Survival protein A is essential for virulence in Yersinia pestis

Synergistic antimicrobial activity of alpha-linolenic acid in combination with tetracycline or florfenicol against multidrug-resistant Salmonella typhimurium

Salmonella is a major foodborne pathogen that can be transmitted from livestock and poultry to humans through the food chain. Due to the widespread use of antibiotics, antibiotic resistance Salmonella has become an important factor threatening food safety. Combining antibiotic and non-antibiotic agents is a promising approach to address the widespread emergence of antibiotic-resistant pathogens. In this study, we investigated the antibiotic resistance profile and molecular characterization of different serotypes of Salmonella isolated from large-scale egg farms using drug susceptibility testing and whole genome sequencing. The synergistic effect of alpha-linolenic acid (ALA) with antibiotics was evaluated using the checkerboard test and time-kill curve. The molecular mechanism of α-linolenic acid synergism was explored using biochemical assays, pull-down assays, and molecular docking. In vivo efficacy of ALA in combination with florfenicol (FFC) or tetracycline (TET) against multidrug-resistant (MDR) Salmonella enterica subsp. enterica serovar typhimurium was also investigated using a mouse model. We found that ALA reduced the minimum inhibitory concentration (MIC) of tetracycline and florfenicol in all strains tested. When ALA (512 mg/L) was combined with florfenicol (32 mg/L) or tetracycline (16 mg/L), we observed disruption of cell membrane integrity, increased outer membrane permeability, lowered cell membrane potential, and inhibition of proton-drive-dependent efflux pumps. The synergistic treatment also inhibited biofilm production and promoted oxidative damage. These changes together led to an increase in bacterial antibiotic susceptibility. The improved efficacy of ALA combination treatment with antibiotics was validated in the mouse model. Molecular docking results indicate that ALA can bind to membrane proteins via hydrogen bonding. Our findings demonstrated that combined treatment using ALA and antibiotics is effective in preventing infections involving MDR bacteria. Our results are of great significance for the scientific and effective prevention and control of antibiotic resistance Salmonella, as well as ensuring food safety.

SurA-like and Skp-like Proteins as Important Virulence Determinants of the Gram Negative Bacterial Pathogens

In the Gram-negative bacteria, many important virulence factors reach their destination via two-step export systems, and they must traverse the periplasmic space before reaching the outer membrane. Since these proteins must be maintained in a structure competent for transport into or across the membrane, they frequently require the assistance of chaperones. Based on the results obtained for the model bacterium Escherichia coli and related species, it is assumed that in the biogenesis of the outer membrane proteins and the periplasmic transit of secretory proteins, the SurA peptidyl-prolyl isomerase/chaperone plays a leading role, while the Skp chaperone is rather of secondary importance. However, detailed studies carried out on several other Gram-negative pathogens indicate that the importance of individual chaperones in the folding and transport processes depends on the properties of client proteins and is species-specific. Taking into account the importance of SurA functions in bacterial virulence and severity of phenotypes due to surA mutations, this folding factor is considered as a putative therapeutic target to combat microbial infections. In this review, we present recent findings regarding SurA and Skp proteins: their mechanisms of action, involvement in processes related to virulence, and perspectives to use them as therapeutic targets.

Salmonella Typhimurium peptidyl-prolyl cis-trans isomerase C (PPIase C) plays a substantial role in protein folding to maintain the protein structure

Salmonella is a well-known food-borne pathogen causing disease in humans and animals worldwide. Peptidyl-prolyl isomerases (PPIases) catalyse the cis-trans isomerisation of prolyl bound, which is a slow and rate-limiting step of protein folding. Here, we present the biochemical and molecular characterisation of a novel multi-domain parvulin-type, PPIases-C from the pathogenic bacteria Salmonella Typhimurium, annotated as rPpiC. The recombinant plasmid PpiC_pET28c was used for protein induction using 1.5 mM concentration of isopropyl-β-D-thiogalactopyranoside at 30 °C. Subsequently, the protein was identified by using the LC-MS technique showing high match score and sequence coverage with available PPIases-C proteins database. Using the succinyl-ala-phe-pro-phe-p nitroanilide as a substrate, V_max of the enzyme was found to be 0.8187 ± 0.1352 µmoles/min and K_m = 1.6014 ± 0.8449 µM, respectively. With this, we conclude that rPpiC protein is an active form of protein from Salmonella Typhimurium and plays an important role in protein folding.

Conformational Dynamics of the Periplasmic Chaperone SurA

The periplasmic protein SurA is the primary chaperone involved in the biogenesis of bacterial outer membrane proteins and is a potential antibacterial drug target. The three-dimensional structure of SurA can be divided into three parts, a core module formed by the N- and C-terminal regions and two peptidyl-prolyl isomerase (PPIase) domains, P1 and P2. Despite the determination of the structures of several SurA-peptide complexes, the functional mechanism of this chaperone remains elusive and the roles of the two PPIase domains are yet unclear. Herein, we characterize the conformational dynamics of SurA by using solution nuclear magnetic resonance and single-molecule fluorescence resonance energy transfer methods. We demonstrate a "closed-to-open" structural transition of the P1 domain that is correlated with both chaperone activity and peptide binding and show that the flexible P2 domain can also occupy conformations that closely contact the NC core module. Our results offer a structural basis for the counteracting roles of the two PPIase domains in regulating the SurA chaperone activity.

Maintaining Integrity Under Stress: Envelope Stress Response Regulation of Pathogenesis in Gram-Negative Bacteria

The Gram-negative bacterial envelope is an essential interface between the intracellular and harsh extracellular environment. Envelope stress responses (ESRs) are crucial to the maintenance of this barrier and function to detect and respond to perturbations in the envelope, caused by environmental stresses. Pathogenic bacteria are exposed to an array of challenging and stressful conditions during their lifecycle and, in particular, during infection of a host. As such, maintenance of envelope homeostasis is essential to their ability to successfully cause infection. This review will discuss our current understanding of the σ^E- and Cpx-regulated ESRs, with a specific focus on their role in the virulence of a number of model pathogens.

Biogenesis and function of the autotransporter adhesins YadA, intimin and invasin

Bacteria often express numerous virulence factors. These virulence factors make them successful pathogens, by e.g. mediating attachment to host cells and thereby facilitating persistence or invasion, or by contributing to the evasion of the host immune system to allow proliferation and spread within the host and in the environment. The site of first contact of Gram negative bacteria with the host is the bacterial outer membrane (OM). Consisting of an asymmetrical lipid bilayer with phospholipids forming the inner, and lipopolysaccharides forming the outer leaflet, the OM harbors numerous integral membrane proteins that are almost exclusively β-barrel proteins. One distinct family of OM β-barrel proteins strongly linked to bacterial virulence are the autotransporter (AT) proteins. During the last years huge progress has been made to better understand the mechanisms underlying the insertion of AT proteins into the OM and also AT function for interaction with the host. This review shortly summarizes our current knowledge about outer membrane protein (OMP) and more specifically AT biogenesis and function. We focused on the AT proteins that we haved studied in most detail: i.e. the Yersinia adhesin A (YadA) and invasin of Yersinia enterocolitica (Ye) as well as its homolog intimin (Int) expressed by enteropathogenic Escherichia coli. In addition, this review provides a short outlook about how we could possibly use this knowledge to fight infection.

Therapeutic Antibodies for Biodefense

Diseases can be caused naturally by biological agents such as bacteria, viruses and toxins (natural risk). However, such biological agents can be intentionally disseminated in the environment by a State (military context) or terrorists to cause diseases in a population or livestock, to destabilize a nation by creating a climate of terror, destabilizing the economy and undermining institutions. Biological agents can be classified according to the severity of illness they cause, its mortality and how easily the agent can be spread. The Centers for Diseases Control and Prevention (CDC) classify biological agents in three categories (A, B and C); Category A consists of the six pathogens most suitable for use as bioweapons (Bacillus anthracis, Yersinia pestis, Francisella tularensis, botulinum neurotoxins, smallpox and viral hemorrhagic fevers). Antibodies represent a perfect biomedical countermeasure as they present both prophylactic and therapeutic properties, act fast and are highly specific to the target. This review focuses on the main biological agents that could be used as bioweapons, the history of biowarfare and antibodies that have been developed to neutralize these agents.

Identifying components required for OMP biogenesis as novel targets for antiinfective drugs

The emergence of multiresistant Gram-negative bacteria requires new therapies for combating bacterial infections. Targeting the biogenesis of virulence factors could be an alternative strategy instead of killing bacteria with antibiotics. The outer membrane (OM) of Gram-negative bacteria acts as a physical barrier. At the same time it facilitates the exchange of molecules and harbors a multitude of proteins associated with virulence. In order to insert proteins into the OM, an essential oligomeric membrane-associated protein complex, the ß-barrel assembly machinery (BAM) is required. Being essential for the biogenesis of outer membrane proteins (OMPs) the BAM and also periplasmic chaperones may serve as attractive targets to develop novel antiinfective agents. Herein, we aimed to elucidate which proteins belonging to the OMP biogenesis machinery have the most important function in granting bacterial fitness, OM barrier function, facilitating biogenesis of dedicated virulence factors and determination of overall virulence. To this end we used the enteropathogen Yersinia enterocolitica as a model system. We individually knocked out all non-essential components of the BAM (BamB, C and E) as well as the periplasmic chaperones DegP, SurA and Skp. In summary, we found that the most profound phenotypes were produced by the loss of BamB or SurA with both knockouts resulting in significant attenuation or even avirulence of Ye in a mouse infection model. Thus, we assume that both BamB and SurA are promising targets for the development of new antiinfective drugs in the future.

Environmental Regulation of Yersinia Pathophysiology

Hallmarks of Yersinia pathogenesis include the ability to form biofilms on surfaces, the ability to establish close contact with eukaryotic target cells and the ability to hijack eukaryotic cell signaling and take over control of strategic cellular processes. Many of these virulence traits are already well-described. However, of equal importance is knowledge of both confined and global regulatory networks that collaborate together to dictate spatial and temporal control of virulence gene expression. This review has the purpose to incorporate historical observations with new discoveries to provide molecular insight into how some of these regulatory mechanisms respond rapidly to environmental flux to govern tight control of virulence gene expression by pathogenic Yersinia.