Superhydrophobic surfaces have been reported to reduce bacterial adhesion, but interactions between bacterial media and solid surfaces at the interface have rarely been associated with the solid area fraction (f) from the Cassie–Baxter wetting state. This study aimed to investigate the effective surface area for bacterial adhesion by analyzing the solid area fraction of surfaces where the bacterial medium is in contact with a solid surface. Also, the self-cleaning ability of the superhydrophobic surface against adhered bacteria was examined. The influences of roughness, surface energy, entrapped air, and surface charge of substrate materials on bacterial adhesion were examined, and the critical surface characteristics that are conducive to reducing Escherichia coli adherence to polymeric surfaces were determined. Moderate hydrophobicity with water contact angle of about 90° produced the highest level of bacterial adhesion. Entrapped air at the interface of superhydrophobic surfaces interfered with the direct contact of bacteria to solid surfaces, leading to less bacterial adhesion. The superhydrophobic surface with a reduced solid area fraction displayed self-cleaning ability, where initially-adhered bacteria were removed by washing. The superhydrophilic substrate with negative zeta potential exhibited limited bacterial binding, due to the reduced hydrophobic interaction and possible repulsive interaction between bacteria and surface. The findings of this study can be utilized for an effective surface design to circumvent bacterial adhesion as an alternative solution to using antibiotics.

Given recent evidence suggesting that the heat-labile enterotoxin (LT) provides a colonization advantage for enterotoxigenicEscherichia coli(ETEC) in vivo, we hypothesized that LT preconditions the host intestinal epithelium for ETEC adherence. To test this hypothesis, we used an in vitro model of ETEC adherence to examine the role of LT in promoting bacterium-host interactions. We present data demonstrating that elaboration of LT promotes a significant increase inE. coliadherence. This phenotype is primarily dependent on the inherent ADP-ribosylation activity of this toxin, with a secondary role observed for the receptor-binding LT-B subunit. Rp-3′,5′-cyclic AMP (cAMP), an inhibitor of protein kinase A, was sufficient to abrogate LT's ability to promote subsequent bacterial adherence. Increased adherence was not due to changes in the surface expression of the host receptor for the K88ac adhesin. Evidence is also presented for a role for bacterial sensing of host-derived cAMP in promoting adherence to host cells.

Many Gram-negative bacterial pathogens use a syringe-like apparatus called a type III secretion system to inject virulence factors into host cells. Some of these effectors are enzymes that modify host proteins to subvert their normal functions. NleB is a glycosyltransferase that modifies host proteins with N-acetyl-d-glucosamine to inhibit antibacterial and inflammatory host responses. NleB is conserved among the attaching/effacing pathogens enterohemorrhagic Escherichia coli (EHEC), enteropathogenic E. coli (EPEC), and Citrobacter rodentium. Moreover, Salmonella enterica strains encode up to three NleB orthologs named SseK1, SseK2, and SseK3. However, there are conflicting reports regarding the activities and host protein targets among the NleB/SseK orthologs. Therefore, here we performed in vitro glycosylation assays and cell culture experiments to compare the activities and substrate specificities of these effectors. SseK1, SseK3, EHEC NleB1, EPEC NleB1, and C. rodentium NleB blocked TNF-mediated NF-κB pathway activation, whereas SseK2 and NleB2 did not. C. rodentium NleB, EHEC NleB1, and SseK1 glycosylated host GAPDH. C. rodentium NleB, EHEC NleB1, EPEC NleB1, and SseK2 glycosylated the FADD (Fas-associated death domain protein). SseK3 and NleB2 were not active against either substrate. We also found that EHEC NleB1 glycosylated two GAPDH arginine residues, Arg¹⁹⁷ and Arg²⁰⁰, and that these two residues were essential for GAPDH-mediated activation of TNF receptor-associated factor 2 ubiquitination. These results provide evidence that members of this highly conserved family of bacterial virulence effectors target different host protein substrates and exhibit distinct cellular modes of action to suppress host responses.

The human pathogens enterohemorrhagic and enteropathogenic Escherichia coli (EHEC and EPEC), as well as the related mouse pathogen Citrobacter rodentium , utilize a type III secretion system (T3SS) to inject multiple effector proteins into host cells. The E. coli O157:H7 strain EDL933 carries two copies of non-locus of enterocyte effacement (LEE)-encoded protein H, designated NleH1 and NleH2, both of which bind to the human ribosomal protein S3 (RPS3), a subunit of NF-κB transcriptional complexes. In this study, we describe significant functional differences between NleH1 and NleH2 in their ability to regulate the host NF-κB pathway. We show that the EHEC and EPEC NleH effectors are functionally equivalent in their ability to affect RPS3 nuclear translocation. NleH1, but not NleH2, inhibited NF-κB activity without altering the kinetics of IκBα phosphorylation/degradation. We also determined that the class I PSD-95/Disc Large/ZO-1 (PDZ)-binding domain of NleH was important for its activity in the NF-κB pathway. In addition to binding RPS3, we found that NleH1 and NleH2 are able to bind to each other in vitro and in vivo , suggesting an additional mechanism by which the E. coli NleH effectors may regulate the extent and duration of NF-κB activation after their T3SS-dependent translocation. We also performed mouse infection experiments and established that mouse mortality and Citrobacter colonization were reduced in mice infected with Δ nleH . Complementing Δ nleH with NleH1 restored Citrobacter virulence and colonization to wild-type levels, whereas complementing with NleH2 reduced them. Taken together, our data show that NleH1 and NleH2 have pronounced functional differences in their ability to alter host transcriptional responses to bacterial infection.

Enterotoxigenic Escherichia coli (ETEC) causes human morbidity and mortality in developing nations and is an emerging threat to food safety in developed nations. The ETEC heat‐labile enterotoxin (LT) not only causes diarrheal disease by deregulating host adenylate cyclase, but also enhances ETEC adherence to intestinal epithelial cells. The mechanism governing this LT pro‐adherence phenotype is unclear. Here we investigated intestinal epithelial cell signal transduction pathways activated by ETEC and quantified the relative importance of these host pathways to LT‐induced ETEC adherence. We show that ETEC activates both NF‐κB and mitogen‐activated protein kinase signalling pathways through mechanisms that are primarily dependent upon LT. LT‐induced NF‐κB activation depends upon the cAMP‐dependent activation of the Ras‐like GTPase Rap1 but is independent of protein kinase A (PKA). By using inhibitors of these pathways, we demonstrate that inhibiting the p38 mitogen‐activated protein kinase prevents LT from increasing ETEC adherence. By contrast, the LT pro‐adherence phenotype appears unrelated to both LT‐induced Rap1 activity and to subsequent NF‐κB activation. We speculate that LT may alter host signal transduction to induce the presentation of ligands for ETEC adhesins in such a way that promotes ETEC adherence. Our findings provide insight into previously unexplored functions of LT and their relative importance to ETEC virulence.