Objective: Daptomycin-resistance in environmental actinomycetes was studied to provide warning systems for emerging clinical resistance.
Methods: In total 49 soil and 10 endophytic acitnomycetes were used in this study. The daptomycin resistant strains were identified by measuring daptomycin resistance profile. Subsequently, daptomycin inactivating assay was preformed to distinguish resistance from other nondestructive mechanisms. Then, the strains of interest were determined by morphology and 16S rRNA gene sequence analysis. Finally, PCR analysis was used to detect the daptomycin acylase gene (dpa) encoding daptomycin acylase in those strains.
Results: All strains tested in this study were resistant towards daptomycin. Of them 24 soil acitnomycetes and 4 endophytic actinomycetes had the ability to inactivate daptomycin, while the remaining strains used other measures to confer resistance. Sequence analysis demonstrated that strains inactivating daptomycin were Streptomyces, Micromonospora and Norcadia. PCR analysis shows that 17.9% strains contained the dpa.
Conclusion: There is very high percentage of resistance in environmental actinomycetes and inactivating daptomycin is one of the main resistant mechanisms.