[Show abstract][Hide abstract] ABSTRACT: Protein-coated microcrystals (PCMCs) were investigated as potential vaccine formulations for a range of model antigens. Presentation of antigens as PCMCs increased the antigen-specific IgG responses for all antigens tested, compared to soluble antigens. When compared to conventional aluminium-adjuvanted formulations, PCMCs modified with calcium phosphate (CaP) showed enhanced antigen-specific IgG responses and a decreased antigen-specific IgG1:IgG2a ratio, indicating the induction of a more balanced Th1/Th2 response. The rate of antigen release from CaP PCMCs, in vitro, decreased strongly with increasing CaP loading but their immunogenicity in vivo was not significantly different, suggesting the adjuvanticity was not due to a depot effect. Notably, it was found that CaP modification enhanced the phagocytosis of fluorescent antigen-PCMC particles by J774.2 murine monocyte/macrophage cells compared to soluble antigen or soluble PCMCs. Thus, CaP PCMCs may provide an alternative to conventional aluminium-based acellular vaccines to provide a more balanced Th1/Th2 immune response.
[Show abstract][Hide abstract] ABSTRACT: A reporter plasmid pSRG has been developed which expresses red fluorescent protein (RFP) from a constitutive prokaryotic
promoter within Pasteurella multocida B:2 and green fluorescent protein (GFP) from a constitutive eukaryotic promoter
within mammalian cells. This construct has been used to determine the location and viability of the bacteria when moving
from the extracellular environment into the intracellular compartment of mammalian cells. Invasion assays with embryonic
bovine lung (EBL) cells and an attenuated AroA- derivative of Pasteurella multocida B:2 (strain JRMT12), harbouring the
plasmid pSRG, showed that RFP-expressing bacteria could be detected intracellularly at 3 h post-invasion. At this stage,
some EBL cells harbouring RFP-expressing bacteria were observed to express GFP simultaneously, indicating release of the
plasmid into the intracellular environment. At 5 h post-invasion, more EBL cells were expressing GFP, while still harbouring
RFP-expressing bacteria. Concurrently, some EBL cells were shown to express only GFP, indicating loss of viable bacteria
within these cells. These experiments proved the functionality of the pSRG dual reporter system and the potential of P.
multocida B:2 JRMT12 for bactofection and delivery of a DNA vaccine.
PLoS ONE 08/2013; 8(8):e71524. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Image processing algorithms were developed and compared with visual assessment from 12 volunteers to quantify the temporal morphological structure of a single Euglena gracilis organism. Representative images of E. gracilis, showing different morphological characteristics from ovate to cylindrical and elongate, were captured with a bright-field video microscopy system. These images were ranked by the volunteers in order from ovate to elongate. The images were analyzed in the spatial and spatial frequency domain, and the order of the images from each analysis was ranked against the visual assessment. The assessment methods agreeing with the volunteer's preferred sequence were an eccentricity measurement (major axis over the sum of the minor axis at three points), the cross correlation of the image without high pass filtering or edge detection, and cross correlation of the power spectral density.
Microscopy and Microanalysis 07/2012; 18(4):798-807. · 2.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A Pasteurella multocida B:2 strain from a case of bovine haemorrhagic septicaemia (HS) and a derivative, JRMT12, that was attenuated by a deletion in the aroA gene, were shown to adhere to, invade and survive within cultured embryonic bovine lung (EBL) cells. By comparison, bovine strains of Mannheimia haemolytica serotype A1 and P. multocida serotype A:3, although able to adhere to EBL cells, were not found intracellularly. The B:2 strains were viable intracellularly over a 7 h period, although a steady decline in viability was noted with time. Entry into the mammalian cells was inhibited by cytochalasin D, indicating that cell uptake was by an actin-dependent process. Viability assessment of EBL cells by trypan blue staining indicated that none of the bacterial strains was toxic for the EBL cells. Transmission electron microscopy (TEM) showed that, after entry into the mammalian cells, the B:2 strain resided in a vacuolar compartment. However, only a low percentage of mammalian cells appeared to contain one or more P. multocida B:2, suggesting that only certain EBL cells in the population were capable of being invaded by, or of taking up, the bacteria. TEM showed that P. multocida A:3 and M. haemolytica A:1 were found loosely adhering to the cell surface of EBL cells and were not detected intracellularly. The cell-invasive capacity of P. multocida B:2 may be a virulence property related to its ability to translocate from the respiratory tract into the blood stream.
[Show abstract][Hide abstract] ABSTRACT: A protein designated Bap-5 (GenBank accession no. AF081494) or BapC (GenBank accession no. AJ277634) has been identified as a member of the Bordetella pertussis autotransporter family and the present work suggests that this protein, like the previously characterised BrkA, is a Bvg-regulated serum resistance factor and virulence determinant. B. pertussis bapC and brkA, bapC mutants were created and, like a brkA mutant, showed greater sensitivity to killing by normal human serum than their parent strains but they were not as sensitive as a bvg mutant. Competition assays also showed an important role for BapC, like BrkA, in virulence of B. pertussis in mice after intranasal infection. Moreover, the bapC and brkA, bapC mutants, like the brkA mutant, were found to be more sensitive to the antimicrobial peptide cecropin P1 than the parent strains. In the genome sequence of B. pertussis strain Tohama, bapC is designated as a pseudogene due, in part, to a frameshift in a poly(C) tract near the 5' end of the gene which creates a truncated BapC protein. Sequence analyses of the bapC region spanning the poly(C) tract of a number of B. pertussis strains showed minor nucleotide and amino acid polymorphisms but it appeared that all had an ORF that would be able to produce BapC.
[Show abstract][Hide abstract] ABSTRACT: The objective of this study was to investigate the haemolytic and cytotoxic activity of Pasteurella multocida B:2 strains, originally from cases of haemorrhagic septicaemia in cattle. All six P. multocida B:2 strains were non-haemolytic on sheep blood agar (SBA) and horse blood agar (HBA) when grown aerobically and on SBA anaerobically but they were haemolytic on HBA when grown anaerobically. No haemolytic activity against horse red blood cells was detected in culture supernates from aerobically or anaerobically grown cultures and only very weak haemolytic activity was obtained in supernates or pellet fractions from sonicated cells. However, after repeated extraction of sonicated cells with Tween 80, haemolytic activity was found in various cell fractions, both Tween-soluble and -insoluble. The Tween-extracted putative haemolysin and other bacterial fractions were also cytotoxic for mouse macrophage-like J774.2 cells. Further characterisation of the putative haemolysin revealed it to be a heat-labile, non-pore-forming protein of molecular weight >10 kDa whose activity was completely destroyed by trypsin and greatly reduced with protease and proteinase K treatment. Congo red also reduced the haemolytic activity. Non-denaturing gel-electrophoresis and RBC agar overlay revealed clear haemolytic zones but suggested that Tween was bound to some component of the P. multocida B:2 fractions and was responsible, to some extent, for the haemolytic activity observed. However, the effect of heat and other reagents on the Tween-extracted fractions and the lack of haemolytic activity in different Tween-extracted cell fractions of organisms other than P. multocida suggested that some proteinaceous component of the organism could indeed act as a haemolysin. This putative haemolysin may be one of the virulence attributes of P. multocida, but its characterisation and role in pathogenesis require further study.
[Show abstract][Hide abstract] ABSTRACT: Although laser sterilisation has been well studied in dentistry and medicine, there have been few studies within the food industry. UV radiation has been used for sterilisation of surfaces and water. The killing effect of microwave radiation has been investigated on many bacteria in food and there has been much controversy over its killing mechanism. In this study, the killing effect of laser, microwave and UV radiation was studied on E. coli and on some spoilage and pathogenic bacteria. The bacterial suspensions were exposed to the treatment processes in sequence and viable cell counts were made before and after each treatment. A difference in the reduction in viable counts was apparent when the sequential treatment was compared with the sum of the individual treatments alone. Similar results were obtained when conventional heating was used in place of microwave radiation. It was found that the order of the treatment processes had a significant influence on killing.
[Show abstract][Hide abstract] ABSTRACT: The probability of infection during air travel was determined by assuming randomised events (sneezing, coughing, vomiting) and the Well-Riley model for the infectivity rate. The potential of using an Excimer laser operating at 248 nm to decontaminate air was experimentally investigated. Infections spread by air travel is of growing concern in recent times with such outbreaks as SARS and Bird Flu occurring. There are also concerns over how the air is re-circulated through cabins and cleaned of microorganisms and chemical contaminants from the fuel. A mathematical model has been developed to assess the risk factors that may lead to passengers on board becoming infected with airborne respiratory diseases and novel methods of decontaminating air have been investigated. Airborne infections are spread when people are in close proximity for a period of time . Being in an enclosed space such as an aeroplane enhances the risk of infection. Large droplets containing micro-organisms are projected into the air whenever an infected person talks, coughs, sneezes, vomits etc, and these can be intercepted by anyone within a range of a few meters. However smaller lighter particles (droplet nuclei) generated from sneezing for example, can remain suspended in the air for a longer time and have a wider range of infection. In the simulation, the aircraft cabin was divided into four sections/cabins so that the effects of proximity and the air recirculation and mixing were modelled. A mathematical model of the airflow affecting the concentration of infectious agents in the cabin was produced. It is clear from these models and recent press articles that there are potentially serious problems associated with aircraft contamination. Overall, the results demonstrated that lasers could be used successfully to decontaminate air. Exploiting lasers as a means to decontaminate air may therefore provide an efficient, alternative method of cleaning air for improved cabin air quality.
Lasers and Electro-Optics 2009 and the European Quantum Electronics Conference. CLEO Europe - EQEC 2009. European Conference on; 07/2009
[Show abstract][Hide abstract] ABSTRACT: Pasteurella multocida serotype B:2 is the causative agent of haemorrhagic septicaemia (HS), a fatal disease of cattle and buffaloes. As a step towards the identification of individual antigens that may protect against HS, proteins present in a sonicated cell extract (SCE) and outer-membrane protein (OMP) preparation of a wild-type P. multocida serotype B:2 were investigated by immunoblotting with sera from calves which had been protected against challenge with a virulent strain of P. multocida B:2 by vaccination with a live-attenuated aroA derivative of the challenge strain. Five proteins in SCE, of approximately 50, 37, 30, 26 and 16 kDa, were recognised by the sera. In an OMP preparation, two bands, at 37 and 50 kDa, were recognised as strongly immunogenic. Mass spectrometry analysis of proteins corresponding in size to those detected by immunoblotting identified the 37 kDa band as OmpA, but the band at 50 kDa was not identified with certainty. A major 30 kDa OMP, identified as OmpH, was not strongly immunogenic.
Research in Veterinary Science 03/2009; 87(2):207-10. · 1.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A comparison was made of the cytotoxic activity and secondary structural features of four recombinant forms of adenylate cyclase toxin (CyaA). These forms were fully functional CyaA, CyaA lacking adenylate cyclase enzymatic activity (CyaA*), and non-acylated forms of these toxins, proCyaA and proCyaA*. At a toxin concentration>1 microg/ml, CyaA* was as cytotoxic towards J774.2 cells as CyaA and mediated cell killing at a faster rate than CyaA. At concentrations<0.5 microg/ml, CyaA* was less cytotoxic than CyaA and, at <0.1 microg/ml of CyaA*, no activity was detected. CyaA, but not CyaA*, was able to induce caspase 3/7 activity, a measure of apoptosis. ProCyaA and proCyaA* had no detectable cytotoxic or apoptotic activity. CyaA caused 50% inhibition of the zymosan-stimulated oxidative burst at 0.003 microg/ml, whereas a approximately 500-fold greater toxin concentration of CyaA* or proCyaA was needed for 50% inhibition. ProCyaA* was inactive. CyaA is a calcium-binding protein and far UV circular dichroism (CD), near UV CD and fluorescence spectra analyses showed that all the forms of CyaA had similar overall structures at different calcium concentrations up to 5.0 mM. At 7.5 mM CaCl2, the far UV spectrum of CyaA altered significantly, indicating a change in secondary structure associated with high beta-sheet content or a beta-aggregated state, whereas the spectrum of CyaA* showed only a slight alteration at this calcium concentration. Near UV CD and fluorescence studies were consistent with a rearrangement of secondary structural elements in the presence of CaCl2 for all CyaA forms. There was a marked dependence on protein concentration of the far UV spectra of these CyaA forms, implying an interaction between individual molecules at higher protein concentrations.
[Show abstract][Hide abstract] ABSTRACT: Tuned cylindrical radial mode ultrasonic horns offer advantages over ultrasonic probes in the design of flow-through devices for bacterial inactivation. This study presents a comparison of the effectiveness of a radial horn and probe in the inactivation of Escherichia coli K12. The radial horn is designed using finite element analysis and the predicted modal parameters are validated using experimental modal analysis. A validated finite element model of the probe is also presented. Visual studies of the cavitation fields produced by the radial horn and probe are carried out using luminol and also backlighting to demonstrate the advantages of radial horns in producing a more focused cavitation field with widely dispersed streamers. Microbiological studies show that, for the same power density, better inactivation of E. coli K12 is achieved using the radial horn and, also, the radial horn offers greater achievable power density resulting in further improvements in bacterial inactivation. The radial horn is shown to be more effective than the probe device and offers opportunities to design in-line flow-through devices for processing applications.
[Show abstract][Hide abstract] ABSTRACT: Three different recombinant forms of CyaA were used to investigate transcriptional responses of murine bone marrow-derived macrophages (BMMs) using Affymetrix Mouse Genome GeneChips. These forms were enzymically active, invasive CyaA, non-enzymically active, invasive CyaA (CyaA*) and non-enzymically active, non-invasive CyaA (proCyaA*). BMMs, treated with 20 ng/ml of CyaA for 24h, showed over 1000 significant changes in gene transcription compared with control cells. CyaA caused an increase in transcription of many inflammatory genes and genes associated with various signalling cascades such as those involved in cyclic AMP-dependent protein kinase A signalling. Most strikingly, CyaA caused down-regulation of numerous genes involved in cell proliferation. CyaA* at 20 ng/ml significantly up-regulated the transcription of only twelve genes after 24h whereas proCyaA* at this concentration significantly increased the transcription of only two genes.
[Show abstract][Hide abstract] ABSTRACT: Three groups of five calves, namely, V1, V2, and V3, were immunized intramuscularly at 4 and 8 weeks of age with ca. 10(9), 10(8), and 10(7) CFU, respectively, of a derivative of Pasteurella multocida B:2 wild-type strain 85020 containing a deletion in the aroA gene (strain JRMT12). The first and second vaccinations resulted in significantly (P < 0.01) higher rectal temperature responses in groups V1 and V2 than in group V3. Serum immunoglobulin M (IgM) and IgG titers did not increase in any group until after the second vaccination and were then significantly higher in groups V1 and V2 than in group V3 (P = 0.001 for both IgM and IgG). All vaccinated groups and three unvaccinated challenge control calves (group CC) were injected subcutaneously at 10 weeks of age with ca. 10(7) CFU of strain 85020. Vaccinated calves survived the challenge, but two CC animals developed clinical disease and were killed for humane reasons. After challenge, mean serum amyloid A concentrations were significantly higher (P < 0.001) in the CC group than in the vaccinated groups. Postmortem examination revealed that calves in the CC group showed the most extensive range of bacteriologically positive tissues and gross and histopathological lesions. Overall, a clear dose-dependent response was present, with those receiving a higher vaccine dose being less affected clinically, bacteriologically, and pathologically by the wild-type challenge. The V2 treatment appeared to give the best combination of high immune response, protection, and safety.
Infection and immunity 12/2007; 75(12):5837-44. · 4.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Adenylate cyclase toxin (CyaA) is an important virulence factor of Bordetella pertussis, the causative agent of whooping cough, and, in its detoxified form, a potential component of acellular pertussis vaccines. This study reports the application of a novel technology, formulation of CyaA as protein-coated microcrystals (PCMC), to improve the performance of CyaA as a vaccine component. CyaA is normally stored in a high urea concentration to prevent aggregation and to maintain stability of the protein. The aim of the work was to stabilise CyaA on a crystalline support to create a dry powder that could be reconstituted in aqueous buffer, free of urea. CyaA, formulated as PCMC with microcrystals of dl-valine, retained full adenylate cyclase (AC) and cell invasive (cytotoxic) activities after solubilistion in urea buffer. After storage as a dry powder at 37 degrees C for 2 weeks, the AC activity recovered from the CyaA-PCMC was only marginally reduced when solubilised in urea buffer. No AC activity was detected after attempts to solubilise CyaA-PCMC in aqueous buffer alone, in the absence of urea. Inclusion of various ionic, non-ionic or zwitterionic detergents in the aqueous buffer had little effect on recovery of CyaA activities. However, preparation of PCMC with CyaA plus calmodulin (CaM) or bovine serum albumin (BSA) or with both proteins allowed restoration of AC and cytotoxic activities of CyaA upon solubilisation in aqueous buffer. Incorporation of BSA and CaM with CyaA allowed essentially full recovery of AC activity but lower recovery of cytotoxicity. CyaA-CaM-BSA-PCMC, after reconstitution in aqueous buffer, induced a strong serum IgG response to CyaA when injected subcutaneously into mice.
[Show abstract][Hide abstract] ABSTRACT: Pertussis toxin (PTx) is a major virulence factor produced by Bordetella pertussis. In its detoxified form (PTd), it is an important component of acellular pertussis vaccines although some residual PTx activity may likely be present because of the limitations of the detoxification processes used. Furthermore, different detoxification procedures have been shown to result in different amino acid side-chain modifications for the resulting PTd. The histamine-sensitisation test (HIST) in mice is currently used for the safety testing of these vaccines. However, an alternative test is needed because of large assay variability and ethical concerns. The ADP-ribosylation enzyme activity of PTx is thought to be the major factor responsible for the histamine-sensitising activity detected in vivo. In the present study, the ADP-ribosylation activity in different acellular pertussis-based combination vaccine formulations was measured and compared with reactivity in the HIST. The results indicated that different products showed differences in ADP-ribosylation activity and a level which would be significant in relation to the reactivity seen in the HIST could not be defined, except for vaccines that contain genetically detoxified PTx, which do not have enzymatic activity nor in vivo toxicity. Different detoxification procedures as well as formulation factors could contribute to this variation. Relying solely on the residual enzyme activity of PTx in vaccines containing chemically detoxified PTd may not fully reflect the in vivo reactivity observed by the HIST. Refinement of the in vitro test to include a step which monitors the B-subunit activity of PTx may provide a better correlation with the in vivo HIST.
[Show abstract][Hide abstract] ABSTRACT: Four recombinant forms of the cell-invasive adenylate cyclase toxin (CyaA) of Bordetella pertussis were compared for the ability to enhance protection against B. pertussis in mice when coadministered with an acellular pertussis vaccine (ACV). The four forms were as follows: fully functional CyaA, a CyaA form lacking adenylate cyclase enzymatic activity (CyaA*), and the nonacylated forms of these toxins, i.e., proCyaA and proCyaA*, respectively. None of these forms alone conferred significant (P > 0.05) protection against B. pertussis in a murine intranasal challenge model. Mice immunized with ACV alone showed significant (P < 0.05) reductions in bacterial numbers in the lungs after intranasal challenge compared with those for control mice. When administered with ACV, both CyaA and CyaA* further reduced bacterial numbers in the lungs of mice after intranasal challenge compared with those for ACV-immunized mice, but the enhanced protection was only significant (P < 0.05) with CyaA*. Coadministration of CyaA* with ACV caused a significant (P < 0.05) increase in immunoglobulin G2a antibody levels against pertactin compared with those in mice immunized with ACV alone. Spleen cells from mice immunized with ACV plus CyaA* secreted larger amounts of interleukin-5 (IL-5), IL-6, gamma interferon (IFN-gamma), and granulocyte-macrophage colony-stimulating factor (GM-CSF) than did cells from mice immunized with ACV plus CyaA or ACV alone after stimulation in vitro with a mixture of B. pertussis antigens. Spleen cells from mice immunized with ACV plus CyaA* also secreted larger amounts of IFN-gamma and GM-CSF than did cells from mice immunized with CyaA* alone after stimulation in vitro with CyaA*. Macrophages from mice immunized with ACV plus CyaA* produced significantly (P < 0.05) higher levels of nitric oxide than did macrophages from mice immunized with CyaA* alone, ACV alone, or ACV plus CyaA after stimulation in vitro with a mixture of B. pertussis antigens or heat-killed B. pertussis cells. These data suggest that the enhancement of protection provided by CyaA* was due to an augmentation of both Th1 and Th2 immune responses to B. pertussis antigens.
Infection and Immunity 01/2007; 74(12):6797-805. · 4.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study examined the ability of the adenylate cyclase toxin (CyaA) of Bordetella pertussis to act as a mucosal adjuvant for other antigens when co-administered by the intranasal route in mice. Two forms of CyaA were used: the cell-invasive, enzymically active form and a cell-invasive toxin lacking adenylate cyclase enzymic activity (CyaA*). Co-administration intranasally (i/n) of CyaA or CyaA* with ovalbumin (Ova) significantly enhanced (P<0.05) anti-Ova IgG and IgA antibody responses in the serum and anti-Ova IgA responses in lung and nasal secretions compared to those generated by immunisation i/n with Ova alone. The effects were greater with CyaA*. Administration of CyaA* with Ova induced priming of Ova-specific T cells in vivo to a greater extent than that obtained after immunisation with Ova alone. Co-administration of CyaA or CyaA* with pertactin (Prn) significantly enhanced (P<0.05) the serum anti-Prn IgG responses and immunisation with Prn and CyaA* significantly increased the anti-Prn IgA responses in the lungs compared with responses after immunisation with Prn alone. Immunisation i/n with Prn alone partially protected mice (P<0.05) against challenge i/n with B. pertussis. Co-administration of CyaA or CyaA* with pertactin (Prn) significantly increased protection (P<0.05) against challenge compared to that obtained with Prn alone. These effects were particularly apparent with CyaA* as the adjuvant.
[Show abstract][Hide abstract] ABSTRACT: Pertussis toxin (PTx) is a major virulence factor produced by Bordetella pertussis and, in its detoxified form PTd, is an important component of pertussis vaccines. The in vivo histamine sensitization test (HIST) is currently used for the safety testing of these vaccines. However, an alternative test is needed because of large assay variability and ethical concerns with regard to animal usage. PTx has two functionally distinct domains: the enzymatic A-protomer and the B-oligomer that facilitates host-cell binding and entry of PTx into the cell. The development of a quantitative PTx binding assay using glycoproteins or defined oligosaccharides is reported. PTx was found to bind preferentially to multiantennary N-glycans, with the highest binding toward the fully sialylated structures. In contrast, PTd lost the ability of PTx to bind to sialylated multiantennary structures but retained some capacity to bind to neutral multiantennary structures. The developed assay was shown to be specific, sensitive, and robust and could be used for investigating the mechanisms of PTx detoxification and for monitoring PTx binding activity in vaccine formulations. This assay could also be used to complement a PTx-enzymatic assay, developed recently, and together they may form the basis of a potential alternative in vitro assay to replace the in vivo HIST.
[Show abstract][Hide abstract] ABSTRACT: Two groups of four calves each were immunized either intramuscularly (i.m. vaccinated) or intranasally (i.n. vaccinated) at 2 and 6 weeks of age with ca. 10(9) CFU of a derivative of P. multocida serotype B:2 strain 85020 containing a deletion in the aroA gene (strain JRMT12). Both groups of calves and three unvaccinated control calves were challenged subcutaneously at 8 weeks of age with ca. 10(7) CFU of the wild-type 85020 strain. The first and second vaccinations caused a significant pyrexia and increase in the mean demeanor score (P <0.05) in i.m. but not i.n. vaccinated calves. Serum agglutinating activity against whole cells of P. multocida strain 85020 and immunoglobulin G antibody concentrations increased after the second vaccination in i.m. but not in i.n. vaccinated animals, and this difference was statistically significant (P <0.05). Concentrations of serum amyloid A (SAA) increased significantly 3 h after both the primary (P <0.05) and booster (P <0.001) i.m. vaccinations, but not in i.n. vaccinated calves. All four i.m. vaccinated calves were solidly immune to challenge with wild-type P. multocida B:2. However, the mean rectal temperatures, demeanor scores, and serum SAA concentrations of i.n. vaccinated and control calves increased significantly (P <0.01). Three i.n. vaccinated and two control calves were killed for humane reasons within 14 h postchallenge, and postmortem examination revealed pathological lesions consistent with hemorrhagic septicemia. These data showed that the aroA mutant strain, given i.m. as two doses 4 weeks apart, acted as an effective live-attenuated vaccine strain to protect calves against challenge with the virulent parent strain.
Infection and Immunity 04/2005; 73(3):1475-81. · 4.07 Impact Factor