Identification of novel genes expressed during host infection in Streptococcus equi ssp. zooepidemicus ATCC35246

Endogenous Type I-C CRISPR-Cas system of Streptococcus equi subsp. zooepidemicus promotes biofilm formation and pathogenicity

Streptococcus equi subsp. zooepidemicus (SEZ) is a significant zoonotic pathogen that causes septicemia, meningitis, and mastitis in domestic animals. Recent reports have highlighted high-mortality outbreaks among swine in the United States. Traditionally recognized for its adaptive immune functions, the CRISPR-Cas system has also been implicated in gene regulation, bacterial pathophysiology, virulence, and evolution. The Type I-C CRISPR-Cas system, which is prevalent in SEZ isolates, appears to play a pivotal role in regulating the pathogenicity of SEZ. By constructing a Cas3 mutant strain (ΔCas3) and a CRISPR-deficient strain (ΔCRISPR), we demonstrated that this system significantly promotes biofilm formation and cell adhesion. However, the deficiency in the CRISPR-Cas system did not affect bacterial morphology or capsule production. In vitro studies showed that the CRISPR-Cas system enhances pro-inflammatory responses in RAW264.7 cells. The ΔCas3 and ΔCRISPR mutant strains exhibited reduced mortality rates in mice, accompanied by a decreased bacterial load in specific organs. RNA-seq analysis revealed distinct expression patterns in both mutant strains, with ΔCas3 displaying a broader range of differentially expressed genes, which accounted for over 70% of the differential genes observed in ΔCRISPR. These genes were predominantly linked to lipid metabolism, the ABC transport system, signal transduction, and quorum sensing. These findings enhance our understanding of the complex role of the CRISPR-Cas system in SEZ pathogenesis and provide valuable insights for developing innovative therapeutic strategies to combat infections.

Galactose-1-phosphate uridyltransferase (GalT), an in vivo-induced antigen of Actinobacillus pleuropneumoniae serovar 5b strain L20, provided immunoprotection against serovar 1 strain MS71

GALT is an important antigen of Actinobacillus pleuropneumoniae (APP), which was shown to provide partial protection against APP infection in a previous study in our lab. The main purpose of the present study is to investigate GALT induced cross-protection between different APP serotypes and elucidate key mechanisms of the immune response to GALT antigenic stimulation. Bioinformatic analysis demonstrated that galT is a highly conserved gene in APP, widely distributed across multiple pathogenic strains. Homologies between any two strains ranges from 78.9% to 100% regarding the galT locus. Indirect enzyme-linked immunosorbent assay (ELISA) confirmed that GALT specific antibodies could not be induced by inactivated APP L20 or MS71 whole cell bacterin preparations. A recombinant fusion GALT protein derived from APP L20, however has proven to be an effective cross-protective antigen against APP sevorar 1 MS71 (50%, 4/8) and APP sevorar 5b L20 (75%, 6/8). Histopathological examinations have confirmed that recombinant GALT vaccinated animals showed less severe pathological signs in lung tissues than negative controls after APP challenge. Immunohistochemical (IHC) analysis indicated that the infiltration of neutrophils in the negative group is significantly increased compared with that in the normal control (P<0.001) and that in surviving animals is decreased compared to the negative group. Anti-GALT antibodies were shown to mediate phagocytosis of neutrophils. After interaction with anti-GALT antibodies, survival rate of APP challenged vaccinated animals was significantly reduced (P<0.001). This study demonstrated that GALT is an effective cross-protective antigen, which could be used as a potential vaccine candidate against multiple APP serotypes.

Capsule of Streptococcus equi subsp. zooepidemicus hampers the adherence and invasion of epithelial and endothelial cells and is attenuated during internalization

Direct interaction between pathogens and host cells often is a prerequisite for colonization, infection and dissemination. Regulated production of capsular polysaccharide (CPS), which is made of hyaluronic acid, is essential for the pathogenicity of Streptococcus equi subsp. Zooepidemicus (SEZ). Here, we constructed a CPS-deleted mutant and analyzed it along with the parental wild-type strain in attachment and invasion of mammalian epithelial and endothelial cell lines. The CPS-deleted mutant exhibited significant increase in adherence and invasion by several orders of magnitude compared with the wild-type strain through quantitative analysis and electron microscopy observation. After the wild-type strain was recovered from invaded cells, its morphology was analyzed by visual methods and scanning electron microscopy, which revealed that its capsule was almost completely absent. Capsule measurements showed a similar result in which CPS production was nearly attenuated to the same extent as in the CPS-deleted mutant. qPCR assays revealed a marked reduction in the transcriptional levels of the CPS biosynthesis genes, has operon. Moreover, the repression in capsular production was stable inheritance. Our findings indicate that SEZ is a facultative intracellular bacterium, capsule attenuation in SEZ contributes to attachment and invasion in interactions with host cells, and the active regulation of capsule breakdown is controlled by SEZ during internalization.

A novel suicide shuttle plasmid for Streptococcus suis serotype 2 and Streptococcus equi ssp. zooepidemicus gene mutation

The mariner-based Himar1 system has been utilized for creating mutant libraries of many Gram-positive bacteria. Streptococcus suis serotype 2 (SS2) and Streptococcus equi ssp. zooepidemicus (SEZ) are primary pathogens of swine that threaten the swine industry in China. To provide a forward-genetics technology for finding virulent phenotype-related genes in these two pathogens, we constructed a novel temperature-sensitive suicide shuttle plasmid, pMar4s, which contains the Himar1 system transposon, TnYLB-1, and the Himar1 C9 transposase from pMarA and the repTAs temperature-sensitive fragment from pSET4s. The kanamycin (Kan) resistance gene was in the TnYLB-1 transposon. Temperature sensitivity and Kan resistance allowed the selection of mutant strains and construction of the mutant library. The SS2 and SEZ mutant libraries were successfully constructed using the pMar4s plasmid. Inverse-Polymerase Chain Reaction (Inverse-PCR) results revealed large variability in transposon insertion sites and that the library could be used for phenotype alteration screening. The thiamine biosynthesis gene apbE was screened for its influence on SS2 anti-phagocytosis; likewise, the sagF gene was identified to be a hemolytic activity-related gene in SEZ. pMar4s was suitable for mutant library construction, providing more information regarding SS2 and SEZ virulence factors and illustrating the pathogenesis of swine streptococcosis.

Streptococcus suis Meningitis: A Systematic Review and Meta-analysis

Background

Streptococcus suis is the most common cause of meningitis in pork consuming and pig rearing countries in South-East Asia. We performed a systematic review of studies on S. suis meningitis to define the clinical characteristics, predisposing factors and outcome.

Methodology

Studies published between January 1, 1980 and August 1, 2015 were identified from main literature databases and reference lists. Studies were included if they were written in West-European languages and described at least 5 adult patients with S. suis meningitis in whom at least one clinical characteristic was described.

Findings

We identified 913 patients with S. suis meningitis included in 24 studies between 1980 and 2015. The mean age was 49 years and 581 of 711 patients were male (82%). Exposure to pigs or pork was present in 395 of 648 patients (61%) while other predisposing factors were less common. 514 of 528 patients presented with fever (97%), 429 of 451 with headache (95%), 462 of 496 with neck stiffness (93%) and 78 of 384 patients (20%) had a skin injury in the presence of pig/pork contact. The case fatality rate was 2.9% and hearing loss was a common sequel occurring in 259 of 489 patients (53%). Treatment included dexamethasone in 157 of 300 (52%) of patients and was associated with reduced hearing loss in S. suis meningitis patients included in a randomized controlled trial.

Conclusion

S. suis meningitis has a clear association with pig and pork contact. Mortality is low, but hearing loss occurs frequently. Dexamethasone was shown to reduce hearing loss.

Meningitis is a common manifestation of Streptococcus suis infection. S. suis is endemic in pork consuming and pig rearing countries. We systematically reviewed the clinical characteristics, predisposing factors and outcome of S. suis meningitis. We identified 913 patients included in 24 studies, with a mean age of 49 years and a majority of male patients (82%). Exposure to pigs or pork was present in 61%, with a skin injury being present in 20%. Fever was present in 97% of patients, headache in 95%, neck stiffness in 93%. The mortality was 2.9% and hearing loss was common occurring in 53% of patients. Dexamethasone was associated with reduced hearing loss.