Computer instruction in learning concepts of streptococcal pharyngitis.

OBJECTIVE: To evaluate a computer-assisted instruction unit covering the basic concepts of streptococcal pharyngitis for effectiveness as a learning tool. DESIGN: Randomized control trial. SETTING: A medical school associated with a tertiary care hospital. PARTICIPANTS: Third-year medical students on a pediatric clerkship from December 1, 1992, to October 31, 1993. INTERVENTION: Students were randomized into a study or a control group and given a pretest on streptococcal pharyngitis. The study group then completed the computer-assisted instruction unit. No attempt was made to distinguish among the clinical experiences of the two groups during the next 4 weeks, after which a second test on streptococcal pharyngitis was given to both groups. MAIN OUTCOME MEASURES: Outcome was measured by scores (percentage correct) from tests given at day 1 and week 4 of the clerkship. RESULTS: The posttest scores of the study group increased by an average of 12.1 above the pretest scores, but the scores of the control group were only 3.4 points higher. The difference between these increases is statistically significant (P < .01, Student's t test). CONCLUSION: Short, well-designed computer-assisted instruction units can be effective tools in medical education.

Spectral analysis of biochemical reactions used for identification of bacteria.

To define parameters for optimizing automated discrimination of bacterial biochemical reactions certain theoretical considerations of spectrophotometric analysis were explored. One-hundred and one recent clinical isolates of gram-negative bacilli (21 species) were inoculated into AP1 20 E strips and read manually after 24 hours. With spectrophotometric scanning, the AP1 reactions could be classified into three analytical categories: pH change, production of new products, and darkening of the medium. Whereas single wavelength analysis gave 2.9% disagreement from the visual, multiple wavelength analyses were uniformly more accurate. The best results for pH change reactions were obtained by calculating a ratio of two wavelengths. New color reactions were best interpreted by demonstration of the new peak, whereas darkening reactions required quantitation of the area under the entire curve. With these methods, a 99.3% overall agreement of individual reactions and a 97% agreement of identification were achieved. Multiple-point analysis of spectra coupled with computerized interpretation of the data should help resolve the problem of equivocal reactions in bacterial identification schemes optimized for spectral analysis.

Generation of hydrogen peroxide by Candida albicans and influence on murine polymorphonuclear leukocyte activity.

Iodide fixation by murine polymorphonuclear leukocytes (PMN) incubated with viable Candida albicans blastoconidia increases directly with yeast cell concentration up to about 3 x 10(6) cells per ml, but above this concentration bound activity declines dramatically. To understand the basis for this decline, we examined the oxidative metabolism of fungi and stimulated PMN and found some remarkable similarities between these cell types. Both produced 14CO2 when incubated with [1-14C]glucose, both reduced cytochrome c, and both fixed radiolabeled iodide, although the fungi required exogenous lactoperoxidase. In dose-response experiments, iodination by fungi with lactoperoxidase was identical to that with PMN, i.e., the maximum bound activity occurred in cultures with 10(6) to 3 x 10(6) blastoconidia per ml. Iodination by fungi with lactoperoxidase was reduced when blastoconidia were incubated at 25 degrees C or in the presence of catalase and the metabolic inhibitors rotenone, antimycin A, and 2-deoxyglucose. Results from assays for oxidation of scopoletin and o-dianisidine showed that 10(6) blastoconidia in 1.0 ml of medium released 0.5 to 0.7 nmol of H2O2 after 1 h, but 3 X 10(6) and 10(7) cells released significantly less H2O2. These results suggest that iodide fixation by PMN and low numbers of fungal cells may reflect a cooperative effort, with fungi generating some H2O2 that reacts with the myeloperoxidase released from the PMN. With high concentrations of blastoconidia, H2O2 activity appeared to be specifically inhibited, possibly to protect fungal cells from damage.

Stimulation of oxidative metabolism in murine polymorphonuclear leukocytes by unopsonized fungal cells: evidence for a mannose-specific mechanism.

Murine polymorphonuclear leukocytes (PMN) are stimulated to produce hydrogen peroxide (H2O2) by some unopsonized fungi, including Coccidioides immitis spherules, Candida albicans blastospores, and Saccharomyces sp. blastospores (zymosan). In this communication we have examined the basis for this stimulation by studying the effects of mannan and its primary constituent, D-mannose, on PMN function in vitro, since this polysaccharide is a significant component in many fungal cell walls. Our results show that mannan stimulated H2O2 production and iodination by PMN and enhanced H2O2 production by cells stimulated with zymosan. Moreover, the amount of H2O2 released by PMN was directly related to the concentration of mannan, and mannan obtained commercially or prepared in our laboratory worked equally well. Mannose, on the other hand, inhibited H2O2 release from PMN stimulated with zymosan or mannan and reduced oxygen consumption, carbon dioxide production, superoxide release, and iodination by these cells as well. With respect to specificity of inhibition, 18 different monosaccharides were examined by using 2 different assays for H2O2 release; and only 2-deoxy-D-glucose, a potent glycolytic inhibitor, reduced H2O2 release from zymosan-stimulated PMN. Furthermore, H2O2 release from cells stimulated with phorbol myristate acetate or opsonized Sephadex was not inhibited by mannose whereas H2O2 release was reduced when PMN were stimulated with C. albicans blastospores or C. immitis spherules in the presence of this sugar. From these data we propose that initiation of PMN oxidative metabolic burst in response to some unopsonized fungi occurs through a mannose-specific mechanism.

Alteration of polymorphonuclear leukocyte activity by viable Candida albicans.

The response of human polymorphonuclear leukocytes (PMN) to blastospores and pseudo-hyphae of the opportunistic fungus Candida albicans has been studied in vitro and in vivo. Of the fungicidal mechanisms elucidated thus far, the myeloperoxidase-hydrogen peroxide-halide system appears to be most effective against cells of this fungus. In our studies on the interaction between murine PMN and blastospores, we assayed the release of H2O2 by PMN incubated with viable or killed, unopsonized or opsonized blastospores by using two assay systems, lysis of murine erythrocytes and oxidation of scopoletin. Our results showed that PMN released increasing amounts of H2O2 when incubated with increasing numbers of opsonized or unopsonized killed blastospores, but released decreasing amounts of H2O2 when incubated with increasing numbers of opsonized or unopsonized viable blastospores. The oxidative metabolic burst by PMN in the presence of viable or killed blastospores was also measured by using reduction of nitroblue tetrazolium and chemiluminescence. Viable blastospores stimulated a stronger metabolic burst than killed blastospores, suggesting that PMN respond to live blastospores more vigorously than killed blastospores; however, live blastospores appear to alter or inhibit the release of H2O2 by PMN.

Growth of Trichophyton mentagrophytes on individual amino acids.

Trichophyton mentagrophytes was tested for its ability to utilize individual amino acids as a source of carbon and nitrogen in basal medium containing 0.4 mM magnesium sulphate (0.1 g/l) in 0.05 M potassium phosphate buffer at pH6.5. Growth was quantitated by measurement of both dry weight and fungal protein. Seventeen naturally occurring amino acids supported growth, serving as a source of both carbon and nitrogen. Seven amino acids failed to support growth under these conditions; however three of these could be metabolized for nitrogen, but not for carbon.

Significance of an in vitro phenomenon in which murine erythrocytes are lysed by autologous spleen cells and spherules of Coccidioides immitis.

Spleen cells from mice immunized with a variety of antigens and incubated in vitro with killed spherules of Coccidioides immitis lyse six to eight times more autologous murine erythrocytes than normal spleen cells and spherules. Cellular and biochemical events in this phenomenon were investigated to ascertain its significance. Kinetic studies suggested that hemolysis results from the activation of some immune cells by spherules. The capacity of spherules to activate these cells is rather unusual because, of the inert particles tested, only zymosan A and crude chitin demonstrated comparable activity. Furthermore, although the hemolytic phenomenon occurred in serum-free medium, more lysis was effected by immune cells and opsonized spherules or zymosan A than by immune cells and untreated fungal particles. Sheep, chicken, and human erythrocytes were not lysed in the hemolytic phenomenon; however, hemoglobin in chicken and sheep erythrocytes was oxidized. Both the murine erythrocyte lysis and oxidation of ovine hemoglobin correlated with the reduction of Nitro Blue Tetrazolium by immune cells adherent to spherules, and both phenomena appeared to be mediated by H2O2 released into the medium by activated cells. Spleen cells reactive with spherules could not be depleted by treatment with iron carbonyl, antiimmunoglobulin plus complement, or anti-brain-associated theta plus complement, but they were partially or completely depleted after rosette formation with erythrocytes coated with antibody or murine complement. Using light and electron microscopy, we noted that immune spleens contained more neutrophils than normal spleens, that these neutrophils reduced Nitro Blue Tetrazolium after stimulation with phorbol myristate acetate, and that they were the most prevalent cell type adherent to spherules after incubation in vitro.

Mycotic flora of the interdigital spaces of the human foot: a preliminary investigation.

A qualitative and quantitative study of the mycotic flora of the interdigital spaces of 27 male volunteers yielded 1,291 moulds and 598 yeasts. Concurrently, a study of garden soil was conducted in order to obtain data concerning the transient-resident status of the fungi recovered from the feet. Of the 120 genera and species of fungi isolated, 51 were recovered from the volunteers, 53 from the soil, and 16 from both categories. The most commonly recovered fungi from the toewebs, in order to occurrence, were Torulopsis candida, Mycelia Sterilia, T. maris, Rhodotorula rubra, Cryptococcus albidus, and species of Aspergillus and Penicillium. Without sign of infection, Cryptococcus neoformans was isolated from 5 volunteers. Candida albicans was not recovered from any subject. Trichophyton mentagraphytes was recovered from 7 volunteers and T. rubrum from one.