Comparative Genome Analysis of Two Streptococcus suis Serotype 8 Strains Identifies Two New Virulence-Associated Genes

Streptococcus suis is an important zoonotic pathogen that can cause meningitis and septicemia in swine and humans. Among numerous pathogenic serotypes, S. suis serotype 8 has distinctive characteristics such as a high detection rate and causing multi-host infection. There is no complete genome of serotype 8 strains so far. In this study, the complete genome of two S. suis serotype 8 strains, virulent strain 2018WUSS151 and non-virulent strain WUSS030, were sequenced. Comparative genomic analysis showed that the homology of the two genomes reaches 99.68%, and the main difference is the distinctive prophages. There are 83 genes unique to virulent strain 2018WUSS151, including three putative virulence-associated genes (PVGs). Two PVGs, padR and marR, are passenger genes in ISSsu2 family transposons that are able to form circular DNA intermediates during transposition, indicating the possibility of horizontal transmission among S. suis strains. The deletion mutant of PVGs marR or atpase attenuated the virulence of serotype 2 virulent SC070731 in a mouse infection model, confirming their role in S. suis virulence. These findings contribute to clarifying the genomic characterization of S. suis serotype 8 and S. suis pathogenesis.

The Identification of Streptococcus pasteurianus Obtained from Six Regions in China by Multiplex PCR Assay and the Characteristics of Pathogenicity and Antimicrobial Resistance of This Zoonotic Pathogen

Streptococcus pasteurianus is a zoonotic pathogen causing meningitis and bacteremia in animals and humans. A lack of accurate and convenient detection methods hinders preventing and controlling diseases caused by S. pasteurianus. Additionally, there is limited knowledge about its pathogenicity and antimicrobial resistance characteristics, as there are only three complete genome sequences available. In this study, we established a multiplex PCR assay for the detection of S. pasteurianus, which was applied to six fecal samples from cattle with diarrhea and 285 samples from healthy pigs. Out of the samples tested, 24 were positive, including 5 from pig tonsils, 18 from pig hilar lymph nodes, and 1 from cattle feces. Two strains were isolated from positive samples, and their complete genomes were sequenced. The two strains were non-virulent in mice and multidrug-resistant by the antimicrobial susceptibility test. We first found the presence of genes tet(O/W/32/O) and lsa(E) in S. pasteurianus, leading to resistance to lincosamides and tetracyclines. The convenient and specific multiplex PCR assay provides essential technical support for epidemiological research, and the complete genome sequence of two non-virulent strains contributes to understanding this zoonotic bacterium's genomic characteristics and pathogenesis.

Pathogenic investigations of Streptococcus pasteurianus, an underreported zoonotic pathogen, isolated from a diseased piglet with meningitis

Streptococcus pasteurianus, an underreported opportunistic pathogen, is considered an increasingly recognized cause of meningitis and bacteremia in many animals and humans worldwide. However, except for some epidemiological studies, there is no report about the gene-deletion mutagenesis, virulence factors, reservoir niches or animal infection models for this pathogen. In this study, we first isolated an S. pasteurianus strain from a newly weaned piglet's brain with meningitis. The genomic sequence of this swine isolate WUSP067 shared high homology with that of two human strains. The comparative genome analysis showed that strain WUSP067 contained a fucose utilization cluster absent in human strains, and it shared 91% identity with that of an integrative and conjugative element (ICE) ICEssuZJ20091101-2 from Streptococcus suis, another important swine bacterial pathogen. Strain WUSP067 was resistant to erythromycin, tulathromycin, lincomycin, clindamycin, doxycycline and gentamycin, and ICEs are vehicles for harbouring antimicrobial resistance genes. The infection model was established using the 3-week-old newly weaned ICR mice. The 50% lethal dose value of strain WUSP067 was 4.0 × 107 colony-forming units per mouse. The infected mice showed severe signs of meningitis and pathological changes in brains. Furthermore, the capsule-deficient mutant was generated using natural transformation, and we showed that capsule was an essential virulence factor for S. pasteurianus. In addition, we found that tonsils and hilar lymph nodes of healthy pigs may be reservoir niches for this bacterium. Thus, our study provided valuable information about the pathogenetic characteristics and antimicrobial resistance of S. pasteurianus and paved the way for studying its pathogenesis.

The characteristics of population structure and antimicrobial resistance of Streptococcus suis serotype 8, a non-negligible pathotype

Streptococcus suis, the leading causative agent of swine streptococcosis, is considered as a severe zoonotic and foodborne pathogen for humans. Characteristics of population structure and pathogenicity of S. suis vary significantly by serotypes. As one of the main pathogenic serotypes causing clinical disease in pigs, very little is known about the pathogenicity, population structure, and antimicrobial resistance of S. suis serotype 8 (SS8). In this study, the genome of 26 SS8 strains isolated from healthy and diseased pigs was sequenced. Together with 38 sequences from NCBI, we found that SS8 population was clustered into 12 sequence types (ST) and 4 minimum core genome (MCG) groups, linked to the geographical distribution. Noteworthily, 10 strains belonged to MCG group 1 which was defined to possess the capacity to cause global outbreaks in our previous study. We found that 75% (9/12) of representative SS8 strains were virulent in mice and zebrafish, including all ST1241 strains. No virulence indicators were identified from 67 putative virulence-associated genes mainly identified among pathogenic serotype 2 strains. Instead, we found that the genotype of some of these genes was correlated to their evolution. All 26 isolates were classified as multidrug-resistant strains by antimicrobial susceptibility testing. The high carrying rate of tetO and ermB, mainly disseminated by integrative mobilizable elements, contributed to the prevalent resistance phenotypes to macrolides, lincosamides and tetracyclines. These findings indicated that the pathogenic potential of SS8 cannot be ignored and provided valuable information for SS8 surveillance.