Biomedical subjects

Brad T Cookson

Publications and source records attributed to Brad T Cookson.

21 records · Page 2Linked to original sources

PubMed2003

Genetic diversity among clinical isolates of Acremonium strictum determined during an investigation of a fatal mycosis.

Primarily saprophytic in nature, fungi of the genus Acremonium are a well-documented cause of mycetoma and other focal diseases. More recently, a number of Acremonium spp. have been implicated in invasive infections in the setting of severe immunosuppression. During the course of routine microbiological studies involving a case of fatal mycosis in a nonmyeloablative hematopoietic stem cell transplant patient, we identified a greater-than-expected variation among strains previously identified as Acremonium strictum by clinical microbiologists. Using DNA sequence analysis of the ribosomal DNA intergenic transcribed spacer (ITS) regions and the D1-D2 variable domain of the 28S ribosomal DNA gene (28S), the case isolate and four other clinical isolates phenotypically identified as A. strictum were found to have <99% homology to the A. strictum type strain, CBS 346.70, at the ITS and 28S loci, while a sixth isolate phenotypically identified only as Acremonium sp. had >99% homology to the type strain at both loci. These results suggest that five out of the six clinical isolates belong to species other than A. strictum or that the A. strictum taxon is genetically diverse. Based upon these sequence data, the clinical isolates were placed into three genogroups.

Acremonium↗

PubMed2002

Rapid identification and differentiation of Candida albicans and Candida dubliniensis by capillary-based amplification and fluorescent probe hybridization.

We developed a rapid genotypic assay to differentiate the germ tube-positive yeasts Candida albicans and Candida dubliniensis. Fluorescently labeled nucleic acid probe binding and subsequent denaturation from the target site in the PCR amplicons produced characteristic peak melting temperatures (T(m)) that identified each species. Peak T(m)s of C. albicans (n = 69) and C. dubliniensis (n = 28) isolates produced in the presence of their respective probes were 61.04 +/- 0.64 degrees C and 60.52 +/- 1.01 degrees C (averages +/- standard deviations). No signal was generated when the C. albicans or C. dubliniensis probes were tested against DNA from their counterparts. Both probes reacted with Candida tropicalis DNA, but the T(m) was 51.85 +/- 0.05 degrees C with the C. albicans probe and 51.92 +/- 0.10 degrees C with the C. dubliniensis probe, differentiating C. tropicalis DNA from C. albicans and C. dubliniensis. A novel hybrid probe was designed to identify both species in a single reaction based on a 4 degrees C difference in peak T(m)s. Our assay is rapid (</=2 h) and allows reliable detection and differentiation of the two germ tube-positive Candida spp.

Candida↗

PubMed2002

Diagnosis of community-acquired pertussis infection: comparison of both culture and fluorescent-antibody assays with PCR detection using electrophoresis or dot blot hybridization.

Diagnosis of Bordetella pertussis infection has been difficult due to the low sensitivity of culture. PCR tests have been shown to be more sensitive than culture, but the reported sensitivity of PCR is variable. We evaluated PCR product detection by using either agarose gel electrophoresis (PCR-gel) or dot blot hybridization with (32)P-labeled oligonucleotide probes, and we compared these methods to both culture and direct fluorescent-antibody (DFA) assays with microscopy for the detection of pertussis. This was done with 225 nasopharyngeal swab specimens collected in community clinic settings. The multiplexed PCR amplified the multiply repeated IS481 B. pertussis sequence and a sequence from the human globin gene as a positive control for specimen adequacy. Of 225 specimens, 179 were judged to be adequate for PCR analysis. Among the adequate specimens, 9, 4, and 10 were culture, DFA, and PCR-gel positive, respectively. The sensitivity of PCR-gel versus culture was 89% while the sensitivity of culture versus PCR-gel was 80%. DFA had the lowest sensitivity. Thirty specimens were positive by PCR with dot blot hybridization; no negative control specimens showed a signal above the background. Among the 79 (44%) adequate specimens with clinical data available, the rates of reported cough or persistent cough were similar for persons who were pertussis positive by each assay. The IS481 PCR, with either electrophoresis or dot blot hybridization, is a sensitive assay; however, at this time it cannot completely replace culture without an overall loss in sensitivity for the detection of pertussis. Further study is required to understand the clinical significance of B. pertussis PCR products detected by dot blot hybridization alone.

Bacteriological Techniques↗