Thermally enhanced neutralization in hyperthermal energy ion scattering.

Neutralization probabilities are presented for hyperthermal energy Na+ ions scattered from a Cu(001) crystal as a function of surface temperature and scattered velocity. A large enhancement in neutralization is observed as the temperature is increased. Velocity-dependent charge transfer regimes are probed by varying the incident energy, with the most prominent surface temperature effects occurring at the lowest energies. The data agree well with results obtained from a model based on the Newns-Anderson Hamiltonian, where the effects of both temperature and velocity are incorporated.

Comparative kinetics of hematoporphyrin derivative uptake and susceptibility of Bacillus subtilis and Streptococcus faecalis to photodynamic action.

Hematoporphyrin derivative (HpD) is widely used in photoradiation therapy of tumors and other diseases, and has been shown to affect the viability of gram positive bacteria. This investigation assessed the efficiency of binding of HpD to Bacillus subtilis and Streptococcus faecalis when HpD-treated organisms were exposed to red light. Kinetic studies indicated that the amount of HpD bound increased with increasing external concentration of HpD until saturation of binding sites was reached. S. faecalis had a higher affinity for HpD and was more susceptible to photoinactivation than B. subtilis. The data from this study suggest that differences in susceptibility of microorganisms to photoinactivation are directly related to the affinity of each strain for HpD.

A case of pseudoparacoccidioidomycosis: detection of the yeast phase of Mucor circinelloides in a clinical specimen.

A case is presented in which yeastlike cells resembling the yeast phase of Paracoccidioides brasiliensis were observed by microscopic examination of a urine sample. A mold identified as Mucor circinelloides was isolated from the specimen. It was converted to the yeast form by cultivation on Sabouraud agar incubated in a GasPak jar at 37 degrees C. The isolate was eventually shown not to be related to the patient's illness; however, the superficial resemblance of the yeast phase to P. brasiliensis caused some confusion in making a correct diagnosis.

Collaborative evaluation of the Abbott Avantage system for identification of frequently isolated nonfermentative or oxidase-positive gram-negative bacilli.

The capability of the Abbott Avantage system to identify 10 species of commonly isolated glucose nonfermentative or oxidase-positive gram-negative bacilli in a 5-h test period was evaluated in a collaborative study. The Avantage nonenteric data base uses 20 biochemical test reactions performed in an expanded Abbott bacterial identification cartridge plus the results of a manual oxidase test. The species included in the Avantage data base are Acinetobacter anitratus, Acinetobacter Iwoffi, Aeromonas hydrophila, Flavobacterium meningosepticum-IIb group, Pseudomonas aeruginosa, Pseudomonas cepacia, Pseudomonas fluorescens-putida group, Pseudomonas maltophilia, Pasteurella multocida, and Plesiomonas shigelloides. The collaborative study included the testing of 200 coded challenge strains in all three laboratories and the subsequent testing of an additional group of 100 to 200 clinical isolates recovered independently by each laboratory. Reference identifications for all isolates were determined by conventional biochemical test reactions. The overall accuracy of identification of the coded challenge strains for the three laboratories was 97%, whereas 95% of 437 clinical isolates and selected stock cultures of clinical derivation were identified correctly.

Collaborative evaluation of the Abbott yeast identification system.

The Abbott yeast identification system (Abbott Laboratories, Diagnostics Division, Irving, Tex.) is a 24-h, instrumental method for identifying medically important yeasts, based on matrix analysis of 19 biochemical reactions and the germ tube test. The system was evaluated in two clinical laboratories by using 179 coded isolates, which included a high percentage of the less frequently encountered species. Based upon results with these coded isolates and from previously obtained laboratory data, the system software was adjusted and accuracy of the yeast identification system was further evaluated with 378 isolates from clinical sources. Of the 378 clinical yeast isolates tested, 364 (96%) were correctly identified with the Abbott system. Isolates were deliberately selected so that germ tube-positive isolates made up less than 10% of the clinical isolates tested.

Amphotericin B tolerance: a characteristic of Candida parapsilosis not shared by other Candida species.

Thirty yeast isolates from clinical specimens were tested for their susceptibility to amphotericin B at 30 C, 37 C, and 39 C. Of the six Candida albicans, five Candida tropicalis, one Candida guilliermondii, one Candida krusei, one Candida pseudotropicalis, two Torulopsis glabrata, and four Cryptococcus neoformans isolates tested, all were inhibited at amphotericin B concentrations of less than or equal to 0.4 micrograms/ml and killed by concentrations of amphotericin B that were less than or equal to 16-fold higher than the minimal inhibitory concentration (MIC). Although growth of Candida parapsilosis was also inhibited by concentrations of amphotericin B of less than or equal to 0.4 micrograms/ml, minimal fungicidal concentrations of amphotericin B were greater than or equal to 32-fold higher than MICs for each of the 10 isolates examined. This unique susceptibility pattern of C. parapsilosis resembles the antibiotic tolerance observed with Staphylococcus aureus. Variations in temperature within the experimental range did not affect the amphotericin B susceptibility for any of the yeasts examined.

Disseminated Saksenaea vasiformis infection.

Herein reported is a second case of human Saksenaea vasiformis infection. This unusual zygomycete was isolated postmortem from the tissues of an immunocompromised woman. The patient died of a disseminated infection that caused cutaneous, pulmonary, and renal infarcts. Clinical and pathologic features of the case and manifestations of zygomycete infection are discussed.

Evaluation of the MS-2 system for rapid identification of Enterobacteriaceae.

The precision, accuracy, and other performance characteristics of the MS-2 (Abbott Laboratories, Diagnostic Division, Dallas, Tex.) system for the identification of Enterobacteriaceae were evaluated in a collaborative study involving three clinical laboratories. When identifying 150 unknown, coded organisms, the MS-2 system was 97%, 98%, and 93% accurate, respectively, in three laboratories. The system showed an overall accuracy of 94% when compared with conventional manual tube methods in identifying 1,154 clinical isolates of 26 species of Enterobacteriaceae. Discrepancies between automated and conventional methods were chiefly caused by biochemical variants, especially among Enterobacter species. The MS-2 system was rapid and simple to operate and produced printed results of bacterial identification in 5 h. The cost of disposable components compared favorably with commercial, visually read systems for identifying Enterobacteriaceae.

Automated detection of microbial growth in blood cultures by using stainless-steel electrodes.

Sterile stainless-steel electrodes implanted in blood culture bottles and monitored electronically were used to detect growth of microorganisms. Each blood culture bottle contained 100 ml of medium and was inoculated with 10 ml of blood seeded with either 300 or 50 colony-forming units of one of several bacterial or yeast species that are commonly isolated from clinical blood cultures. Growth was indicated by a voltage change of at least 0.1 mV/min with an increasing slope over at least three consecutive 15-min intervals. This method was compared to the conventional visual method for detecting microbial growth in broth. Growth detection by both techniques was confirmed by subculture to solid media. Of the 163 cultures seeded with the high inoculum (300 colony-forming units) and confirmed as being positive, 148 (90.8%) were positive by the electronic detection system (EDS). At the lower inoculum (50 colony-forming units), 47 of 53 (88.7%) positive cultures were detected by EDS. Twelve of the 21 false-negatives by the EDS were cultures seeded with Cryptococcus neoformans. Excluding C. neoformans, the rate of detection of growth was 96.0%. Microbial growth was detected an average of 18 h earlier by EDS than by the conventional system in 176 (90.2%) of the cultures. Also examined were 156 patient blood cultures: 13 were positive both by EDS and by conventional methods.

Clinical laboratory evaluation of a screening medium (CN screen) for Cryptococcus neoformans.

Results obtained with 433 yeast isolates indicated that the CN screen medium could be used with confidence for presumptive identification of Cryptococcus neoformans. Of 49 C. neoformans isolates tested, only four stock isolates yielded false-negative results upon initial testing. After repeated subculturing on Sabouraud agar and retesting, these four isolates yielded correct results. Essentially, no false-positive results were obtained, and the data suggested that false-negative results could be eliminated by using fresh isolates of C. neoformans preincubated at 25 degrees C on Sabouraud glucose agar.

Assimilation of protocatechuic acid and p-hydroxybenzoic acid as an aid to laboratory identification of Candida parapsilosis and other medically important yeasts.

Test for the ability of yeasts isolated from clinical specimens to utilize protocatechuic acid and p-hydroxybenzoic acid were carried out by using techniques that are commonly employed to test assimilation of carbon sources. A total of 60 isolates of Candida parapsilosis and 5 isolates of Candida humicola readily assimilated these two phenolic acids, whereas other Candida species gave uniformly negative results. Cryptococcus albidus, Cryptococcus terreus, and some isolates of Cryptococcus laurentii also assimilated protocatechuate and p-hydroxybenzoate, whereas Cryptococcus neoformans did not. Results of these tests suggest that assimilation of protocatechuate and p-hydroxybenzoate may be a useful characteristic, when used in conjunction with traditional tests, for identifying C. parapsilosis and C. albidus.

Evaluation of the new API 20C strip for yeast identification against a conventional method.

The new API 20C yeast identification system together with appropriate microscopic morphology determinations achieved a 97% correlation with a rapid conventional method. Whereas a group composed of Candida, Torulopsis, Saccharomyces, and Rhodotorula was identified with ease (98% overall correlation), a second group, containing Cryptococcus, Trichosporon, and Geotrichum species, appeared to give the system the most difficulty (90% correlation). Within this group particular difficulty was encountered in identifying varieties of Cryptococcus albidus, C. terreus, C. laurentii, Trichosporon beigelli, and Geotrichum spp. as to species. The API 20C system should be incubated the full 72 h prescribed by the manufacturer. However, when used in conjunction with appropriate morphological tests, presumptive identifications of some Candida and Torulopsis species may be made at 24 to 48 h. To facilitate identifications of the more difficult group of yeasts, ancillary tests for determining nitrate reductase, urease, and phenol oxidase activities should be considered as additions to the strip. Incorporating the phenol oxidase test would be especially important for identification of Cryptococcus neoformans, a yeast which should be identified as quickly and as accurately as possible. The API 20C system with computer assistance has proved to be an easy-to-inoculate, versatile, and fairly rapid method of yeast identification, giving results comparable to those obtained by conventional methodologies.

Clinical evaluation of the Uni-Yeast-Tek system for rapid presumptive identification of medically important yeasts.

The results of over 400 tests for identification of clinical yeast isolates as to species using the Uni-Yeast-Tek (UYT) system in comparison with a more conventional system are reported. The conventional system utilized a total of 23 individual tests, including both fermentation and assimilation tests, whereas the UYT system included only 11 separate tests. In the initial phase of the study, coded unknown isolates were evaluated by each of two technologists using both methods independently. After this initial evaluation, the two methods were used in parallel for routine testing of yeast isolates as they were obtained from clinical specimens. A further evaluation of the UYT system was carried out by retrospectively analyzing the species reported from a clinical mycology laboratory during two separate time periods in which different approaches to yeast identification were employed. A total of 92% of the isolates tested with the UYT system were correctly reported within 72 h, 96% were correctly named after 1 week of incubation, and 97% were correctly reported after 2 weeks of incubation of UYT plates at 30 degrees C when results of the two phases of the study were analyzed together. With the conventional system, 88% of the isolates were correctly reported at 72 h, 96% at 1 week, and 98% after 2 weeks of incubation of biochemical tests. Retrospective analysis of laboratory records revealed no major changes in species reported after adoption of the UYT system for routine testing of clinical isolates. The data presented in this report suggest that the UYT system can be expected to yield rapid presumptive identification of clinical yeast isolates with reasonable confidence when certain minor limitations that are discussed in the text are taken into account.