A. Pascual et al., COMPARISON OF BROTH MICRODILUTION AND E-TEST FOR SUSCEPTIBILITY TESTING OF NEISSERIA-MENINGITIDIS, Journal of clinical microbiology, 34(3), 1996, pp. 588-591
The susceptibilities of 54 clinical isolates of Neisseria meningitidis
to penicillin, cefotaxime, ceftriaxone, cefepime, imipenem, ciproflox
acin, chloramphenicol, and rifampin were determined by the microdiluti
on method in both cation-adjusted Mueller-Hinton broth (CAMHB) and Hae
mophilus test medium (HTM). Poor growth was observed in 16.6 and 9% of
the strains in CAMHB and HTM, respectively. As a result, the growth o
f the 54 N. meningitidis strains was evaluated in three other commerci
ally available batches of CAMHB and in one in-house batch of HTM. Poor
growth was observed for 9.3 to 16.6% of the strains in all four batch
es, More important, three of the CAMHB batches failed to support growt
h for 3.7 to 33.3% of the strains; 3.7% of the strains did not grow in
the in-house-prepared HTM. Ten (18.7%) strains were relatively resist
ant to penicillin (RRP; MIC, >0.125 mu g/ml) in CAMHB and 13 (24%) str
ains were RRP in HTM. The percentages of agreement obtained by using C
AMHB as the reference ranged from 78% for cefepime to 100% for ceftria
xone, Seven minor errors were observed for penicillin; five of them we
re for strains susceptible to penicillin in CAMHB and RRP in HTM. All
strains were susceptible to the other antimicrobial agents evaluated.
The growth of N. meningitidis was also evaluated in four batches of Mu
eller-Hinton agar (MHA). In two of them, 3.7 and 44.4% of the strains
did not grow, and considering all four batches, 5,5 to 11.1% grew poor
ly. All strains grew adequately in MHA supplemented with blood (MHA-b)
. The activities of penicillin and cefotaxime were also evaluated by t
he E-test in MHA and MHA-b. The proportion of RRP strains were 24% in
MHA and 59% in MHA-b. For penicillin, the percentages of agreement of
the E-test with the microdilution method in CAMHB (reference) were 64.
8 and 70.3% in MHA and MHA-b, respectively. For cefotaxime, the agreem
ent was 98.1%. Minor errors for the penicillin MIC were detected for 3
8% of the strains tested. Further studies are needed to define adequat
e culture media for reference methods to evaluate the susceptibility o
f N, meningitidis to antimicrobial agents.