SUSCEPTIBILITY TO NEW FLUOROQUINOLONES OF XANTHOMONAS (STENOTROPHOMONAS) MALTOPHILIA (Xm) ISOLATES AT THE TORONTO HOSPITAL 1991-1994.

A.M. Phillips*, J. Strauss, J. Burt, J.M. Conly,

Department of Microbiology, The Toronto Hospital, University of Toronto, Toronto, Ontario.

Recent evidence suggest that Xm represents a unique therapeutic challenge due to its increasing appearance as a pathogen in severely immunocompromised patients and its resistance to multiple antimicrobial agents. With the recognition of a multi-year multi-unit outbreak of respiratory tract colonization and infection with Xm at our institution the in-vitro susceptibilities to the new fluoroquinolones were examined to determine if increasing resistance to ciprofloxacin was occurring and to examine the susceptibilities to other potential fluoroquinolones. The MIC50 and MIC90 of ciprofloxacin (Cp), clinafloxacin (Cn), levofloxacin (L), sparfloxacin (S), oxfloxacin (O), pefloxacin (P) and DU-6859a were determined on 150 non-duplicate isolates (1991-1994) using the agar dilution method according to NCCLS recommendations. The MIC50, MIC90, and MIC ranges for the compounds are as follows:

FLUOROQUINOLONE COMPOUNDS
MIC

(mg/L)

 Cp Cn L S O P DU-6859a
MIC50

MIC90

RANGE

 1.0

8.0

0.5-8.0

 0.06

0.25

0.06-1.0

 0.5

2.0

0.125-4.0

 0.125

1.0

0.125-2.0

 >8.0

>8.0

------

 2.0

8.0

1.0-32.0

 0.125

0.5

0.03-1.0

There was no apparent increase in the susceptibility to ciprofloxacin with 25.6%, 47.9%, and
47.3% of all isolates being susceptible at a MIC <1 mg/L for each of the years of the study 1991-1993, respectively, for which complete data was available. From these data, we conclude that the newer fluoroquinolones, DU-6859a, clinafloxacin, levofloxacin and sparfloxacin are most active against Xm and that over a 3 year period no apparent increase in ciprofloxacin resistance has been noted in our institution.

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