Heterologous expression of Intimin and IpaB fusion protein in Lactococcus lactis and its mucosal delivery elicit protection against pathogenicity of Escherichia coli O157 and Shigella flexneri in a murine model

Genomics and pathotypes of the many faces of Escherichia coli

Escherichia coli is the most researched microbial organism in the world. Its varied impact on human health, consisting of commensalism, gastrointestinal disease, or extraintestinal pathologies, has generated a separation of the species into at least eleven pathotypes (also known as pathovars). These are broadly split into two groups, intestinal pathogenic E. coli (InPEC) and extraintestinal pathogenic E. coli (ExPEC). However, components of E. coli's infinite open accessory genome are horizontally transferred with substantial frequency, creating pathogenic hybrid strains that defy a clear pathotype designation. Here, we take a birds-eye view of the E. coli species, characterizing it from historical, clinical, and genetic perspectives. We examine the wide spectrum of human disease caused by E. coli, the genome content of the bacterium, and its propensity to acquire, exchange, and maintain antibiotic resistance genes and virulence traits. Our portrayal of the species also discusses elements that have shaped its overall population structure and summarizes the current state of vaccine development targeted at the most frequent E. coli pathovars. In our conclusions, we advocate streamlining efforts for clinical reporting of ExPEC, and emphasize the pathogenic potential that exists throughout the entire species.

Genomic, Antimicrobial, and Aphicidal Traits of Bacillus velezensis ATR2, and Its Biocontrol Potential against Ginger Rhizome Rot Disease Caused by Bacillus pumilus

Ginger rhizome rot disease, caused by the pathogen Bacilluspumilus GR8, could result in severe rot of ginger rhizomes and heavily threaten ginger production. In this study, we identified and characterized a new Bacillus velezensis strain, designated ATR2. Genome analysis revealed B. velezensis ATR2 harbored a series of genes closely related to promoting plant growth and triggering plant immunity. Meanwhile, ten gene clusters involved in the biosynthesis of various secondary metabolites (surfactin, bacillomycin, fengycin, bacillibactin, bacilysin, difficidin, macrolactin, bacillaene, plantazolicin, and amylocyclicin) and two clusters encoding a putative lipopeptide and a putative phosphonate which might be explored as novel bioactive compounds were also present in the ATR2 genome. Moreover, B. velezensis ATR2 showed excellent antagonistic activities against multiple plant pathogenic bacteria, plant pathogenic fungi, human pathogenic bacteria, and human pathogenic fungus. B. velezensis ATR2 was also efficacious in control of aphids. The antagonistic compound from B. velezensis ATR2 against B.pumilus GR8 was purified and identified as bacillomycin D. In addition, B. velezensis ATR2 exhibited excellent biocontrol efficacy against ginger rhizome rot disease on ginger slices. These findings showed the potential of further applications of B. velezensis ATR2 as a biocontrol agent in agricultural diseases and pests management.

Recent Progress in Shigella and Burkholderia pseudomallei Vaccines

Significant advancement has been made in the development of vaccines against bacterial pathogens. However, several roadblocks have been found during the evaluation of vaccines against intracellular bacterial pathogens. Therefore, new lessons could be learned from different vaccines developed against unrelated intracellular pathogens. Bacillary dysentery and melioidosis are important causes of morbidity and mortality in developing nations, which are caused by the intracellular bacteria Shigella and Burkholderia pseudomallei, respectively. Although the mechanisms of bacterial infection, dissemination, and route of infection do not provide clues about the commonalities of the pathogenic infectious processes of these bacteria, a wide variety of vaccine platforms recently evaluated suggest that in addition to the stimulation of antibodies, identifying protective antigens and inducing T cell responses are some additional required elements to induce effective protection. In this review, we perform a comparative evaluation of recent candidate vaccines used to combat these two infectious agents, emphasizing the common strategies that can help investigators advance effective and protective vaccines to clinical trials.

Genomic Analysis of a Novel Phage Infecting the Turkey Pathogen Escherichia coli APEC O78 and Its Endolysin Activity

Due to the increasing spread of multidrug-resistant (MDR) bacteria, phage therapy is considered one of the most promising methods for addressing MDR bacteria. Escherichia coli lives symbiotically in the intestines of humans and some animals, and most strains are beneficial in terms of maintaining a healthy digestive tract. However, some E. coli strains can cause serious zoonotic diseases, including diarrhea, pneumonia, urinary tract infections, and hemolytic uremic syndrome. In this study, we characterized a newly isolated Myoviridae phage, vB_EcoM_APEC. The phage vB_EcoM_APEC was able to infect E. coli APEC O78, which is the most common MDR E. coli serotype in turkeys. Additionally, the phage's host range included Klebsiella pneumoniae and other E. coli strains. The genome of phage vB_EcoM_APEC (GenBank accession number MT664721) was 35,832 bp in length, with 52 putative open reading frames (ORFs) and a GC content of 41.3%. The genome of vB_EcoM_APEC exhibited low similarity (79.1% identity and 4.0% coverage) to the genome of Acinetobacter phage vB_AbaM_IME284 (GenBank no. MH853787.1) according to the nucleotide Basic Local Alignment Search Tool (BLASTn). Phylogenetic analysis revealed that vB_EcoM_APEC was a novel phage, and its genome sequence showed low similarity to other available phage genomes. Gene annotation indicated that the protein encoded by orf11 was an endolysin designated as LysO78, which exhibited 64.7% identity (91.0% coverage) with the putative endolysin of Acinetobacter baumannii phage vB_AbaM_B9. The LysO78 protein belongs to glycoside hydrolase family 19, and was described as being a chitinase class I protein. LysO78 is a helical protein with 12 α-helices containing a large domain and a small domain in terms of the predicted three-dimensional structure. The results of site-directed mutagenesis indicated that LysO78 contained the catalytic residues E54 and E64. The purified endolysin exhibited broad-spectrum bacteriolytic activity against Gram-negative strains, including the genera Klebsiella, Salmonella, Shigella, Burkholderia, Yersinia, and Pseudomonas, as well as the species Chitinimonas arctica, E. coli, Ralstonia solanacearum, and A. baumannii. An enzymatic assay showed that LysO78 had highly lytic peptidoglycan hydrolases activity (64,620,000 units/mg) against E. coli APEC O78, and that LysO78 had lytic activity in the temperature range of 4-85 °C, with an optimal temperature of 28 °C and optimal pH of 8.0, and was active at pH 3.0-12.0. Overall, the results suggested that LysO78 might be a promising therapeutic agent for controlling MDR E. coli APEC O78 and nosocomial infections caused by multidrug-resistant bacteria.

Plasmid Replicons for the Production of Pharmaceutical-Grade pDNA, Proteins and Antigens by Lactococcus lactis Cell Factories

The Lactococcus lactis bacterium found in different natural environments is traditionally associated with the fermented food industry. But recently, its applications have been spreading to the pharmaceutical industry, which has exploited its probiotic characteristics and is moving towards its use as cell factories for the production of added-value recombinant proteins and plasmid DNA (pDNA) for DNA vaccination, as a safer and industrially profitable alternative to the traditional Escherichia coli host. Additionally, due to its food-grade and generally recognized safe status, there have been an increasing number of studies about its use in live mucosal vaccination. In this review, we critically systematize the plasmid replicons available for the production of pharmaceutical-grade pDNA and recombinant proteins by L. lactis. A plasmid vector is an easily customized component when the goal is to engineer bacteria in order to produce a heterologous compound in industrially significant amounts, as an alternative to genomic DNA modifications. The additional burden to the cell depends on plasmid copy number and on the expression level, targeting location and type of protein expressed. For live mucosal vaccination applications, besides the presence of the necessary regulatory sequences, it is imperative that cells produce the antigen of interest in sufficient yields. The cell wall anchored antigens had shown more promising results in live mucosal vaccination studies, when compared with intracellular or secreted antigens. On the other side, engineering L. lactis to express membrane proteins, especially if they have a eukaryotic background, increases the overall cellular burden. The different alternative replicons for live mucosal vaccination, using L. lactis as the DNA vaccine carrier or the antigen producer, are critically reviewed, as a starting platform to choose or engineer the best vector for each application.