The actin cytoskeleton is a dynamic structure necessary for cell and tissue organization, including the maintenance of epithelial barriers. Disruption of the epithelial barrier coincides with alterations of the actin cytoskeleton in several disease states. These disruptions primarily affect the paracellular space, which is normally regulated by tight junctions. Thereby, the actin cytoskeleton is a common and recurring target of bacterial virulence factors. In order to manipulate the actin cytoskeleton, bacteria secrete and inject toxins and effectors to hijack the host cell machinery, which interferes with host-cell pathways and with a number of actin binding proteins. An interesting model to study actin manipulation by bacterial effectors is Escherichia coli since due to its genome plasticity it has acquired diverse genetic mobile elements, which allow having different E. coli varieties in one bacterial species. These E. coli pathotypes, including intracellular and extracellular bacteria, interact with epithelial cells, and their interactions depend on a specific combination of virulence factors. In this paper we focus on E. coli effectors that mimic host cell proteins to manipulate the actin cytoskeleton. The study of bacterial effector-cytoskeleton interaction will contribute not only to the comprehension of the molecular causes of infectious diseases but also to increase our knowledge of cell biology.

EspC is a non-locus of enterocyte effacement (LEE)-encoded autotransporter produced by enteropathogenic Escherichia coli (EPEC) that is secreted to the extracellular milieu by a type V secretion system and then translocated into epithelial cells by the type III secretion system. Here, we show that this efficient EspC delivery into the cell leads to a cytopathic effect characterized by cell rounding and cell detachment. Thus, EspC is the main protein involved in epithelial cell cytotoxicity detected during EPEC adhesion and pedestal formation assays. The cell detachment phenotype is triggered by cytoskeletal and focal adhesion disruption. EspC-producing EPEC is able to cleave fodrin, paxillin, and focal adhesion kinase (FAK), but these effects are not observed when cells are infected with an espC isogenic mutant. Recovery of these phenotypes by complementing the mutant with the espC gene but not with the espC gene mutated in the serine protease motif highlights the role of the protease activity of EspC in the cell detachment phenotype. In vitro assays using purified proteins showed that EspC, but not EspC with an S256I substitution [EspC S256I ], directly cleaves these cytoskeletal and focal adhesion proteins. Kinetics of protein degradation indicated that EspCproducing EPEC first cleaves fodrin (within the 11th and 9th repetitive units at the Q1219 and D938 residues, respectively), and this event sequentially triggers paxillin degradation, FAK dephosphorylation, and FAK degradation. Thus, cytoskeletal and focal adhesion protein cleavage leads to the cell rounding and cell detachment promoted by EspC-producing EPEC.

Aim: This study investigated the susceptibility of Enterotoxigenic Escherichia coli to curcumin, as well as its synergistic effect with 12 antimicrobial drugs. Methods and Results: Our study shows that curcumin did not affect bacterial growth. The antimicrobial susceptibility of curcumin and antibiotic synergy were identified using disc diffusion on Mueller-Hinton agar. The strain of Enterotoxigenic Escherichia coli used was resistant to Ampicillin, Amoxicillin/Clavulanic acid, Ampicillin/Sulbactam, Ciprofloxacin, and Cefazolin. There was synergy between curcumin and the majority of antibiotics tested. Maximum synergy was observed with combinations of 330 µg/mL curcumin and Ceftazidime, followed by Cefotaxime, Amoxicillin/Clavulanic acid, Ampicillin, Aztreonam, Trimethoprim, Ciprofloxacin, Ceftriaxone, Cefazolin, Tetracycline, and Imipenem. Conclusion: Our findings indicated that curcumin might be useful as a combinatorial strategy to combat the antibiotic resistance of Enterotoxigenic Escherichia coli.

No abstract