The spontaneously produced lysogenic prophage phi456 promotes bacterial resistance to adverse environments and enhances the colonization ability of avian pathogenic Escherichia coli strain DE456

In the last decade, prophages that possess the ability of lysogenic transformation have become increasingly significant. Their transfer and subsequent activity in the host have a significant impact on the evolution of bacteria. Here, we investigate the role of prophage phi456 with high spontaneous induction in the bacterial genome of Avian pathogenic Escherichia coli (APEC) DE456. The phage particles, phi456, that were released from DE456 were isolated, purified, and sequenced. Additionally, phage particles were no longer observed either during normal growth or induced by nalidixic acid in DE456Δphi456. This indicated that the released phage particles from DE456 were only phi456. We demonstrated that phi456 contributed to biofilm formation through spontaneous induction of the accompanying increase in the eDNA content. The survival ability of DE456Δphi456 was decreased in avian macrophage HD11 under oxidative stress and acidic conditions. This is likely due to a decrease in the transcription levels of three crucial genes-rpoS, katE, and oxyR-which are needed to help the bacteria adapt to and survive in adverse environments. It has been observed through animal experiments that the presence of phi456 in the DE456 genome enhances colonization ability in vivo. Additionally, the number of type I fimbriae in DE456Δphi456 was observed to be reduced under transmission electron microscopy when compared to the wild-type strain. The qRT-PCR results indicated that the expression levels of the subunit of I fimbriae (fimA) and its apical adhesin (fimH) were significantly lower in DE456Δphi456. Therefore, it can be concluded that phi456 plays a crucial role in helping bacterial hosts survive in unfavorable conditions and enhancing the colonization ability in DE456.

In vitro selection and optimization of high-affinity aptamer for milk allergen α-lactalbumin and its application in dual-mode detection

Milk is one of the most common sources of protein in people’s daily lives, and it is also recognized by the World Health Organization (WHO) as one of the eight categories of food allergies to human beings. α-lactalbumin (α-La) is the main cause of milk allergy. In this study, a single-stranded DNA aptamer with high binding affinity to α-La were selected using systematic evolution of ligands by exponential enrichment (SELEX) method. Compared with the full-length sequence, the binding affinity of the truncated aptamer LA-1t for α-La was increased six times using fluorescence analysis. Circular dichroism (CD) indicated that the secondary structure of LA-1t contained a typical hairpin structure. Through the docking simulation of LA-1t and α-La, these experimental results were further explained theoretically, and the recognition mechanism was explained. Finally, the colorimetric and fluorescence signal of boron nitride quantum dots anchored to porous CeO₂ nanorods (BNQDs/CeO₂) were modulated by FAM-labeled LA-1t to achieve highly selective and sensitive determination of α-La. This dual-mode sensing strategy displayed sensitive recognition for α-La in a linear range of 5–4,000 ng/ml with the LOD was 3.32 ng/ml (colorimetry) and 0.71 ng/ml (fluorescence), respectively. Simultaneously, the colorimetry/fluorescence dual-mode sensing strategy was applied for detecting α-La in spiked real samples and demonstrated good stability and reliability.

Bio-inspired Nanoenzyme Synthesis and Its Application in A Portable Immunoassay for Food Allergy Proteins

Nanozymes as a cost-effective and robust enzyme mimic have attracted widespread attention in the development of novel analytical methods. Herein, a new nanozyme-enhanced surface-enhanced Raman scattering (SERS) immunoassay platform was successfully developed using a peroxidase-mimicking nanozyme to replace the natural enzymes as a catalytic label of the enzyme-linked immunosorbent assay for the detection of allergy proteins. In this platform, the peroxidase-mimicking nanozymes as a catalytic label could catalyze the oxidation of the Raman-inactive reporter [i.e., leucomalachite green (LMG)] to generate Raman-active malachite green (MG) with H₂O₂. Moreover, the produced MG Raman signal was further enhanced by the formed Raman "hot spot" through MG-induced gold nanoparticle aggregation, which could be recorded by a portable Raman spectrometer. On this basis, the established nanozyme-enhanced SERS immunoassay showed improved accuracy, high sensitivity, and good selectivity and was used for accurate quantification of α-lactalbumin (α-LA). With this method, α-LA could be detected with a limit of detection as low as 0.01 ng/mL. Moreover, the method was also verified by performing in food samples and showed satisfactory recoveries and high reliability. This study not only provides insight into the use of a nanozyme to establish new analytical methods but also broadens the applications of nanozymes in a food safety assay.

Prophage phiv205-1 facilitates biofilm formation and pathogenicity of avian pathogenic Escherichia coli strain DE205B

Avian colibacillosis caused by avian pathogenic Escherichia coli (APEC) causes significant economic losses to the poultry industry worldwide and is also a leading potential threat to human health. Bacteriophages integrate into the host bacterial chromosome, and are an important source of genetic variation and have a major impact on bacterial evolution. Previously, we predicted prophage phiv205-1 in APEC strain DE205B. Here, to determine the function of prophage phiv205-1, we constructed the prophage deletion mutant DE205BΔphiv205-1. Compared with the wild-type (WT) APEC strain DE205B, the adherence and invasive abilities of DE205BΔphiv205-1 were reduced by 41.88 %(P < 0.05). Further, the mutant strain had 52.38 % reduced biofilm formation compared with the WT strain (P < 0.001). Chick challenge showed that the median lethal dose (LD₅₀) of the mutant strain and WT strain was 3.13 × 10⁵ colony-forming units (CFU) and 3.86 × 10⁴ CFU, respectively, indicating that the mutant strain had decreased virulence compared with the WT strain. Furthermore, in vivo studies showed that, compared with the WT strain, DE205BΔphiv205-1 bacterial loads were reduced by 1.6-fold (P < 0.05) and 4.8-fold (P < 0.001) in the lungs and brains, respectively, of the infected chicks. In conclusion, the prophage phiv205-1 contributes to the virulence of APEC strain DE205B by facilitating the adherence, biofilm formation, and colonization abilities of its host strain.