(73/3442) Evidence for a general-purpose genotype in Candida albicans, highly prevalent in multiple geographical regions, patient types and types of infection.
Epidemiological studies, using the probe Ca3, have shown that in a given patient population a single cluster of genetically related Candida albicans isolates usually predominates. The authors have investigated whether these local clusters are part of a single group, geographically widespread and highly prevalent as an aetiological agent of various types of candidiasis. An unrooted neighbour-joining tree of 266 infection-causing C. albicans isolates (each from a different individual) from 12 geographical regions in 6 countries was created, based on genetic distances generated by Ca3 fingerprinting. Thirty-seven per cent of all isolates formed a single genetically homogeneous cluster (cluster A). The remainder of isolates were genetically diverse. Using the maximum branch length within cluster A as a cut-off, they could be divided into 37 groups, whose prevalence ranged between 0.3% and 9%. Strains from cluster A were highly prevalent in all but one geographical region, with a mean prevalence across all regions of 41%. When isolates were separated into groups based on patient characteristics or type of infection, strains from cluster A had a prevalence exceeding 27% in each group, and their mean prevalence was 43% across all patient characteristics. These data provide evidence that cluster A constitutes a general-purpose genotype, which is geographically widespread and acts as a predominant aetiological agent of all forms of candidiasis in all categories of patients surveyed. (+info)
(74/3442) Genomic heterogeneity in synchronous hepatocellular carcinomas.
BACKGROUND: Hepatocellular carcinoma (HCC) arising in cirrhosis is frequently multifocal. Whether HCC develops monoclonally or multiclonally is an unresolved question. Of the multiple tumour nodules present in many patients, it has not been established whether the smaller lesions represent intrahepatic metastases or de novo cancers. AIMS: To assess the degree of genomic heterogeneity in synchronous HCCs in cirrhosis. METHODS: The arbitrarily primed polymerase chain reaction technique was utilised to compare the DNA fingerprint of HCCs and regenerative nodules (RNs) removed from cirrhotic explant livers. RESULTS: Polymorphic genomic heterogeneity was noted in 54 HCCs and 31 RNs microdissected. Even satellite nodules in close proximity within the same segment of the liver were found to have distinct genomic patterns. CONCLUSION: Such genomic heterogeneity in synchronous HCCs may explain poor patient survival after surgical resection. If the smaller tumours are de novo lesions rather than metastases (as these data suggest), then current concepts regarding liver resection as a curative treatment modality for HCC may require reassessment. (+info)
(75/3442) Exogenous reinfection as a cause of recurrent tuberculosis after curative treatment.
BACKGROUND: For decades it has been assumed that postprimary tuberculosis is usually caused by reactivation of endogenous infection rather than by a new, exogenous infection. METHODS: We performed DNA fingerprinting with restriction-fragment-length polymorphism analysis on pairs of isolates of Mycobacterium tuberculosis from 16 compliant patients who had a relapse of pulmonary tuberculosis after curative treatment of postprimary tuberculosis. The patients lived in areas of South Africa where tuberculosis is endemic. Medical records were reviewed for clinical data. RESULTS: For 12 of the 16 patients, the restriction-fragment-length polymorphism banding patterns for the isolates obtained after the relapse were different from those for the isolates from the initial tuberculous disease. This finding indicates that reinfection was the cause of the recurrence of tuberculosis after curative treatment. Two patients had reinfections with a multidrug-resistant strain. All 15 patients who were tested for the human immunodeficiency virus were seronegative. CONCLUSIONS: Exogenous reinfection appears to be a major cause of postprimary tuberculosis after a previous cure in an area with a high incidence of this disease. This finding emphasizes the importance of achieving cures and of preventing anyone with infectious tuberculosis from exposing others to the disease. (+info)
(76/3442) Genotypic and phenotypic relationships between clinical and environmental isolates of Stenotrophomonas maltophilia.
While the gram-negative bacterium Stenotrophomonas maltophilia is used in biotechnology (e.g., for biological control of plant pathogens and for bioremediation), the number of S. maltophilia diseases in humans has dramatically increased in recent years. A total of 40 S. maltophilia isolates from clinical and environmental sources (plant associated and water) was investigated to determine the intraspecies diversity of the group and to determine whether or not the strains could be grouped based on the source of isolation. The isolates were investigated by phenotypic profiling (enzymatic and metabolic activity and antibiotic resistance patterns) and by molecular methods such as temperature-gradient gel electrophoresis of the 16S rRNA gene fragment, PCR fingerprinting with BOX primers, and pulsed-field gel electrophoresis (PFGE) after digestion with DraI. Results of the various methods revealed high intraspecies diversity. PFGE was the most discriminatory method for typing S. maltophilia when compared to the other molecular methods. The environmental strains of S. maltophilia were highly resistant to antibiotics, and the resistance profile pattern of the strains was not dependent on their source of isolation. Computer-assisted cluster analysis of the phenotypic and genotypic features did not reveal any clustering patterns for either clinical or environmental isolates. (+info)
(77/3442) Application of different genotyping methods for Pseudomonas aeruginosa in a setting of endemicity in an intensive care unit.
Colonization with Pseudomonas aeruginosa was studied by taking serial swab specimens from the oropharynges and anuses and tracheal and gastric aspirates from patients in an intensive care unit during a 10-month period in a setting of endemicity. Nineteen (10%) of the 192 patients included in the study were colonized on admission, while another 30 (16%) patients acquired P. aeruginosa while in the hospital. Typing of 353 isolates was performed by random amplified polymorphic DNA (RAPD) analysis, and 56 strains were selected for further typing by RAPD analysis, pulsed-field gel electrophoresis (PFGE), and amplified fragment length polymorphism (AFLP) analysis. By these methods, 42, 44, and 44 genotypes were found, respectively. Computer-aided cluster analysis indicated that similar groups of related isolates were obtained by each method. By taking admission periods into account, analysis of the typing results suggested cross-acquisition of P. aeruginosa for five patient pairs. The small number of transfers and the large number of genotypes found indicate that most P. aeruginosa strains were derived from the patients themselves. The numbers of observed typing patterns and band differences between related isolates were counted for each typing method. AFLP analysis with primers without a selective base proved to be the most discriminatory method, followed by PFGE, AFLP analysis (with one selective base), and RAPD analysis. On the basis of a comparison with established strain differentiation criteria for PFGE, the criteria for differentiation of P. aeruginosa by AFLP analysis are presented. (+info)
(78/3442) Molecular markers reveal exclusively clonal reproduction in Trichophyton rubrum.
Genotypic variability among 96 Trichophyton rubrum strains which displayed different colony morphologies and were collected from four continents was investigated. Twelve markers representing 57 loci were analyzed by PCR fingerprinting, amplified fragment length polymorphism, and random amplified monomorphic DNA markers. Interestingly, none of the methods used revealed any DNA polymorphism, indicating a strictly clonal mode of reproduction and a strong adaptation to human skin. (+info)
(79/3442) Microevolutionary changes in Candida albicans identified by the complex Ca3 fingerprinting probe involve insertions and deletions of the full-length repetitive sequence RPS at specific genomic sites.
The 11 kb complex DNA fingerprinting probe Ca3 is effective both in cluster analyses of Candida albicans isolates and in identifying microevolutionary changes in the size of hypervariable genomic fragments. A 2.6 kb EcoRI fragment of Ca3, the C fragment, retains the capacity to identify these microevolutionary changes, and when the C fragment is cleaved with SacI, the capacity is retained exclusively by a 1 kb subfragment, C1, which contains a partial RPS repeat element. The microevolutionary changes identified by Ca3, therefore, may involve reorganization of RPS elements dispersed throughout the genome. To test this possibility, hypervariable fragments from several strains of C. albicans were sequenced and compared. The results demonstrate that the microevolutionary changes identified by Ca3 are due to the insertion and deletion of full-length tandem RPS elements at specific genomic sites dispersed throughout the C. albicans genome. The RPS elements at these dispersed sites are bordered by the same upstream and downstream sequences. The frequency of recombination was estimated to be one recombination per 1000 cell divisions by following RPS reorganization in vitro. The results are inconsistent with unequal recombination between homologous or heterologous chromosomes, but consistent with intrachromosomal recombination. Two alternative models of intrachromosomal recombination are proposed: unequal sister-chromatid exchange and slipped misalignment at the replication fork. (+info)
(80/3442) Genetically distinct dog-derived and human-derived Sarcoptes scabiei in scabies-endemic communities in northern Australia.
Overcrowding is a significant factor contributing to endemic infection with Sarcoptes scabiei in human and animal populations. However, since scabies mites from different host species are indistinguishable morphologically, it is unclear whether people can be infected from scabies-infested animals. Molecular fingerprinting was done using three S. scabiei-specific single locus hypervariable microsatellite markers, with a combined total of 70 known alleles. Multilocus analysis of 712 scabies mites from human and dog hosts in Ohio, Panama and Aboriginal communities in northern Australia now shows that genotypes of dog-derived and human-derived scabies cluster by host species rather than by geographic location. Because of the apparent genetic separation between human scabies and dog scabies, control programs for human scabies in endemic areas do not require resources directed against zoonotic infection from dogs. (+info)
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