Distribution of smf-1, rmlA, spgM and rpfF genes among Stenotrophomonas maltophilia isolates in relation to biofilm-forming capacity.

The molecular mechanisms involved in biofilm formation inStenotrophomonas maltophilia are poorly understood. Here, we examined whether the presence of smf-1, rmlA, spgM and rpfF genes is associated with biofilm formation and antibiotic resistance in S. maltophilia. A total of 150 S. maltophilia isolates were collected from three tertiary-care hospitals in Iran and were identified through PCR amplification of the 23S rRNA gene. Biofilm formation was determined by microtitre plate assay. Presence of smf-1, rmlA, spgM and rpfF genes was examined by PCR. Among the isolates examined, 148 (98.7%) were able to produce biofilm, of which 69 (46.0%) were strong biofilm-producers, whereas 32 (21.3%) and 47 (31.3%) were moderate and weak biofilm-producers, respectively. The frequency ofsmf-1, rmlA, spgM and rpfF was 99.3%, 98.0%, 97.3% and 70.0%, respectively. Statistical analysis indicated a direct correlation between presence of the rpfF gene and biofilm formation (P < 0.001). The high prevalence of smf-1 (99.3%) among the isolates is noted and there was a significant association between smf-1 and biofilm-forming ability (P < 0.01), but lower than rpfF. Additionally, a direct association was found between resistance to ticarcillin/clavulanate, ceftazidime, ciprofloxacin and doxycycline and strong biofilm formation in the S. maltophilia isolates (P < 0.01). This study demonstrated thatS. maltophilia clinical isolates significantly differ in biofilm-forming ability. Moreover, presence of rpfF and smf-1, but not spgM, could be associated with biofilm formation. This study highlights the importance of rpfF in formation of biofilm compared with the other genes involved.

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