Biomedical subjects

Meredith Stewart

Publications and source records attributed to Meredith Stewart.

3 recordsLinked to original sources

PubMed2005

A comparison of haemagglutination, haemagglutination inhibition and PCR for the detection of psittacine beak and feather disease virus infection and a comparison of isolates obtained from loriids.

Psittacine beak and feather disease (PBFD) is recognized as a threat for endangered psittacine birds in Australia, New Zealand and South Africa. Several diagnostic methods for the detection of beak and feather disease virus (BFDV) infection have been developed but there are few studies comparing the relative merits or sensitivity and specificity of each diagnostic test. In this report, the results of PCR, haemagglutination (HA) and haemagglutination inhibition (HI) testing of diagnostic samples collected from 679 samples from a range of psittacine bird species suspected of being infected with BFDV are summarized and compared. There was a strong agreement (kappa = 0.757; P<0.0001) between PCR and HA testing of feather samples and PCR-negative birds were 12.7 times more likely to have HI antibody than PCR-positive birds. False-positive HA results with titres up to 1:320 were identified in six feather samples that were PCR negative; the haemagglutination detected in these samples was not inhibited by anti-BFDV antisera and was removed by filtration through a 0.22 microm filter. Similarly, one false-negative PCR result was detected in a feather sample that had a high HA titre (>1:40,960) and four false-positive PCR results were detected in a batch of four feather samples. Of 143 birds that were feather PCR positive, only two had detectable HI antibody, and these birds were also feather HA negative, suggesting that they were developing immunity to recent infection. All birds with HI antibody were negative on feather HA testing. The assays confirmed BFDV infection in two endangered swift parrots (Lathamus discolor) and phylogenetic analysis of the sequence data generated from ORF V1 of these isolates provide further evidence of BFDV genotypes clustering in parallel with the Loriidae, Cacatuidae and Psittacidae.

Animals↗

PubMed2005

TaqMan real-time reverse transcription-PCR and JDVp26 antigen capture enzyme-linked immunosorbent assay to quantify Jembrana disease virus load during the acute phase of in vivo infection.

Jembrana disease virus (JDV) is an acutely pathogenic lentivirus that affects Bali cattle in Indonesia. The inability to propagate the virus in vitro has made it difficult to quantitate JDV and determine the kinetics of virus replication during the acute phase of the disease process. We report for the first time two techniques that enable quantification of the virus and the use of these techniques to quantify the virus load during the acute phase of the disease process. A one-step JDV gag [corrected] TaqMan real-time reverse transcription-PCR (RT-PCR) assay was developed for the detection and quantification of JDV RNA in plasma. The limit of detection was 9.8 x 10(2) JDV viral RNA copies over 35 cycles, equivalent to 4.2 x 10(4) JDV genome copies/ml, and a peak virus load of 1.6 x 10(12) during the acute febrile period. An antigen capture enzyme-linked immunosorbent assay (ELISA) was also developed to quantify the levels of JDV capsid (JDVp26) over a linear range of 10 to 200 ng/ml. Viral RNA and JDVp26 levels were correlated in 48 plasma samples obtained from experimentally infected cattle. A significant positive correlation (R = 0.860 and r(2) = 0.740) was observed between the two techniques within the range of their detection limits. The relatively insensitive capture ELISA provides an economical and feasible method for monitoring of virus in the absence of more sensitive techniques.

Animals↗

PubMed2003

Tracking the acetate threshold using DO-transient control during medium and high cell density cultivation of recombinant Escherichia coli in complex media.

DO-transient nutrient controllers use the dissolved oxygen signal to attempt acetate threshold tracking during fed-batch cultivation of recombinant E. coli. Here we apply DO-transient control to the production of Jembrana disease virus protein in complex Super Luria medium and compare performance against a high-limit pH-stat controller. For induction at medium cell density (harvest between 31 and 32.5 g dcw L) a total productivity of 0.27 g L h was achieved as compared to 0.24 g L h with the high-limit pH-stat. For induction at high cell density (harvest at 60 g dcw L), decreased productivity (0.12 g L h) was attributed to the effect of acetate accumulation on recombinant protein formation and a concomitant lowering of the critical growth rate. Our results suggest that complex media provides a difficult environment for the application of acetate threshold tracking DO-transient control because of difficulties in re-oxidizing acetate, and apparent localized production of acetate below the production threshold (as detected by the DO-transient controller as SPOUR(crit)). Configuring the DO-transient controller to avoid aggressive threshold probing is suggested as a means to improve performance and reduce acetate accumulation in complex media.

Acetates↗