首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 296 毫秒
1.
Plasmid-mediated antibiotic resistance was first discovered in Edwardsiella ictaluri in the early 1990s, and in 2007 an E. ictaluri isolate harboring an IncA/C plasmid was recovered from a moribund channel catfish Ictalurus punctatus infected with the bacterium. Due to the identification of multidrug resistance plasmids in aquaculture and their potential clinical importance, we sought to determine whether the modified live E. ictaluri vaccine strain in AQUAVAC-ESC harbors such plasmids, so that the use of this vaccine will not directly contribute to the pool of bacteria carrying plasmid-borne resistance. Antimicrobial sensitivity testing of the E. ictaluri parent isolate and vaccine strain demonstrated that both were sensitive to 15 of the 16 antimicrobials tested. Total DNA from each isolate was analyzed by polymerase chain reaction (PCR) using a set of 13 primer pairs specific for conserved regions of the IncA/C plasmid backbone, and no specific products were obtained. PCR-based replicon typing of the parent isolate and vaccine strain demonstrated the absence of the 18 commonly occurring plasmid incompatibility groups. These results demonstrate that the vaccine strain does not carry resistance to commonly used antimicrobials and provide strong support for the absence of IncA/C and other commonly occurring plasmid incompatibility groups. Therefore, its use should not directly contribute to the pool of bacteria carrying plasmid-borne resistance. This work highlights the importance of thoroughly investigating potential vaccine strains for the presence of plasmids or other transmissible elements that may encode resistance to antibiotics.  相似文献   

2.
Abstract

Edwardsiella ictaluri, the etiological agent of enteric septicemia of catfish (ESC), is the leading cause of bacterial disease in commercially raised channel catfish Ictalurus punctatus. Little work has been conducted at a genotypic level to determine potential virulence characteristics, but the production of chondroitin sulfatase is a suspected virulence factor. Using transpositional mutagenesis, we created stable E. ictaluri mutants that are deficient in chondroitinase activity. Channel catfish were challenged by injection with E. ictaluri transposon mutant MI15. None of the catfish challenged with the mutant died or showed signs of ESC. These fish were held for 2 weeks and then challenged by injection with the known virulent parent strain of E. ictaluri. The challenged naive control fish showed clinical signs of and a mortality rate consistent with ESC, whereas catfish that had been injected with MI15 prior to challenge with the parent strain were resistant to disease. This work represents a preliminary study to suggest a possible role of chondroitin sulfatase activity in the virulence of E. ictaluri.  相似文献   

3.
Enteric septicemia of catfish (ESC), caused by Edwardsiella ictaluri, is the most problematic bacterial disease affecting catfish aquaculture in the southeastern United States. Efforts to develop an effective ESC vaccine have had limited industrial success. In commercial settings, ESC vaccines are typically administered by immersion when fry are transferred from the hatchery to rearing ponds. While this approach is a practical method of mass delivery, this strategy administers vaccines to very young fish, which lack a fully developed immune system. To circumvent this limitation, an oral vaccination strategy was evaluated as a means of immunizing catfish at the fingerling stage of production, when fish possess a more complete immune arsenal. A virulent E. ictaluri isolate (S97-773) was attenuated by successive passage on media containing increasing concentrations of rifamycin. In laboratory trials, cultured vaccine was diluted and mixed with feed (100 mL diluted vaccine/454 g feed). This mixture was then fed to Channel Catfish Ictalurus punctatus fingerlings. Two separate dilutions of cultured vaccine (1:10 and 1:100) were used to create the vaccine–feed mixture, equating to estimated doses of 5 × 107 and 5 × 106 CFU/g of feed, respectively. After 30 d, catfish were exposed by immersion (1 × 106 CFU/mL) to the virulent parental strain of E. ictaluri. The target dose (1:100 dilution, ～5 × 106 CFU/g of feed) offered exceptional protection (relative percent survival = 82.6–100%). In addition, negligible deaths occurred in fish vaccinated at 10 times the target dose (1:10 dilution, ～5 × 107 CFU/g of feed). In pond trials, antibody production increased 18-fold in orally vaccinated fish. When compared with nonvaccinated controls, vaccination significantly improved survival, feed fed, feed conversion, biomass produced, and total harvest. This research demonstrates Channel Catfish can be successfully immunized in a commercial setting against E. ictaluri with a single dose of an orally delivered, live attenuated, E. ictaluri vaccine.

Received July 31, 2014; accepted March 2, 2015  相似文献   


4.
Non‐typhoidal Salmonella (NTS) are a significant source of foodborne illness worldwide, with disease symptoms most often presenting as self‐limiting gastroenteritis; however, occasionally the infection spreads and becomes invasive, frequently requiring anti‐microbial treatment. The cattle‐adapted Dublin serovar of NTS has commonly been associated with invasive illness and anti‐microbial resistance (AMR). Here, the enhanced resolution conferred by whole‐genome sequencing was utilized to elucidate and compare the resistome and genetic relatedness of 14 multidrug‐resistant (MDR) and one pan‐susceptible S. Dublin, isolated primarily in Pennsylvania, from fresh retail meat (one isolate) and humans (14 isolates). Twelve different genetic AMR determinants, including both acquired and chromosomal, were identified. Furthermore, comparative plasmid analysis indicated that AMR was primarily conferred by a putative IncA/C2 plasmid. A single pan‐susceptible S. Dublin isolate, collected from the same timeframe and geographical region as the MDR isolates, did not carry an IncA/C2 replicon sequence within its genome. Moreover, the pan‐susceptible isolate was genetically distinct from its MDR counterparts, as it was separated by ≥267 single nucleotide polymorphisms (SNPs), whereas there was a ≤38 SNP distance between the MDR isolates. Collectively, this data set advances our understanding of the genetic basis of the highly drug‐resistant nature of S. Dublin, a serovar with significant public health implications.  相似文献   

5.
Multidrug-resistant Salmonella enterica serovar Typhimurium (S. Typhimurium) isolates with four different antimicrobial resistance patterns obtained from a beef cattle farm were characterized to determine their clonality. Macrorestriction analysis of genomic DNA revealed that these four isolates are closely related to each other and can be classified as a newly emerged pulsed-field gel electrophoresis type among cattle: cluster VII. Three of the four isolates showed resistance to extended-spectrum cephalosporins (ESCs), and this resistance was mediated by AmpC β-lactamase encoded by the bla(CMY-2) gene in a 190-kbp IncA/C plasmid. Results of restriction analysis and IncA/C backbone PCR suggest that the three 190-kbp plasmids are identical and that a 70-kbp IncA/C plasmid of the ESC-susceptible isolate is derived from the 190-kbp plasmid by a deletion event. Three isolates harboured a virulence-resistance plasmid (165 or 180 kbp), and restriction analysis revealed that these plasmids were identical or closely related to each other. These results suggest that the four S. Typhimurium cluster VII isolates originate from a common ancestor that probably invaded the farm prior to the salmonellosis outbreak. Antimicrobial resistance patterns may not necessarily reflect the relationships of the isolates.  相似文献   

6.
  相似文献   

7.
Cephalexin is a first generation cephalosporin commonly used in dogs for treatment of pyoderma. The objective of this study was to evaluate the in vivo effects of cephalexin on selection of Escherichia coli resistant to extended-spectrum cephalosporins. A cohort study was conducted on 13 dogs presenting clinical signs of pyoderma and treated with cephalexin and 22 healthy dogs that had not been treated with antibiotics during the previous six months. Selective plating of faeces on MacConkey agar plates containing cefotaxime (CTX) yielded growth of CTX-resistant E. coli for eight of the 13 treated dogs (62%), whereas no growth was observed for any of the control dogs (Fisher exact test, P<0.001). PCR and sequence analysis identified bla(CMY-2) in all eight dogs. PCR-based replicon typing and restriction fragment length polymorphism (RFLP) of E. coli transformants revealed location of bla(CMY-2) on indistinguishable IncI1 plasmids in five of the eight dogs. One representative of these five epidemiologically related IncI1 plasmids was further characterized as sequence type (ST2) by plasmid multilocus sequence typing (pMLST). E. coli from the remaining three dogs harboured bla(CMY-2) on distinct plasmids with non-typeable replicons. A single isolate was classified as an extraintestinal pathogenic E. coli (ExPEC) due to the presence of iutA, papC and sfa/foc. The results provide a strong indication that cephalexin selects for E. coli producing plasmid-borne CMY-2 β-lactamase. The isolation of a specific IncI1 plasmid carrying bla(CMY-2) from five epidemiologically unrelated dogs suggests that cephalexin use may contribute to the spread of this plasmid lineage among Danish dogs.  相似文献   

8.
Resistance to Serum Complement,iss, and Virulence of Avian Escherichia coli   总被引：2，自引：0，他引：2  
Control of avian colibacillosis is hampered by lack of easily identifiable markers for virulent Escherichia coli. Resistance to serum complement appears to be a widespread trait of virulent avian E. coli, suggesting that bacterial factors promoting survival in serum may be useful in discriminating between virulent and avirulent isolates. Such distinguishing factors may prove useful in diagnostic protocols or as targets in future colibacillosis control protocols. Interestingly, the factors responsible for resistance to complement differ in the E. coli isolated from mammalian and avian hosts, which may reflect differences in the nature of avian and mammalian colibacillosis. In some cases, genetic determinants for serum complement resistance in avian E. coli are found on aerobactin- or Colicin V-encoding plasmids. One such gene, iss, first described for its role in the serum resistance associated with a ColV plasmid from a human E. coli isolate, occurs much more frequently in isolates from birds with colibacillosis than in faecal isolates from healthy birds. Efforts to identify the genomic location of iss in a single, virulent avian E. coli isolate have revealed that it occurs in association with several purported virulence genes, all linked to a large conjugative R plasmid. At this time, it is not known whether iss merely marks the presence of a larger pathogenicity unit or is itself a contributor to virulence. Nevertheless, the presence of the complement-resistance determinant, iss, may be a marker of virulent avian E. coli exploitable in controlling avian colibacillosis.  相似文献   

9.
Abstract

Mortality associated with Edwardsiella ictaluri infection is a serious impediment to the commercial production of fingerling Channel Catfish Ictalurus punctatus. A patented, live, attenuated, orally delivered vaccine has been developed that offers exceptional protection against E. ictaluri infection in both laboratory and small-scale pond trials. Further vaccine development is contingent on the successful completion of large-scale field trials that accurately reflect industry conditions. This current work focuses on the validation of fermentation protocols and the optimization of downstream processing procedures to produce sufficient quantities of vaccine to conduct commercial-scale field trials. Eight vaccine serials were produced from a master seed stock (S97-773-340X2) in a 50-L floor model fermenter over two consecutive years. Following fermentation, cells were harvested, concentrated 10-fold, and cryogenically stored (?74°C). To assess processing protocols and determine shelf life of cryogenically stored vaccine, serials were tested for cell viability and vaccine potency at various intervals over 24 months. There were no significant differences in cell viability between the fresh vaccine and the stored frozen product. All serials provided a high level of protection (77–100% relative percent survival) against E. ictaluri infection in juvenile Channel Catfish and exhibited excellent poststorage viability. This data demonstrates that the live, attenuated, orally delivered vaccine can be stored at ?74°C for at least 2 years with no reduction in cell viability or vaccine potency.

Received May 17, 2016; accepted January 19, 2017 Published online April 4, 2017  相似文献   

10.
Abstract

Edwardsiella ictaluri and Flavobacterium columnare are two bacterial pathogens that affect channel catfish Ictalurus punctatus aquaculture. At the Catfish Genetics Research Unit (U.S. Department of Agriculture, Agricultural Research Service), some progress has been made in selectively breeding for resistance to E. ictaluri; however, the susceptibility of these families to F. columnare is not known. Our objectives were to obtain baseline information on the susceptibility of channel catfish families (maintained as part of the selective breeding program) to E. ictaluri and F. columnare and to determine whether the spleen index and plasma levels of mannose-binding lectin (MBL) are predictive indicators of susceptibility to these pathogens. Four channel catfish families were used: family A was randomly chosen from spawns of fish that were not selectively bred for resistance; families B, C, and D were obtained after selection for resistance to E. ictaluri. All four families were immersion challenged with both bacterial pathogens; the spleen index and plasma MBL levels of unchallenged fish from each family were determined. Mean cumulative percent mortality (CPM) after E. ictaluri challenge ranged from 4% to 33% among families. Families A and B were more susceptible to F. columnare (mean CPM of three independent challenges = 95% and 93%) than families C and D (45% and 48%), demonstrating that there is genetic variation in resistance to F. columnare. Spleen index values and MBL levels were not significantly different, indicating that these metrics are not predictive indicators of F. columnare or E. ictaluri susceptibility in the four tested families. Interestingly, the two families that exhibited the highest CPM after F. columnare challenges had the lowest CPM after E. ictaluri challenge. Further research on larger numbers of families is needed to determine whether there is any genetic correlation between resistance to E. ictaluri and resistance to F. columnare.

Received November 18, 2011; accepted February 23, 2012  相似文献   

11.
Abstract

Administration of various immunostimulants to fish has resulted in enhanced immune responses. The purpose of this study was to determine if feeding Spirulina, a processed form of the blue-green alga Spirulina platensis, enhanced specific and nonspecific immunity and resistance against Edwardsiella ictaluri infection in channel catfish Ictalurus punctatus. Peritoneal phagocytes from fish fed Spirulina showed enhanced phagocytosis to zymosan and increased chemotaxis to E. ictaluri exoantigen. No significant difference in mortality due to E. ictaluri existed between fish fed Spirulina and fish fed a basal diet. No significant difference in antibody titer or in the percentage of fish positive for E. ictaluri antibody was found between the groups after immunization with formalin-killed E. ictaluri. Spirulina-fed fish had significantly higher antibody titers to key hole limpet hemocyanin (KLH) on day 22, and a greater percentage of these fish were positive for KLH antibody on days 15 and 36. Feeding Spirulina enhanced nonspecific cellular immune responses such as chemotaxis and phagocytosis but did not provide protection against infection with E. ictaluri. The use of Spirulina in feed resulted in enhanced antibody responses to KLH, a thymus-dependent antigen, but not to E. ictaluri, a thymus-independent antigen. These results indicate that stimulation of the nonspecific immune system of channel catfish does not provide enhanced protection from E. ictaluri.  相似文献   

12.
Abstract

The effects of intraperitoneal injection of squalene, an oil adjuvant, on nonspecific mortality of channel catfish Ictalurus punctatus and on their resistance to experimental Edwardsiella ictaluri infection were studied. Yearling channel catfish were assigned to control (N = 22) or squalene (N = 25) treatment groups, and mortality was monitored for 14 d following treatment. On day 14 both groups were infected with E. ictaluri, the causative agent of enteric septicemia of catfish, and mortality was monitored for an additional 11 d. Before infection, mortality did not differ between groups. After E. ictaluri infection, fish that received squalene were at a substantially higher risk of dying than control fish (relative risk after squalene treatment = 6.86). These results suggest that intraperitoneal administration of squalene, although not directly toxic, decreased resistance to E. ictaluri infection.  相似文献   

13.
Abstract

Wild and domestic populations of channel catfish Ictalurus punctatus were examined to determine the distribution of the disease called enteric septicemia of catfish (ESC) in California. The causative agent of ESC, Edwardsiella ictaluri, was isolated from five separate sites in California. Two of these isolations were from rectal swabs of asymptomatic fish, confirming that a carrier state may exist. Normal-appearing fish with serum antibody titer to E. ictaluri were commonly found in domestic channel catfish populations, suggesting that many fish become infected but recover. Wild channel catfish with antibody to E. ictaluri were also found in major reservoirs and water distribution canals. Edwardsiella ictaluri appears to be widely distributed within California.  相似文献   

14.
Abstract

Edwardsiella ictaluri is the causative agent of enteric septicemia of catfish, which, during the past 5 years, has become the most serious infectious disease problem of cultured channel catfish Ictalurus punctatus. We compared 40 isolates of E. ictaluri from different geographical regions and host fish species. From the biophysical tests, a pH of 7.0–7.5 and a temperature of 25–30°C were optimum growth conditions for all E. ictaluri isolates. All isolates grew well in media with an NaCl concentration of 0.5% or less, but none of the E. ictaluri isolates grew in media with a concentration of 2.0 or 5.0% NaCl. Biochemically, 42 out of 46 tests gave the same reaction for all 40 isolates. The only observed differences were in gas production at 25°C, the o-nitrophenylbeta-D-galactopyranoside test, ornithine decarboxylation, and D-mannose utilization. Serologically, identical agglutinin titers (1:80) to E. ictaluri-specific rabbit antisera were observed, and all isolates cross-agglutinated with four different antisera. Based on the biophysical, biochemical, and serological reactions of 40 isolates of E. ictaluri, identification of distinct strains was not possible, although some were slightly different biotypically.  相似文献   

15.
The potential of bambermycins (a growth-promoting antimicrobial approved for turkeys, broilers, and swine) to overcome or control plasmid-mediated antimicrobial resistance was determined in a series of in vitro experiments. Four possible modes of action of bambermycins were studied: synergistic effect with 12 other antimicrobials, elimination of resistance (R) plasmids from Escherichia coli, selective killing or inhibition of E coli carrying R plasmids, and inhibition of R plasmid transfer. Bambermycins had no synergistic activity with the other drugs tested and had little effect on eliminating plasmids from host bacteria. Dependent on plasmid type, bambermycins decreased or increased transfer frequency of R plasmids. Bambermycins also selectively inhibited growth of bacteria harboring certain R plasmids.  相似文献   

16.
Abstract

Enteric septicemia of catfish (ESC) was transmitted horizontally from channel catfish Icialurus punctatus that had died from Edwardsiella ictaluri infection to contact channel catfish during 2 d of habitation in a tank. The contact channel catfish became positive for E. ictaluri antibody, became infected with this bacterium, and had signs of ESC and died within 12 d postexposure. Edwardsiella ictaluri was recovered from 24 of the 30 contact channel catfish that died from ESC, as well as from 9 of the 25 tested contact survivors. The cannibalizing of E. ictaluri-infected fish, or the shedding of E. ictaluri from dead fish, or both, were shown to be mechanisms of horizontal transmission of ESC among channel catfish.  相似文献   

17.
Abstract

The aroA gene of Edwardsiella ictaluri was cloned and sequenced, and the sequence data were used to construct a deletion–insertion mutation in the aroA gene. The mutated gene was transferred into a virulent, wild-type E. ictaluri strain by conjugation and allelic exchange. Putative aroA mutants were confirmed phenotypically by demonstrating a need for supplementation with aromatic metabolites to support growth in minimal media. The genetic construction was evaluated by using the polymerase chain reaction to amplify appropriate regions of the aroA deletion–insertion, and DNA sequencing of the amplified products confirmed the predicted construction. A selected mutant, LSU-E1, was passed 30 times in nonselective media with no reversion to the wild-type following screening of 1.6 × 1011 colony-forming units. The mutant was demonstrated via injection to be attenuated more than 5 logs10 compared with the wild-type E. ictaluri strain, and it was avirulent by immersion and oral routes. Tissue persistence studies indicated that the mutant maintained the ability to invade following immersion exposure, but no viable cells were detected after 48–72 h. Significant levels of protection from disease were demonstrated following immersion vaccination of channel catfish Ictalurus punctatus.  相似文献   

18.
Abstract

The specificity of channel catfish Ictalurus punctatus serum antibody to Edwardsiella ictaluri was characterized by microtiter agglutination assay. There was no correlation between antibody titer to Aeromonas hydrophila and antibody titer to E. ictaluri in wild or feral channel catfish. Anti-E. ictaluri antibodies in naturally infected channel catfish were not removed by adsorption by nine other species of bacteria found in the channel catfish intestine and fish ponds. Channel catfish immunized with nine other species of bacteria did not develop substantial antibody titer to E. ictaluri. The antibody response of channel catfish to E. ictaluri is highly specific, and the microtiter agglutination test is a specific indicator of previous exposure to E. ictaluri  相似文献   

19.
Molecular epidemiology of Salmonella Heidelberg in an equine hospital   总被引：1，自引：0，他引：1  
From 1992 to 1997, multi-drug resistant (MDR) Salmonella Heidelberg isolates were cultured from a number of horses hospitalised in a veterinary hospital in Victoria, Australia. To examine the relationships between the cases, 28 isolates from the hospital were compared by pulsed field gel electrophoresis (PFGE), IS200 element profiles, antimicrobial resistance patterns, plasmid profiles and phage typing. The PFGE patterns following digestion with XbaI and BlnI restriction endonucleases showed that the isolates from the veterinary hospital originated from a common source. These isolates also had indistinguishable IS200 profiles. However, PFGE was more discriminatory than IS200 profiles. All the veterinary hospital isolates and one independent isolate had the same antimicrobial resistance pattern and had at least one plasmid in common. Localisation of antimicrobial resistance genes indicated that the veterinary hospital isolates had more than one plasmid carrying resistance genes and that the genes encoding sulphathiazole and trimethoprim resistance were not on these plasmids. Phage typing was ineffective as 22 of the 28 isolates were untypeable. In conclusion, the combination of different methods used for epidemiological studies suggested that a single strain of MDR S. Heidelberg was isolated from horses admitted to the hospital for 6 years and caused salmonellosis in susceptible horses within that period with no apparent correlation between the antimicrobials used and retention of its MDR phenotype.  相似文献   

20.
Eighty-six Salmonella enteritidis isolates obtained during a surveillance program of poultry farms in Maine were subjected to phage-typing, plasmid profiling and fingerprinting, outer-membrane polypeptide analysis, and antimicrobial sensitivity testing. Isolates were obtained from a variety of sources, including poultry-farm environmental samples, chicken organ samples, human stool samples, cat feces, and live-trapped rats and mice. These isolates were compared with 21 S. enteritidis isolates originating outside of Maine. Phage types isolated in Maine included 13a (60%); 14b (29%); 23 (5%); 8 (2%); and 2 (2%). All S. enteritidis isolates from Maine carried plasmid DNA, and 97% of these isolates carried a 40.3-megadalton plasmid alone (6%) or in conjunction with several smaller plasmids (91%). All 52 phage-type 13a isolates harbored 40.3- and 3.0-megadalton plasmids. All 25 phage-type 14b isolates carried 3.3- and 1.3-megadalton plasmids, and 22 isolates also carried the 40.3-megadalton plasmid. All isolates displayed highly similar outer-membrane polypeptide profiles and were sensitive to a variety of antimicrobials commonly used against gram-negative organisms. The above data suggest that phage type and plasmid content may be related in the cases of phage-type 13a and 14b isolates, and that traditional plasmid-borne antimicrobial resistance determinants were not present in Maine isolates. Results also indicate that phage-typing can be a valuable epizootiological tool for monitoring the potential spread of these strains throughout the Northeast.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号