Mycology quality assessment: United Kingdom national scheme.

A mycology quality assessment scheme introduced in 1986 was assessed: 289 laboratories participated in the scheme, and six distributions, each containing four specimens, were made. Levels of performance varied considerably among participating laboratories: performance was highest with the commoner organisms distributed, but some laboratories, encouragingly, achieved a consistently high level of species identification. A questionnaire distributed to participants showed that a wide range of methods are commonly used, some of which are contrary to good practice. As the scheme continues, selection of organisms considered to be relevant and of use to participants will become difficult.

Cutaneous Scedosporium apiospermum infection in an immunocompromised patient.

Scedosporium apiospermum infection occurred in the left forearm of a patient who was taking oral prednisolone for pulmonary fibrosis. The infection appeared to follow a scratch from a blackcurrant bush. This is the first reported case in the United Kingdom of a cutaneous infection from Scedosporium apiospermum in an immunocompromised patient.

Evaluation of the AUXACOLOR system, a new method of clinical yeast identification.

AIMS: To compare the AUXACOLOR yeast identification system with the API 20C system. METHODS: Yeast isolates (n = 215), comprising 16 species, were identified using the AUXACOLOR system and the API 20C system. Isolates that could not be identified with the API 20C system or which produced discrepant results in the two systems were identified by assimilation and fermentation procedures. RESULTS: AUXACOLOR correctly identified 150 (85.7%) of 175 germ tube negative isolates while API 20C identified 155 (88.6%). Incorrect identifications were more common with API 20C (7.4%) than with AUXACOLOR (3.7%). Of 110 isolates of four common pathogens (Candida glabrata, C parapsilosis, C tropicalis, and Cryptococcus neoformans), 82.7% (91/110) were identified by AUXACOLOR while API 20C identified 74.5% (82/110). Of 65 less common germ tube negative isolates, 55.4% (36/65) were identified by AUXACOLOR while API 20C identified 63.1% (41/65). CONCLUSION: Although it has a limited database of 26 species, the AUXACOLOR system is a useful method for identification of germ tube negative clinical yeast isolates. Compared with the API 20C, the AUXACOLOR system is simpler and quicker to set up, easier to interpret, and comparable in cost.

Chaetomium pneumonia in patient with acute myeloid leukaemia.

A patient with relapsed refractory acute myeloid leukaemia developed typical fungal lung lesions despite intravenous amphotericin B prophylaxis. Chaetomium globosum was cultured from the resected right lower lobe. Histology showed branching hyphae negative for common Aspergillus species by immunohistochemical staining. Previous reports of invasive disease caused by Chaetomium and some applications of immunohistochemical staining for Aspergillus are discussed.

Hazards to laboratory staff posed by fungal pathogens.

There is sufficient evidence from the literature to demonstrate the risk involved in handling the dimorphic pathogens without suitable containment facilities. The number of fungi considered a severe hazard is fortunately low, but impeccable working practices and continuous vigilance are necessary to minimize accidents and to prevent them leading to worse catastrophies. The continuing discovery of new opportunistic pathogenic fungi requires frequent, objective and cautious review of the hazard groupings to accommodate them.

Rhizopus microsporus in wooden tongue depressors: a major threat or minor inconvenience?

The investigation and management of an apparent outbreak of Rhizopus spp. in a London paediatric referral centre between September 1995 and April 1996 is described. The organism was identified in microbiological surveillance samples from 23 patients nursed in four hospital areas. Investigations revealed the presence of the organism in spatulae from all ward areas investigated and from closed boxed containers held in the central hospital stores obtained from a new supplier. In contrast, culture of spatulae from the initial supplier failed to yield any fungal isolates. The incident was reported to the Medical Device Agency (MDA), the Central Public Health Laboratory Service (CPHLS) and the Birmingham PHLS. A statement was prepared for the weekly Communicable Disease Report and a hazard warning issued by the MDA. The spatulae were withdrawn from use and the contract with the original supplier was re-established. This incident resulted in contamination of samples only and no patient involvement. It highlights the problems which may follow use of equipment for unintended purposes and the need for good manufacturing practice guidelines to be applied to non-sterile equipment used in direct patient care.

Schizophyllum commune: an unusual isolate from a patient with allergic fungal sinusitis.

We describe the first case of allergic fungal sinusitis (AFS) associated with Schizophyllum commune. Histological diagnosis was made on the mucinous material from the sinus which contained eosinophils, fungal hyphae and Charcot-Leyden crystals. The fungal isolate was identified as S. commune on the basis of its colonial morphology and minute peg-like outgrowths from vegetative hyphae and clamp connections. The optimal treatment of AFS is not known but may involve surgical debridement followed by systemic corticosteroids, gradually reduced, with the patient being maintained on inhaled corticosteroids. Oral itraconazole could be added to the regimen of those patients in whom frequent recurrences occur after debridement or when there is histological evidence of severe pressure erosion.

Disseminated zygomycosis (mucormycosis) caused by Saksenaea vasiformis.

A 14-year-old child from Iraq presented with an acute febrile illness accompanied by large necrotic skin lesions and bronchopneumonia from which he subsequently died. The infection was caused by an unusual zygomycete fungus Saksenaea vasiformis. Previous reports of infection with this organism are rare and tissue invasion has usually followed traumatic injury. In the child reported here no predisposing abnormalities were apparent.

Systemic mycosis due to Penicillium marneffei in a patient with antibody to human immunodeficiency virus.

Systemic mycosis due to Penicillium marneffei is described in a man infected with human immunodeficiency virus and who had travelled in S.W. China. He responded completely to treatment with amphotericin B and a prolonged course of ketoconazole. Problems of diagnosis are discussed and all previously reported cases reviewed.

Modelling the transverse-mode response of a two-port SAW resonator.

An equation is derived for the transverse-mode frequencies of a two-port surface-acoustic-wave (SAW) resonator with uniform reflection gratings. It is postulated that only odd-order (symmetric) transverse modes should be excited in such a grating, due to its symmetrical placement with respect to the interdigital transducer (IDT). Frequency response modeling involves a summation of one-dimensional transmission-matrix computations for the fundamental mode and participating transverse ones. Excellent agreement is obtained between theory and experiment for a 360-MHz resonator with three close-in transverse modes, attributed to symmetric modes of odd order m=3, 5, 7.

Sampling effect of distributed reflector arrays within a single-phase unidirectional SAW transducer.

A noteworthy feature of the group-type single-phase unidirectional transducer is that it can permit wideband low-loss surface-acoustic-wave (SAW) comb filter operation. This is shown to be due to the sampling imposed by the distributed reflector gratings. The capability is illustrated theoretically and experimentally for a 65-MHz comb filter on 128 degrees Y-X lithium niobate, with 5 comb modes of 585-kHz bandwidth each, together with 2.6-dB minimum insertion loss and overall 50% fractional bandwidth.

Design of a phase-locked multimode SAW oscillator.

A 60-100 MHz multimode SAW (surface acoustic wave) oscillator with comb spacing Deltaf=10 MHz used a low-loss SPUDT (single-phase unidirectional transducer) comb filter in conjunction with two varactor-based control elements and two feedback loops, for mode selection and stability enhancement over long dwell times. The end aim is to reduce close-in phase noise over that of the unlocked oscillator, corresponding to improved intermediate-term time-domain stability. Frequency deviation was less than 20 Hz over two hours in each of the five comb modes.

Modeling a longitudinally coupled dual-mode leaky-SAW resonator filter with enhanced upper-sideband suppression.

Recently, it has been experimentally reported that enhanced upper-sideband suppression of a longitudinally coupled (first/third) dual-mode leaky SAW (LSAW) resonator filter may be obtained by incorporation of a selectively valued capacitor between input and output terminals. In this paper, coupling-of-modes (COM) and bandstop-filter modeling is applied to realize this enhanced suppression. Tradeoffs are examined between upper and lower side-band suppression levels caused by the ensuing capacitive coupling between input and output terminals. Good agreement is obtained between this theory and reported experimental results for an 800-MHz band cellular filter.

Conductance measurements on a leaky SAW harmonic one-port resonator.

Conductance measurements are reported on a leaky SAW (LSAW) harmonic one-port resonator on a 64 degrees Y-X LiNbO(3) substrate. This employed a short three-finger IDT for fundamental and second harmonic operation together with long reflection gratings. Conductances were measured with and without the end gratings. From an analysis of the measurements, it was deduced that, for optimum second harmonic performance, the grating stop-band frequency should be higher than the IDT unperturbed center frequency. This result is in contrast to fundamental frequency resonator designs in which the end grating stop-band frequency is placed below the IDT center frequency for optimum performance.

A theoretical and experimental study of low-loss SAW filters with interdigitated interdigital transducers.

A study of low-loss surface-acoustic-wave (SAW) interdigitated interdigital transducer (IIDT) structures is presented. A model based on mixed scattering matrices was used in the analysis. It is shown that the inherent comb frequency response of the IIDT can be smoothed by slanting the transducers in the structure. Alternatively, the combs can be enhanced to produce a compact low-loss feedback element for potential application in multimode oscillators. Experimental verification of the analysis is provided by a 3:2 slanted-finger IIDT filter with a 10% relative bandwidth of 5.9-dB insertion loss, and a comb filter with 13.4-dB insertion loss and comb spacing of about 3 MHz. The measured responses agree quite well with the theory.

Injection locking techniques for a 1-GHz digital receiver using acoustic-wave devices.

The use of surface-transverse-wave (STW) resonator-based oscillators as amplifiers and as carrier recovery elements is discussed. It is demonstrated that these oscillators can amplify phase-shift-keyed signals with very little added noise, while providing a constant output power. Their performance in carrier recovery amplifications is analyzed. Experimental results showing the amplification with more than 80 dB of dynamic range of a 2 Mb/s BPSK signal and the carrier recovery of an 8 Mb/s signal with a 1-GHz STW oscillator are shown.

Aspects of modeling the frequency response of a two-port waveguide-coupled SAW resonator-filter.

Coupling-of-modes-in-time and coupling-of-modes-in-space analyses are applied to the modeling of a two-port two-pole waveguide-coupled SAW resonator filter. Modeling is applied to a lumped equivalent circuit and a distributed circuit. While the accuracy of the coupling estimation dictates the exact mode-splitting and bandwidth, the ensuing computations can give a good representation of the amplitude and phase response, including the effect of degenerate transverse modes.

Transverse modes in one-port SAW resonators.

The S(11) and equivalent S(21) frequency responses of a one-port surface acoustic wave (SAW) resonator with transverse modes derived from one-dimensional coupling-of-modes and transmission-matrix analysis. The two-dimensional nature of the problem is approximated by a summation of one-dimensional mode responses for each transverse mode. Comparison between theory and experimental data for a commercial 280-MHz one-port SAW resonator shows good agreement for the placement of transverse modes.

Mode selection in a multimode SAW oscillator using FM chirp mixing signal injection.

Mode-selection control of a multimode surface-acoustic-wave (SAW) oscillator has been obtained using SAW linear FM chirp signal injection. The prototype 60-100-MHz SAW oscillator design employed a single-phase unidirectional transducer (SPUDT) low-loss comb filter in the feedback loop, with minimum insertion loss of approximately 3.7 dB. Mode selection was achieved using an injection signal derived from the mixed output of two 27.5-52.5-MHz up- and down-chirp SAW filters. Mode switching times of less, similar2 mus were obtained. The device could be useful as a local oscillator on frequency-agile radars, where hopping is required over a moderate number of frequencies.