Simultaneous Identification of Potential Pathogenicity Factors of Mycoplasma agalactiae in the Natural Ovine Host by Negative Selection

Genes required for survival and proliferation of Mycoplasma bovis in association with host cells

Mycoplasma bovis is an important emerging pathogen of cattle and bison, but our understanding of the genetic basis of its interactions with its host is limited. The aim of this study was to identify genes of M. bovis required for interaction and survival in association with host cells. One hundred transposon-induced mutants of the type strain PG45 were assessed for their capacity to survive and proliferate in Madin-Darby bovine kidney cell cultures. The growth of 19 mutants was completely abrogated, and 47 mutants had a prolonged doubling time compared to the parent strain. All these mutants had a similar growth pattern to the parent strain PG45 in the axenic media. Thirteen genes previously classified as dispensable for the axenic growth of M. bovis were found to be essential for the growth of M. bovis in association with host cells. In most of the mutants with a growth-deficient phenotype, the transposon was inserted into a gene involved in transportation or metabolism. This included genes coding for ABC transporters, proteins related to carbohydrate, nucleotide and protein metabolism, and membrane proteins essential for attachment. It is likely that these genes are essential not only in vitro but also for the survival of M. bovis in infected animals.

IMPORTANCE

Mycoplasma bovis causes chronic bronchopneumonia, mastitis, arthritis, keratoconjunctivitis, and reproductive tract disease in cattle around the globe and is an emerging pathogen in bison. Control of mycoplasma infections is difficult in the absence of appropriate antimicrobial treatment or effective vaccines. A comprehensive understanding of host-pathogen interactions and virulence factors is important to implement more effective control methods against M. bovis. Recent studies of other mycoplasmas with in vitro cell culture models have identified essential virulence genes of mycoplasmas. Our study has identified genes of M. bovis required for survival in association with host cells, which will pave the way to a better understanding of host-pathogen interactions and the role of specific genes in the pathogenesis of disease caused by M. bovis.

Diversity and antigenic potentials of Mycoplasmopsis bovis secreted and outer membrane proteins within a core genome of strains isolated from North American bison and cattle

Mycoplasmopsis bovis is a worldwide economically important pathogen of cattle that can cause or indirectly contribute to bovine respiratory disease. M. bovis is also a primary etiological agent of respiratory disease in bison with high mortality rates. A major challenge in the development of an efficacious M. bovis vaccine is the design of antigens that contain both MHC-1 and MHC-2 T-cell epitopes, and that account for population level diversity within the species. Publicly available genomes and sequence read archive libraries of 381 M. bovis strains isolated from cattle (n = 202) and bison (n = 179) in North America were used to identify a core genome of 575 genes, including 38 that encode either known or predicted secreted or outer membrane proteins. The antigenic potentials of the proteins were characterized by the presence and strength of their T-cell epitopes, and their protein variant diversity at the population-level. The proteins had surprisingly low diversity and varying predictive levels of T-cell antigenicity. These results provide a reference for the selection or design of antigens for vaccine testing against strains infecting North American cattle and bison.

Mycoplasma agalactiae Vaccines: Current Status, Hurdles, and Opportunities Due to Advances in Pathogenicity Studies

Contagious agalactia (CA) is a serious multietiological disease whose classic etiological agent is Mycoplasma agalactiae and which causes high morbidity and mortality rates in infected herds. CA is classified as a notifiable disease by the World Organization for Animal Health due to its significant worldwide economic impact on livestock, primarily involving goat and sheep farms. The emergence of atypical symptoms and strains of M. agalactiae in wildlife ungulates reestablishes its highly plastic genome and is also of great epidemiological significance. Antimicrobial therapy is the main form of control, although several factors, such as intrinsic antibiotic resistance and the selection of resistant strains, must be considered. Available vaccines are few and mostly inefficient. The virulence and pathogenicity mechanisms of M. agalactiae mainly rely on surface molecules that have direct contact with the host. Because of this, they are essential for the development of vaccines. This review highlights the currently available vaccines and their limitations and the development of new vaccine possibilities, especially considering the challenge of antigenic variation and dynamic genome in this microorganism.

Detection of Putative Virulence Genes alr, goiB, and goiC in Mycoplasma hominis Isolates from Austrian Patients

In Mycoplasma hominis, two genes (alr and goiB) have been found to be associated with the invasion of the amniotic cavity, and a single gene (goiC) to be associated with intra-amniotic infections and a high risk of preterm birth. The syntopic presence of Ureaplasma spp. in the same patient has been shown to correlate with the absence of goiC in M. hominis. The aim of our study was to investigate the presence of alr, goiB, and goiC genes in two groups of M. hominis isolates collected from symptomatic and asymptomatic male and non-pregnant female patients attending an Outpatients Centre. Group A consisted of 26 isolates from patients with only M. hominis confirmed; group B consisted of 24 isolates from patients with Ureaplasma spp. as the only co-infection. We extracted DNA from all M. hominis isolates and analysed the samples for the presence of alr, goiB, and goiC in a qPCR assay. Additionally, we determined their cytotoxicity against HeLa cells. We confirmed the presence of the alr gene in 85% of group A isolates and in 100% of group B isolates; goiB was detected in 46% of the samples in both groups, whereas goiC was found in 73% of group A and 79% of group B isolates, respectively. It was shown that co-colonisation with Ureaplasma spp. in the same patient had no effect on the presence of goiC in the respective M. hominis isolate. We did not observe any cytotoxic effect of the investigated isolates on human cells, regardless of the presence or absence of the investigated genes.

Sheep Infection Trials with 'Phase-Locked' Vpma Expression Variants of Mycoplasma agalactiae-Towards Elucidating the Role of a Multigene Family Encoding Variable Surface Lipoproteins in Infection and Disease

The significance of large multigene families causing high-frequency surface variations in mycoplasmas is not well-understood. Previously, VpmaY and VpmaU clonal variants of the Vpma family of lipoproteins of M. agalactiae were compared via experimental sheep infections using the two corresponding ‘Phase-Locked Mutants’. However, nothing is known about the infectivity of the remaining four Vpma expression variants VpmaX, VpmaW, VpmaZ and VpmaV as they were never evaluated in vivo. Here, in vivo infection and disease progression of all six Vpma expressers constituting the Vpma family of type strain PG2 were compared using the corresponding xer1-disrupted PLMs expressing single well-characterized Vpmas. Each of the six PLMs were separately evaluated using the intramammary sheep infection model along with the control phase-variable wildtype strain PG2. Thorough bacteriological, pathological and clinical examinations were performed, including assessment of milk quality, quantity and somatic cell counts. Altogether, the results indicated that the inability to vary the Vpma expression phase does not hamper the initiation of infection leading to mastitis for all six PLMs, except for PLMU, which showed a defect in host colonization and multiplication for the first 24 h p.i. and pathological/bacteriological analysis indicated a higher potential for systemic spread for PLMV and PLMX. This is the first study in which all isogenic expression variants of a large mycoplasma multigene family are tested in the natural host.

Novel role of Vpmas as major adhesins of Mycoplasma agalactiae mediating differential cell adhesion and invasion of Vpma expression variants

Mycoplasma agalactiae exhibits antigenic variation by switching the expression of multiple surface lipoproteins called Vpmas. Although implicated to have a significant influence on the pathogenicity, their exact role in pathogen-host interactions has not been investigated so far. Initial attachment to host cells is regarded as one of the most important steps for colonization but this pathogen lacks the typical mycoplasma attachment organelle. The aim of this study was to determine the role of Vpmas in adhesion of M. agalactiae to host cells. 'Phase-Locked' Mutants (PLMs) steadily expressing single well-characterized Vpma lipoproteins served as ideal tools to evaluate the role of each of the six Vpmas in cytadhesion, which was otherwise not possible due to the high-frequency switching of Vpmas in the wildtype strain PG2. Using in vitro adhesion assays with HeLa and sheep mammary epithelial (MECs) and stromal (MSCs) cells, we could demonstrate differences in the adhesion capabilities of each of the six PLMs compared to the wildtype strain. The PLMV mutant expressing VpmaV exhibited the highest adhesion rate, whereas PLMU, which expresses VpmaU showed the lowest adhesion values explaining the reduced in vivo fitness of PLMU in sheep during experimental intramammary and conjunctival infections. Furthermore, adhesion inhibition assays using Vpma-specific polyclonal antisera were performed to confirm the role of Vpmas in M. agalactiae cytadhesion. This led to a significant decrease (p<0.05) in the adhesion percentage of each PLM. Immunofluorescence staining of TX-114 phase proteins extracted from each PLM showed binding of the respective Vpma to HeLa cells and MECs proving the direct role of Vpmas in cytadhesion. Furthermore, as adhesion is a prerequisite for cell invasion, the ability of the six PLMs to invade HeLa cells was also evaluated using the gentamicin protection assay. The results showed a strong correlation between the adhesion rates and invasion frequencies of the individual PLMs. This is the first report that describes a novel function of Vpma proteins in cell adhesion and invasion. Besides the variability of these proteins causing surface antigenic variation, the newly identified phenotypes are likely to play critical roles in the pathogenicity potential of this ruminant pathogen.

Comprehensive RNA-Seq Profiling to Evaluate the Sheep Mammary Gland Transcriptome in Response to Experimental Mycoplasma agalactiae Infection

Mycoplasma agalactiae is a worldwide serious pathogen of small ruminants that usually spreads through the mammary route causing acute to subacute mastitis progressing to chronic persistent disease that is hard to eradicate. Knowledge of mechanisms of its pathogenesis and persistence in the mammary gland are still insufficient, especially the host-pathogen interplay that enables it to reside in a chronic subclinical state. This study reports transcriptome profiling of mammary tissue from udders of sheep experimentally infected with M. agalactiae type strain PG2 in comparison with uninfected control animals using Illumina RNA-sequencing (RNA-Seq). Several differentially expressed genes (DEGs) were observed in the infected udders and RT-qPCR analyses of selected DEGs showed their expression profiles to be in agreement with results from RNA-Seq. Gene Ontology (GO) analysis revealed majority of the DEGs to be associated with mycoplasma defense responses that are directly or indirectly involved in host innate and adaptive immune responses. Similar RNA-Seq analyses were also performed with spleen cells of the same sheep to know the specific systemic transcriptome responses. Spleen cells exhibited a comparatively lower number of DEGs suggesting a less prominent host response in this organ. To our knowledge this is the first study that describes host transcriptomics of M. agalactiae infection and the related immune-inflammatory responses. The data provides useful information to further dissect the molecular genetic mechanisms underlying mycoplasma mastitis, which is a prerequisite for designing effective intervention strategies.

Genetic loci of Mycoplasma agalactiae involved in systemic spreading during experimental intramammary infection of sheep

Mycoplasmas are amongst the most successful pathogens of both humans and animals yet the molecular basis of mycoplasma pathogenesis is poorly understood. This is partly due to the lack of classical virulence factors and little similarity to common bacterial pathogenic determinants. Using Mycoplasma agalactiae as a model we initiated research in this direction by screening a transposon mutant library in the natural sheep host using a negative selection method. Having successfully identified putative factors involved in the colonization of local infection and lymphogenic sites, the current study assessed mutants unable to spread systemically in sheep after experimental intramammary infection. Analysis of distant body sites for complete absence of mutants via SSM PCR revealed that additional set of genes, such as pdhB, oppC, oppB, gtsB, MAG1890, MAG5520 and MAG3650 are required for systemic spreading apart from those that were necessary for initial colonization. Additional in vitro studies with the mutants absent at these systemic sites confirmed the potential role of some of the respective gene products concerning their interaction with host cells. Mutants of pdhB, oppC and MAG4460 exhibited significantly slower growth in the presence of HeLa cells in MEM medium. This first attempt to identify genes exclusively required for systemic spreading provides a basis for further in-depth research to understand the exact mechanism of chronicity and persistence of M. agalactiae.