RESUMEN
The acquisition of bla OXA genes encoding different carbapenem-hydrolyzing class-D ß-lactamases (CHDL) represents a main determinant of carbapenem resistance in the nosocomial pathogen Acinetobacter baumannii. The blaOXA-58 gene, in particular, is generally embedded in similar resistance modules (RM) carried by plasmids unique to the Acinetobacter genus lacking self-transferability. The ample variations in the immediate genomic contexts in which blaOXA-58 -containing RMs are inserted among these plasmids, and the almost invariable presence at their borders of non-identical 28-bp sequences potentially recognized by the host XerC and XerD tyrosine recombinases (pXerC/D-like sites), suggested an involvement of these sites in the lateral mobilization of the gene structures they encircle. However, whether and how these pXerC/D sites participate in this process is only beginning to be understood. Here, we used a series of experimental approaches to analyze the contribution of pXerC/D-mediated site-specific recombination to the generation of structural diversity between resistance plasmids carrying pXerC/D-bounded bla OXA-58- and TnaphA6-containing RM harbored by two phylogenetically- and epidemiologically-closely related A. baumannii strains of our collection, Ab242 and Ab825, during adaptation to the hospital environment. Our analysis disclosed the existence of different bona fide pairs of recombinationally-active pXerC/D sites in these plasmids, some mediating reversible intramolecular inversions and others reversible plasmid fusions/resolutions. All of the identified recombinationally-active pairs shared identical GGTGTA sequences at the cr spacer separating the XerC- and XerD-binding regions. The fusion of two Ab825 plasmids mediated by a pair of recombinationally-active pXerC/D sites displaying sequence differences at the cr spacer could be inferred on the basis of sequence comparison analysis, but no evidence of reversibility could be obtained in this case. The reversible plasmid genome rearrangements mediated by recombinationally-active pairs of pXerC/D sites reported here probably represents an ancient mechanism of generating structural diversity in the Acinetobacter plasmid pool. This recursive process could facilitate a rapid adaptation of an eventual bacterial host to changing environments, and has certainly contributed to the evolution of Acinetobacter plasmids and the capture and dissemination of bla OXA-58 genes among Acinetobacter and non-Acinetobacter populations co-residing in the hospital niche.
RESUMEN
Candida and dermatophyte species are the most common causes of superficial mycoses because their treatment can be difficult due to limitations of current antifungal drugs in terms of toxicity, bioavailability, interactions, narrow-spectrum activity, and development of resistance. Photodynamic therapy (PDT) involves the topical administration of a photosensitizer in combination with light of an appropriate wavelength and molecular oxygen that produces reactive oxygen species (ROS), which promote damage to several vital components of the microorganism. Tagetes species are known as a source of thiophenes, biologically active compounds whose antifungal activity is enhanced by irradiation with UVA. The present investigation evaluated Tagetes minuta extracts as a photosensitizer on growth of Candida and dermatophytes and their effect on Candida virulence factors. T. minuta root hexane and dichloromethane extracts demonstrated high photodynamic antifungal activity. Bioautographic assays and chromatographic analysis revealed the presence of five thiophenes with reported photodynamic antifungal activities under UVA. Analysis of ROS production indicated that both type I and II reactions were involved in the activity of the extracts. In addition, the extracts inhibited virulence factors of Candida, such as adherence to epithelial surfaces and germ tube formation and showed efficacy against different Candida morphologies: budding cells, cells with germ tube and biofilms. Results suggested that PDT with T. minuta extracts might become a valuable alternative to the already established antifungal drugs for the treatment of superficial fungal infections.