Biomedical subjects
P D Johnson
Publications and source records attributed to P D Johnson.
Attentional function in secondary school students receiving isoniazid prophylaxis for tuberculosis infection.
Reports have suggested that isoniazid treatment may be associated with poor concentration and subtle reduction in memory. This study examines attentional function and processing speed in a group of 25 adolescents who received isoniazid prophylaxis for at least 6 months. As adolescents often face major educational assessment milestones, such cognitive side effects may have important implications. Participants were assessed before treatment, 1 month into treatment and at least 1 week after treatment cessation. Measures included the Paced Auditory Serial Addition Test and subtests of the appropriate Wechsler scale sensitive to attention and speed of information processing. Isoniazid does not appear to cause significant adverse effects on attentional function in adolescents.
Identification of Mycobacterium ulcerans in the environment from regions in Southeast Australia in which it is endemic with sequence capture-PCR.
We recently described the use of PCR to identify the environmental source of Mycobacterium ulcerans during an outbreak of ulcerative disease that occurred in a localized region of southeast Australia. The PCR used was based on amplification of the M. ulcerans-specific insertion sequence, IS2404. In this study we developed a new test that is a substantial improvement over the original PCR method in terms of sensitivity, reliability, and ease of use. In the new method magnetic bead sequence capture-PCR is used to detect two M. ulcerans sequences (IS2404 and IS2606) and total mycobacterial 16S ribosomal DNA. We used sequence capture-PCR to test water and plant material collected over a 12-month period during 1998 and 1999 from sites near the centers of two distinct foci of M. ulcerans infections. A golf course irrigation system in one area and a small shallow lake in another area repeatedly were PCR positive for M. ulcerans. Nearby sites and sites unrelated to the endemic areas were negative. Based on the PCR data, a most-probable-number method was used to estimate the concentration of M. ulcerans cells in positive samples from both regions. This procedure resulted in average concentrations of 0.5 cell per 100 ml of water and 40 cells per 100 g of detritus. Loss of the PCR signal coincided with a decrease in ulcerative disease in each area. These results provide further evidence that M. ulcerans may be transmitted from a point environmental source and demonstrate the utility of magnetic bead sequence capture-PCR for identification of nonculturable microbial pathogens in the environment.
Comparative genetic analysis of Mycobacterium ulcerans and Mycobacterium marinum reveals evidence of recent divergence.
Previous studies of the 16S rRNA genes from Mycobacterium ulcerans and Mycobacterium marinum have suggested a very close genetic relationship between these species (99.6% identity). However, these organisms are phenotypically distinct and cause diseases with very different pathologies. To investigate this apparent paradox, we compared 3,306 nucleotides from the partial sequences of eight housekeeping and structural genes derived from 18 M. ulcerans strains and 22 M. marinum strains. This analysis confirmed the close genetic relationship inferred from the 16S rRNA data, with nucleotide sequence identity ranging from 98.1 to 99.7%. The multilocus sequence analysis also confirmed previous genotype studies of M. ulcerans that have identified distinct genotypes within a geographical region. Single isolates of both M. ulcerans and M. marinum that were shown by the sequence analysis to be the most closely related were then selected for further study. One- and two-dimensional pulsed-field gel electrophoresis was employed to compare the architecture and size of the genome from each species. Genome sizes of approximately 4.4 and 4.6 Mb were obtained for M. ulcerans and M. marinum, respectively. Significant macrorestriction fragment polymorphism was observed between the species. However, hybridization analysis of DNA cleaved with more frequently cutting enzymes identified significant preservation of the flanking sequence at seven of the eight loci sequenced. The exception was the 16S rRNA locus. Two high-copy-number insertion sequences, IS2404 and IS2606, have recently been reported in M. ulcerans, and significantly, these elements are not present in M. marinum. Hybridization of the AseI restriction fragments from M. ulcerans with IS2404 and IS2606 indicated widespread genome distribution for both of these repeated sequences. Taken together, these data strongly suggest that M. ulcerans has recently diverged from M. marinum by the acquisition and concomitant loss of DNA in a manner analogous to the emergence of M. tuberculosis, where species diversity is being driven mainly by the activity of mobile DNA elements.
A simple PCR method for rapid genotype analysis of Mycobacterium ulcerans.
Two high-copy-number insertion sequences, IS2404 and IS2606, were recently identified in Mycobacterium ulcerans and were shown by Southern hybridization to possess restriction fragment length polymorphism between strains from different geographic origins. We have designed a simple genotyping method that captures these differences by PCR amplification of the region between adjacent copies of IS2404 and IS2606. We have called this system 2426 PCR. The method is rapid, reproducible, sensitive, and specific for M. ulcerans, and it has confirmed previous studies suggesting a clonal population structure of M. ulcerans within a geographic region. M. ulcerans isolates from Australia, Papua New Guinea, Malaysia, Surinam, Mexico, Japan, China, and several countries in Africa were easily differentiated based on an array of 4 to 14 PCR products ranging in size from 200 to 900 bp. Numerical analysis of the banding patterns suggested a close evolutionary link between M. ulcerans isolates from Africa and southeast Asia. The application of 2426 PCR to total DNA, extracted directly from M. ulcerans-infected tissue specimens without culture, demonstrated the sensitivity and specificity of this method and confirmed for the first time that both animal and human isolates from areas of endemicity in southeast Australia have the same genotype.
Effect of anti-tuberculosis treatment on the tuberculin interferon-gamma response in tuberculin skin test (TST) positive health care workers and patients with tuberculosis.
SETTING: Public hospital, Victoria, Australia. OBJECTIVE: To evaluate the effect of multidrug treatment and isoniazid (INH) chemoprophylaxis on the tuberculin interferon-y assay (QIFN) in 19 patients with culture-confirmed Mycobacterium tuberculosis and 119 health care workers (HCWs) with tuberculin skin tests (TST) > or =15 mm. DESIGN: Patients with M. tuberculosis were treated with standard medication and tested with QIFN at diagnosis and at regular intervals over a 12-month period. All HCWs, 59 (50%) of whom were prescribed INH chemoprophylaxis, were tested with QIFN at baseline, 2, 4, 6 and 12 months. RESULTS: QIFN results in patients with tuberculosis were consistent and reproducible. At the initial time point QIFN assays were positive for M. tuberculosis in 67%, and once positive, the QIFN assay remained so over the 12-month period. In the HCWS, initial QIFN assays were positive in 73 (61%). During the 12-month study, 91 HCWs had a QIFN assay on at least two occasions. The overall reproducibility between tests was fair (kappa statistic = 0.45), and was little affected by administration of INH. CONCLUSION: These data suggest that although the QIFN assay is generally positive in patients with proven tuberculosis, it does not provide clinically useful information during the first 12 months of treatment with multidrug chemotherapy or INH chemoprophylaxis.
Using scenarios in chronic disease management guidelines for primary care.
The Prodigy system is a guideline-based decision-support system designed to assist general practitioners in England choose the appropriate therapeutic action for their patients. As part of the system, we developed a novel model for encoding clinical guidelines for managing patients with chronic diseases such as asthma and hypertension. The model structures a guideline as a set of choices to be made by the clinician. It models patient scenarios which drive decision making and are used to synchronize the management of a patient with guideline recommendations. The model is robust with respect to available input data and leaves the control of decision-making to the clinician. We have built execution engines to verify the computability of the model. We intend to test the model integrated in up to 200 live systems from at least four system vendors in English General practice.
Outcome of a screening program for vancomycin-resistant enterococci in a hospital in Victoria.
OBJECTIVE: To screen for faecal colonisation with vancomycin-resistant enterococci (VRE) among potentially at-risk patients. DESIGN: Infection control screening program. SETTING: Monash Medical Centre (a tertiary care hospital), Melbourne, Victoria, in the seven months from June 1997. PATIENTS: Patients in the Renal, Oncology and Intensive Care (ICU) Units. MAIN OUTCOME MEASURES: Presence of VRE in a rectal swab or faecal specimen taken at admission and at regular intervals during inpatient stay; presence of vancomycin-resistance genes (vanA, vanB and vanC) assessed by polymerase chain reaction (PCR); genetic clonality of isolates assessed by pulsed-field gel electrophoresis (PFGE). RESULTS: 574 patients (356 renal, 134 ICU and 84 oncology) were screened; 12 were colonised with VRE--nine renal inpatients, two having peritoneal dialysis or incentre haemodialysis, and one ICU patient. Nine isolates were Enterococcus faecalis (seven positive for vanB and two negative for all three resistance genes) and three were Enterococcus faecium (all positive for vanB). Eight were high-level gentamicin resistant. PFGE suggested genetic clonality between the index isolate and five other isolates from renal patients. No specific clinical practice was associated with VRE colonisation. Attempts to clear rectal carriage with oral ampicillin/amoxycillin or bacitracin were of limited success. Although antibiotic prescribing in the Renal Unit was generally consistent with defined protocols, use of vancomycin and third-generation cephalosporins has been further restricted. CONCLUSIONS: Renal inpatients in our institution appear most at risk of VRE colonisation (4.6% overall) and therefore of VRE infection. Routine screening, especially of potentially high-risk patients, should be considered in major Australian hospitals.
Tuberculin-purified protein derivative-, MPT-64-, and ESAT-6-stimulated gamma interferon responses in medical students before and after Mycobacterium bovis BCG vaccination and in patients with tuberculosis.
QuantiFERON-TB (QIFN) (CSL Limited) is a whole-blood assay for the recognition of infection with Mycobacterium tuberculosis. QIFN measures gamma interferon (IFN-gamma) production when purified protein derivatives (PPDs) of mycobacteria are incubated with venous blood samples. The specificity of QIFN in medical students before and after BCG immunization was assessed, and sensitivity in patients with tuberculosis was assessed. Antigens were PPD derived from M. tuberculosis and two M. tuberculosis-specific proteins, ESAT-6 and MPT-64. Of 60 medical students, all of whom had 0-mm tuberculin skin tests (TSTs) at study entry, 58 (97%) were initially classified as negative for M. tuberculosis infection by PPD QIFN. Five months after BCG immunization, 7 of 54 students (13%) had a TST result of >/=10 mm and 11 of 54 students (20%) tested positive by PPD QIFN. ESAT-6- and MPT-64-stimulated IFN-gamma responses in the medical students were negative prior to and after BCG immunization. For patients with active tuberculosis, 12 of 19 (63%) were positive by PPD QIFN, 11 of 19 (58%) were positive by ESAT-6 QIFN, and 0 of 12 were positive by MPT-64 QIFN. In conclusion, PPD QIFN was negative in 97% of a low-risk population who had not received BCG and who had negative TSTs. The specificities of both the TST and PPD QIFN were reduced following BCG immunization. PPD QIFN and ESAT-6 QIFN were of similar and moderate sensitivity in patients with active tuberculosis, but ESAT-6 QIFN is likely to be more specific because it is not influenced by past BCG exposure.
Identification and characterization of IS2404 and IS2606: two distinct repeated sequences for detection of Mycobacterium ulcerans by PCR.
Molecular analysis of Mycobacterium ulcerans has revealed two new insertion sequences (ISs), IS2404 and IS2606. IS2404 was identified by complete sequencing of a previously described repetitive DNA segment from M. ulcerans. This element is 1,274 bp long, contains 12-bp inverted repeats and a single open reading frame (ORF) potentially encoding a protein of 327 amino acids (aa), and apparently generates 7-bp direct repeats upon transposition. Amino acid similarity was found between the putative transposase and those encoded by ISs in other bacterial sequences from Aeromonas salmonicida (AsIs1), Escherichia coli (H repeat element), Vibrio cholerae (VcIS1), and Porphyromonas gingivalis (PGIS2). The second IS, IS2606, was discovered by sequence analysis of a HaeIII fragment of M. ulcerans genomic DNA containing a repetitive sequence. This element is 1,404 bp long, with 12-bp inverted repeats and a single ORF potentially encoding a protein of 445 aa. Database searches revealed a high degree of amino acid identity (70%) with the putative transposase of IS1554 from M. tuberculosis. Significant amino acid identity (40%) was also observed with transposases from several other microorganisms, including Rhizobium meliloti (ISRm3), Burkholderia cepacia (IS1356), Corynebacterium diphtheriae, and Yersinia pestis. PCR screening of DNA from 45 other species of mycobacteria with primers for IS2404 confirm that this element is found only in M. ulcerans. However, by PCR, IS2606 was also found in Mycobacterium lentiflavum, another slow-growing member of the genus Mycobacterium that is apparently genetically distinct from M. ulcerans. Testing the sensitivity of PCR based on IS2404 and IS2606 primers demonstrated the ability to detect 0.1 and 1 M. ulcerans genome equivalents, respectively. The ability to detect small numbers of cells by using two gene targets will be particularly useful for analyzing environmental samples, where there may be low concentrations of M. ulcerans among large numbers of other environmental mycobacteria.
Respiratory symptoms and duration of residence in immigrant teenagers living in Melbourne, Australia.
OBJECTIVE: Examination of the relation between respiratory symptoms and time since arrival in Australia in immigrant teenagers living in Melbourne. DESIGN: Two stage, stratified, cross sectional survey. SETTING: High schools (n = 51). SUBJECTS: 9794 people aged 13-19 years. MAIN OUTCOME MEASURES: Prevalence of wheeze during a 12 month period, region of birth, duration of residence in Australia. RESULTS: The estimated population 12 month period prevalence of wheeze was 18.9% (95% confidence interval (CI), 18.0 to 19.9). In subjects born outside Australia, residence for five to nine years in Australia was associated with a 2.1-fold (CI, 1.1 to 4.0) increase in the odds of self reported wheeze; after 10-14 years, this risk increased 3.4-fold (CI, 1.8 to 6.7). There was no difference in severity of wheeze, measured by reported frequency of attacks, between Australian born and non-Australian born subjects. CONCLUSIONS: The notion of a continued secular increase in the prevalence of wheezing is not supported. There is a time dose effect on the prevalence of symptoms in subjects born outside Australia and now living in Melbourne, which is independent of age and country of birth.
Effects of head posture on headgear force application.
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Tipranavir (PNU-140690): a potent, orally bioavailable nonpeptidic HIV protease inhibitor of the 5,6-dihydro-4-hydroxy-2-pyrone sulfonamide class.
A broad screening program previously identified phenprocoumon (1) as a small molecule template for inhibition of HIV protease. Subsequent modification of this lead through iterative cycles of structure-based design led to the activity enhancements of pyrone and dihydropyrone ring systems (II and V) and amide-based substitution (III). Incorporation of sulfonamide substitution within the dihydropyrone template provided a series of highly potent HIV protease inhibitors, with structure-activity relationships described in this paper. Crystallographic studies provided further information on important binding interactions responsible for high enzymatic binding. These studies culminated in compound VI, which inhibits HIV protease with a Ki value of 8 pM and shows an IC90 value of 100 nM in antiviral cell culture. Clinical trials of this compound (PNU-140690, Tipranavir) for treatment of HIV infection are currently underway.
Prevalence of tuberculosis infection in Melbourne secondary school students.
OBJECTIVE: To estimate the prevalence of asymptomatic Mycobacterium tuberculosis infection in Melbourne secondary school students. DESIGN: Cross-sectional Mantoux testing of a partly random and partly targeted sample of secondary school students, designed to enable estimation of prevalence by region of birth. SETTING: Fifty-one State and Catholic secondary schools in metropolitan Melbourne during 1995. PARTICIPANTS: Australian and overseas-born students in Years 9 and 10. OUTCOME MEASURES: Proportions of students with positive Mantoux reactions (defined as induration at 48 hours of > or = 5 mm with a history of recent exposure; > or = 10 mm and no prior BCG vaccination; > or = 15 mm and prior BCG vaccination). RESULTS: Of 2586 students potentially eligible for testing, evaluable results were obtained from 1274 (49%). The overall prevalence of infection for Melbourne students in Years 9 and 10 was 2.5% (95% CI, 1.1-3.9%). Main predictors of a positive test were birth overseas and number of years residing overseas. Prevalence varied considerably by region of birth, and was very low in students born in Australia (0.7%), "other developed countries" (0.7%), and Southern Europe (0). The highest rates were observed in students born in Indochina (15.9%), other countries in South East Asia (10.2%), and Eastern Europe (10.2%). CONCLUSIONS: The risk of a young person becoming infected with M. tuberculosis while living in Melbourne is very low. Our results do not indicate a need for the reintroduction of mass screening in Victorian schools. If targeted screening were to be considered, the group most likely to benefit would be recently arrived migrants from Indochina.
Cardiac teratogenicity of trichloroethylene metabolites.
OBJECTIVES: The hypothesis of this study was that metabolites of trichloroethylene (TCE), dichloroethylene (DCE) and related compounds were responsible for fetal cardiac teratogenic effects seen when TCE or DCE is consumed by pregnant rats during organogenesis. Identification of teratogenic metabolites would allow more accurate assessment of environmental contaminants and public health risks from contaminated water or possibly municipal water supplies which, when chlorinated, may produce these potentially dangerous chemicals. BACKGROUND: Human epidemiologic studies and previous teratogenic studies using chick embryos and fetal rats have shown an increased incidence of congenital cardiac lesions in animals exposed to TCE and DCE. METHODS: Metabolites and compounds studied in drinking water exposure included: trichloroacetic acid (TCAA), monochloroacetic acid (MCAA), trichloroethanol (TCEth), carboxy methylcystine (CMC), trichloroacetaldehyde (TCAld), dichloroacetaldehyde (DCAld), and dichlorovinyl cystine (DCVC). Compounds were administered to pregnant rats during fetal heart development. RESULTS: Fetuses of rats receiving 2,730 ppm TCAA in drinking water were the only group that demonstrated a significant increase in cardiac defects (10.53%) compared with controls (2.15%) on a per fetus basis (p = 0.0001, Fischer's exact test), and a per litter basis (p = 0.0004, Wilcoxon and p = 0.0015, exact permutation tests). Trichloroacetic acid also demonstrated an increased number of implantation and resorption sites (p < 0.05) over controls. Other maternal and fetal variables showed no statistically significant differences between treated and untreated groups. CONCLUSIONS: Of the metabolites tested, only TCAA appeared to be a specific cardiac teratogen in the fetus when imbibed by the maternal rat.
The role of social and cognitive processes in children's adjustment to community violence.
This study examined associations of community violence exposure and psychological well-being among 99 8-12 year old children (M = 10.7 years) using home interviews with mothers and children. Both moderators and mediators of the links between violence exposure and well-being were tested. After demographics and concurrent life stressors were controlled for violence exposure was significantly associated with intrusive thinking, anxiety, and depression. Regression analyses indicated that intrusive thinking partially mediated associated between violence exposure and internalizing symptoms. Planned comparisons revealed that violence exposure had the strongest effect on well-being among children with low social support or high levels of social strains. Furthermore, children with high levels of intrusive thinking were most likely to show heightened internalizing symptoms when they had inadequate social support.
Candidal epididymo-orchitis: case report and review.
We describe a case of epididymo-orchitis with candiduria and histologically proven epididymal abscesses due to Candida albicans and review six previously reported cases. Candidal epididymo-orchitis occurs in patients with recognized risk factors for candidal infection, often after instrumentation of the urinary tract. Cases caused by both C. albicans and Candida glabatra have been described. Drainage or orchidectomy may be required for definitive diagnosis and treatment. Treatment with oral antifungals alone has been effective in two cases.
Detection of an aberrant motile larval form in the brain of a patient with neurocysticercosis.
Neurocysticercosis is the most common parasitic infection of the central nervous system in humans. The adult pork tape worm, Taenia solium, resides in the lumen of the intestine, and the only structural element of an adult worm usually found within a tissue cyst in the brain or in muscle is a single invaginated scolex. We report a highly unusual, and perhaps unique, occurrence of neurocysticercosis in which an aberrant worm-like larval form, 12.5 cm in length, was found within a cyst in brain parenchyma.