A Robinson

A. G. M. Buiting

B Holmes

D Peele

G Wauters

IJ Micklewright

J. R. Lo-Ten-Foe

K Varettas

L Soler

M Vaneechoutte

M. A. C. Ververs

English

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BRIEF REPORT
Comparative evaluation of automated reading
versus visual interpretation with the BBL Crystal
enteric/nonfermenter identification system
in a clinical setting
J. R. Lo-Ten-Foe & M. A. C. Ververs & A. G. M. Buiting
Published online: 23 May 2007
# Springer-Verlag 2007
The BBL Crystal enteric/nonfermenter identification sys-
tem (Becton Dickinson, Sparks, MD, USA) is a miniatur-
ized commercial system that is widely used to identify more
than 500 gram-negative bacilli [1–4]. The system is designed
to identify members of the family Enterobacteriaceae as
well as common isolates of clinically significant glucose-
nonfermenting gram-negative bacilli. Many of the tests used
in this system are modifications of classical methods. Included
among them are tests for fermentation, oxidation, degradation
and hydrolysis of various substrates. In addition, there are
chromogen-linked substrates to detect enzymes used by
microbes to metabolize various substrates. The reaction
patterns are converted into a ten-digit profile number. In
addition, indole and oxidase tests are performed. The reaction
patterns for the substrates of a wide variety of gram-negative
bacilli are stored in the BBL Crystal identification database.
Identification is achieved by comparing the substrate reaction
patterns of the test isolate with those stored in the database.
The reaction patterns for the substrates can be interpreted
visually, using the Crystal light box and color chart, or with
the BBL Crystal autoreader (Becton Dickinson). Two
calculations are made—biotype validity and a confidence
value. The BBL Crystal autoreader is designed to read
Crystal miniaturized systems and subsequently transfer the
automated readings to a personal computer for identifica-
tion with the database. The advantage of using the BBL
Crystal autoreader is it eliminates subjective human inter-
pretation of the readings; in addition, it increases speed and
eases execution. The BBL Crystal enteric/nonfermenter ID
system (Becton Dickinson) is generally accepted as a reli-
able method for identifying gram-negative bacilli [5–7].
The objective of our study was to use clinical isolates to test
whether the BBL Crystal autoreader generates consistent
results compared to manual reading of the substrate reaction
patterns.
A total of nine ATCC reference strains were included as
quality controls (ATCC17925 Acinetobacter lwoffii,
ATCC5030 Enterobacter cloacae, ATCC25922 Escherichia
coli, ATCC33495 Klebsiella pneumoniae, ATCC8427
Proteus vulgaris, ATCC35032 Pseudomonas aeruginosa,
ATCC13525 Pseudomonas fluorescens, ATCC49128
Pseudomonas putida, ATCC13637 Stenotrophomonas
maltophilia). These ATCC reference strains were correctly
identified using the BBL Crystal enteric/nonfermenter
identification system in combination with either visual
interpretation or utilization of the BBL Crystal autoreader.
Visual interpretation was performed separately by three
experienced laboratory technicians.
In total, we tested 200 gram-negative bacillus strains
isolated from urine (n=80), sputum (n=55), blood (n=20) or
tissue samples (n=45) according to the manufacturer’s
instructions. We subsequently interpreted the results both
visually and automatically using the BBL Crystal autoreader.
The isolates were considered representative of those com-
monly encountered in the clinical laboratory and included 150
Enterobacteriaceae and 50 glucose nonfermenting bacilli. The
gram-negative bacilli we included were independent isolates
that were recently obtained from clinical specimens processed
in the medical microbiology laboratory of our hospital. These
clinical isolates included K. pneumoniae (n=16), Klebsiella
oxytoca (n=10), Salmonella spp. (n=12), Shigella spp. (n=3),
Shigella sonnei (n=2), E. coli (n=19), Enterobacter aerogenes
Eur J Clin Microbiol Infect Dis (2007) 26:443–444
DOI 10.1007/s10096-007-0317-1
J. R. Lo-Ten-Foe (*) :M. A. C. Ververs :A. G. M. Buiting
Division of Medical Microbiology,
St. Elisabeth Ziekenhuis Tilburg,
Hilvarenbeeksweg 60,
5000 AS Tilburg, The Netherlands
e-mail: j.lotenfoe@elisabeth.nl
(n=12), Enterobacter cancerogenus (n=1), E. cloacae (n=
12), P. vulgaris (n=5), Proteus penneri (n=1), Proteus
mirabilis (n=12), Serratia marcescens (n=10), Serratia
liquefaciens (n=1), Serratia odorifera (n=1), Citrobacter
freundii (n=5), Citrobacter amalonaticus (n=2), Citrobacter
koseri (n=5), Yersinia enterocolitica (n=2), Hafnia alvei
(n=4), Providencia rettgeri (n=1), Providencia alcalifaciens
(n=1), Providencia rustigiani (n=1), Morganella morganii
(n=8), Aeromonas hydrophila (n=1), Pasteurella multocida
(n=3). Glucose nonfermenting clinical isolates included
P. aeruginosa (n=18), P. putida (n=1), Pseudomonas stutzeri
(n=1), S. maltophilia (n=12), A. lwoffii (n=5), Sphingomonas
paucimobilis (n=1), Acinectobacter baumannii (n=9),
Plesiomonas shigelloides (n=1), Chryseobacterium indolo-
genes (n=2). Discrepancies between the methods of interpre-
tation were resolved by confirming the identity of the clinical
strains using phenotypic testing methods or 16S rDNA
sequencing as described by Vaneechoutte et al. [8].
Discrepancies were noted in three isolates. One P. putida
strain was visually interpreted as P. stutzeri (confidence
value 0.4916) or P. fluorescens (confidence value 0.3406),
while the BBL Crystal autoreader identified it as P.
aeruginosa (confidence value 0.4612), P. putida (confi-
dence value 0.3034), or P. fluorescens (confidence value
0.2022). Neither method of interpretation resulted in correct
identification to the species level, indicating the BBL
Crystal enteric/nonfermenter ID system has a limited ability
to correctly identify this strain. In the second case an E. coli
strain was identified correctly with visual interpretation, but
interpretation using the BBL Crystal autoreader resulted in
an unacceptable profile. Retesting the sample with the BBL
Crystal enteric/nonfermenter identification system followed
by both methods of interpretation resulted in an unaccept-
able profile with visual interpretation and a correct
identification in the BBL Crystal autoreader. In the third
case, a H. alvei strain yielded an unacceptable profile with
both methods of interpretation. If we omit the first and third
cases, considering them reflections of the limitation of the
BBL identification Crystal enteric/nonfermenter identifica-
tion system itself rather than a failure of the two interpre-
tation methods, we find a concordance of 99.5% between
the BBL Crystal autoreader and visual interpretation.
Investigation of the differences in the ten-digit codes
generated by either visual interpretation or the BBL Crystal
autoreader, revealed no obvious bias in either method.
Based on these data, we conclude that the BBL Crystal
autoreader performs well as an alternative to the visual
interpretation of the BBL Crystal reaction patterns in a
clinical setting. The major advantages of this method are its
increased speed and the elimination of subjective human
interpretation of the readings. The BBL Crystal autoreader
would be a useful addition to the microbiology laboratories
of most hospitals.
References
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Comparative evaluation of automated reading versus visual interpretation with the BBL Crystal enteric/nonfermenter identification system in a clinical setting

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Comparative evaluation of automated reading versus visual interpretation with the BBL Crystal enteric/nonfermenter identification system in a clinical setting

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