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Antimicrobial Agents and Chemotherapy, October 2002, p. 3283-3285, Vol. 46, No. 10
0066-4804/02/$04.00+0 DOI: 10.1128/AAC.46.10.3283-3285.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Comparison of In Vitro Activities of Gatifloxacin and Ciprofloxacin against Four Taxa of Rapidly Growing Mycobacteria
Barbara A. Brown-Elliott,* Richard J. Wallace, Jr., Christopher J. Crist, Linda Mann, and Rebecca W. Wilson
Department of Microbiology, University of Texas Health Center, Tyler, Texas 75708
Received 6 May 2002/
Returned for modification 23 May 2002/
Accepted 9 July 2002

ABSTRACT
By using current NCCLS broth microdilution methods, we found
that gatifloxacin inhibited 90% of the isolates of the
Mycobacterium fortuitum group at

0.12 µg/ml and 90% of the
Mycobacterium chelonae isolates at

4 µg/ml. Gatifloxacin was generally
fourfold more active than ciprofloxacin. We recommend that both
gatifloxacin and ciprofloxacin be tested routinely against rapidly
growing mycobacteria.

TEXT
The fluoroquinolones have become increasingly important in the
treatment of infections due to mycobacteria. Previous studies
involving a wide variety of clinical bacterial isolates and
the new 8-methoxy quinolone, gatifloxacin, have shown that gatifloxacin
is more active than ciprofloxacin against untreated strains
(
1,
5) and that its activity (MIC) is less affected overall
by mutations responsible for increasing quinolone resistance.
Thus, we undertook a comparative study of the in vitro susceptibilities
of the rapidly growing mycobacteria (RGM) to gatifloxacin and
ciprofloxacin.
(A portion of this study was presented at the 41st Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, Ill., 16 to 19 December 2001.)
We tested ciprofloxacin and gatifloxacin against 124 random clinical isolates of RGM. Isolates included Mycobacterium abscessus (24 isolates), M. chelonae (32 isolates), the M. fortuitum group (39 isolates, including 20 isolates of M. fortuitum, 7 isolates of M. peregrinum, 3 isolates of M. mageritense, 4 isolates of sorbitol-positive M. fortuitum third biovariant, and 5 isolates of sorbitol-negative M. fortuitum third biovariant), M. smegmatis group (3 isolates of M. wolinskyi and 2 isolates each of M. smegmatis sensu stricto and M. goodii) (2), M. immunogenum (2 isolates) (16), and M. mucogenicum (20 isolates). Susceptibilities were determined only once for each isolate.
The American Type Culture Collection (ATCC) strains of RGM studied included M. fortuitum ATCC 6841T, M. peregrinum ATCC 14467T, M. peregrinum ATCC 700686, M. abscessus ATCC 19977T, M. chelonae ATCC 35752T, M. smegmatis sensu stricto ATCC 19420T, M. wolinskyi ATCC 700010T, M. goodii ATCC 700504T, sorbitol-positive M. fortuitum third biovariant ATCC 49403, and sorbitol-negative M. fortuitum third biovariant ATCC 49404.
RGM were identified by using conventional methods, including drug susceptibility patterns (15), carbohydrate utilization tests, and PCR restriction enzyme analysis of a 439-bp sequence (Telenti fragment) of the 65-kDa hsp gene (8, 10).
MICs were determined by use of the NCCLS-approved broth microdilution technique (6, 7). MICs of gatifloxacin were 0.12 to 32 µg/ml, while those of ciprofloxacin were 0.12 to 16 µg/ml (one lot number of panels used contained concentrations of ciprofloxacin of
0.25 to 16 µg/ml). The MIC breakpoints indicating susceptibility, moderate susceptibility (intermediate), and resistance to gatifloxacin were
2, 4, and
8 µg/ml, and those for ciprofloxacin were
1, 2, and
4 µg/ml (the NCCLS breakpoints for Enterobacteriaceae and Staphylococcus species) (6). Gatifloxacin breakpoints for RGM have not yet been addressed by the NCCLS (7).
For quality control tests, Staphylococcus aureus ATCC 29213 and Escherichia coli ATCC 25922 were used. Acceptable MIC ranges for S. aureus ATCC 29213 are 0.03 to 0.12 and 0.12 to 0.5 µg/ml for gatifloxacin and ciprofloxacin, respectively. Acceptable MIC ranges for E. coli ATCC 25922 are 0.008 to 0.03 and 0.004 to 0.016 µg/ml for gatifloxacin and ciprofloxacin, respectively (6).
Results for the major species (groups) of pathogenic RGM are shown in Tables 1 and 2. Generally, the MICs of gatifloxacin for all of the RGM except M. abscessus were 1 to 4 dilutions lower than those of ciprofloxacin.
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TABLE 1. Comparison of ranges, MIC50s, MIC90s, and percentages of gatifloxacin- and ciprofloxacin-susceptible mycobacteria
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For the
M. fortuitum group, 39 of 39 (100%) of the isolates
were susceptible to gatifloxacin at MICs of

0.5 µg/ml,
whereas only 32 of 39 (82%) were susceptible to ciprofloxacin
at

0.5 µg/ml (Table
2).
Of the M. chelonae isolates, 31 of 32 (97%) were susceptible or intermediate to gatifloxacin at an MIC of
4 µg/ml, compared to 1 of 32 (6%) to ciprofloxacin at 2 µg/ml and 17 of 32 (59%) to ciprofloxacin at 4 µg/ml.
Of the 24 isolates of M. abscessus tested against gatifloxacin, only 21% were intermediate or susceptible, while 12% of the same isolates tested against ciprofloxacin were such.
The gatifloxacin MICs for all seven isolates of the three members of the M. smegmatis group (M. smegmatis sensu stricto [3], M. wolinskyi [2], and M. goodii [2]) were
0.12 µg/ml (data not shown). The MICs required for 50% inhibition (MIC50s) of M. smegmatis sensu stricto, M. goodii, and M. wolinskyi were 1,
0.12, and 1 µg/ml, respectively (data not shown).
The ciprofloxacin and gatifloxacin MIC test results for 10 mycobacterial ATCC isolates are shown in Table 3. Quality control results were within the acceptable ranges defined by the NCCLS (6, 7).
The only oral drugs currently available for
M. chelonae that
inhibit >90% isolates at clinically active levels are the
macrolides (clarithromycin or azithromycin) (
3,
12) and linezolid
(
4,
13). Clarithromycin is the drug of choice for disease caused
by
M. chelonae, but monotherapy has a significant risk for mutational
resistance (estimated to be 10 to 15%) in the setting of disseminated
cutaneous disease in immunosuppressed individuals (
9,
14). Linezolid
use is limited by its high cost and concerns for long-term hematologic
toxicity (
4,
13). On the basis of the present results, gatifloxacin
is the third oral agent to inhibit >90% of
M. chelonae isolates
at clinically achievable levels.
Currently there are no clinical data available for results of treatment with gatifloxacin for infections caused by RGM.
The NCCLS has recommended that the fluoroquinolone ciprofloxacin be tested against the RGM (7) but clearly has not predicted gatifloxacin activity against M. chelonae. We recommend that both gatifloxacin and ciprofloxacin be routinely tested against the RGM at the concentrations in broth previously noted.
Since the gatifloxacin MICs for the M. fortuitum group isolates are lower than those of ciprofloxacin, these isolates may be less likely to develop clinical resistance to gatifloxacin following a single mutational event. As this resistance is a problem with M. fortuitum and the earlier fluoroquinolones, the use of monotherapy with the M. fortuitum group is precluded (11).

ACKNOWLEDGMENTS
We thank both Bristol-Myers Squibb for its support of this research
and Joanne Woodring for preparing the manuscript.

FOOTNOTES
* Corresponding author. Mailing address: Department of Microbiology at the University of Texas Health Center, 11937 US Hwy 271, Tyler, TX 75708. Phone: (903) 877-7685. Fax: (903) 877-7652. E-mail:
barbara.elliott{at}uthct.edu.


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Antimicrobial Agents and Chemotherapy, October 2002, p. 3283-3285, Vol. 46, No. 10
0066-4804/02/$04.00+0 DOI: 10.1128/AAC.46.10.3283-3285.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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