Pseudomonas aeruginosa infections associated with biofilm are a significant clinical challenge due to the limited efficacy of traditional antibiotics or combination therapies. Hence, exploring novel strategies and assessing different compounds for their anti-biofilm or anti-quorum sensing (QS) properties is imperative. One of the various applications of silver nanoparticles (AgNPs) is to use them as an antimicrobial agent to target bacteria resistant to common antibiotics. This study evaluates the anti-biofilm and anti-virulence effect of biosynthesized AgNPs against P. aeruginosa PAO1 at subinhibitory concentration levels. Minimum inhibitory concentrations (MICs) and biofilm formation capacity were evaluated by the microdilution method and crystal violet method, respectively. Motility assay and virulence factors were investigated in the presence of AgNPs. It was observed that green-synthesized AgNPs at sub-MIC (50 μg/mL) suppressed P. aeruginosa biofilm formation by 78 %. Increased dose-dependent inhibitory effects on virulence phenotypes (LasB elastase, LasA protease, pyocyanin, and motility) regulated by QS were observed. In addition, the relative expression levels of biofilm-related genes including algC, pslA, and pelA were analyzed using RT-qPCR. The expression level of QS-regulated biofilm genes after AgNPs treatment sub-MIC led to a decrease in the expression of algC, pslA, and pelA by 77 %, 83 %, and 68 %, respectively. The findings of this study demonstrated how green AgNPs can effectively inhibit QS at sub-MIC concentrations, indicating their potential as antivirulence agents to deal with challenges related to biofilm formation and antimicrobial resistance in P. aeruginosa. This presents a promising alternative to traditional antibiotics in antimicrobial therapy.

Background: Antimicrobial resistance (AMR) in bacterial isolates from food producing animals not only challenges the preventive and therapeutic strategies in veterinary medicine, but also threatens public health. Genetic elements placed on both chromosome and plasmids could be involved in AMR. In the present study, the associations of genomic backbone and plasmids with AMR were evaluated. We also provided some primary evidences that which genetic lineages potentially host certain groups of plasmids. Results: In the current study, 72 avian pathogenic Escherichia coli (APEC) strains were examined. Isolates resistant to tetracycline and trimethoprim-sulfamethoxazole (87.5%; each), and harboring bla_TEM (61.1%) were dominant. Moreover, phylogroup D was the most prevalent phylogroup in total (23.6%), and among multidrug-resistant (MDR) isolates (14/63). The most prevalent Inc-types were also defined as follows: IncP (65.2%), IncI1 (58.3%), and IncF group (54.1%). Significant associations among phylogroups and AMR were observed such as group C to neomycin (p = 0.002), gentamicin (p = 0.017) and florfenicol (p = 0.036). Furthermore, group D was associated with bla_CTX. In terms of associations among Inc-types and AMR, resistance to aminoglycoside antibiotics was considerably linked with IncP (p = 0.012), IncI1 (p = 0.038) and IncA/C (p = 0.005). The bla_TEM and bla_CTX genes presence were connected with IncI1 (p = 0.003) and IncFIC (p = 0.013), respectively. It was also shown that members of the D phylogroup frequently occured in replicon types FIC (8/20), P (13/47), I1 (13/42), HI2 (5/14) and L/M (3/3). Conclusions: Accorging to the results, it seems that group D strains have a great potential to host a variety of plasmids (Inc-types) carrying different AMR genes. Thus, based on the results of the current study, phyogroup D could be a potential challenge in dealing with AMR in poultry. There were more strong correlations among Inc-types and AMR compared to phylotypes and AMR. It is suggested that in epidemiological studies on AMR both genomic backbone and major plasmid types should be investigated.

One of the major bacterial infectious diseases in the poultry industry is avian pathogenic Escherichia coli (APEC), which causes colibacillosis in chickens. To develop a novel nucleic acid-free bacterial ghost (BG) vaccine against the O78:K80 serotype of APEC, in this study we constructed a plasmid that harbored E-lysis and S nuclease (SNUC). Following the expression, the O78:K80 bacteria lost all of their cytoplasmic content and nucleic acids by enzymatic digestion. The functionality of these two proteins in the production procedure of bacterial ghosts was confirmed by monitoring the number of colonies, scanning electron microscopy imaging, gel electrophoresis of genomic DNA, and qPCR on the plasmid content of bacterial ghosts. The protective efficacy of the ghost vaccine generated from O78:K80 serotype of APEC was tested in chickens by injection and inhalation routes and compared with that in chickens that received the injection of a killed vaccine. The O78:K80 BG vaccine candidate, used as injection and inhalation, in comparison with the killed vaccine, triggered higher proinflammatory cytokine expression including IL-6, IL-1β, and TNFSF15; a higher level of antibody-dependent humoral (IgY and IgA) and cellular immune responses (IFNγ and lymphocyte proliferation); and lower lesion scores. According to the results of this study, we suggest that the bacterial ghost technology has the potential to be applied for the development of novel vaccines against avian colibacillosis. This technology provides an effective and reliable approach to make multivalent vaccines for more prevalent APEC strains involved in the establishment of this infectious disease in the poultry industry.