Cytotoxicity of Streptococcus agalactiae secretory protein on tilapia cultured cells

Identification of ClpB, a molecular chaperone involved in the stress tolerance and virulence of Streptococcus agalactiae

Bacterial ClpB is an ATP-dependent disaggregate that belongs to the Hsp100/Clp family and facilitates bacterial survival under hostile environmental conditions. Streptococcus agalactiae, which is regarded as the major bacterial pathogen of farmed Nile tilapia (Oreochromis niloticus), is known to cause high mortality and large economic losses. Here, we report a ClpB homologue of S. agalactiae and explore its functionality. S. agalactiae with a clpB deletion mutant (∆clpB) exhibited defective tolerance against heat and acidic stress, without affecting growth or morphology under optimal conditions. Moreover, the ΔclpB mutant exhibited reduced intracellular survival in RAW264.7 cells, diminished adherence to the brain cells of tilapia, increased sensitivity to leukocytes from the head kidney of tilapia and whole blood killing, and reduced mortality and bacterial loads in a tilapia infection assay. Furthermore, the reduced virulence of the ∆clpB mutant was investigated by transcriptome analysis, which revealed that deletion of clpB altered the expression levels of multiple genes that contribute to the stress response as well as certain metabolic pathways. Collectively, our findings demonstrated that ClpB, a molecular chaperone, plays critical roles in heat and acid stress resistance and virulence in S. agalactiae. This finding provides an enhanced understanding of the functionality of this ClpB homologue in gram-positive bacteria and the survival strategy of S. agalactiae against immune clearance during infection.

Geographical, Temporal and Host-Species Distribution of Potentially Human-Pathogenic Group B Streptococcus in Aquaculture Species in Southeast Asia

Group B Streptococcus (GBS) is a major pathogen of humans and aquatic species. Fish have recently been recognized as the source of severe invasive foodborne GBS disease, caused by sequence type (ST) 283, in otherwise healthy adults in Southeast Asia. Thailand and Vietnam are among the major aquaculture producers in Southeast Asia, with GBS disease reported in fish as well as frogs in both countries. Still, the distribution of potentially human-pathogenic GBS in aquaculture species is poorly known. Using 35 GBS isolates from aquatic species in Thailand collected from 2007 to 2019 and 43 isolates from tilapia collected in Vietnam in 2018 and 2019, we have demonstrated that the temporal, geographical, and host-species distribution of GBS ST283 is broader than previously known, whereas the distribution of ST7 and the poikilothermic lineage of GBS are geographically restricted. The gene encoding the human GBS virulence factor C5a peptidase, scpB, was detected in aquatic ST283 from Thailand but not in ST283 from Vietnam or in ST7 from either country, mirroring current reports of GBS strains associated with human sepsis. The observed distribution of strains and virulence genes is likely to reflect a combination of spill-over, host adaptation through the gain and loss of mobile genetic elements, and current biosecurity practices. The plastic nature of the GBS genome and its importance as a human, aquatic, and potentially foodborne pathogen suggests that active surveillance of GBS presence and its evolution in aquaculture systems may be justified.

Comparative genome analysis of Streptococcus strains to identify virulent genes causing neonatal meningitis

AIM

To determine Streptococcus agalactiae genes responsible for causing neonatal meningitis.

BACKGROUND

Streptococcus agalactiae strain 2603 V/R is causative agent of neonatal meningitis, maternal infection and sepsis in young children. World health organisation reported high burden of new born death caused by this bacterium. Streptococcus agalactiae colonizing epithelial cells of vagina and endothelial cells have high resistance to available antibiotic drugs which makes it essential to determine new drug targets.

OBJECTIVES

To compare the genome of selected strain with the non-pathogenic strains of streptococcus and identify the virulent and antibiotic resistant genes for adaptation in host environment.

METHOD

The whole genome of human pathogen Streptococcus agalactiae strain 2603 V/R was analysed and compared with Streptococcus dysgalactiae strains using visualization and annotation tools. Genomic islands, mobile genetic elements, virulent and resistant genes were studied.

RESULTS

Genetically pathogenic strain is most similar to Streptococcus dysgalactiae subsp. equisimilis strain NCTC 7136. Comparative analysis revealed the importance of capsular polysaccharides and surface proteins responsible for avoiding immune system attachment to host epithelial cells and virulent behaviour. High number of genes coding for antibiotics resistance may provide a competitive advantage for survival of pathogenic Streptococcus agalactiae strain 2603 V/R in its niche.

CONCLUSIONS

The comparative analysis of pathogenic strain Streptococcus agalactiae with non-pathogenic strains of Streptococcus dysgalactiae provided new insights in pathogenicity that could aid in recognization for new regions and genes for development of new drug development strategies considering presence of high number of resistance genes.

Combining segments 9 and 10 in DNA and recombinant protein vaccines conferred superior protection against tilapia lake virus in hybrid red tilapia (oreochromis sp.) compared to single segment vaccines

Tilapia lake virus (TiLV) now affects Nile tilapia culture worldwide, with no available commercial vaccine for disease prevention. DNA and recombinant protein-based vaccines were developed and tested following viral isolation and characterization. The viral strain isolated from diseased hybrid red tilapia (Oreochromis sp.) shared high levels of morphological and genomic similarity (95.49-99.52%) with other TiLV isolates in the GenBank database. TiLV segment 9 (Tis9) and segment 10 (Tis10) DNA vaccines (pcDNA-Tis9 and pcDNA-Tis10) and recombinant protein vaccines (Tis9 and Tis10) were prepared and tested for their efficacy in juvenile hybrid red tilapia. Fish were immunized with either single vaccines (pcDNA-Tis9, pcDNA-Tis10, Tis9 and Tis10) or combined vaccines (pcDNA-Tis9 + pcDNA-Tis10 and Tis9 + Tis10) by intramuscular injection and intraperitoneal injection for DNA and protein vaccines, respectively. Negative controls were injected with PBS or a naked pcDNA3.1 vector in the same manner. An experimental challenge with TiLV was carried out at 4 weeks post-vaccination (wpv) by intraperitoneal injection with a dose of 1 × 105 TCID50 per fish. Relative percent survival (RPS) ranged from 16.67 ± 00.00 to 61.11 ± 9.62%. The Tis10 and pcDNA-Tis10 vaccines conferred better protection compared to Tis9 and pcDNA-Tis9. Highest levels of protection were observed in pcDNA-Tis9 + pcDNA-Tis10 (61.11 ± 9.62%) and Tis9 + Tis10 (55.56 ± 9.62%) groups. Specific antibody was detected in all vaccinated groups at 1-4 wpv by Dot Blot method, with the highest integrated density at 2 and 3 wpv. In silico analysis of Tis9 and Tis10 revealed a number of B-cell epitopes in their coil structure, possibly reflecting their immunogenicity. Findings suggested that the combination of Tis9 and Tis10 in DNA and recombinant protein vaccine showed high efficacy for the prevention of TiLV disease in hybrid red tilapia.