Evaluation of the New Outer Membrane Protein A Epitope-based Vaccines for Mice Model of Acinetobacter baumannii Associated Pneumonia and Sepsis Infection

Nosocomial infections caused by Acinetobacter baumannii (A. baumannii) are considered as a global serious problem in hospitalized patients because of emerging antibiotic resistance. Immunotherapy approaches are promising to prevent such infections. In our previous study, five antigenic epitopes of outer membrane protein A (OmpA), as the most dangerous virulence molecule in A. baumanii, were predicted in silico. In this study, the investigators evaluated some immunological aspects of the peptides.Five peptides were separately injected into C5BL/6 mice; then the cytokine production (interleukin-4 and interferon-gamma) of splenocytes and opsonophagocytic activity of immunized serum were assessed. To identify the protective function of the peptides, animal models of sepsis and pneumonia infections were actively and passively immunized with selected peptides and pooled sera of immunized mice, respectively. Then, their survival rates were compared with the non-infected controls.Based on the results, activated spleen cells in P127 peptide-immunized mice exhibited an increased level of IFN-γ compared with the other experimental groups, but not about the IL-4 concentration. The results of the opsonophagocytic assay revealed an appropriate killing the activity of produced antibodies against A. baumannii in a dose-dependent manner. Further, the survival rates of the mice under passive immunization with the immunized sera or active immunization with P127 peptide were significantly more than those in the control group. Moreover, the survival rate of the P127 peptide immunized group was considerably higher than that of the other peptide-immunized group.In conclusion, findings indicated that peptides derived from OmpA can be used as a promising tool for designing the epitope-based vaccines against infections caused by A. baumannii.

Structure and functions of bacterial outer membrane protein A, a potential therapeutic target for bacterial infection

: Outer membrane protein A (OmpA) is a unique outer membrane protein which is abundantly present in the outer membrane of Gram‐negative bacteria. OmpA is a transmembrane structural protein with a conserved amino acid sequence among different bacteria. This protein is involved in a number of functions like adhesion, toxicity, invasiveness, and biofilm formation in Gram-negative bacteria. Many studies have proposed that OmpA could be a therapeutic target for bacterial infection. Our review focusses on the studies involving recent development in the structure and functions of OmpA and further discussing its potential as a therapeutic target for bacterial infection.

Salmonella Typhimurium outer membrane protein A (OmpA) renders protection against nitrosative stress by promoting SCV stability in murine macrophage

Porins are highly conserved bacterial outer membrane proteins having β barrel structure and are majorly involved in the selective transport of charged molecules across the membrane. Despite having huge contributions in the pathogenesis of many gram-negative bacteria, their role remains elusive in salmonellosis. In this study, we have characterized the pathogenic role of porins majorly found on the outer membrane of Salmonella Typhimurium (such as OmpA, OmpC, OmpD, and OmpF) paying the utmost importance to OmpA. The outer membrane protein A (OmpA) of Salmonella Typhimurium has shown a multifaceted role in our study. We have observed that deletion of ompA from wildtype Salmonella has made it more prone to phagocytosis and weakly proliferative in macrophages. Whereas, in epithelial cells STM ΔompA was found to be invasion deficient and hyper-proliferative. The poor colocalization of STM ΔompA with LAMP-1 confirmed impaired stability of SCV membrane around the intracellular bacteria, which further resulted in the release of the knockout strain to the cytosol of macrophage where it is bombarded with reactive nitrogen intermediates (RNI). The cytosolic localization of STM ΔompA was found to be responsible for the downregulation of SPI-2 encoded virulent factor SpiC which is required for suppressing the activity of iNOS. The reduced recruitment of nitrotyrosine on wildtype Salmonella staying in the cytosol of macrophage by ectopically expressing Listeriolysin O (LLO) strongly proves the pro-bacterial role of OmpA against host nitrosative stress. The time-dependent increase in 405/ 488 ratio of STM ΔompA pQE60-Grx1-roGFP2 exposed to in vitro acidified nitrite suggested RNI dependent redox burst which further answered the reason for its enhanced sensitivity towards nitrosative stress. Our study further demonstrated loss of integrity and enhanced porosity in the bacterial outer membrane in absence of OmpA. The enhanced porosity of the bacterial outer membrane was further attributed to the upregulated expression of larger porins namely ompC, ompD, and ompF. In comparison with STM ΔompA ΔompC and ΔompA ΔompF, the enhanced uptake of nitrite and greater recruitment of nitrotyrosine on intracellular STM ΔompA ΔompD demonstrate the involvement of OmpC and OmpF in the entry of excess nitrite in ompA deficient bacteria.

Detection of Chlamydiaceae in Swiss wild birds sampled at a bird rehabilitation centre

BackgroundAnnually, 800–1500 wild birds are admitted to the rehabilitation centre of the Swiss Ornithological Institute, Sempach, Lucerne, Switzerland. The workers of the centre come in close contact with the avian patients and might therefore be exposed to zoonotic agents shed by these birds, such as Chlamydia psittaci.MethodsIn the present study, 91 choanal, 91 cloacal and 267 faecal swabs from 339 wild birds of 42 species were investigated using a stepwise diagnostic approach.ResultsChlamydiaceae were detected in 0.9 per cent (0.3–2.6 per cent) of birds (n=3), all of them members of the Columbidae family. The Chlamydiaceae species of two of these birds (one Eurasian collared dove, one fancy pigeon) were identified as C psittaci types B and E by PCR and outer membrane protein A genotyping.ConclusionThe findings of the current study suggest that zoonotic transmission of Chlamydiaceae is very unlikely for songbird and waterfowl species tested herein, while pigeons might pose a risk to workers at rehabilitation centres.