Outer Membrane Protein F Is Involved in Biofilm Formation, Virulence and Antibiotic Resistance in Cronobacter sakazakii

In some Gram-negative bacteria, ompF encodes outer membrane protein F (OmpF), which is a cation-selective porin and is responsible for the passive transport of small molecules across the outer membrane. However, there are few reports about the functions of this gene in Cronobacter sakazakii. To investigate the role of ompF in detail, an ompF disruption strain (ΔompF) and a complementation strain (cpompF) were successfully obtained. We find that OmpF can affect the ability of biofilm formation in C. sakazakii. In addition, the variations in biofilm composition of C. sakazakii were examined using Raman spectroscopy analyses caused by knocking out ompF, and the result indicated that the levels of certain biofilm components, including lipopolysaccharide (LPS), were significantly decreased in the mutant (ΔompF). Then, SDS-PAGE was used to further analyze the LPS content, and the result showed that the LPS levels were significantly reduced in the absence of ompF. Therefore, we conclude that OmpF affects biofilm formation in C. sakazakii by reducing the amount of LPS. Furthermore, the ΔompF mutant showed decreased (2.7-fold) adhesion to and invasion of HCT-8 cells. In an antibiotic susceptibility analysis, the ΔompF mutant showed significantly smaller inhibition zones than the WT, indicating that OmpF had a positive effect on the influx of antibiotics into the cells. In summary, ompF plays a positive regulatory role in the biofilm formation and adhesion/invasion, which is achieved by regulating the amount of LPS, but is a negative regulator of antibiotic resistance in C. sakazakii.

Immunotherapy with IgY Antibodies toward Outer Membrane Protein F Protects Burned Mice against Pseudomonas aeruginosa Infection

Burn patients with multidrug-resistant Pseudomonas aeruginosa infections commonly suffer from high morbidity and mortality, which present a major challenge to healthcare systems throughout the world. Outer membrane protein F (OprF), as a main outer membrane porin, is required for full virulence expression of P. aeruginosa. The aim of this study was to evaluate the protective efficacy of egg yolk-specific antibody (IgY) raised against recombinant OprF (r-OprF) protein in a murine burn model of infection. The hens were immunized with r-OprF, and anti-r-OprF IgY was purified using salt precipitation. Groups of mice were injected with different regimens of anti-OprF IgY or control IgY (C-IgY). Infections were caused by subcutaneous injection of P. aeruginosa strain PAO1 at the burn site. Mice were monitored for mortality for 5 days. The functional activity of anti-OprF IgY was determined by in vitro invasion assays. Immunotherapy with anti-OprF IgY resulted in a significant improvement in the survival of mice infected by P. aeruginosa from 25% to 87.5% compared with the C-IgY and PBS. The anti-OprF IgY decreased the invasion of P. aeruginosa PAO1 into the A549. Passive immunization with anti-OprF IgY led to an efficacious protection against P. aeruginosa burn infection in the burn model.

Determining the amphipol distribution within membrane-protein fibre samples using small-angle neutron scattering

Detergent micelles can solubilize membrane proteins, but there is always a need for a pool of free detergent at the critical micellar concentration to maintain the micelle–monomer equilibrium. Amphipol polymeric surfactants (APols) have been developed to replace conventional detergents in membrane-protein studies, but the role of free amphipol is unclear. It has previously been shown that the removal of free APol causes monodisperse outer membrane protein F (OmpF) to form long filaments. However, any remaining APol could not be resolved using electron microscopy. Here, small-angle neutron scattering with isotope contrast matching was used to separately determine the distributions of membrane protein and amphipol in a mixed sample. The data showed that after existing free amphipol had been removed from monodisperse complexes, a new equilibrium was established between protein–amphipol filaments and a pool of newly liberated free amphipol. The filaments consisted of OmpF proteins surrounded by a belt of Apol, whilst free oblate spheroid micelles of Apol were also present. No indications of long-range order were observed, suggesting a lack of defined structure in the filaments.

Assessment of Protective Properties of the Recombinant Complex of the Outer Membrane Protein F and the Toxoid of Pseudomonas aeruginosa

Pseudomonas aeruginosa induces the complications after burns, injuries, surgical interventions and appears to be one of the main causative agents of nosocomial infections. This pathogen has the high resistance to the antibacterial preparations, therefore the immunoprophylaxis is considered as one of the major approaches to reduce Pseudomonas infection. Objective: The aim of our investigation is to study the protective properties of the recombinant complex of the outer membrane protein F (OprF) and a non-toxic variant of the exotoxin A (toxoid) against Pseudomonas infection. Methods: The recombinant proteins which contained the additional histidine residues were synthesized into Escherichia coli with isopropyl-βD-thyogalactopyranoside (IPTG). The recombinant proteins were purified by affinity chromatography on Ni-Sepharose. The preparations of recombinant proteins were injected intraperitoneally into the mice. Aluminum hydroxide was used as an adjuvant. For an experimental infection in mice, animals were challenged intraperitoneally by a live virulent culture of P. aeruginosa (PA-103 strain). Results: The best protective effect for the complex containing 25 μg OprF and 50 μg toxoid was identified when we used the double immunization of mice (Index of efficiency of the protective properties in this case was 4.0). Indexes of efficiency of separated recombinant proteins which were injected twice in the same doses were 2.0 for OprF и 2.3 for toxoid. The triple immunization of animals was inefficient for separated recombinant proteins in the same doses. The injection of doses which were lowered twice (12.5 μg for OprF and 25 μg for toxoid) resulted in increased survival of mice immunized by individual proteins (indexes of efficiency: 3 for OprF and и 3,5 for toxoid). However when we administered to the complex of proteins with the same doses Index of efficiency was 2.8. Conclusion: It was shown that the maximum protective effect in a short time is achieved by the combination of double immunization and the mixture of the recombinant proteins OprF and the 25 and 50 μg doses of recombinant toxoid .