Serratia marcescens resistance profile and its susceptibility to photodynamic antimicrobial chemotherapy

Highlights • S. marcescens resistance profile and its susceptibility to PACT were performed. • Bacterial resistance increases when CLSI 2007 and CLSI 2015 were compared. • S. marcescens planktonic cultures and early biofilms are susceptible to PACT. ABSTRACT Background Some authors have reported the antimicrobial action of photodynamic antimicrobial chemotherapy (PACT) on bacteria related to nosocomial infections but there are few studies evaluating PACT on Serratia marcescens grown as planktonic cultures or as biofilms. The purpose of this study was to analyze the S. marcescens resistance profile and its susceptibility to PACT. Methods Initially, 55 S. marcescens strains isolated from environmental, oral and extra-oral infections were tested by antimicrobial resistance to cefotaxime (CTX), imipenem (IPM), ciprofloxacin (CIP), tobramycin (TOB) and doxycycline (DOX) using E-test® . Following, isolates grown as planktonic cultures or biofilms were submitted to PACT using the association of a light-emitting diode and toluidine blue (TBO). The E-test® results demonstrated intermediated sensitive strains to CTX, IMP, TOB, and DOX; and resistant strains to CTX, TOB, DOX and CIP. Also, CTX and IMP demonstrated variation when CLSI 2007 and CLSI 2015 were compared. Results Planktonic cultures and biofilms submitted to PACT demonstrated counts varying from 1011 to 107 for planktonic cultures and 1010 to 107 for biofilms. There were no statistical differences in the results when planktonic cultures and biofilms were compared. Conclusions Increase in the profile of S. marcescens resistance was observed when CLSI 2007 and CLSI 2015 were compared. Also, IMP remains as the drug with lower rate of resistance. Additionally, both S. marcescens planktonic cultures and early biofilms are susceptible to PACT under tested conditions.