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D C Coleman

Publications and source records attributed to D C Coleman.

At least 37 records · Page 2Linked to original sources
PubMed1999

Identification of Candida dubliniensis based on temperature and utilization of xylose and alpha-methyl-D-glucoside as determined with the API 20C AUX and vitek YBC systems.

To have a better understanding of the role of Candida dubliniensis in clinical infections, it is essential that microbiology laboratories can identify this species rapidly and accurately in clinical specimens. C. dubliniensis has been reported to lack the ability to utilize xylose (XYL) and alpha-methyl-D-glucoside (MDG) and to grow poorly or not at all at 45 degrees C, whereas Candida albicans isolates utilize XYL and MDG and usually grow well at 45 degrees C. We tested 66 isolates of C. dubliniensis and 100 isolates of C. albicans with both the API 20C AUX and Vitek YBC systems to evaluate the ability of the XYL and MDG tests contained within each of these systems to distinguish between the two species. The ability to grow at 45 degrees C was also examined. None of the C. dubliniensis isolates grew at 45 degrees C, and 23 of 100 C. albicans isolates (23%) exhibited poor or no growth at 45 degrees C. The XYL and MDG tests contained within the API 20C AUX system were both negative for all 66 C. dubliniensis isolates and were positive for 98 (XYL) and 56 (MDG) of the 100 C. albicans isolates. With the Vitek system, 64 of 66 C. dubliniensis isolates (97.0%) were XYL negative and 63 (95.0%) were MDG negative. Conversely, 96 of 100 C. albicans isolates (96.0%) were XYL positive and 100 (100.0%) were MDG positive with the Vitek system. Clinical microbiology laboratories could use lack of growth at 45 degrees C and a negative XYL test with either the API 20C AUX or Vitek yeast identification system to provide a presumptive identification of C. dubliniensis. A negative MDG test result with either system would also be helpful but may misclassify C. albicans as C. dubliniensis, especially when the API 20C AUX system is used.

Candida↗
PubMed1999

In vitro susceptibilities of Candida dubliniensis isolates tested against the new triazole and echinocandin antifungal agents.

Candida dubliniensis is a newly recognized fungal pathogen causing mucosal disease in AIDS patients. Although preliminary studies indicate that most strains of C. dubliniensis are susceptible to established antifungal agents, fluconazole-resistant strains have been detected. Furthermore, fluconazole-resistant strains are easily derived in vitro, and these strains exhibit increased expression of multidrug resistance transporters, especially MDR1. Because of the potential for the development of resistant strains of C. dubliniensis, it is prudent to explore the in vitro activities of several of the newer triazole and echinocandin antifungals against isolates of C. dubliniensis. In this study we tested 71 isolates of C. dubliniensis against the triazoles BMS-207147, Sch 56592, and voriconazole and a representative of the echinocandin class of antifungal agents, MK-0991. We compared the activities of these agents with those of the established antifungal agents fluconazole, itraconazole, amphotericin B, and 5-fluorocytosine (5FC) by using National Committee for Clinical Laboratory Standards microdilution reference methods. Our findings indicate that the vast majority of clinical isolates of C. dubliniensis are highly susceptible to both new and established antifungal agents. Strains with decreased susceptibilities to fluconazole remained susceptible to the investigational agents as well as to amphotericin B and 5FC. The increased potencies of the new triazole and echinocandin antifungal agents may provide effective therapeutic options for the treatment of infections due to C. dubliniensis.

AIDS-Related Opportunistic Infections↗
PubMed1999

Rapid PCR test for discriminating between Candida albicans and Candida dubliniensis isolates using primers derived from the pH-regulated PHR1 and PHR2 genes of C. albicans.

The development of a satisfactory means to reliably distinguish between the two closely related species Candida albicans and Candida dubliniensis in the clinical mycology laboratory has proved difficult because these two species are phenotypically so similar. In this study, we have detected homologues of the pH-regulated C. albicans PHR1 and PHR2 genes in C. dubliniensis. Restriction fragment length polymorphism analysis suggests that there are significant sequence differences between the genes of the two species. In order to exploit this apparent difference, oligonucleotide primers based on the coding sequence of the C. albicans PHR1 structural gene were designed and used in PCR experiments. Use of these primers with C. albicans template DNA from 17 strains yielded a predicted 1.6-kb product, while C. dubliniensis template DNA from 19 strains yielded no product. We therefore propose that PCR using these primers is a rapid and reliable means of distinguishing the two germ tube- and chlamydospore-producing species C. albicans and C. dubliniensis.

Apoenzymes↗
PubMed1998

Prokaryotes: the unseen majority.

The number of prokaryotes and the total amount of their cellular carbon on earth are estimated to be 4-6 x 10(30) cells and 350-550 Pg of C (1 Pg = 10(15) g), respectively. Thus, the total amount of prokaryotic carbon is 60-100% of the estimated total carbon in plants, and inclusion of prokaryotic carbon in global models will almost double estimates of the amount of carbon stored in living organisms. In addition, the earth's prokaryotes contain 85-130 Pg of N and 9-14 Pg of P, or about 10-fold more of these nutrients than do plants, and represent the largest pool of these nutrients in living organisms. Most of the earth's prokaryotes occur in the open ocean, in soil, and in oceanic and terrestrial subsurfaces, where the numbers of cells are 1.2 x 10(29), 2.6 x 10(29), 3.5 x 10(30), and 0. 25-2.5 x 10(30), respectively. The numbers of heterotrophic prokaryotes in the upper 200 m of the open ocean, the ocean below 200 m, and soil are consistent with average turnover times of 6-25 days, 0.8 yr, and 2.5 yr, respectively. Although subject to a great deal of uncertainty, the estimate for the average turnover time of prokaryotes in the subsurface is on the order of 1-2 x 10(3) yr. The cellular production rate for all prokaryotes on earth is estimated at 1.7 x 10(30) cells/yr and is highest in the open ocean. The large population size and rapid growth of prokaryotes provides an enormous capacity for genetic diversity.

Prokaryotic Cells↗
PubMed1998

Identification and expression of multidrug transporters responsible for fluconazole resistance in Candida dubliniensis.

Candida dubliniensis is a recently described Candida species associated with oral candidosis in human immunodeficiency virus (HIV)-infected and AIDS patients, from whom fluconazole-resistant clinical isolates have been previously recovered. Furthermore, derivatives exhibiting a stable fluconazole-resistant phenotype have been readily generated in vitro from fluconazole-susceptible isolates following exposure to the drug. In this study, fluconazole-resistant isolates accumulated up to 80% less [3H] fluconazole than susceptible isolates and also exhibited reduced susceptibility to the metabolic inhibitors 4-nitroquinoline-N-oxide and methotrexate. These findings suggested that C. dubliniensis may encode multidrug transporters similar to those encoded by the C. albicans MDR1, CDR1, and CDR2 genes (CaMDR1, CaCDR1, and CaCDR2, respectively). A C. dubliniensis homolog of CaMDR1, termed CdMDR1, was cloned; its nucleotide sequence was found to be 92% identical to the corresponding CaMDR1 sequence, while the predicted CdMDR1 protein was found to be 96% identical to the corresponding CaMDR1 protein. By PCR, C. dubliniensis was also found to encode homologs of CDR1 and CDR2, termed CdCDR1 and CdCDR2, respectively. Expression of CdMDR1 in a fluconazole-susceptible delta pdr5 null mutant of Saccharomyces cerevisiae conferred a fluconazole-resistant phenotype and resulted in a 75% decrease in accumulation of [3H]fluconazole. Northern analysis of fluconazole-susceptible and -resistant isolates of C. dubliniensis revealed that fluconazole resistance was associated with increased expression of CdMDR1 mRNA. In contrast, most studies showed that overexpression of CaCDR1 was associated with fluconazole resistance in C. albicans. Increased levels of the CdMdr1p protein were also detected in fluconazole-resistant isolates. Similar results were obtained with fluconazole-resistant derivatives of C. dubliniensis generated in vitro, some of which also exhibited increased levels of CdCDR1 mRNA and CdCdr1p protein. These results demonstrate that C. dubliniensis encodes multidrug transporters which mediate fluconazole resistance in clinical isolates and which can be rapidly mobilized, at least in vitro, on exposure to fluconazole.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

The Haemophilus influenzae HtrA protein is a protective antigen.

The htrA gene from two strains of nontypeable Haemophilus influenzae has been cloned and sequenced, and the encoded approximately 46-kDa HtrA proteins were found to be highly conserved. H. influenzae HtrA has approximately 55% identity with the Escherichia coli and Salmonella typhimurium HtrA stress response proteins, and expression of the H. influenzae htrA gene was inducible by high temperature. Recombinant HtrA (rHtrA) was expressed from E. coli, and the purified protein was found to have serine protease activity. rHtrA was found to be very immunogenic and partially protective in both the passive infant rat model of bacteremia and the active chinchilla model of otitis media. Immunoblot analysis indicated that HtrA is antigenically conserved in encapsulated and nontypeable H. influenzae species. Site-directed mutagenesis was performed on the htrA gene to ablate the endogenous serine protease activity of wild-type HtrA, and it was found that eight of nine recombinant mutant proteins had no measurable residual proteolytic activity. Two mutant proteins were tested in the animal protection models, and one, H91A, was found to be partially protective in both models. H91A HtrA may be a good candidate antigen for a vaccine against invasive H. influenzae type b disease and otitis media and is currently in phase I clinical trials.

Amino Acid Sequence↗
PubMed1998

Rapid identification of Candida dubliniensis by indirect immunofluorescence based on differential localization of antigens on C. dubliniensis blastospores and Candida albicans germ tubes.

There is a clear need for the development of a rapid and reliable test for the identification of Candida dubliniensis and for the discrimination of this species from Candida albicans. In the present study we have investigated the potential use of C. dubliniensis-specific antigens as a basis for its identification. We produced an anti-C. dubliniensis serum which, after adsorption with C. albicans blastospores, was found to differentially label C. dubliniensis isolates in an indirect immunofluorescence test. In this test, the antiserum reacted with blastospores and germ tubes of C. dubliniensis and with blastospores of Candida krusei and Rhodotorula rubra but did not react with blastospores of several other Candida species including C. albicans. The antiserum also reacted with C. albicans germ tubes. The anti-C. dubliniensis adsorbed serum reacted with specific components of 25, 28, 37, 40, 52, and 62 kDa in the C. dubliniensis extract and with a variety of antigens from other yeast species. The antigens from non-C. dubliniensis yeasts showing reactivity with the anti-C. dubliniensis adsorbed serum are mostly expressed within the cell walls of these yeast species, and this reactivity does not interfere with the use of the anti-C. dubliniensis adsorbed serum in an indirect immunofluorescence test for the rapid identification of C. dubliniensis.

AIDS-Related Opportunistic Infections↗
PubMed1998

Importance of Candida species other than Candida albicans as opportunistic pathogens.

Candida species other than C. albicans have become a significant cause of infection in humans. Several of the more commonly isolated of these species are less susceptible to commonly used azole antifungal drugs, a factor that poses significant difficulties for effective treatment. The modern mycology laboratory has an important role to play in several aspects relating to these organisms, including therapy, detection, identification and epidemiological analysis. The application of molecular techniques and phylogenetic analysis has led to the identification of a new species of Candida associated with mucosal candidiasis in HIV-infected individuals named Candida dubliniensis, the clinical significance of which is currently under investigation. Molecular techniques are also being applied to the analysis of determinants involved in pathogenicity of species such as Candida glabratta. These approaches should lead to a better understanding of these organisms and there ability to cause disease and should also provide more effective treatment.

AIDS-Related Opportunistic Infections↗
PubMed1997

Antifungal drug susceptibilities of oral Candida dubliniensis isolates from human immunodeficiency virus (HIV)-infected and non-HIV-infected subjects and generation of stable fluconazole-resistant derivatives in vitro.

Candida dubliniensis is a recently described species of Candida associated with oral candidiasis in human immunodeficiency virus (HIV)-infected individuals. Nineteen oral isolates of C. dubliniensis recovered from 10 HIV-positive and 4 HIV-negative individuals and one vaginal isolate from an additional HIV-negative subject were assessed for fluconazole susceptibility by broth microdilution (BMD), hyphal elongation assessment, and Etest. The susceptibilities of these 20 isolates to itraconazole and amphotericin B and of 10 isolates to ketoconazole were also determined by BMD only. Sixteen of the C. dubliniensis isolates were susceptible to fluconazole (MIC range, 0.125 to 1.0 microgram ml-1), and four (recovered from two AIDS patients) were fluconazole resistant (MIC range, 8 to 32 micrograms ml-1). Fluconazole susceptibility data obtained by hyphal elongation assessment correlated well with results obtained by BMD, but the corresponding Etest MIC results were one to four times higher. All of the isolates tested were found to be sensitive to itraconazole, ketoconazole, and amphotericin B. Sequential exposure of two fluconazole-sensitive (MIC, 0.5 microgram ml-1) C. dubliniensis isolates to increasing concentrations of fluconazole in agar medium resulted in the recovery of derivatives which expressed a stable fluconazole-resistant phenotype (BMD-determined MIC range, 16 to 64 micrograms ml-1), even after a minimum of 10 consecutive subcultures on drug-free medium and following prolonged storage at -70 degrees C. The clonal relationship between the parental isolates and their respective fluconazole-resistant derivatives was confirmed by genomic DNA fingerprinting and karyotype analysis. The results of this study demonstrate that C. dubliniensis is inherently susceptible to commonly used antifungal drugs, that fluconazole resistance does occur in clinical isolates, and that stable fluconazole resistance can be readily induced in vitro following exposure to the drug.

Antifungal Agents↗
PubMed1997

Outer membrane protein D15 is conserved among Haemophilus influenzae species and may represent a universal protective antigen against invasive disease.

We have cloned and sequenced the d15 gene from two strains of Haemophilus influenzae type b (Hib) and two strains of nontypeable H. influenzae (NTHI). The nucleotide and deduced protein sequences of d15 are highly conserved, with only a small variable region identified near the carboxyl terminus of the protein. Analysis of upstream sequences revealed that the H. influenzae d15 gene may be part of a large potential operon of closely spaced open reading frames, including one with significant homology to the Escherichia coli cds gene encoding CDP-diglyceride synthetase. Southern blot analysis demonstrated that the d15 gene is also present in H. influenzae types a, c, d, e, and f and in Haemophilus parainfluenzae. A recombinant D15 (rD15) protein was expressed in good quantity in E. coli from the inducible T7 promoter, and monospecific anti-rD15 antibodies were raised. Immunoblot analysis of H. influenzae serotypes a, b, c, d, e, and f, NTHI, and H. parainfluenzae lysates revealed that they all expressed a cross-reactive D15-like protein. Purified rD15 was found to be highly immunogenic in mice, guinea pigs, and rabbits, and passive transfer of anti-rD15 antibodies protected infant rats from challenge with H. influenzae type b or type a in infant rat models of bacteremia. Thus, D15 is a highly conserved antigen that is protective in animal models and it may be a useful component of a universal subunit vaccine against Haemophilus infection and disease.

Amino Acid Sequence↗
PubMed1996

Sequences of the genes encoding the A, B and C subunits of the Haemophilus influenzae dimethylsulfoxide reductase complex.

The genes (dms) encoding the dimethylsulfoxide reductase protein complex have been cloned and sequenced from Haemophilus influenzae (Hi) type b (Hib) strain Eagan. The Hib dms genes are arranged as an operon whose genomic organization is similar to that of the Escherichia coli (Ec) dmsABC operon. The deduced Hib DmsA, and DmsB and DmsC amino-acid sequences are highly homologous to their Ec counterparts and nearly identical to the recently published sequences of the Hi type-d strain Rd Dms proteins. Hi dimethylsulfoxide reductase appears to be a new member of the superfamily of oxidoreductase enzymes.

Base Sequence↗
PubMed1996

Cloning and expression of the Haemophilus influenzae transferrin receptor genes.

The genomic transferrin receptor genes (tbpA and tbpB) from two strains of Haemophilus influenzae type b (Hib) and two strains of non-typable H. influenzae (NTHi) have been cloned and sequenced. The deduced protein sequences of the H. influenzae tbpA genes were 95-100% conserved and those of the tbpB genes were 66-100% conserved. The tbpB gene from one strain of NTHi was found to encode a truncated Tbp2 protein. The tbpB genes from four additional NTHi strains were amplified by the polymerase chain reaction (PCR) utilizing primers derived from the conserved N-terminal sequences of Tbp1 and Tbp2 and were found to encode full-length proteins. Although several bacterial species express transferrin receptors, when the Tbp1 and Tbp2 sequences from different organisms were compared, there was only limited homology. Recombinant Tbp1 and Tbp2 proteins were expressed from Escherichia coli and antisera were raised to the purified proteins. There was significant antigenic conservation of both Tbp1 and Tbp2 amongst H. influenzae strains, as determined by Western blot analysis. In a passive model of bacteraemia, infant rats were protected from challenge with Hib after transfer of anti-rTbp2 antiserum, but not after anti-rTbp1 antiserum.

Amino Acid Sequence↗
PubMed1996

Molecular genetic approaches to identification, epidemiology and taxonomy of non-albicans Candida species.

The reported incidence of fungal infections associated with non-albicans species from the Candida genus is increasing. Most of these infections occur in immunocompromised patients, particularly those infected with HIV. The role of molecular genetic techniques alongside the existing techniques for the identification and typing of these organisms is discussed. Species-specific genomic DNA fragments cloned from C. tropicalis and C. krusei have been developed for identification and strain typing. Analysis of tRNA profiles has been shown to be effective for the identification of C. glabrata, C. guilliermondii, C. parapsilosis and C. tropicalis. A PCR method employing primers complimentary to large ribosomal subunit genes and the lanosterol-alpha-demethylase gene has been applied for several species, including C. glabrata, C. krusei and C. tropicalis. Strain typing by comparison of genomic DNA fingerprints has been demonstrated for C. tropicalis and C. krusei following hybridisation analysis with species-specific probes. Synthetic oligonucleotide probes--which do not have to be species-specific and which can detect minor polymorphisms--have also been used for strain typing of isolates of several non-albicans species. Random amplification of polymorphic DNA (RAPD) has also been used for analysis of C. glabrata, C. lusitaniae and C. tropicalis isolates. The potential for the application of these and other techniques to Candida spp. taxonomy--and the example of a recently discovered novel species, C. dubliniensis--is discussed.

Candida↗
PubMed1996

Genomic DNA fingerprinting of clinical isolates of Helicobacter pylori using short oligonucleotide probes containing repetitive sequences.

The ability of oligonucleotide probes containing short repetitive sequence motifs to differentiate between isolates of Helicobacter pylori was investigated. Genomic DNA preparations from H. pylori were digested with the restriction enzyme HindIII, electrophoresed in agarose gels and transferred to nylon filters. Five separate oligonucleotide probes were tested for hybridization sequentially to fingerprint the digested DNA from a panel of 29 clinical isolates and one type strain of H. pylori, and their relative discriminatory abilities were assessed. Four probes, (GACA)4, (GT)8, (GTG)5 and (GGAT)4, were each shown to yield highly informative hybridization band profiles allowing differentiation of H. pylori isolates. The DNA fingerprints of individual isolates obtained with each probe were distinct and reproducible. Direct comparison with ribotyping revealed that oligonucleotide fingerprinting had far superior discriminatory power. Computer-assisted similarity analysis of (GGAT)4-generated hybridization profiles of pairwise combinations of H. pylori isolates revealed that there was no correlation between ribotype and oligonucleotide fingerprint patterns. The results of this study demonstrate that oligonucleotide probes containing microsatellite sequences provide a new and powerful tool for isolate discrimination of H. pylori.

DNA Fingerprinting↗
PubMed1996

A rapid microwave-in situ hybridization method for the definitive diagnosis of oral hairy leukoplakia: comparison with immunohistochemistry.

As a diagnostic technique, in situ hybridization requires a long processing time, a degree of expertise and may be difficult to handle routinely in some laboratories. To simplify the in situ hybridization method, we have modified a microwave in situ hybridization technique and applied it to oral hairy leukoplakia (OHL) biopsies obtained from 10 HIV-seropositive patients (definitively diagnosed by a conventional in situ hybridization technique) with appropriate controls. It was necessary to design a novel chamber to avoid drying of sections during the hybridization step. This modified microwave in situ hybridization technique was equispecific and equisensitive to the conventional technique and it shortens the hybridization time from overnight incubation to 14 minutes. To determine the sensitivity of our microwave in situ hybridization method we applied it to previously documented tongue tissue obtained from an AIDS autopsy without clinical evidence of OHL, but found to contain Epstein-Barr virus (EBV) by conventional in situ hybridization. This tissue specimen acted as a low EBV copy number, positive control. The sensitivity of immunohistochemistry using three different commercial detection kits was compared to that of in situ hybridization on the same tissues, following optimisation steps. This included the use of 2 cycles of primary and biotinylated secondary antibodies (antibody double cycling). Clearly positive signals for EBV were detected in all OHL biopsies with the Vectastain Elite ABC and the Histostain-SP kits. The sensitivity of the three commercial detection kits was evaluated at immunohistochemistry level by their application to the low-EBV copy number positive control specimen. Signals for EBV antigen in the low copy number positive control specimen were obtained only with the Vectastain Elite ABC kit. This indicates that, in this application, use of the Vectastain Elite ABC kit gives comparable sensitivity for immunohistochemistry to that found by in situ hybridiation.

AIDS-Related Opportunistic Infections↗
PubMed1995

An epidemiological study of Candida species infection in cancer patients using genetic fingerprinting and morphotyping.

During a six-week period a cluster of four cases of Candida fungaemia occurred in a mixed haematology/oncology unit of a large Dublin teaching hospital. A study was conducted to determine whether the cluster of cases was caused by a particular strain. Nine patients were studied; five who were colonized with Candida spp. and four who developed Candida fungaemia. Twenty-two clinical isolates of Candida spp. were collected and identified. Three of the patients with fungaemia yielded Candida albicans from blood cultures and C. tropicalis was isolated from the fourth patient. C. albicans isolates were serotyped, morphotyped and analysed by DNA fingerprinting of total cellular DNA using the cloned C. albicans-specific, mid-repeat sequence element 27A as a molecular probe. All C. albicans isolates were of serotype A. Eight distinguishable types were identified by both morphotyping and DNA typing from 19 C. albicans isolates recovered from seven individual patients, although there were several discrepancies. Of three patients from whom two or more isolates of C. albicans were recovered on separate occasions, two yielded recurrent isolates with different morphotype codes. However, in both cases, the recurrent isolates from individual patients yielded indistinguishable, or closely related, DNA fingerprint profiles. Both morphotyping and DNA fingerprint analysis readily distinguished the three blood culture isolates of C. albicans. We conclude that the Candida spp. infections in the unit were not due to cross-infection and were probably related to the patients' indigenous flora.

Candida↗