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R D Adam

Publications and source records attributed to R D Adam.

At least 19 recordsLinked to original sources
PubMed1998

Structural basis of karyotype heterogeneity in Giardia lamblia.

The molecular karyotype of a series of Giardia lamblia isolates representing the two major genotypes (Groups 1 and 3) was generated by assigning 13 genetic markers to chromosomes separated by pulsed-field gel electrophoresis. The co-localization identified five linked groups of genetic markers in Group 1 isolates. For each of the five linkage groups, there were up to four size variants that hybridized with the same genetic markers. Long range physical maps of the regions flanking the low copy number genetic markers indicated that these size variants were homologous chromosomes. The linkage groups were similar in Group 1 and 3 isolates. The core of each chromosome was stable while the subtelomeres were variable. The location of the ribosomal DNA repeats was variable among the different isolates and they were found in the subtelomeric regions of any of the five linkage groups. The data suggest a functional ploidy of at least four. Hypervariable subtelomeric regions of homologous chromosomes provide the structural basis of the chromosome size heterogeneity that is characteristic of G. lamblia.

Animals↗
PubMed1998

Molecular comparison of Giardia lamblia isolates.

Giardia lamblia (also Giardia duodenalis, Giardia intestinalis) isolates have been variably divided into two or three genotypes by different investigators. We have compared the triose phosphate isomerase sequences of the three genotypes (Groups 1, 2, and 3) described by Nash and shown that Groups 1 and 2 are similar, while Group 3 is markedly different from Groups 1 and 2, indicating that Group 1/2 and Group 3 correspond to the two major genotypes identified by other investigators. We have also analysed three Chinese isolates and showed that two fit into Group 3, while the third contained a mixture of Groups 1 and 3 isolates. These results confirm the relatedness of G. lamblia isolates from throughout the world, and established the feasibility of using DNA amplification and sequence analysis for detecting mixed isolates.

Amino Acid Sequence↗
PubMed1996

Rhinocerebral mucormycosis. Therapy with amphotericin B lipid complex.

Rhinocerebral mucormycosis with intracranial involvement has a high mortality. The standard therapy consists of aggressive surgical débridement accompanied by high doses of amphotericin B deoxycholate. Even with this therapy, the mortality rate has been 48% in the series reported since 1980. We treated a 60-year-old diabetic woman with rhinocerebral mucormycosis involving the cavernous sinus whose infection responded to medical therapy with amphotericin B lipid complex. To our knowledge, this is the only well-documented medical cure of a patient with rhinocerebral mucormycosis and intracranial involvement.

Amphotericin B↗
PubMed1996

The molecular epidemiology of Giardia lamblia: a sequence-based approach.

Animals are commonly considered to be potential sources for Giardia lamblia infections in humans, but the extent of zoonotic transmission of G. lamblia remains controversial because of inadequate understanding of its epidemiology. A better understanding of the epidemiology of G. lamblia may be facilitated by a more effective means for classifying G. lamblia isolates. To develop a sequence-based classification system, the gene encoding the metabolic enzyme triose phosphate isomerase (tim) was sequenced from a number of G. lamblia isolates of various host origins. Restriction enzymes were identified that can distinguish among isolates without the need for sequencing, simplifying the application of this approach to the epidemiologic investigation of giardiasis. Isolates from a previously reported epidemic of giardiasis were accurately classified by this technique, further verifying its utility for epidemiologic investigation.

Animals↗
PubMed1995

A group of Giardia lamblia variant-specific surface protein (VSP) genes with nearly identical 5' regions.

The surfaces of Giardia lamblia trophozoites contain one of a set of variant-specific surface proteins. The genes encoding these proteins are highly conserved at the 3' terminus, but frequently demonstrate little similarity in the remainder of the coding region. This report describes a family of vsp genes highly similar to a repeat-containing vsp gene (vspC5) at the 5' coding and flanking regions, but which diverge abruptly from vspC5 in the first repeat and do not themselves contain full copies of the repeat. This observation suggests the possibility that recombination among different vsp genes may have played a role in development of the vsp gene repertoire.

Amino Acid Sequence↗
PubMed1995

Technical note: an evaluation of a Diamentor based system for estimation of spot film dose-area product values.

In the audit of barium studies it is not common to assess the contribution of spot films to the total dose. This study investigates the accuracy with which the number of spot films and associated dose-area product (DAP) may be estimated. The study was undertaken for barium enemas, the swallow part of barium swallow studies, and the abdominal part of barium meal studies on X-ray sets with film-screen radiography, digital fluorography and 100 mm camera fluorography. DAP readings from a Diamentor were input to a computer at a rate of three per second and the difference in successive DAP values calculated. These data were used to assess the number and total DAP from spot films. For Diamentor based systems which sample the DAP values at three times per second the threshold algorithm works well for film-screen radiography of barium meals and enemas. However, the estimated number of spot films is generally in error. For the Diamentor M2 it is unlikely that the sample rate can be increased to a high enough value to provide sufficient accuracy for all barium studies obtained using all spot film modalities, although use of the modified threshold algorithm has the potential to provide some increase in accuracy.

Algorithms↗
PubMed1994

Allele-specific expression of a variant-specific surface protein (VSP) of Giardia lamblia.

The surfaces of Giardia lamblia trophozoites demonstrate variable expression of a set of cysteine-rich surface proteins, called variant-specific surface proteins (VSP). The cloned Giardia line, WBA6, expresses a 170 kD VSP (VSPA6 or CRP170) which contains approximately 18 to 23 copies of a 65 amino acid repeat. We have cloned the expressed vspA6 gene containing 23 repeats from a genomic library as well as copies of the vspA6 gene with only 8 or 9 repeats from both WBA6 and from WB1269, a cloned line derived from WBA6 which has lost the expressed copy of the gene. The recombinant clones containing the genes with only 8 or 9 repeats have 8 nucleotide substitutions in the coding region. All the recombinant clones map to the same chromosomal location, yet RNA sequencing and comparison with the transcript size indicate that only the clone with 23 repeats contains a gene producing a stable transcript. The most likely interpretation of these data is that G.lamblia trophozoites contain multiple alleles of the vspA6 gene of which only one is expressed.

Alleles↗
PubMed1994

AIDS debate continues.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Giardia lamblia trophozoites contain multiple alleles of a variant-specific surface protein gene with 105-base pair tandem repeats.

Giardia lamblia trophozoites undergo antigenic variation of a variant-specific surface protein (VSP). All VSPs that have been reported have had high cysteine contents, including numerous copies of a CXXC motif. The first vsp gene described (vspA6; from the cloned line, WBA6), contained 21 copies of a 195 base pair tandem repeat, but other reported VSPs have not contained repeats. In this report, we describe the vsp gene from WBC5, a cloned line derived from WBA6. The vspC5 gene contains short 5' and 3' regions flanking 26 copies of a 105-bp tandem repeat, which comprises 93% of the coding region. In addition to the copy containing 26 repeats, the genome contains other copies of the vspC5 with fewer copies of the repeat. The sequences flanking the repeats are identical, and all copies map to the same location on chromosomal Band 5, suggesting that multiple alleles of the vspC5 gene are present.

Alleles↗
PubMed1994

Mucormycosis: emerging prominence of cutaneous infections.

Twenty-five patients with mucormycosis were seen at two university-affiliated hospitals from 1979 to 1993. These cases included 10 cutaneous, 9 rhinocerebral, and 3 disseminated infections, as well as one case each of pulmonary, renal, and peritoneal dialysis catheter-related infection. Eleven of the patients were diabetic and seven had ketoacidosis, including four who became acidotic after admission to the hospital. The mortality rates associated with rhinocerebral, disseminated, and pulmonary infections were 78%-100%, while those associated with cutaneous and miscellaneous forms were zero. In view of the prominence of cutaneous infections, the 10 cases of cutaneous mucormycosis (in addition to a case from a community hospital) are reported in detail. Systemic diseases were present in four of the 11 patients. Local factors leading to infection were identified in nine of the cases and included motor vehicle accident-related and other trauma, surgery, a spider bite, and an intravenous infusion catheter. The cases of cutaneous mucormycosis reported in the literature have been analyzed for identification of predisposing factors, treatment, and outcome. Aggressive surgical debridement is the most important component of therapy, and administration of amphotericin B is a useful adjunct. Skin grafting is useful as a method of repairing defects left by extensive debridement.

Adolescent↗
PubMed1994

Size heterogeneity among antigenically related Giardia lamblia variant-specific surface proteins is due to differences in tandem repeat copy number.

Giardia lamblia undergoes antigenic variation by modulating the expression of the different genes that comprise the trophozoite's variant-specific surface protein (VSP) repertoire. We studied an epitope that is conserved among VSPs expressed by cloned trophozoite lines derived from the independent G. lamblia isolates WB, G3M, Be-2, and CAT. The epitope recognized by monoclonal antibody 6E7 lies entirely within the region of tandemly repeated 65-amino-acid units that is characteristic of these size-variant VSPs. Northern (RNA) hybridization, cDNA cloning, and DNA sequence analysis indicate that size heterogeneity among these VSPs is due to differences in the number of repetitive units.

Amino Acid Sequence↗
PubMed1992

Chromosome-size variation in Giardia lamblia: the role of rDNA repeats.

Giardia lamblia trophozoites contain at least five sets of chromosomes that have been categorized by chromosome-specific probes. Pulsed field separations of G. lamblia chromosomes also demonstrated minor bands in some isolates which stained less intensely with ethidium than the major chromosomal bands. Two of the minor bands of the E11 clone of the ISR isolate, MBa and MBb, were similar to each other and to chromosomal band I by hybridization to total chromosomal DNA and by hybridization of specific probes. In order to determine the extent of this similarity, I have developed a panel of probes for many of the Pacl restriction fragments and have shown that most of the Pacl and Notl fragments found in MBa are also present in MBb. The differences are found in both telomeric regions. At one end, MBb contains a 300 kb region not found in MBa. At the other end of MBb is a 160 kb region containing the rDNA repeats which is bounded on one end by the telomeric repeat and on the other by sites for multiple enzymes that do not digest the rDNA repeats. The corresponding region of MBa is 23 kb in size. The size difference is consistent with the eightfold greater number of rDNA repeats in MBb than MBa and suggests that 30% of the size difference is accounted for by different numbers of copies of the rDNA repeat. MBa of another ISR clone (ISR G5) is 150 kb larger in size than MBa of ISR E11. The data suggest that MBa and MBb are homologous chromosomes of different sizes and that a portion of the size difference is accounted for by different copy numbers of the rDNA repeat.

Animals↗
PubMed1992

The cysteine-rich protein gene family of Giardia lamblia: loss of the CRP170 gene in an antigenic variant.

Giardia lamblia trophozoites demonstrate variable expression of a repertoire of cysteine-rich surface antigens in vitro and in vivo. The size of the repertoire has been estimated at 20 to 184, and specific variants can be detected after approximately 12 generations of in vitro growth for the WB isolate. In earlier studies, we cloned a portion of the gene for a 170-kDa surface antigen (CRP170) and demonstrated by DNA sequencing that it was cysteine rich (12%) and contained 2.6 copies of a tandemly repeated 195-bp pair sequence. The clone hybridized to multiple bands on a Southern blot of G. lamblia DNA in a pattern that was variable among the cloned lines but did not correlate with expression of CRP170. We have now cloned a nearly full length cDNA as well as genomic clones for CRP170 from the WBA6 cloned isolate. In addition, we have isolated a cDNA clone from the WB1269 line (expressing CRP72), an antigenic variant which was derived from WBA6. Sequence analysis of the CRP170 and CRP72 genes revealed marked C-terminal amino acid homology, suggesting a conserved functional role such as membrane anchoring. The CRP170 repeat oligonucleotide hybridized to a stairstep of bands approximately 6 kb in size on HindIII-digested WBA6 DNA representing the expressed copy(ies) of CRP170. In contrast, there was no hybridization to a fragment of similar size in WB1269, suggesting that WB1269 trophozoites have lost the expressed copy of the CRP170 gene.

Amino Acid Sequence↗
PubMed1992

Passive tube and suction drainage after elective cholecystectomy--a comparison using ultrasonography.

Daily ultrasonography of the gallbladder bed was performed in patients with suction or passive tube drains after elective cholecystectomy. A total of 19 patients was randomized to suction drainage and 17 to passive tube drainage. A policy of early drain removal was followed. No significant difference was found between the volume drained and the size of collection detected in either group. Significant bile leaks were detected and were adequately drained by suction and passive tube drains. There were no complications from drains. In view of these findings, we advocate short-term drainage of the gallbladder bed after both open and laparoscopic cholecystectomy using the drain of the surgeon's choice.

Abdomen↗
PubMed1991

Telomeric location of Giardia rDNA genes.

Giardia lamblia telomeres have been isolated from a library enriched for repaired chromosome ends by (i) screening with a Plasmodium falciparum telomere and (ii) differential hybridization with Bal 31-digested and total G. lamblia DNA. Analysis of three clones isolated by this strategy has identified multiple tandem repeats of the 5-mer TAGGG. An oligonucleotide containing these repeats recognizes Bal 31-sensitive bands in Southern hybridizations and detects all G. lamblia chromosomes in pulsed-field gel electrophoresis separations. An abrupt transition from the G. lamblia rDNA sequence to telomeric repeats has been found in all three clones. In two of the clones the transition occurs at the same site, near the beginning of the large subunit rDNA sequence. In the third clone the transition occurs at a site in the intergenic spacer sequence between the rDNA genes. Hybridization of an rDNA probe to a pulsed-field separation of G. lamblia chromosomes indicates that rDNA genes are present on several chromosomes but vary in location from isolate to isolate. These results suggest that rRNA genes are clustered at telomeric locations in G. lamblia and that these clusters are mobile.

Animals↗
PubMed1991

The biology of Giardia spp.

Gardia spp. are flagellated protozoans that parasitize the small intestines of mammals, birds, reptiles, and amphibians. The infectious cysts begin excysting in the acidic environment of the stomach and become trophozoites (the vegetative form). The trophozoites attach to the intestinal mucosa through the suction generated by a ventral disk and cause diarrhea and malabsorption by mechanisms that are not well understood. Giardia spp. have a number of unique features, including a predominantly anaerobic metabolism, complete dependence on salvage of exogenous nucleotides, a limited ability to synthesize and degrade carbohydrates and lipids, and two nuclei that are equal by all criteria that have been tested. The small size and unique sequence of G. lamblia rRNA molecules have led to the proposal that Giardia is the most primitive eukaryotic organism. Three Giardia spp. have been identified by light lamblia, G. muris, and G. agilis, but electron microscopy has allowed further species to be described within the G. lamblia group, some of which have been substantiated by differences in the rDNA. Animal models and human infections have led to the conclusion that intestinal infection is controlled primarily through the humoral immune system (T-cell dependent in the mouse model). A major immunogenic cysteine-rich surface antigen is able to vary in vitro and in vivo in the course of an infection and may provide a means of evading the host immune response or perhaps a means of adapting to different intestinal environments.

Animals↗