We sought to characterize the antibiotic susceptibility of strains of Stenotrophomonas maltophilia (SMA) isolated from clinical samples, and the role of SMA biofilm in antibiotic resistance.
Fifty-one clinical SMA isolates were obtained from patients with nosocomial infection in the surgical wards and ICUs of six general hospitals in Tianjin, China. In vitro models of SMA biofilms were established and confirmed by scanning electron microscopy (SEM) and fluorescence microscopy (FSM) with silver staining. The minimal inhibitory concentrations (MIC) and biofilm inhibitory concentrations (BIC) of commonly used antibiotics were determined.
47 of 51 strains were resistant to three or more antibiotics. 42 of 51 strains formed SMA biofilms in vitro. SMA biofilm formation greatly reduced sensitivity to most tested antibiotics, but not to levofloxacin (LEV). However, in the presence of erythromycin (ERY) SEM revealed that LEV inhibited SMA biofilm formation. Factorial ANOVA revealed that erythromycin (ERY) enhanced susceptibility to LEV, cefoperazone/sulbactam (SCF), and piperacillin (PIP) (p<0.05), and an ΔE model revealed that LEV and ERY acted synergistically in biofilms, suggesting specific use of combined macrolide therapy may represent an effective treatment for SMA infection.
Antibiotics could act synergistically to combat the protection conferred to clinical isolates of SMA by biofilms. Macrolide antibiotics may be effective where used in combination.