Biomedical subjects

Peter A White

Publications and source records attributed to Peter A White.

29 records · Page 2Linked to original sources

PubMed2003

Chloramphenicol-resistant Neisseria meningitidis containing catP isolated in Australia.

Earlier workers have described chloramphenicol resistance in meningococci isolated from cerebrospinal fluid sampled in patients in Vietnam (11 cases) and France (one case) during 1987-1996. Here we describe two distinct serogroup B strains isolated in Australia in 1994 and 1997, and found among approximately 1400 invasive meningococcal isolates examined in Australia over a 9 year period. Both were phenotypically chloramphenicol resistant on disc, Etest and agar inclusion MIC and acetylated chloramphenicol examination. DNA amplification and sequencing confirmed the presence of catP and the 3' end of tnpV from Tn4451, a mobilizable element from Clostridium perfringens, although other sequences were not present. Tn4451 has inserted into a gene designated TIGR locus NMB1350 in both isolates with no loss of DNA and no apparent interruption of virulence genes. This second report of chloramphenicol-resistant meningococci is in a setting with a very low volume of systemic chloramphenicol use, but where the high topical use may contribute to recombination events in vivo. Methods for screening for chloramphenicol resistance in meningococci and the in vitro parameters that define this resistance are ill defined.

Aged↗

PubMed2003

The presence of an intrahepatic cytotoxic T lymphocyte response is associated with low viral load in patients with chronic hepatitis C virus infection.

BACKGROUND/AIMS: The role of cytotoxic T lymphocytes (CTL) in limiting viral replication and producing hepatocellular injury in patients with chronic hepatitis C virus (HCV) infection is controversial. METHODS: Intrahepatic and peripheral blood HCV-specific CTL activity against the entire HCV polyprotein was assessed in 26 patients. CTL responses were assessed after effector lymphocytes were re-stimulated for 6 days in vitro using HCV-vaccinia virus-infected autologous cells expressing HCV antigens. Serum and hepatic viral loads were measured and immunohistochemistry for CD3 and CD8 was performed to localise and enumerate effector cells in liver. RESULTS: A positive CTL response was detected in 39/52 (75%) of assays conducted with intrahepatic mononuclear cells and 21/52 (40%) of peripheral blood assays (P<0.001). The presence of an intrahepatic CTL response was associated with low hepatic viral load (P=0.004). Hepatic lobular infiltration by CD8(+)T cells correlated weakly with serum alanine aminotransferase levels (r=0.42, P=0.04) and no relationship was demonstrated between CTL activity and histological evidence of liver damage. CONCLUSIONS: HCV-specific CTL activity is found more commonly in liver than in blood. An inverse relationship between CTL responses and viral load supports the hypothesis that HCV-specific CTL limit viral replication in patients with chronic HCV infection.

Adult↗

PubMed2003

Making causal judgments from the proportion of confirming instances: the pCI rule.

It is proposed that causal judgments about contingency information are derived from the proportion of confirmatory instances (pCI) that are evaluated as confirmatory for the causal candidate. In 6 experiments, pCI values were manipulated independently of objective contingencies assessed by the deltaP rule. Significant effects of the pCI manipulations were found in all cases, but causal judgments did not vary significantly with objective contingencies when pCI was held constant. The experiments used a variety of stimulus presentation procedures and different dependent measures. The power PC theory, a weighted version of the deltaP rule, the Rescorla-Wagner associative learning model (R. A. Rescorla & A. R Wagner, 1972), and the deltaD rule, which is the frequency-based version of the pCI rule, were unable to account for the significant effects of the pCI manipulations. These results are consistent with a general explanatory approach to causal judgment involving the evaluation of evidence and updating of beliefs with regard to causal hypotheses.

Decision Making↗

PubMed2003

Causal judgment as evaluation of evidence: the use of confirmation and disconfirmatory information.

There are four kinds of contingency information: occurrences and nonoccurrences of an effect in the presence and absence ofa cause. In two experiments participants made judgements about sets of stimulus materials in which one of these four kinds had zero frequency. The experiments tested two kinds of predictions derived from the evidential evaluation model of causal judgement, which postulates that causal judgement depends on the proportion of instances evaluated as confirmatory for the cause being judged. The model predicts significant effects of manipulating the frequency of one kind of contingency information in the absence of changes in the objective contingency. The model also predicts that extra weight will be given to one kind of confirmatory information when the other kind has zero frequency, and to one kind of disconfirmatory information when the other kind has zero frequency. Results supported both sets of predictions, and also disconfirmed predictions of the power probabilistic contrast theory of causal judgement. This research therefore favours an account of causal judgement in which contingency information is transformed into evidence, and judgement is based on the n et confirmatory or disconfirmatoryvalue of the evidence.

Analysis of Variance↗

PubMed2003

Polymerase chain reaction screening for integrons can be used to complement resistance surveillance programs.

Integrons have been recognised as important contributors to the acquisition and dissemination of antibiotic resistance in Gram-negative bacteria. In a collection of 19 multi-antibiotic resistant Gram-negative clinical isolates, 47 per cent (9/19) of strains were found to contain one or more integron, using a polymerase chain reaction (PCR) based screening method. Resistance gene cassettes within the integrons were amplified, sequenced and characterised. Antibiotic susceptibility testing demonstrated that resistance phenotypes correlated with the resistance conferred by gene cassettes identified. PCR-screening for integrons and gene cassettes provides a rapid technique for the identification of genetic determinants of resistance in Gram-negative bacteria. Such screening could assist in guiding treatment regimens and complement existing antibiotic resistance surveillance programs by providing information on molecular mechanisms of both resistance and resistance dissemination.

Anti-Bacterial Agents↗

PubMed2003

Effects of wording and stimulus format on the use of contingency information in causal judgment.

There are four kinds of contingency information: occurrences and nonoccurrences of an effect in the presence and in the absence of a cause. Previous studies have shown that these four kinds are not given equal weight in causal judgment. The present research was designed to test two hypotheses about this unequal weighting: that weightings are influenced by the form of the question and other features of the stimulus materials and that unequal weightings occur, in part, because individual differences in the use of contingency information are not evenly distributed across the four kinds of information. Support was found for both hypotheses. However, the effects of question wording were not always as had been predicted, indicating that more needs to be learned about how people interpret the task, instructions, and materials they are given.

Humans↗

PubMed2002

Norwalk-like virus 95/96-US strain is a major cause of gastroenteritis outbreaks in Australia.

Norwalk-like viruses (NLVs) were detected using a nested reverse transcriptase-polymerase chain reaction (RT-PCR) with primers directed to the RNA polymerase region. Samples were examined from 11 separate outbreaks of gastroenteritis and five sporadic cases of childhood gastroenteritis between 1997 and 2000. Phylogenetic analysis of the 298 bp sequences showed that all strains belong to NLV genogroup II and the majority of the sequenced isolates (30/36) were members of the 95/96-US subset of strains associated with outbreaks recorded worldwide between 1995 and 1996. This was confirmed by analysis of the full length capsid region of a representative Australian isolate. This study demonstrates the usefulness of targeting primers for NLVs to the predominant circulating genotype(s) and confirms the spread of this subtype globally, including the Southern Hemisphere.

Adolescent↗

PubMed2002

Perceiving a strong causal relation in a weak contingency: further investigation of the evidential evaluation model of causal judgement.

Contingency information is information about the occurrence or nonoccurrence of a certain effect in the presence or absence of a candidate cause. An objective measure of contingency is the deltaP rule, which involves subtracting the probability of occurrence of an effect when a causal candidate is absent from the probability of occurrence of the effect when the candidate is present. Causal judgements conform closely to deltaP but deviate from it under certain circumstances. Three experiments show that such deviations can be predicted by a model of causal judgement that has two components: a rule of evidence, that causal judgement is a function of the proportion of relevant instances that are judged to be confirmatory for the causal candidate, and a tendency for information about instances in which the candidate is present to have greater effect on judgement than instances in which the candidate is absent. Two experiments demonstrate how this model accounts for some recently published findings. A third experiment shows that it is possible to use the model to predict the occurrence of high causal judgements when the objective contingency is close to zero.

Attitude to Health↗

PubMed2002

Causal judgement from contingency information: judging interactions between two causal candidates.

In two experiments participants judged the extent to which occurrences and non-occurrences of an effect could be attributed to an interaction between two causal candidates A and B. In Experiment I judgements were influenced by the proportion of instances normatively evaluated as confirmatory for the interaction interpretation, when the objective contingency was held constant. Information about instances in which both candidates were present and the effect occurred was more influential than information about instances in which both candidates were absent and the effect did not occur. In Experiment 2 the occurrence rate of the effect when both candidates were present, when A alone was present, when B alone was present, and when both were absent was manipulated. Interaction judgements were mainly determined by occurrence rate when both were present. There was also a significant effect of occurrence rate when both were absent, but the other two occurrence rates had no significant effect. These results are interpreted as supporting a general model in which causal judgements are made according to the proportion of instances evaluated as supporting the interpretation being judged.

Adult↗

PubMed2002

Quantification of hepatitis C virus in human liver and serum samples by using LightCycler reverse transcriptase PCR.

A highly sensitive, non-probe-based, real-time quantitative reverse transcriptase PCR was developed for viral load measurements in both serum and liver samples from patients with hepatitis C virus (HCV) infection. With synthetic RNA, the linearity of the approach was conserved over a wide range of HCV copy numbers. There was a strong correlation between hepatic and serum viral load measurements (r = 0.689, P = 0.004, n = 15), indicating that the level of viremia reflected the amount of virus present in the liver.

Hepacivirus↗

PubMed2002

Epidemic strains of Shigella sonnei biotype g carrying integrons.

Class 2 integrons (Tn7) were found in all randomly selected epidemic (n = 27) and preepidemic (n = 13) strains of multiresistant Shigella sonnei biotype g. A class 1 integron was also found in two epidemic strains. Gene cassettes within these integrons account for resistance to commonly used therapeutic agents.

Adult↗