Glaesserella parasuis serotype 4 HPS4-YC disrupts the integrity of the swine tracheal epithelial barrier and facilitates bacterial translocation.

Glaesserella parasuis (G. parasuis) is a commensal bacterium in the upper respiratory tract of pigs that can also cause the swine Glässer disease, which induces an intensive inflammatory response and results in significant economic losses to the swine industry worldwide. G. parasuis can cause disease through infection of the respiratory tract, resulting in systemic infection, but the mechanism is largely unknown. Recently we showed that Glaesserella parasuis serotype 4 (GPS4) increased swine tracheal epithelial barrier permeability, resulting in easier bacterial translocation. Tight junction proteins (TJ) play a crucial role in maintaining the integrity and impermeability of the epithelial barrier. GPS4 decreased the expression of the TJ ZO-1 and occludin in swine tracheal epithelial cells (STEC). Furthermore, the proinflammatory cytokines IL-6, IL-8 and TNF-α were significantly upregulated in GPS4-infected STEC, and both the MAPK and NF-κB signaling pathways were activated and contributed to the expression of TNF-α. We demonstrate that the production of proinflammatory cytokines, especially TNF-α, during GPS4 infection was involved in barrier dysfunction. Additionally, animal challenge experiments confirmed that GPS4 infection downregulated TJ in the lungs of piglets and induced a severe inflammatory response. In general, G. parasuis infection downregulated the expression of TJ and induced massive secretion of proinflammatory cytokines, resulting in epithelial barrier disruption and favoring bacterial infection. This study allowed us to better understand the mechanism by which G. parasuis crosses the respiratory tract of pigs.

Respiratory and Reproductive Impairment of Commercial Layer Chickens After Experimental Infection with Gallibacterium anatis Biovar haemolytica.

The prevalence of Gallibacterium anatis in poultry production has increased over the last two decades. However, only a few studies have explored the pathogenicity of this bacterium in commercial layer chickens. This trial studied the aspects of the pathogenicity of a Gallibacterium anatis biovar haemolytica local Egyptian isolate (previously registered as strain B14 with GenBank accession no. KJ026147). We used 500 base pairs of a 16S ribosomal RNA gene and the 16S-23S ribosomal RNA intergenic spacer, partial sequence in an experimental infection trial in commercial White Shaver layer chickens aged 19 wk. The hens were divided into three groups of 40 birds each. The hens in Groups 1 and 2 were experimentally infected through the intranasal (IN) and intravenous (IV) routes, respectively, with a dose of 0.2 ml/bird containing 1.2 × 109 colony-forming units/ml. In contrast, Group 3 was kept as a noninfected control group. Both IN and IV infections resulted in a delayed egg laying for 1 wk and a significant (P ≤ 0.05) drop in egg production by 7.81% and 10.28% compared with the control group over 7 wk. Severe lesions in the form of hemorrhagic pneumonia, catarrhal tracheitis, ovarian follicle and oviductal regression, and septicemia were evident on necropsy, demonstrating the pathogenicity of G. anatis as a primary pathogen.

A Commensal Bacterium Promotes Virulence of an Opportunistic Pathogen via Cross-Respiration.

UNLABELLED: Bacteria rarely inhabit infection sites alone, instead residing in diverse, multispecies communities. Despite this fact, bacterial pathogenesis studies primarily focus on monoculture infections, overlooking how community interactions influence the course of disease. In this study, we used global mutant fitness profiling (transposon sequencing [Tn-seq]) to determine the genetic requirements for the pathogenic bacterium Aggregatibacter actinomycetemcomitans to cause disease when coinfecting with the commensal bacterium Streptococcus gordonii Our results show that S. gordonii extensively alters A. actinomycetemcomitans requirements for virulence factors and biosynthetic pathways during infection. In addition, we discovered that the presence of S. gordonii enhances the bioavailability of oxygen during infection, allowing A. actinomycetemcomitans to shift from a primarily fermentative to a respiratory metabolism that enhances its growth yields and persistence. Mechanistically, respiratory metabolism enhances the fitness of A. actinomycetemcomitans in vivo by increasing ATP yields via central metabolism and creating a proton motive force. Our results reveal that, similar to cross-feeding, where one species provides another species with a nutrient, commensal bacteria can also provide electron acceptors that promote the respiratory growth and fitness of pathogens in vivo, an interaction that we term cross-respiration. IMPORTANCE: Commensal bacteria can enhance the virulence of pathogens in mixed-species infections. However, knowledge of the mechanisms underlying this clinically relevant phenomenon is lacking. To bridge this gap, we comprehensively determined the genes a pathogen needs to establish coinfection with a commensal. Our findings show that the metabolism of the pathogen is low-energy-yielding in monoinfection, but in coinfection, the commensal improves the fitness of the pathogen by increasing the bioavailability of oxygen, thereby shifting the pathogen toward a high-energy-yielding metabolism. Similar to cross-feeding, this interaction, which we term cross-respiration, illustrates that commensal bacteria can provide electron acceptors that enhance the virulence of pathogens during infection.

Aggregatibacter aphrophilus ventriculitis following C1-C2 transarticular screw fixation.

OBJECTIVE: Central nervous system (CNS) infections after cervical spine surgery are a rare but serious complication and may be caused by uncommon pathogens. We report the case of a 57-year-old male who developed slowly progressive mental confusion with headaches, increased daytime sleepiness and mild gait disturbance within the last 3 weeks. Six weeks prior to admission to our department, he underwent an atlantoaxial fusion by C1-C2 transarticular screw fixation for rheumatoid arthritis related C1-C2 multidirectional instability. METHODS: We analyzed clinical and neuroradiological findings. RESULTS: The findings were consistent with communicating hydrocephalus secondary to ventriculitis and the left C1-C2 screw was found to be misplaced with perforation of the dura. The situation was interpreted as implant related surgical site infection of the cerebrospinal fluid followed by ventriculitis and hydrocephalus. Bacterial broad range 16S rRNA gene PCR from the cerebrospinal fluid (CSF) followed by sequencing identified Aggregatibacter aphrophilus as the causative agent, while conventional cultures remained negative due to its fastidious growth. The patient was successfully treated with a lumbar drain and intravenous ceftriaxone. CONCLUSIONS: To our knowledge, this is the first report of Aggregatibacter aphrophilus ventriculitis following C1-C2 transarticular screw fixation.

Co-infection with Bovine Herpesvirus 4 and Histophilus somni Significantly Extends the Service Period in Dairy Cattle with Purulent Vaginal Discharge.

The aim of the study was to investigate the effect of Bovine Herpesvirus 4 (BoHV-4) and Histophilus (H.) somni on fertility rate of cows in a Hungarian Holstein-Friesian dairy herd with purulent vaginal discharge (PVD). Non-pregnant cows (n = 188) with mature corpus luteum were treated with cloprostenol and 3 days later if they did not show oestrus, were examined by rectal palpation. Animals showing PVD (n = 60/31.9%/) and 14 controls with normal vaginal discharge (Score 0) were randomly selected and further examined by ultrasonography and blood samples were collected for detecting BoHV-4 DNA and transcervical guarded swabs were collected from the uterus for bacteriological examination. Although the majority of the examined animals were infected with BoHV-4 and H. somni including the control animals as well, in group of animals with PVD score 3, fewer animals became pregnant and the duration between the first treatment to pregnancy was significantly extended. Based on these clinical and comparative data, our results confirm that these two microorganisms together may impair important reproductive parameters which may cause large economic losses to dairy farms.

Aggregatibacter actinomycetemcomitans, a potent immunoregulator of the periodontal host defense system and alveolar bone homeostasis.

Aggregatibacter actinomycetemcomitans is a perio-pathogenic bacteria that has long been associated with localized aggressive periodontitis. The mechanisms of its pathogenicity have been studied in humans and preclinical experimental models. Although different serotypes of A. actinomycetemcomitans have differential virulence factor expression, A. actinomycetemcomitans cytolethal distending toxin (CDT), leukotoxin, and lipopolysaccharide (LPS) have been most extensively studied in the context of modulating the host immune response. Following colonization and attachment in the oral cavity, A. actinomycetemcomitans employs CDT, leukotoxin, and LPS to evade host innate defense mechanisms and drive a pathophysiologic inflammatory response. This supra-physiologic immune response state perturbs normal periodontal tissue remodeling/turnover and ultimately has catabolic effects on periodontal tissue homeostasis. In this review, we have divided the host response into two systems: non-hematopoietic and hematopoietic. Non-hematopoietic barriers include epithelium and fibroblasts that initiate the innate immune host response. The hematopoietic system contains lymphoid and myeloid-derived cell lineages that are responsible for expanding the immune response and driving the pathophysiologic inflammatory state in the local periodontal microenvironment. Effector systems and signaling transduction pathways activated and utilized in response to A. actinomycetemcomitans will be discussed to further delineate immune cell mechanisms during A. actinomycetemcomitans infection. Finally, we will discuss the osteo-immunomodulatory effects induced by A. actinomycetemcomitans and dissect the catabolic disruption of balanced osteoclast-osteoblast-mediated bone remodeling, which subsequently leads to net alveolar bone loss.

Aggregatibacter actinomycetemcomitans leukotoxin (LtxA; Leukothera) induces cofilin dephosphorylation and actin depolymerization during killing of malignant monocytes.

Leukotoxin (LtxA; Leukothera), a protein toxin secreted by the oral bacterium Aggregatibacter actinomycetemcomitans, specifically kills white blood cells (WBCs). LtxA binds to the receptor known as lymphocyte function associated antigen-1 (LFA-1), a ß2 integrin expressed only on the surface of WBCs. LtxA is being studied as a virulence factor that helps A. actinomycetemcomitans evade host defences and as a potential therapeutic agent for the treatment of WBC diseases. LtxA-mediated cell death in monocytes involves both caspases and lysosomes; however, the signalling proteins that regulate and mediate cell death remain largely unknown. We used a 2D-gel proteomics approach to analyse the global protein expression changes that occur in response to LtxA. This approach identified the protein cofilin, which underwent dephosphorylation upon LtxA treatment. Cofilin is a ubiquitous actin-binding protein known to regulate actin dynamics and is regulated by LIM kinase (LIMK)-mediated phosphorylation. LtxA-mediated cofilin dephosphorylation was dependent on LFA-1 and cofilin dephosphorylation did not occur when LFA-1 bound to its natural ligand, ICAM-1. Treatment of cells with an inhibitor of LIMK (LIMKi) also led to cofilin dephosphorylation and enhanced killing by LtxA. This enhanced sensitivity to LtxA coincided with an increase in lysosomal disruption, and an increase in LFA-1 surface expression and clustering. Both LIMKi and LtxA treatment also induced actin depolymerization, which could play a role in trafficking and surface distribution of LFA-1. We propose a model in which LtxA-mediated cofilin dephosphorylation leads to actin depolymerization, LFA-1 overexpression/clustering, and enhanced lysosomal-mediated cell death.

Effects of experimental challenge of ewes with Mannheimia haemolytica on subsequent milk composition.

The objective was to describe the physicochemical changes during the early phase of subclinical mastitis and to associate them with pathological findings. A Mannheimia haemolytica strain was deposited into one teat duct of 25 ewes and the clinical, bacteriological, cytological, physicochemical (pH, milk composition), gross-pathological and histological findings were subsequently recorded. The organism was consistently isolated from samples of teat duct material (140/150) but not from mammary secretion (50/150). California Mastitis Test (CMT) scores increased (>1) and remained high (143/150 samples) after challenge; polymorphonuclear neutrophils (PMN) predominated in milk films, but the proportion of lymphocytes and macrophages progressively increased. Increased pH values (>7.0) were recorded in the mammary secretion from the challenged side. Furthermore, content of fat, total proteins and lactose therein decreased markedly. Histological changes (leucocytic infiltration, destruction of epithelial cells) were observed in the mammary parenchyma of the ewes. The present results confirm that the reduction of milk constituents is the effect of cellular damage and can occur soon after infection.