Comparative In-Vitro Susceptibilities of New Quinolones Against Clinical Isolates of Xanthomonas maltophilia

J. STRAUSS*, J. BURT, A.M. PHILLIPS, J.M.CONLY

The Toronto Hospital, University of Toronto, Toronto, Ontario, Canada

Infections caused by Xanthomonas maltophilia (Xm) are increasingly recognized in patients with compromised host defence mechanisms. Available quinolones such as ciprofloxacin and ofloxacin are only marginally active against this organism. The purpose of this study was to compare the in-vitro activity of several novel fluoroquinolones with those of similar fluoroquinolones against clinically significant isolates of Xm collected between 1990 and 1993 at our institution. The MIC₅₀/MIC₉₀ of ciprofloxacin (Cp), clinafloxacin(Cn), WIN57273 (WIN), PD 127596 (PD), levofloxacin(L), sparfloxacin(S), ofloxacin(O), perfloxacin(P), and DU-6859a (DU) were determined for 151 non-duplicate isolates of Xm using the agar dilution method according to NCCLS guidelines. The MIC₅₀/MIC₉₀ for the compounds were as follows: 1.0/8.0 (CP); 0.06/0.25(Cn); 1.0/2.0(WIN; 0.5/2.0 (PD); 0.5/2.0(L); 0.125/1.0(S); >8.0/ >8.0(O); 2.0/8.0(P); and 0.125/0.5(DU). For 51 strains with an MIC to Cp of >2.0 g/ml, 51% and 84% of the strains were susceptible to DU-6859a and 65% and 86% were susceptible to clinafloxacin at MICs of 0.125 and 0.5 g/ml respectively. Among clinically significant Xm isolates, including ciprofloxacin-resistant strains, DU-6859a and clinafloxacin have considerable activity and may be useful oral quinolone agents for the treatment of infections due to this organism.