Effects of inflammatory stimuli on responses of macrophages to Mycoplasma bovis infection

Effects of inflammatory stimuli on the development of Mycoplasma bovis pneumonia in experimentally challenged calves

Many cattle infected with Mycoplasma bovis remain healthy while others develop severe chronic respiratory disease. We hypothesized that inflammatory stimuli such as co-pathogens worsen disease outcomes in M. bovis-infected calves. Calves (n=24) were intrabronchially inoculated with M. bovis and either killed bacterial lysate, transient M. haemolytica infection, or saline. Caseonecrotic lesions developed in 7/7 animals given M. haemolytica and M. bovis compared to 2/8 given M. bovis with no inflammatory stimulus, and 6/9 animals given bacterial lysate and M. bovis (P=0.01). Animals receiving M. haemolytica and M. bovis had more caseonecrotic foci in lungs than those receiving M. bovis with no inflammatory stimulus (median = 21 vs 0; P = 0.01), with an intermediate response (median = 5) in animals given bacterial lysate. In addition to caseonecrotic foci, infected animals developed neutrophilic bronchiolitis that appeared to develop into caseonecrotic foci, peribronchiolar lymphocytic cuffs that were not associated with the other lesions, and 4 animals with bronchiolitis obliterans. The data showed that transient lung inflammation at the time of M. bovis infection provoked the development of caseonecrotic bronchopneumonia, and the severity of inflammation influenced the number of caseonecrotic foci that developed. In contrast, caseonecrotic lesions were few or absent in M. bovis-infected calves without a concurrent inflammatory stimulus. These studies provide insight into how caseonecrotic lesions develop within the lung of M. bovis-infected calves. This and other studies suggest that controlling co-pathogens and harmful inflammatory responses in animals infected with M. bovis could potentially minimize development of M. bovis caseonecrotic bronchopneumonia.

The Identification of a Novel Nucleomodulin MbovP467 of Mycoplasmopsis bovis and Its Potential Contribution in Pathogenesis

Mycoplasmopsis bovis is a causative agent of crucial diseases in both dairy and beef cattle leading to substantial economic losses. However, limited control measures for M. bovis-related diseases exist due to a lack of understanding about the virulence factors of this pathogen, a common challenge in mycoplasma research. Consequently, this study aimed to characterize a novel nucleomodulin as a virulence-related factor of M. bovis. Employing bioinformatic tools, we initially predicted MbovP467 to be a secreted protein with a nuclear localization signal based on SignalP scores and the cNLS (Nuclear Localization Signal) Mapper, respectively. Subsequently, the MbovP467 gene was synthesized and cloned into a pEGFP plasmid with EGFP labeling to obtain a recombinant plasmid (rpEGFP-MbovP467) and then was also cloned in pET-30a with a consideration for an Escherichia coli codon bias and expressed and purified for the production of polyclonal antibodies against the recombinant MbovP467 protein. Confocal microscopy and a Western blotting assay confirmed the nuclear location of MbovP467 in bovine macrophages (BoMacs). RNA-seq data revealed 220 up-regulated and 20 down-regulated genes in the rpEGFP-MbovP467-treated BoMac group compared to the control group (pEGFP). A GO- and KEGG-enrichment analysis identified associations with inflammatory responses, G protein-coupled receptor signaling pathways, nuclear receptor activity, sequence-specific DNA binding, the regulation of cell proliferation, IL-8, apoptotic processes, cell growth and death, the TNF signaling pathway, the NF-κB signaling pathway, pathways in cancer, and protein families of signaling and cellular processes among the differentially expressed up-regulated mRNAs. Further experiments, investigating cell viability and the inflammatory response, demonstrated that MbovP467 reduces BoMac cell viability and induces the mRNA expression of IL-1β, IL-6, IL-8, TNF-α, and apoptosis in BoMac cells. Further, MbovP467 increased the promoter activity of TNF-α. In conclusion, this study identified a new nucleomodulin, MbovP467, for M. bovis, which might have an important role in M. bovis pathogenesis.

Mannheimia haemolytica increases Mycoplasma bovis disease in a bovine experimental model of BRD

Amongst the bacterial pathogens associated with the bovine respiratory disease syndrome (BRD) in cattle are Mannheimia haemolytica and Mycoplasma bovis. The interaction between these two pathogens has not been investigated before; thus, there are gaps in the knowledge of why and how a previous infection with M. haemolytica allows the development of M. bovis-related lesions. We hypothesized that upon M. haemolytica infection, inflammatory products are produced in the lung and that these inflammatory products stimulate M. bovis to produce proteases and lipases that degrade lipids and proteins important for lung function. In this work, we identified several M. bovis proteases and lipases whose expression was modulated by M. haemolytica products in vitro. We performed co-infection animal challenges to develop a model to test vaccine protection. A prior exposure to BHV-1 followed by infection with M. bovis and M. haemolytica resulted in severe pathology and the BHV-1 infection was abandoned. When M. bovis and M. haemolytica were introduced into the lungs by bronchoscopy, we found that M. haemolytica resulted in worsening of the respiratory disease caused by M. bovis. We performed a proof-of-concept trial where animals were immunized with the M. bovis proteins identified in this study and challenged with both pathogens. Despite detecting significant humoral immune responses to the antigens, the experimental vaccine failed to protect against M. bovis disease.

Development of a long-read next generation sequencing workflow for improved characterization of fastidious respiratory mycoplasmas

Mycoplasma cynos and Mycoplasma felis are often associated with canine and feline infectious respiratory disease in dogs and cats, respectively. Mycoplasmas have a reduced genome and dearth of many biosynthetic pathways, making them dependent on rich medium for growth. Due to this fastidious nature, mycoplasmas have been historically underdiagnosed. The aim of this study was to develop a cost-effective and accurate sequencing workflow for genotypic characterization of clinical isolates of M. cynos and M. felis using a rapid long-read sequencing platform. We explored the following critical aspects of bacterial whole genome sequencing, including: (i) five solid and liquid-based culture approaches based on a specialized media formulation for Mycoplasma culture, (ii) three DNA extraction methods modified for long-read sequencing purposes, and (iii) two de novo assembly platforms, Flye and Canu, as key components of a bioinformatics pipeline. DNA extraction method 1, a solid-phase and column-based kit with enzymatic lysis, provided the best DNA quality and concentration followed by high coverage and sequencing contiguity. This was obtained with a culture volume of 45 ml in modified Hayflick's broth incubated for 48 h. DNA extracted directly from colonies on agar or from small broth volumes (6 ml) did not meet the criteria required for long-read sequencing. Overall, Flye generated more contiguous assemblies than the Canu assembler and was more time efficient. This 4-5 day sample-to-sequence workflow provides the scientific and clinical communities with a more comprehensive tool than laborious conventional methods for complete genomic characterization of M. cynos and M. felis clinical isolates.