Antimicrobial photodynamic therapy against clinical isolates of carbapenem-susceptible and carbapenem-resistant Acinetobacter baumannii
Infections caused by Acinetobacter baumannii have become a challenge for healthcare professionals because of the rapid increase in Gram-negative bacteria resistant to carbapenem antibiotics. The objective of this study was to evaluate the effect of antimicrobial photodynamic therapy (aPDT) against different strains of A. baumannii isolated from patients with infectious process and hospitalized at the intensive care unit of the hospitals of São Jose dos Campos, São Paulo. These isolates were obtained from the Valeclin Clinical Analysis Laboratory (SP, Brazil) and were tested for susceptibility to the carbapenems imipenem and meropenem by determination of the minimal inhibitory concentration (MIC) using the broth microdilution method. The strains susceptible and resistant to these antibiotics were submitted to aPDT using methylene blue and a low-level laser with a wavelength of 660 nm and fluence of 39.5 J/cm2 (energy of 15 J and time of 428 s). The number of colony-forming units (CFU/mL) was analyzed by ANOVA and the Tukey test. The laboratory of origin of the clinical isolates identified 1.54% of 13,715 strains tested over a period of 8 months as A. baumannii. Among the A. baumannii isolates, 58% were resistant to carbapenems by the disk diffusion test. Susceptible isolates exhibited MIC of 0.5 to 1 μg/mL and resistant isolates of 64 to > 128 μg/mL. PDT reduced the number of A. baumannii cells for all isolates tested, with this reduction ranging from 63 to 88% for susceptible isolates and from 26 to 97% for resistant isolates. The percentage of viability was dependent on the strain analyzed. In conclusion, these data indicate that PDT could be an alternative strategy for the control of infections caused by carbapenem-resistant A. baumannii.
KeywordsAcinetobacter baumannii Antimicrobials Antimicrobial photodynamic therapy Antimicrobial resistance
Role of funding source
This study was supported by the São Paulo Council of Research - FAPESP, Brazil (Grant 2014/03937-6).
M.M.M received a doctoral fellowship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil).
P.P.B received a doctoral fellowship from FAPESP, Brazil (Grant 2012/15250-0).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no competing interests.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This study was approved by the Ethics Committee (Process: 24409813.9.0000.0077) of the Institute of Science and Technology of Univ. Estadual Paulista (ICT/UNESP).
This article does not contain any studies with animals performed by any of the authors.
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