Evaluation of the Biolog MicroStation System for yeast identification

Journal of Medical & Veterinary Mycology 1996, 34, 349-352 Accepted 9 May 1996 Evaluation of the Biolog MicroStation System for yeast identification M. R. McGINNIS,* T. C. MOLINA, t D. L. PIERSON$ & S. K. MISHRAt *Medical MycologyResearchCenter, WHO CollaboratingCenter for Tropical Diseasesand Department of Pathology, University of Texas Medical Branch, Galveston,TX 77555-0609; tKRUG Life Sciences, 1290 Hercules Drive, Suite 120, Houston, TX 77058; and ~BiomedicalOperationsand ResearchBranch, NASA~JohnsonSpace Center, Houston, TX 77058, USA Keywords automation, Biolog, yeast identification, yeast taxonomy Introduction The Biolog MicroStation has been designed to provide microbiologists with a versatile system that can identify bacteria and yeasts of environmental, medical and veterinary importance. In addition to its identification potential, the system can be used to study microbial metabolic capabilities and to conduct strain typing owing to the extensive number of substrates that can be tested. The Biolog yeast identification system uses 94 biochemical tests to distinguish the various yeast taxa contained within its database. The Biolog system is similar to the Vitek System [1] in that they both measure the ability of test isolates to use substrates for growth, and then provide a computer generated identification. We have previously evaluated the efficacy of the Biolog system to identify gram-negative bacteria [2]. Of the reference strains tested, 98% were identified to genus, whereas 76% were identified to species within 4-24 h. The identification of some authentic strains was found to be unreliable; because of this experience with the bacteriological component of the Biolog system, we decided to Correspondence: Dr M. R. McGinnis, Medical Mycology Research Center, WHO Collaborating Center for Tropical Diseases and Department of Pathology, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-0609, USA. Tel.: (409) 74%0603; Fax: (409) 747-0605; E-mail: . © 1996 1SHAM evaluate the capability of the system to identify yeasts. The purpose of this report is to document the system's ability to identify environmental and medically important yeasts. Materials and methods The yeast isolates included in this study consisted of type strains, authentic isolates and isolates previously identified by standard methods [3]. Two groups of taxa were selected, which included 129 isolates belonging to 13 genera and 38 species (Table 1) that were included in the Biolog database (release 3.5, Biolog, Hayward, CA) and 30 isolates classified in three genera and 15 species (Table 2) not included in their database. All isolates were maintained at - 7 0 °C prior to this study in the culture collection at the University of Texas Medical Branch (UTMB) at Galveston. The automated Biolog MicroStation with MicroLog 3 software (Biolog) was used throughout this study. The MicroStation consists of an IBM personal computer and a microplate reader. The database contains 267 yeast species classified in 53 genera that are known to occur in the environment. Some of these taxa have been documented as human and animal pathogens, especially in immunocompromized individuals. One hundred and fifty-nine isolates representing 16 genera and 53 species of yeasts were processed with the Biolog MicroStation System for yeast identification. Thirteen genera and 38 species were included in the Biotog database. For these 129 isolates, correct identifications to the species level were 13.2, 39"5 and 48.8% after 24, 48 and 72 hours incubation at 30 °C, respectively. Three genera and 15 species which were not included in the Biolog database were also tested. Of the 30 isolates studied, 16.7, 53"3 and 56.7% of the isolates were given incorrect names from the system's database after 24, 48 and 72 h incubation at 30 °C, respectively. The remaining isolates of this group were not identified. McGinnis et al. Table 1 Yeast taxa included in Biolog database Results (h) 24 48 72 N C I N C I N C I Bullera alba (1) Candida albicans (13) C. ciferrii (2) C. diddensiae (1) C. famata (11) C. geochares (2) C. glabrata (4) C guittiermondii (2) C. intermedia (1) C. kefyr (8) C. krusei (14) C. [ipolytica (1) C. lusitaniae (8) C. magnoliae (1) C. maris (1) C. norvegensis (1) C. parapsilosis (8) C. utilis (1) C. rugosa (2) C. tropicalis (4) Cryptococcus albidus (2) C. laurentii (3) C. neoformans (10) Debaryomyces maramus (1) Hanseniospora uvarum (1) H),popichia burtonii (1) Lodderomyces elongisporus (1) Metschnikowia pulcherrima (1) Pichia farinosa (1) P. haplophilia (2) Pichia membranaefaciens (1) P. ohmeri (2) Rhodotorula aurantiaca (1) R. glutinis (1) R. minuta (1) Saccharomyces cerevisiae (7) Torulospora delbrueckii (2) Trichosporon beigelii (5) 0 12 2 1 7 2 4 2 1 3 13 0 6 1 1 1 8 1 1 3 1 2 9 1 1 1 1 1 1 1 0 2 1 1 l 4 2 4 0 0 0 0 0 0 0 0 0 5 0 1 2 0 0 0 0 0 1 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 2 0 1 1 1 0 0 4 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0 0 3 0 0 1 6 0 0 0 2 0 0 7 2 1 8 0 4 0 1 0 1 2 0 0 1 8 1 0 0 2 2 0 4 1 0 9 0 2 1 1 1 0 0 6 t 0 1 0 0 1 1 0 6 1 1 1 5 0 7 1 2 0 4 0 5 1 5 0 1 4 3 0 4 4 0 0 0 0 0 0 1 1 0 7 1 2 0 0 1 1 0 0 0 0 0 0 0 0 1 1 1 7 1 2 0 0 0 1 0 0 1 1 2 0 2 2 0 0 6 0 0 2 0 2 1 1 0 3 2 0 0 1 0 2 0 0 1 1 6 1 1 0 2 2 0 0 1 0 0 0 1 0 0 0 1 0 0 1 1 0 0 0 0 1 1 1 0 0 0 1 0 0 1 0 0 2 0 0 1 0 0 1 1 0 1 0 0 2 0 0 0 0 2 0 1 0 2 0 1 0 1 5 0 0 0 1 0 0 1 1 0 2 0 0 0 0 5 2 1 1 3 2 1 2 N, no identification; C, correct identification; I, incorrect identification. Yeasts included in this study were subcultured f r o m frozen cultures to S a b o u r a u d glucose agar ( S G A ) and then incubated at 25 °C. Isolates were m a i n t a i n e d at 25 °C on S G A until needed. The colonial purity o f the isolates was visually verified. F o l l o w i n g the m a n u f a c t u r e r ' s instruction, each isolate was subcultured o n t o B U Y agar (Biolog) and i n c u b a t e d at 25 °C for 24M8 h. U s i n g Biolog Y T turbidity standards, a q u e o u s yeast suspensions p r e p a r e d f r o m the g r o w t h on B U Y agar were adjusted to 4 4 - 5 1 % T. O n e h u n d r e d / t l of i n o c u l u m was a d d e d to each well o f the M i c r o P l a t e (Biolog), after which the plates were put into large plastic bags to m i n i m i z e d e h y d r a t i o n . The plates were incubated at 30 °C for 24, 48 and 72 h, at which times they were read by the plate reader set at a wavelength o f 590 nm. Quality control strains Candida albicans ( A T C C 10231), C. geochares ( A T C C 36852), Cryptococcus laurentii ( A T C C 18803) and Pichia haplophila ( A T C C 24240) were p u r c h a s e d f r o m B i o l o g and run c o n c u r r e n t l y with the test isolates. © 1996 ISHAM, Journal of Medical & Veterinary Mycology 34, 349-352 Yeast (no. of isolates studied) Biolog MicroStat (...truncated)