Investigating antimicrobial resistance pattern and detection of the sul genes in Stenotrophomonas maltophilia isolates in Bushehr, Iran

Introduction and Objectives: Stenotrophomonas maltophilia can be resistant to various antimicrobial drugs. Emerging resistance to trimethoprim-sulfamethoxazole (SXT) poses a serious threat to the therapy of infections caused by this organism. The sul and dfrA genes could contribute to the resistance to SXT. We aimed to determine antimicrobial resistance pattern and to investigate the presence of sul and dfrA genes in S. maltophilia isolates in Bushehr, Iran. Materials and Methods: A total of 87 S. maltophilia isolates (67 clinical and 20 environmental isolates) were collected in Bushehr, Iran. The clinical isolates were collected from three hospitals and the environmental isolates were collected from various sources in two hospitals and one dental clinic. The isolates were identified by biochemical methods and PCR. Antimicrobial susceptibility testing was performed by disk diffusion and determination of MIC using MIC Test Strip. To assess the presence of sul1, sul2, sul3, dfrA1, dfrA5, dfrA12, dfrA17, class 1 integron, and insertion sequence common region (ISCR) elements, PCR was performed. Results: All isolates were susceptible to minocycline and levofloxacin. Eighty-four isolates (96.6%) were susceptible to SXT and three isolates (3.4%) which were environmental, were SXT-resistant. The MIC values of SXT for three SXT-resistant isolates were ≥32μg/ml. Resistance rate to ceftazidime, ticarcillin-clavulanate, and chloramphenicol were 75.9%, 69%, and 65.5%, respectively. All three (100%) SXT-resistant isolates carried sul1 gene and class 1 integron. Among 84 SXT-susceptible isolates, 14 (16.7%) and 7 (8.3%) were sul1-positive and sul2-positive, respectively. Of the 17 sul1-positive isolates, 15 harbored class 1 integron. The sul3 and dfrA genes as well as ISCR were not detected. Conclusions: Our results support that SXT, levofloxacin, and minocycline are good therapeutic options for S. maltophilia infections in Bushehr. The presence of SXT-resistant S. maltophilia in hospital environment, suggests that it may act as a reservoir for this bacterium.

Keywords:

Stenotrophomonas maltophilia , sul genes , trimethoprim-sulfamethoxazole