Antibiotic Synergistic Interaction Against Multidrug Resistant <i>Stenotrophomonas Maltophilia</i> Strains From Environmental Settings

Abstract

The susceptibility profile of Stenotrophomonas maltophilia strains showed a high phenotypic homogeneity despite their high genomic diversity. Most of the isolates tested were resistant to three or more antibiotics belonging to five different groups. S. maltophilia isolates were resistant to aztreonam (91.3 %), cefepime (85.9%), ceftazidime (86.6 %), ciprofloxacin (81.8 %), gentamicin (88.8 %), levofloxacin (84.8 %), meropenem (93.5 %) and piperacillin/tazobactam (92.9 %). Among the antibiotics tested, ticarcillin/clavulanate acid and trimethoprim/sulfamethoxazole were effective against 88.1% and 92.5% of the isolates respectively. Ninety percent of the isolates were susceptible to trimethoprim-sulfamethoxazole, with MICs at which 50 and 90% of isolates were inhibited (MIC₅₀ and MIC₉₀) of 0.5 and 2 μg ml^-1, respectively). Time-kill studies revealed that ticarcillin/clavulanate was bactericidal against S. maltophilia after 3 h of incubation at concentrations equivalent to twice the MIC and 4 times the MIC. Synergism was demonstrated by most pairs of antimicrobial agents. Ticarcillin/clavulanate plus piperacillin/tazobactam inhibited 71.6% of the strains, while trimethoprim/sulfamethoxazole plus ticarcillin/clavulanate inhibited 82.9%, ciprofloxacin plus piperacillin/tazobactam inhibited 69.4% of the strains. Our findings confirm that S. maltophilia exhibited high degree of resistance to the antibiotics tested, and show that trimethoprim /sulfamethoxazole and ticarcillin/clavulanate had good activity against S. maltophilia.

 Keywords: Bactericidal, synergy, infectious disease, bacteristatic, virulence factors