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Journal of Clinical Microbiology, November 2000, p. 4167-4170, Vol. 38, No. 11
Department of Pathology, University of Texas
Medical Branch, Galveston, Texas 77555-0740
Received 23 June 2000/Returned for modification 27 July
2000/Accepted 22 August 2000
The performances of two continuously monitoring mycobacterial
culture systems
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Comparison of the BACTEC MGIT 960 and ESP Culture
System II for Growth and Detection of Mycobacteria
ESP Culture System II (ESP II; Trek Diagnostics, Inc.,
Westlake, Ohio) and BACTEC MGIT 960 (BD Biosciences, Sparks, Md.)
were
compared. In addition to both liquid media, all specimens were plated
onto Middlebrook 7H11/7H11 selective agar. A total of 3,151 specimens
of all types (56.3% were respiratory specimens) were cultured; 231 (7.3%) yielded mycobacteria. The most common species recovered were
Mycobacterium avium complex (69 isolates) and
Mycobacterium tuberculosis complex (MTBC; 65 isolates). The recovery rates for ESP II, BACTEC MGIT 960, and Middlebrook agar, respectively, were 71.2, 63.9, and 61.8% for all mycobacteria; 70.2, 72.6, and 66.3% for all mycobacteria except Mycobacterium gordonae; and 73.8, 84.6, and 87.7% for MTBC. For liquid plus solid medium combinations, recovery rates for all mycobacteria and for
MTBC, respectively, were 84.1 and 92.3% for ESP II plus Middlebrook
agar and 81.5 and 98.5% for BACTEC MGIT 960 plus Middlebrook agar. The
differences in recovery of all mycobacteria by ESP II and by BACTEC
MGIT 960 were not significant; for the individual species, the only
significant difference was recovery of more isolates of M. gordonae by ESP II. For those isolates recovered in both
automated systems, mean times to detection of all mycobacteria and
MTBC, respectively, were 15.8 and 17.4 days for ESP II and 12.5 and
11.9 days for BACTEC MGIT 960 (P < 0.05).
False-positive signals occurred with 23 (0.7%) BACTEC MGIT 960 cultures and 84 (2.7%) ESP II cultures (P < 0.01).
Overall contamination rates were 17.1% for BACTEC MGIT 960, 18.9% for
ESP II, and 11.0% for Middlebrook agar. In summary, the ESP II and
BACTEC MGIT 960 systems performed comparably with regard to growth and
detection of mycobacteria, and the contamination rates were similar.
However, with ESP II, times to detection of all mycobacteria and of
MTBC were significantly longer, the recovery rate of M. gordonae was significantly higher, and the number of
false-positive signals was greater than with BACTEC MGIT 960.
*
Corresponding author. Mailing address: Department of
Pathology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0740. Phone: (409) 772-4851. Fax: (409) 772-5683. E-mail: nmwillia{at}utmb.edu.
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