Anti-Infectives Research Center, Department ofPathology, University ofIowa. College ofMedicine ... polis, Ind. (S. D. Allen);St. Francis Regional Medical. Center ...
Vol. 31, No. 10
JOURNAL OF CLINICAL MICROBIOLOGY, OCt. 1993, p. 2828-2830
0095-1137/93/102828-03$02.00/0 Copyright X 1993, American Society for Microbiology
Interpretive Accuracy of the Disk Diffusion Method for Testing Newer Orally Administered Cephalosporins against Morganella morganii DOUGLAS J. BIEDENBACH, RONALD N. JONES,* AND MERIDITH E. ERWIN Anti-Infectives Research Center, Department of Pathology, University of Iowa College of Medicine, Iowa City, Iowa 52242 Received 26 April 1993/Returned for modification 7 June 1993/Accepted 2 July 1993
Eight newer orally administered cephems (cefdinir, cefetamet, cefixime, cefpodoxime, cefprozil, ceftibuten, cefuroxime, and loracarbef) were tested against 100 clinical strains of MorganeUla morganii to determine the extent of serious interpretive very major (false-susceptible) errors when current criteria for the disk diffusion test are applied. Agar dilution MICs and disk diffusion tests were performed as recommended by the National Committee for Clinical Laboratory Standards (Villanova, Pa.) (NCCLS), and the methods were compared by regression analysis using the method of least squares and by error rate bounding. The following results are listed in the order of increasing error rates: cefdinir, loracarbef, and cefprozil, 97% resistance to each drug by both methods. The MICs of loracarbef for all 100 strains were >32 ,ug/ml. Cefprozil MICs ranged from 16 to 32 ,ug/ml, with the MICs for 99 strains being >32 ,ug/ml, and cefdinir MICs for 94 strains were >8 ,ug/ml (range, 1 to 8 ,ug/ml). These results are generally consistent with previously published findings (4, 7-9, 11). These drug-organism combinations are unlikely to have any interpretive testing problems because of the high resistance percentage of this species and because this organism complies with the established breakpoint criteria. In contrast, ceftibuten has a potent activity against M. morganii, with 77% of the strains proven susceptible by both methods. Furthermore, M. morganii strains were among the
VOL. 31, 1993
NOTES
2829
TABLE 1. Comparison of the MIC and disk diffusion test results of eight newer cephems for 100 M. morganu clinical isolatesa % by MIC category
>8
Disk category (zone criterion)b
S
S (220) I (17-19) R (C16)
1 0 0
0 0 1
0 0 98
S (218)
R (30
agar (13).
3.
vertical lines.
0.83)
is
14.
(mm)
Scattergram of cefetamet results comparing reference dilution MICs (14) with the zone diameters around 10-pg disks NCCLS interpretive criteria are represented by horizontal (15);
FIG.
and
25
20
15
plotted
The
ation regression equ,
as a dashed
line.
Barry, A. L., R. N. Jones, and the Collaborative Antimicrobial Susceptibility Testing Group. 1990. Interpretive criteria and quality control limits for ceftibuten disk susceptibility tests. J.
(y = 16.1 - 0.17x; r =
15.
Kuwahara. 1984. In vitro and in vivo antibacterial properties of FK 027, a new orally active cephem antibiotic. Antimicrob. Agents Chemother. 25:98-104. Leitner, F., T. A. Pursiano, R. E. Buck, Y. H. Tsai, D. R. Chisholm, M. Misiek, J. V. Desiderio, and R. E. Kessler. 1987. BMY 28100, a new oral cephalosporin. Antimicrob. Agents Chemother. 31:238-243. Mine, Y., T. Kamimura, and Y. Watanabe. 1988. In vitro antibacterial activity of FK482: a new orally active cephalosporin. J. Antibiot. 41:1873-1889. National Committee for Clinical Laboratory Standards. 1990. Approved standard M2-A4. Performance standards for antimicrobial disk susceptibility tests, 4th ed. National Committee for Clinical Laboratory Standards, Villanova, Pa. National Committee for Clinical Laboratory Standards. 1990. Approved standard M7-A2. Methods for dilution antimicrobial tests for bacteria that grow aerobically, 2nd ed. susceptibility National Committee for Clinical Laboratory Standards, Villanova, Pa. National Committee for Clinical Laboratory Standards. 1992. Fourth informational supplement, M100-S4. Performance standards for antimicrobial susceptibility testing. National Committee for Clinical Laboratory Standards, Villanova, Pa.
