Detecção e caracterização de virulência e de resistência a drogas antimicrobianas de isolados nosocomiais de Stenotrophomonas maltophilia

Abstract

Stenotrophomonas maltophilia is an important opportunistic and emerging pathogen commonly related to nosocomial infections and found in different environmental sources, including hospital settings. This microorganism is recognized for presenting intrinsic resistance to a range of important antimicrobials as well as to acquire resistance by horizontal gene transfer, which reduces the effective options for the treatment of infections caused by this organism. Therefore, the aim of this study was to determine the presence of S. maltophilia in the nosocomial environment and characterize the resistance of the environmental isolates, as well as clinical isolates obtained in the same hospital. Then, environmental samples were collected in the general ICU and the Unified Health System hospitalization unit of the São Lucas Hospital, Porto Alegre, Brazil. In addition, 100 clinical isolates were sent by the Clinical Pathology Laboratory of the same hospital. All samples were analyzed using a specific protocol for S. maltophilia detection by PCR developed in this study targeting 23S rRNA gene. Subsequently, the antimicrobial resistance was evaluated against ceftazidime, chloramphenicol, levofloxacin, minociclin and trimethoprim/sulfamethoxazole (TMP/SMX). The presence of integrons was verified in all isolates and those that presented reduced susceptibility to TMP/SMX was evaluated the presence of sul1 and sul2 gene, as well as was determined the plasmid profile. All isolates were submitted to detection of smf-1 gene. Among the 936 samples collected in the nosocomial environment, S. maltophilia was identified in 28. High rates of susceptibility to minocycline, levofloxacin and chloramphenicol were observed, and all of the 19 isolates that presented reduced susceptibility to TMP/SMX carried the sul1 gene, 14 of them presented class 1 integron and nine isolates showed simultaneously sul1 and sul2. All isolates that carried the sul2 gene also presented the 7.3 kb plasmid. The smf-1 gene was detected in 31 S. maltophilia isolates. The presence of S. maltophilia in hospital environment and medical devices indicates the permanence of this microorganism in the nosocomial environment, what can constitute a risk to infection for other hospitalized patients. In addition, the data obtained in this study in relation to TMP/SMX susceptibility can suggest that the resistance to these drugs have the tendency to increase, especially due to resistance determinants to these drugs can be associated to mobile genetic elements, which may facilitate horizontal transfer and the spread of these resistance genes.