Apoptosis is a form of cell death by which the body maintains the homeostasis of the internal environment. Apoptosis is an initiative cell death process that is controlled by genes and is mainly divided into endogenous pathways (mitochondrial pathway), exogenous pathways (death receptor pathway), and apoptotic pathways induced by endoplasmic reticulum (ER) stress. The homeostasis imbalance in ER results in ER stress. Under specific conditions, ER stress can be beneficial to the body; however, if ER protein homeostasis is not restored, the prolonged activation of the unfolded protein response may initiate apoptotic cell death via the up-regulation of the C/EBP homologous protein (CHOP). CHOP plays an important role in ER stress-induced apoptosis and this review focuses on its multifunctional roles in that process, as well as its role in apoptosis during microbial infection. We summarize the upstream and downstream pathways of CHOP in ER stress induced apoptosis. We also focus on the newest discoveries in the functions of CHOP-induced apoptosis during microbial infection, including DNA and RNA viruses and some species of bacteria. Understanding how CHOP functions during microbial infection will assist with the development of antimicrobial therapies.

Type III secretion systems (T3SSs) are crucial for bacterial infections because they deliver effector proteins into host cells. The Escherichia coli type III secretion system 2 (ETT2) is present in the majority of E. coli strains, and although it is degenerate, ETT2 regulates bacterial virulence. An ATPase is essential for T3SS secretion, but the function of the ETT2 ATPase has not been demonstrated. Here, we show that EivC is homologous to the β subunit of F0F1 ATPases and it possesses ATPase activity. To investigate the effects of ETT2 ATPase EivC on the phenotype and virulence of avian pathogenic Escherichia coli (APEC), eivC mutant and complemented strains were constructed and characterized. Inactivation of eivC led to impaired flagella production and augmented fimbriae on the bacterial surface, and, consequently, reduced bacterial motility. In addition, the eivC mutant strain exhibited attenuated virulence in ducks, diminished serum resistance, reduced survival in macrophage cells and in ducks, upregulated fimbrial gene expression, and downregulated flagellar and virulence gene expression. The expression of the inflammatory cytokines interleukin (IL)-1β and IL-8 were increased in HD-11 macrophages infected with the eivC mutant strain, compared with the wild-type strain. These virulence-related phenotypes were restored by genetic complementation. These findings demonstrate that ETT2 ATPase EivC is involved in the motility and pathogenicity of APEC.

Mycoplasma synoviae is an avian pathogen that can lead to respiratory tract infections and arthritis in chickens and turkeys, resulting in serious economic losses to the poultry industry. Enolase reportedly plays important roles in several bacterial pathogens, but its role in M. synoviae has not been established. Therefore, in this study, the enolase encoding gene (eno) of M. synoviae was amplified from strain WVU1853 and expressed in E. coli BL21 cells. Then the enzymatic activity, immunogenicity and binding activity with chicken plasminogen (Plg) and human fibronectin (Fn) was evaluated. We demonstrated that the recombinant M. synoviae enolase protein (rMsEno) can catalyze the conversion of 2-phosphoglycerate (2-PGA) to phosphoenolpyruvate (PEP), the Km and Vmax values of rMsEno were 1.1 × 10-3 M and 0.739 μmol/L/min, respectively. Western blot and immuno-electron microscopy analyses confirmed that enolase was distributed on the surface and within the cytoplasm of M. synoviae cells. The binding assays demonstrated that rMsEno was able to bind to chicken Plg and human Fn proteins. A complement-dependent mycoplasmacidal assay demonstrated that rabbit anti-rMsEno serum had distinct mycoplasmacidal efficacy in the presence of complement, which also confirmed that enolase was distributed on the surface of M. synoviae. An inhibition assay showed that the adherence of M. synoviae to DF-1 cells pre-treated with Plg could be effectively inhibited by treatment with rabbit anti-rMsEno serum. These results reveal that M. synoviae enolase has good catalytic activity for conversion of 2-PGA to PEP, and binding activity with chicken Plg and human Fn. Rabbit anti-rMsEno serum displayed an obvious complement-dependent mycoplasmacidal effect and adherent inhibition effect. These results suggested that the M. synoviae enolase plays an important role in M. synoviae metabolism, and could potentially impact M. synoviae infection and immunity.

Inappropriate use of antibiotics has accelerated to the emergence of multidrug-resistant bacteria, becoming a major health threat. Moreover, bacterial biofilms contribute to antibiotic resistance and prolonged infections. Bacteriophage (phage) therapy may provide an alternative strategy for controlling multidrug-resistant bacterial infections. In this study, a broad-host-range phage, SHWT1, with lytic activity against multidrug-resistant Salmonella was isolated, characterized and evaluated for the therapeutic efficacy in vitro and in vivo. Phage SHWT1 exhibited specific lytic activity against the prevalent Salmonella serovars, such as Salmonella Pullorum, Salmonella Gallinarum, Salmonella Enteritidis, and Salmonella Typhimurium. Morphological analysis showed that phage SHWT1 was a member of the family Siphoviridae and the order Caudovirales. Phage SHWT1 had a latent period of 5 min and burst size of ~150 plaque-forming units (PFUs)/cell. The phage was stable from pH 3-12 and 4–65°C. Phage SHWT1 also showed capacity to lyse Salmonella planktonic cells and inhibit the biofilm formation at optimal multiplicity of infection (MOI) of 0.001, 0.01, 0.1, and 100, respectively. In addition, phage SHWT1 was able to lyse intracellular Salmonella within macrophages. Genome sequencing and phylogenetic analyses revealed that SHWT1 was a lytic phage without toxin genes, virulence genes, antibiotic resistance genes, or significant genomic rearrangements. We found that phage SHWT1 could successfully protect mice against S. enteritidis and S. typhimurium infection. Elucidation of the characteristics and genome sequence of phage SHWT1 demonstrates that this phage is a potential therapeutic agent against the salmonellosis caused by multidrug-resistant Salmonella.

Type VI secretion systems (T6SSs) contribute to pathogenicity in many pathogenic bacteria. Three distinguishable T6SS loci have been discovered in avian pathogenic Escherichia coli (APEC). The sequence of APEC T6SS2 locus is highly similar to the sequence of the newborn meningitis E. coli (NMEC) RS218 T6SS locus, which might contribute to meningitis pathogenesis. However, little is known about the function of APEC T6SS2. We showed that the APEC T6SS2 component organelle trafficking protein (DotU) could elicit antibodies in infected ducks, suggesting that DotU might be involved in APEC pathogenicity. To investigate DotU in APEC pathogenesis, mutant and complemented strains were constructed and characterized. Inactivation of the APEC dotU gene attenuated virulence in ducks, diminished resistance to normal duck serum, and reduced survival in macrophage cells and ducks. Furthermore, deletion of the dotU gene abolished hemolysin-coregulated protein (Hcp) 1 secretion, leading to decreased interleukin (IL)-6 and IL-8 gene expression in HD-11 chicken macrophages. These functions were restored for the complementation strain. Our results demonstrated that DotU plays key roles in the APEC pathogenesis, Hcp1 secretion and intracellular host response modulation.

Newcastle disease (ND) caused by virulent Newcastle disease virus (NDV) is an acute, highly contagious and fatal viral disease affecting most species of birds. Ducks are generally considered to be natural reservoirs or carriers of NDV while being resistant to NDV strains, even those most virulent for chickens; however, natural ND cases in ducks have been gradually increasing in recent years. In the present study, ducks of different breeds and ages were experimentally infected with duck origin virulent NDV strain duck/Jiangsu/JSD0812/2008 (JSD0812) by various routes to investigate the pathogenicity of NDV in ducks. Six breeds (mallard, Gaoyou, Shaoxing, Jinding, Shanma, and Pekin ducks) were infected intramuscularly (IM) with JSD0812 strain at the dose of 5 × 10⁸ ELD₅₀. Susceptibility to NDV infection among breeds varied, per morbidity and mortality. Mallard ducks were the most susceptible, and Pekin ducks the most resistant. Fifteen-, 30-, 45-, 60-, and 110-day-old Gaoyou ducks were infected with JSD0812 strain at the dose of 5 × 10⁸ ELD₅₀ either IM or intranasally (IN) and intraocularly (IO), and their disease development, viral shedding, and virus tissue distribution were determined. The susceptibility of ducks to NDV infection decreased with age. Most deaths occurred in 15- and 30-day-old ducklings infected IM. Ducks infected IN and IO sometimes exhibited clinical signs, but seldom died. Clinical signs were primarily neurologic. Infected ducks could excrete infectious virus from the pharynx and/or cloaca for a short period, which varied with bird age or inoculation route; the longest period was about 7 days. The rate of virus isolation in tissues from infected ducks was generally low, even in those from dead birds, and it appeared to be unrelated to bird age and infection route. The results confirmed that some of the naturally occurring NDV virulent strains can cause the disease in ducks, and that ducks play an important role in the epidemiology of ND. The prevention of NDV spread in ducks should receive more attention and research in terms of preventing the occurrence and prevalence of ND.