Detection of histoplasma antigen by a quantitative enzyme immunoassay

The second-generation Histoplasma antigen immunoassay is semiquantitative, expressing results as a comparison to a negative control, which requires repeat testing of the prior specimen with the current specimen to accurately determine a change in antigen. Reporting results in this manner often is confusing to the ordering physician and laboratory. Development of a quantitative assay could improve accuracy, reduce interassay variability, and eliminate the need to test the prior sample with the current sample in the same assay. Calibrators with known concentrations of Histoplasma antigen were used to quantitate antigen in specimens from patients with histoplasmosis and from controls. Samples from cases of disseminated histoplasmosis or other mycoses and controls were tested to evaluate the performance characteristics of the quantitative assay. Paired specimens were evaluated to determine if quantitation eliminated the need to test the current and prior specimens in the same assay to assess a change in antigen. The sensitivity in samples from patients with AIDS and disseminated histoplasmosis was 100% in urine and 92.3% in serum. Cross-reactions occurred in 70% of other endemic mycoses, but not in aspergillosis. Specificity was 99% in controls with community-acquired pneumonia, medical conditions in which histoplasmosis was excluded, or healthy subjects. A change in antigen level categorized as an increase, no change, or decrease based on antigen units determined in the same assay agreed closely with the category of change in nanograms/milliliter determined from testing current and prior specimens in different assays. Sensitivity, specificity, and interassay precision are excellent in the new third-generation quantitative Histoplasma antigen immunoassay.

Production of extracellular proteolytic activity by Histoplasma capsulatum grown in Histoplasma-macrophage medium is limited to restriction fragment length polymorphism class 1 isolates

Extracellular proteolytic activity was studied for 28 strains of Histoplasma capsulatum var. capsulatum and 2 strains of H. capsulatum var. duboisii. Secreted protease activity assessed by skim milk agarose clearance was limited solely to H. capsulatum var. capsulatum restriction fragment length polymorphism (RFLP) class 1 strains. There was a difference in proteolytic activity levels among class 1 strains. Extracellular proteolytic activity was further determined during growth of those strains in liquid medium using azodye-impregnated protein substrates. In general, the highest activities were measured when azocollagen was used, whereas azocasein and azoalbumin were cleaved less efficiently. The activity was inhibited by phenylmethylsulfonyl fluoride, 4-(2-aminoethyl) benzenesulfonyl fluoride, antipain, and chymostatin, indicating, thereby, the presence of chymotrypsin-like serine proteases. Chromatographic analyses as well as variable substrate use at different culture times revealed production of at least 2 different enzyme pools of the same serine-like protease family. Our results demonstrate a distinctive ability of RFLP class 1 isolates to produce and secrete serine proteinase-type activity. This peculiarity may be relevant to the biology and pathogenesis of this particular clade of H. capsulatum isolates. Overall, the feature of extracellular proteolytic activity production enables a convenient and unequivocal identification of RFLP class 1 isolates and, thereby, can be used in H. capsulatum strain differentiation and typing.

Urine polymerase chain reaction is not as sensitive as urine antigen for the diagnosis of disseminated histoplasmosis

We developed a colorimetric microtiter plate polymerase chain reaction enzyme immunoassay (PCR-EIA) for the detection of Histoplasma capsulatum in urine. The specificity of the PCR assay was confirmed using H. capsulatum (positive control) and Blastomyces dermatitidis (negative control) isolates. The analytical sensitivity of the PCR assay was determined by testing urine samples spiked with freshly grown H. capsulatum organisms and was 2 yeasts per reaction in urine and 0.2 yeasts per reaction in urine sediment after centrifugation. Fifty-one urine specimens positive for H. capsulatum antigen and 25 urine specimens from healthy volunteers were tested blindly. Patient specimens also were cultured for H. capsulatum. The PCR assay was positive in 4 (7.8%) of 51 urine specimens containing antigen and negative in urine specimens from healthy volunteers. The positive PCR results occurred in 4 of 5 urine specimens that were positive by culture, and each exhibited high level of antigenuria (>20 U). Urine cultures were not positive in 24 urine specimens with an antigenuria of 1-19.9 U, but were positive in 5 of 27 urine specimens with antigenuria >20 U. Thus, positive PCR results in urine specimens correlate with positive culture results, but not with antigenuria. The low sensitivity of this PCR assay in urine limits its use in the diagnosis of disseminated histoplasmosis.

Evaluation and testing of computed radiography systems

The implementation of film replacement digital radiographic imaging systems throughout Europe is now gathering momentum. Such systems create the foundations for totally digital departments of radiology, since radiographic examinations constitute the most prevalent modality. Although this type of development will lead to improvements in the delivery and management of radiological service, such widespread implementation of new technology must be carefully monitored. The implementation of effective QA tests on installation, at periodic intervals and as part of a routine programme will aid this process. This paper presents the results of commissioning tests undertaken on a number of computed radiography imaging systems provided by different manufacturers. The aim of these tests was not only to provide baseline performance measurements against which subsequent measurements can be compared but also to explore any differences in performance, which might exist between different units. Results of measurements will be presented for (1) monitor and laser printer set-up; (2) imaging plates, including sensitivity, consistency and uniformity; (3) resolution and contrast detectability; and (4) signal and noise performance. Results from the latter are analysed in relationship with both system and quantum noise components.

Pathogenic differences between North American and Latin American strains of Histoplasma capsulatum var. capsulatum in experimentally infected mice

Clinical differences in histoplasmosis between North America and Brazil prompted investigation of experimental infection with representative strains. Mortality was higher with Latin American strains, and lung pathology showed large necrotizing granuloma with prominent neutrophilic infiltration. Chronic disease was unique to the North American strain.

Antifungal therapy for central nervous system histoplasmosis, using a newly developed intracranial model of infection

The outcome of central nervous system (CNS) histoplasmosis is often unfavorable. Although fluconazole plays an integral role in treatment of fungal meningitis, its role in the treatment of histoplasmosis is hampered by reduced activity and potential development of resistance. A murine model of CNS histoplasmosis was used to evaluate the hypothesis that a combination of amphotericin B and fluconazole therapy would be superior to amphotericin B monotherapy. Groups of B6C3F(1) mice were infected by injection of Histoplasma capsulatum into the subarachnoid space. The addition of fluconazole hindered the antifungal effect of amphotericin B, as determined by measurement of fungal burden, suggesting antagonism in the brain. Fluconazole was less effective as a single agent than was amphotericin B, despite the greater penetration of fluconazole into brain tissues. The hypothesis that amphotericin B-fluconazole combination therapy would be superior to amphotericin B monotherapy for treatment of CNS histoplasmosis was not supported by this study.

DNA fingerprinting of serial Candida albicans isolates obtained during itraconazole prophylaxis in patients with AIDS

During a randomized double-blind placebo-controlled study testing the efficacy of itraconazole for prophylaxis of systemic and mucosal fungal infections in patients with acquired immune deficiency syndrome, 298 patients were enrolled with 295 evaluable. Of those, 46 patients were considered prophylaxis failures because of recurrent oral or esophageal candidiasis. Oropharyngeal fungal cultures were taken at the time of suspected thrush or Candida esophagitis, but not at baseline. All of the Candida spp. isolates were cultured on CHROMagar Candida medium then identified using API 20 AUX strips. Antifungal susceptibility testing was performed following the National Committee for Clinical Laboratory Standards M-27A guidelines. Sequential isolates were genotyped using randomly amplified polymorphic DNA. Polymerase chain reaction fingerprints were generated using two repetitive sequence primers, (GGA)7 and (GACA)4. The study group consisted of 23 patients, nine from the itraconazole arm and 14 from the placebo arm, who were prophylaxis failures and had more than two C. albicans isolates. Five of 23 had isolates showing a > or =4-fold reduction in susceptibility; four of these patients were in the itraconazole prophylaxis arm and one was in the placebo arm. Three of the five had yeast isolations showing changes in banding patterns over time. Such changes may indicate genetic changes in the same strain that could be linked to acquired resistance to itraconazole, or acquisition of a new strain, or emergence of a previously minor component of the original population.

Typing of Histoplasma capsulatum isolates based on nucleotide sequence variation in the internal transcribed spacer regions of rRNA genes

The nucleotide sequences of internal transcribed spacer (ITS) regions of rRNA genes of 24 isolates of Histoplasma capsulatum were examined. The results indicate that the sequences of ITS regions in different isolates are not identical. Sequence variations were found at 20 positions in the 496 bp that were sequenced. Ten different sequence patterns, designated types A through H, were observed when the sequences from the 24 isolates were aligned. Twelve isolates from Indianapolis were classified into four different types. Two isolates from New York belonged to type G. Three isolates from different cities were type F. The remaining six isolates were of different types.

Comparison of radioimmunoassay and enzyme-linked immunoassay methods for detection of Histoplasma capsulatum var. capsulatum antigen

The purpose of this study was to compare the conventional radioimmunoassay (RIA) to an enzyme-linked immunoassay (EIA) for the measurement of Histoplasma antigen in banked urine specimens. A correlation between the two methods would allow the EIA to be used as a nonradioactive alternative to the established 125I RIA. The study used stored urine from patients diagnosed with histoplasmosis during an outbreak in Indianapolis which began in 1988. Control specimens from healthy adults, patients with other fungal infections, urinary tract infections, or nonfungal pneumonia were also tested. Both the RIA and EIA were run concurrently. The RIA system measured antigen levels of 0.4 to 27.0 RIA units, while the EIA measured antigen levels of 0.6 to 20.1 units. Both the EIA and RIA detected measurable antigen levels in urine from 50 of 56 patients (89%) with disseminated disease and 11 of 30 patients (37%) with self-limiting disease. One of 96 control specimens, from a patient with paracoccidioidomycosis, was positive with both systems. Antigen levels measured by EIA correlated well with those measured by the established RIA method (correlation coefficient, 0.974). The EIA is an acceptable alternative to the RIA for measuring Histoplasma antigen levels in urine specimens.