRRL 100132 for exploitation in aquaculture.     

Identification of Omp38 by immunoproteomic analysis and evaluation as a potential vaccine antigen against Aeromonas hydrophila in Chinese breams

Aeromonas hydrophila is a fish pathogen causing systemic infections in aquatic environments, and determining its antigenic proteins is important for vaccine development to reduce economic losses in aquaculture worldwide. Here, an immunoproteomic approach was used to identify immunogenic outer membrane proteins (OMPs) of the Chinese vaccine strain J-1 using convalescent sera from Chinese breams. Seven unique immunogenic proteins were identified by two-dimensional (2-D) electrophoresis and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-TOF-MS). One protein of interest, Omp38, was expressed, and its immunogenicity and protective efficacy were evaluated in Chinese breams. The two groups of fish immunized with the inactivated vaccine and recombinant Omp38 protein showed significant serum IgM antibody levels after vaccination, compared with the fish injected with PBS buffer. In addition, the superoxide dismutase (SOD) activity, lysozyme (LSZ) activity and phagocytosis activity of head kidney lymphocytes of immunized groups were significantly higher than those of the control. The fish receiving inactivated vaccine and recombinant Omp38 protein developed a protective response to a live A. hydrophila challenge 45 days post-immunization, as demonstrated by increased survival of vaccinated fish over the control and by decreased histological alterations in vaccinated fish. Furthermore, protective effect was better in Omp38 group than in the inactivated vaccine group. These results suggest that the recombinant Omp38 protein could effectively stimulate both specific and non-specific immune responses and protect against A. hydrophila infection. Therefore, Omp38 may be developed as a potential vaccine candidate against A. hydrophila infection.     

Optimized Expression of <Emphasis Type="Italic">Helicobacter pylori</Emphasis><Emphasis Type="Italic">ureB</Emphasis> Gene in the <Emphasis Type="Italic">Lactococcus lactis</Emphasis> Nisin-Controlled Gene Expression (NICE) System and Experimental Study of Its Immunoreactivity

In the development of an oral vaccine against Helicobacter pylori, H. pylori urease subunit B (UreB) was expressed in a food-grade delivery vehicle, Lactococcus lactis NZ3900. The ureB gene (Genbank accession no. FJ436980) was amplified by polymerase chain reaction (PCR) from MEL-Hp27. The PCR-amplified ureB gene was cloned in the E. coli–L. lactis shuttle vector pNZ8110 and transformed into E. coli MC1061. After the transformant had been identified, the recombinant plasmid was purified and electrotransformed into L. lactis NZ3900. The conditions of UreB expression in the L. lactis transformant were optimized by orthogonal experiment. The maltose binding protein (MBP)-UreB fusion protein expressed by TB₁/pMAL-c2X-ureB was used to cultivate mice polyclonal anti-UreB serum after purification by the amylose prepacked column. The Western blot method was adopted to confirm whether the UreB expressed by L. lactis transformant had immunoreactivity. The optimized conditions for UreB expression were as follows. Nisin 40 ng/ml was added to the medium when the recombinant grew to OD₆₀₀≈0.30–0.40 and the induction time lasted 5 h. As a result, the maximum yield of UreB was 27.26 μg/mL of medium, and the maximum percentage of UreB in cell extracts of the L. lactis transformant reached its peak at 20.19%. Western blot analysis showed that the UreB protein expressed by L. lactis transformant had favorable immunoreactivity. All these results make an appealing case for construction of the food-grade vaccine for H. pylori.     

Immobilization of Lactococcus lactis to cellulosic material by cellulose‐binding domain of Cellvibrio japonicus

Aims: Immobilization of whole cells can be used to accumulate cells in a bioreactor and thus increase the cell density and potentially productivity, also. Cellulose is an excellent matrix for immobilization purposes because it does not require chemical modifications and is commercially available in many different forms at low price. The aim of this study was to construct a Lactococcus lactis strain capable of immobilizing to a cellulosic matrix. Methods and Results: In this study, the Usp45 signal sequence fused with the cellulose‐binding domain (CBD) (112 amino acids) of XylA enzyme from Cellvibrio japonicus was fused with PrtP or AcmA anchors derived from L. lactis. A successful surface display of L. lactis cells expressing these fusion proteins under the P45 promoter was achieved and detected by whole‐cell ELISA. A rapid filter paper assay was developed to study the cellulose‐binding capability of these recombinant strains. As a result, an efficient immobilization to filter paper was demonstrated for the L. lactis cells expressing the CBD‐fusion protein. The highest immobilization (92%) was measured for the strain expressing the CBD in fusion with the 344 amino acid PrtP anchor. Conclusions: The result from the binding tests indicated that a new phenotype for L. lactis with cellulose‐binding capability was achieved with both PrtP (LPXTG type anchor) and AcmA (LysM type anchor) fusions with CBD. Significance and Impact of the Study: We demonstrated that an efficient immobilization of recombinant L. lactis cells to cellulosic matrix is possible. This is a step forward in developing efficient immobilization systems for lactococcal strains for industrial‐scale fermentations.     

Dual recombinant Lactococcus lactis for enhanced delivery of DNA vaccine reporter plasmid pPERDBY

Food grade Lactococcus lactis has been widely used as an antigen and DNA delivery vehicle. We have previously reported the use of non‐invasive L. lactis to deliver the newly constructed immunostimulatory DNA vaccine reporter plasmid, pPERDBY. In the present report, construction of dual recombinant L. lactis expressing internalin A of Listeria monocytogenes and harboring pPERDBY (LL InlA + pPERDBY) to enhance the efficiency of delivery of DNA by L. lactis is outlined. After confirmation and validation of LL InlA + pPERDBY, its DNA delivery potential was compared with previously developed non‐invasive r‐ L. lactis::pPERDBY. The use of invasive L. lactis resulted in around threefold increases in the number of enhanced green fluorescent protein‐expressing Caco‐2 cells. These findings reinforce the prospective application of invasive strain of L. lactis for delivery of DNA/RNA and antigens.     

Stereology and computer assisted three-dimensional reconstruction as tools to study probiotic effects of Aeromonas hydrophila on the digestive tract of germ-free Artemia franciscana nauplii

Aims: Validation of stereology and three‐dimensional reconstruction for monitoring the probiotic effect of Aeromonas hydrophila on the gut development of germ‐free Artemia franciscana nauplii. Methods and Results: Germ‐free Artemia nauplii were cultured using Baker’s yeast and dead Aer. hydrophila. Live Aer. hydrophila were added on the first day to the treatment group. The gut length and volume were monitored on days two and four using stereology and three‐dimensional reconstruction. Both methods showed comparable results. Stereology was least labour intensive to estimate volumes, while three‐dimensional reconstructions rendered architectural and topographical data of the gut. Moreover, a positive effect of probiotic bacterium, Aer. hydrophila is likely. Conclusion: Slight increment in the growth of the digestive tract of A. franciscana nauplii exerted by probiotic bacteria could be detected using stereology and three‐dimensional reconstruction. Significance and Impact of the Study: The gnotobiotic Artemia rearing system is unique to investigate the effects of micro‐organisms on the development of nauplii. However, in the base of this model system, only survival counts and length measurements exist as monitoring tools. Therefore, additional tools such as stereology and three‐dimensional reconstruction are prerequisite to obtain more powerful analysis.     

Food-Grade Expression of <Emphasis Type="Italic">Helicobacter pylori</Emphasis> UreB Subunit in <Emphasis Type="Italic">Lactococcus lactis</Emphasis> and its Immunoreactivity

Helicobacter pylori is the principal cause of chronic active gastritis, peptic ulcer, and gastric cancer. To develop an oral vaccine against H. pylori infection, we had expressed the H. pylori ureB gene (Genbank accession no. FJ436980) in nisin-controlled expression vectors using Lactococcus lactis NZ3900 as host. The ureB gene was amplified by PCR from a H.pylori strain MEL-Hp27. Then the ureB gene was fused translationally downstream of the nisin-inducible promoter nisA in a L. lactis plasmid pNZ8149. Lactose utilization based on the complementation of the lacF gene was used as a dominant selection marker for the food-grade expression system employing L. lactis NZ3900. The conditions of UreB expression in this system were optimized by orthogonal experiment. The optimized conditions have been determined as follows: induction of expression was carried out at the cells density of OD₆₀₀ ≈ 0.4 with 25 ng/ml nisin, and harvest after 5 h. The maximum percentage of recombinant UreB was estimated to be 7% of total soluble cellular proteins and the yield was 12.9 μg/ml. Western blot demonstrated that the UreB protein was expressed in the L. lactis transformant and had favorable immunoreactivity. These results indicated that the lactococci-derived vaccines could be promising candidates as alternative vaccine strategies for preventing H. pylori infection.     

Detection of aerolysin gene in <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis> isolated from fish and pond water

Aerolysin is a hemolytic toxin encoded by aerolysin gene (1482 bp) that plays a key role in the pathogenesis of Aeromonas hydrophila infection in fish. New speciesspecific primers were designed to amplify 326 bp conserved region of aerolysin gene for A. hydrophila. Twenty-five isolates of A. hydrophila recovered from fish and pond water were studied for detection of aerolysin gene. Aerolysin gene was detected in 85% of the isolates during the study. The designed primers were highly specific and showed no cross reactivity with Escherichia coli, Aeromonas veronii, Vibrio cholerae, Flavobacterium spp., Chyseobacterium spp. and Staphylococcus aureus. The sensitivity limit of primers for detection of aerolysin gene in the genomic DNA of A. hydrophila was 5 pg.     

Loss of Plasmid-Mediated Oligopeptide Transport System in Lactococci: Another Reason for Slow Milk Coagulation

Fast milk-coagulating (Fmc⁺) strains of lactococci are known to segregate slow milk-coagulating (Fmc⁻) variants, which has been attributed to loss of proteinase (Prt) activity encoded by plasmid DNA. It was found that the Fmc⁻phenotype could also be due to loss of a plasmid encoding an oligopeptide permease (Opp) system. InLactococcus lactissubsp.lactis(L. lactis) C2O, lactose metabolism (Lac) and Prt were linked to pJK550 and the Opp system to pJK430. InLactococcus lactissubsp.cremorisSK11, known to possess Prt on a 78-kb plasmid, DNA sequence analysis of a 7.4-kb region from the Lac plasmid, pSK11L, revealed that it possessed the Opp system. The Lac plasmid inL. lactisC2 encoded both the Prt and Opp systems. Fmc⁻derivatives ofL. lactisC2 were missing theprtgenes and had Opp integrated into the chromosome, possibly due to transposition events. Growth studies showed the Opp systems were functional and, in combination with Prt, produced the Fmc⁺phenotype.     

Functional expression of mouse insulin-like growth factor-I with food-grade vector in Lactococcus lactis NZ9000

Aims: To functionally express the recombinant mouse insulin‐like growth factor‐I (rtmIGF‐I) in Lactococcus lactis NZ9000 with a food‐grade vector. Methods and Results: The rtmIGF‐I encoding sequence was inserted into secreted food‐grade vector pLEB688 and transformed into L. lactis NZ9000. The expression of the recombinant protein rtmIGF‐I was confirmed by tricine‐SDS‐PAGE analysis and Western blot. The concentration of this recombinant protein was 3 mg l^?1 in the medium fraction. Further experiment demonstrated that the recombinant protein was biologically active and promoted NIH3T3 cell proliferation in a concentration‐dependent manner. Conclusions: The rtmIGF‐I was expressed in L. lactis and located into the medium fraction. The optimal final concentration which could promote NIH3T3 cell proliferation after incubation was 100 ng ml^?1. Significance and Impact of the Study: The rtmIGF‐I was functionally expressed in L. lactis NZ9000 with a food‐grade vector. Thus, the recombinant L. lactis NZ9000 could act as a host for the production of rtmIGF‐I for further study. The recombinant strain could serve as an IGF‐I delivery system.     

Attenuation of a virulent Aeromonas hydrophila with novobiocin and pathogenic characterization of the novobiocin‐resistant strain

Aim

To determine whether novobiocin resistance strategy could be used to attenuate a virulent Aeromonas hydrophila AH11P strain and to characterize the growth and pathogenic differences between the novobiocin‐resistant strain and its virulent parent strain AH11P.

Methods and Results

A novobiocin‐resistant strain AH11NOVO was obtained from a virulent Aer. hydrophila strain AH11P through selection of resistance to novobiocin. AH11NOVO was found to be avirulent to channel catfish (Ictalurus punctatus), whereas AH11P was virulent. When AH11NOVO vaccinated channel catfish were challenged with AH11P at 14 days postvaccination, relative per cent of survival of vaccinated fish was 100%. The cell proliferation rate of AH11NOVO was found to be significantly (P < 0·05) less than that of AH11P. In vitro motility assay revealed that AH11NOVO was nonmotile, whereas AH11P was motile. AH11NOVO had significantly (P < 0·05) lower in vitro chemotactic response to catfish mucus than that of AH11P. Although the ability of AH11NOVO to attach catfish gill cells was similar to that of AH11P, the ability of AH11NOVO to invade catfish gill cells was significantly (P < 0·05) lower than that of AH11P.

Conclusions

The novobiocin‐resistant AH11NOVO is attenuated and different from its parent AH11P in pathogenicity.

Significance and Impact of the Study

The significantly lower chemotactic response and invasion ability of AH11NOVO compared with that of its virulent parent strain AH11P might shed light on the pathogenesis of Aer. hydrophila.     

Comparative proteomic analysis of four biotechnological strains Lactococcus lactis through label-free quantitative proteomics

Lactococcus lactis is a bacteria with high biotechnological potential, where is frequently used in the amino acid production and production of fermented dairy products, as well as drug delivery systems and mucosal vaccine vector. The knowledge of a functional core proteome is important extremely for both fundamental understanding of cell functions and for synthetic biology applications. In this study, we characterized the L. lacits proteome from proteomic analysis of four biotechnological strains L. lactis: L. lactis subsp. lactis NCDO2118, L. lactis subsp. lactis IL1403, L. lactis subsp. cremoris NZ9000 and L. lactis subsp. cremoris MG1363. Our label-free quantitative proteomic analysis of the whole bacterial lysates from each strains resulted in the characterization of the L. lactis core proteome that was composed by 586 proteins, which might contribute to resistance of this bacterium to different stress conditions as well as involved in the probiotic characteristic of L. lactis. Kegg enrichment analysis shows that ribosome, metabolic pathways, pyruvate metabolism and microbial metabolism in diverse environments were the most enriched. According to our quantitative proteomic analysis, proteins related to translation process were the more abundant in the core proteome, which represent an important step in the synthetic biology. In addition, we identified a subset of conserved proteins that are exclusive of the L. lactis subsp. cremoris or L. lactis subsp. lactis, which some are related to metabolic pathway exclusive. Regarding specific proteome of NCDO2118, we detected ‘strain-specific proteins’. Finally, proteogenomics analysis allows the identification of proteins, which were not previously annotated in IL1403 and MG1363. The results obtained in this study allowed to increase our knowledge about the biology of L. lactis, which contributes to the implementation of strategies that make it possible to increase the biotechnological potential of this bacterium.     

The Aer2 receptor from Vibrio cholerae is a dual PAS‐heme oxygen sensor

The diarrheal pathogen Vibrio cholerae navigates complex environments using three chemosensory systems and 44–45 chemoreceptors. Chemosensory cluster II modulates chemotaxis, whereas clusters I and III have unknown functions. Ligands have been identified for only five V. cholerae chemoreceptors. Here, we report that the cluster III receptor, VcAer2, binds and responds to O₂. VcAer2 is an ortholog of Pseudomonas aeruginosa Aer2 (PaAer2) but differs in that VcAer2 has two, rather than one, N‐terminal PAS domain. We have determined that both PAS1 and PAS2 form homodimers and bind penta‐coordinate b‐type heme via an Eη‐His residue. Heme binding to PAS1 required the entire PAS core, but receptor function also required the N‐terminal cap. PAS2 functioned as an O₂‐sensor [ , 19 μM], utilizing the same Iβ Trp (W276) as PaAer2 to stabilize O₂. The crystal structure of PAS2‐W276L was similar to that of PaAer2‐PAS but resided in an active conformation mimicking the ligand‐bound state, consistent with its signal‐on phenotype. PAS1 also bound O₂ [ , 12 μM], although O₂ binding was stabilized by either a Trp residue or Tyr residue. Moreover, PAS1 appeared to function as a signal modulator, regulating O₂‐mediated signaling from PAS2 and resulting in activation of the cluster III chemosensory pathway.     

Diversity of extracellular proteases among Aeromonas determined by zymogram analysis

Aims: The current research was aimed at comparing extracellular proteolytic activities and zymogram profiles among Aeromonas spp. Methods and Results: Extracellular proteases of 47 strains of Aeromonas were analyzed by substrate (casein and gelatin) co‐polymerized SDS‐PAGE, and caseinolytic activity was determined using azocasein. Large variation on caseinolytic activity was evidenced. In general, the caseinolytic activity of Aeromonas hydrophila strains was significantly higher than that of other Aeromonas species. Several caseinolytic and gelatinolytic profiles were detected in Aeromonas. Cluster analysis allowed separating Aeromonas strains in four and three groups, based on their caseinolytic and gelatinolytic profiles, respectively. Although not specific patterns were evident, most Aer. hydrophila strains were clustered together and differed from Aeromonas caviae strains. The main caseinases of Aer. hydrophila were a serine protease with an apparent molecular weight (AMW) of 56 kDa and a metalloprotease with AMW of 22 kDa. Gelatinase profiles were characterized by the presence of high molecular weight metalloproteases (84 and 93 kDa), although the most active enzyme was a serine protease with AMW of 56 kDa. Other new caseinases and gelatinases were detected in specific Aeromonas strains. Conclusions: Aeromonas strains exhibited several extracellular proteolytic profiles, with a larger inter than intraspecific variation. Moreover, zymogram analyses allowed identifying new caseinases and gelatinases in Aeromonas. Significance and Impact of the Study: This is the first report on the intra‐ and interspecific variation of proteolytic profiles in Aeromonas determined by zymogram analysis, including the detection of new caseinases and gelatinases in this genus.     

Secretory expression of K88 (F4) fimbrial adhesin FaeG by recombinant <Emphasis Type="Italic">Lactococcus lactis</Emphasis> for oral vaccination and its protective immune response in mice

K88 (F4) fimbrial adhesin, FaeG, was expressed extracellularly in Lactococcus lactis using a nisin-controlled gene expression system. The antibody response and protective efficacy of the recombinant bacteria (L. lactis [spNZ8048-faeG]) against live enterotoxigenic E. coli (ETEC) C₈₃₅₄₉ challenge were evaluated in ICR mice. Mice vaccinated with L. lactis [spNZ8048-faeG] had a significantly increased antigen-specific IgG level in the serum and decreased mortality rate (P < 0.05) compared with the control. This indicates that oral immunization of L. lactis [spNZ8048-faeG] can induce an immune-response protection upon challenge with live ETEC in ICR mice. An erratum to this article can be found at     

Immunoproteomic analysis and identification of novel immunogenic proteins from Vibrio harveyi

Aims: The main aim of this study was to screen novel immunogenic proteins of Vibrio harveyi, which could be vaccine candidates. Methods and Results: Whole‐cell proteins of V. harveyi, strain Li01 and Huang01, were first separated by isoelectric focusing, followed by 2D‐PAGE, respectively. Immunogenic proteins were identified by Western blotting, using Epinephelus coioides antisera against V. harveyi strain Li01. Western blot analyses revealed 16 shared immunogenic protein spots in both strains. All of the immunogenic proteins were successfully identified and corresponded to 15 proteins. None of these proteins have been previously reported as immunogenic for V. harveyi. Of the 15 proteins, 11 are specific immunoreactive proteins and four are nonspecific immunoreactive proteins. Furthermore, outer membrane protein N (spot 2) and oligopeptide ATP‐binding cassette (ABC) transporter (spot 3) were used as immunogens to immunize E. coioides for investigation of their protective abilities and activities. The E. coioides immunized with OmpN has abilities to fight against infections caused by V. harveyi Li01 and Huang01. However, vaccination with oligopeptide ABC transporter induces low protective immune response in fish. Conclusions: Eleven novel specific antigens were found, and OmpN could potentially be used as vaccine candidate for the development of novel vaccine against V. harveyi. Significance and Impact of the Study: These data show that immunoproteomics methods can be successfully applied in identifying immunogenic proteins of V. harveyi, which helps to search for the protective antigens in future.     

Neutrophil activity affects Oreochromis mossambicus (Peters, 1852) antibody production against heat‐killed Aeromonas hydrophila vaccine

Aeromonas hydrophila is one of the important and most common pathogens of warm water fish. Prophylactic and therapeutic measures against A. hydrophila infection are essential to prevent loss of fish production in aquaculture. A heat‐killed vaccine was developed against three strains of A. hydrophila, namely O21, O26 and O28, and analysed for their comparative immunogenicity in Oreochromis mossambicus (Peters, 1852). Studied were the neutrophil activity and specific antibody response of the host against the vaccines, which showed that neutrophil activity was highest for the heat‐killed O21, but that the heat‐killed O28 produced the highest antibody titres. The antibody cross‐reactivity tests indicated that the antibody raised against O28 was pan‐reactive whereas it was less cross‐reactive in O21. Thus strain O28 may be used as a vaccine candidate for a pan‐protection of fish from various strains of A. hydrophila infections. However, further rigorous studies with different fish species and bacterial strains are needed to confirm these results.     

High yield expression of an AHL-lactonase from <Emphasis Type="Italic">Bacillus</Emphasis> sp. B546 in <Emphasis Type="Italic">Pichia pastoris</Emphasis> and its application to reduce <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis> mortality in aquaculture

Background  

Aeromonas hydrophila is a serious pathogen and can cause hemorrhagic septicemia in fish. To control this disease, antibiotics and chemicals are widely used which can consequently result in "superbugs" and chemical accumulation in the food chain. Though vaccine against A. hydrophila is available, its use is limited due to multiple serotypes of this pathogen and problems of safety and efficacy. Another problem with vaccination is the ability to apply it to small fish especially in high numbers. In this study, we tried a new way to attenuate the A. hydrophila infection by using a quorum quenching strategy with a recombinant AHL-lactonase expressed in Pichia pastoris.     

A small IncQ-type plasmid carrying the quinolone resistance (qnrS2) gene from Aeromonas hydrophila

Aims: To investigate the qnrS2 gene encoded by a plasmid obtained from Aeromonas hydrophila. Methods and Results: To investigate the full‐length sequence of the plasmid carrying qnrS2 (plasmid designated pAHH04) from the strain SNUFPC‐A10, the full‐length coding sequence of the qnrS region was first amplified. The remaining part of the plasmid was read outwards from this region. The plasmid pAHH04 contained the repC, repA, mobA and mobC genes, and its total size was 7191 bp with a G+C content of 60%. Conclusions: This study describes the full‐length sequence of a plasmid carrying the qnrS2 gene from Aer. hydrophila. The plasmid pAHH04 carried plasmid replication and mobilization genes from IncQ‐type plasmids. Significance and Impact of the Study: The isolated qnrS2 gene encoded by a plasmid from an Aer. hydrophila strain is of significant importance because it emphasizes the problem of antibiotic resistance as well as the ability of the determinants to spread among the different bacterial species that impact human health.