Mechanism of Resistance Development in E. coli against TCAT, a Trimethoprim-Based Photoswitchable Antibiotic

During the last decades, a continuous rise of multi-drug resistant pathogens has threatened antibiotic efficacy. To tackle this key challenge, novel antimicrobial therapies are needed with increased specificity for the site of infection. Photopharmacology could enable such specificity by allowing for the control of antibiotic activity with light, as exemplified by trans/cis-tetra-ortho-chloroazobenzene-trimethoprim (TCAT) conjugates. Resistance development against the on (irradiated, TCATa) and off (thermally adapted, TCATd) states of TCAT were compared to that of trimethoprim (TMP) in Escherichia coli mutant strain CS1562. Genomics and transcriptomics were used to explore the acquired resistance. Although TCAT shows TMP-like dihydrofolate reductase (DHFR) inhibition in vitro, transcriptome analyses show different responses in acquired resistance. Resistance against TCATa (on) relies on the production of exopolysaccharides and overexpression of TolC. While resistance against TCATd (off) follows a slightly different gene expression profile, both indicate hampering the entrance of the molecule into the cell. Conversely, resistance against TMP is based on alterations in cell metabolism towards a more persister-like phenotype, as well as alteration of expression levels of enzymes involved in the folate biosynthesis. This study provides a deeper understanding of the development of new therapeutic strategies and the consequences on resistance development against photopharmacological drugs

Odontogenic Epithelium: Immunolabeling of Ki-67, EGFR and Survivin in Pericoronal Follicles, Dentigerous Cysts and Keratocystic Odontogenic Tumors

The aim of this study was to evaluate the biological profile of odontogenic epithelium by immunolabeling of epidermal growth factor receptor (EGFR), Ki-67 and survivin in keratocystic odontogenic tumors (KOT), dentigerous cysts (DC), and pericoronal follicles (PF). Immunohistochemical analysis was performed in 13 KOTs, 14 DCs and 9 PFs. Immunolabeling was analyzed in the basal and suprabasal layers of KOTs and DCs, and in the islands of odontogenic epithelium and/or reduced enamel epithelium of PFs. KOTs showed the highest proliferation rate among the three groups, mainly in suprabasal layers. EGFR immunolabeling was observed mainly in the cytoplasm in basal and suprabasal layers of KOTs and in the suprabasal layer of DCs. Immunolabeling in both membrane and cytoplasm was greater in PFs. In PFs, membrane-only staining was observed. Survivin immunolabeling showed a greater percentage of positive cells (scoring +++) in the suprabasal layer of KOTs. In DCs, both layers showed similar percentages of cells scoring +++; PFs showed the highest percentage of these cells. In KOTs, epithelial cells showed stimulus-independent neoplastic proliferative characteristics, suggesting the presence of a suprabasal proliferative compartment, maintained by inhibition of apoptosis. In DCs, the basal layer seemed to proliferate in response to stimulus. Although PFs showed low proliferative activity, the expression of EGFR indicates that some cells have a high capacity to respond to stimuli, which could probably explain the origin of odontogenic lesions