Susceptibility of Clinical Isolates of Xanthomonas maltophilia(Xm) to Newer Antimicrobial Agents with Evidence of Increasing Resistance to -Lactams.

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

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

Infections caused by Xm have been increasingly recognized in compromised patient populations. We determined the susceptibilities of 153 non-duplicate isolates collected between late 1990 and early 1994 using the agar dilution method according to NCCLS guidelines. Agents tested included ciprofloxacin(Cp), clinafloxacin(Cn), levofloxacin(L), sparfloxacin(S), pefloxacin(p), DU-6859a(DU), WIN 57273(WIN), PD 127596(PD), plus 11 other agents - minocylcine(M), doxycline(D), chloramphenicol(C), ticarcillin/clavulante(T/C), amikacin(A), trimethoprim-sulphamethoxazole(T/S), cefotaxime(CTX), ceftazidime(CTZ), tobramycin(T), piperacillin(Pip), and piperacillin/tazobactam(P/T). The MIC₅₀/MIC₉₀ (g/ml) for the most active agents were as follows: 0.5/2.0(M); 32/64(T/C); <0.25/1.25/<0.25/1.25 (T/S); 16/128(CTZ); 16/128 (Pip); 16/128 (p/T); 1/8 (Cp); 0.06/0.25 (Cn); 0.5/2.0 (L); 0.125/1.0 (S); 2.0/8.0 (P); and 0.125/0.5 (DU). The level of susceptibility to piperacillin (MIC <64 g/ml) and ceftazidime (< 8 g/ml) decreased from 87% to 36% and 36% to 26% respectively from 1990-91 to 1993-94. There was an increase in susceptibility to ciprofloxacin with 26% and 47% of isolates being susceptible (MIC< 1 g/ml) for similar time periods. For 51 strains with and MIC to Cp >2.0 g/ml, 51% and 65% of the strains were susceptible to DU and CN at 0.125 g/ml and 84% and 86% respectively were susceptible at 0.5 g/ml. We conclude that T/S, T/C, Cn, DU, and S are the most active agents vs Xm and that resistance to -lactams has increased in our institution.