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J Clin Microbiol. 1989 April; 27(4): 654-656

Poor performance of BACTEC NR 730 blood culture system in early detection of Neisseria meningitidis.

Microbiology Laboratory, Children's Hospital Medical Center, Oakland, California 94609.

ABSTRACT

During an 8-month period at Children's Hospital, Oakland, Calif., a 9% rate for positive blood culture for children with Neisseria meningitidis meningitis was identified. The blood culture system used in each case was the BACTEC NR 730. This rate seemed significantly lower than previous rates (33 to 55%) (P.R. Dodge and M.N. Swartz, N. Engl. J. Med. 272:1003-1010, 1965; A.L. Hoyne and R.H. Brown, Ann. Intern. Med. 28:248-259, 1948; S. Levin and M.B. Painter, Ann. Intern. Med. 64:1049-1057, 1966). The low rate prompted our study. With 14 test strains, anaerobic and aerobic BACTEC bottles were evaluated for their ability to support and detect the growth of N. meningitidis. Sodium polyanetholesufonate (SPS) and inoculum size, two factors thought to affect the growth of N. meningitidis, were controlled for by use of bottles with and without SPS and by inoculum sizes simulating the magnitudes of bacteremia previously described for children infected with N. meningitidis (L.J. La Scolea, Jr., D. Dryja, T.D. Sullivan, L. Mosovich, N. Ellerstein, and E. Neter, J. Clin. Microbiol. 13:478-482, 1981). BACTEC failed to detect growth in aerobic bottles after 6 h of incubation, while 76 of 80 bottles (95%) showed growth when subcultured. At 24 h, BACTEC detected growth in only 29 of 80 bottles (36%); when subcultured, all 80 cultures grew confluently. At 48 h, BACTEC detected growth in the remaining 53 bottles. BACTEC failed to detect growth in anaerobic bottles at 6 h and at 1, 2, 4, and 5 days of incubation despite growth in subculture. Subcultures from bottles with tryptic soy broth with and without SPS showed growth in 63 to 76 bottles in 6 h and in all bottles after 24 h. The presence of SPS in BACTEC bottles had no effect on growth detection. On the basis of these studies and our clinical experience, we find the NR 730 system to be insensitive and unsuitable for detection of N.meningitidis in </= 24h. However, all test strains were detected after 48h.