Genome sequences of antibiotic-resistant Streptococcus suis strains isolated from human patients and diseased and asymptomatic pigs in Thailand.

Streptococcus suis, a zoonotic bacterial pathogen, has negative economic impacts on both intensive swine production and human health worldwide. Whole-genome sequencing and comparative genomic analysis have been widely used for comprehensive classification and investigation of the genetic basis of several S. suis strains obtained from distinct hosts in different geographic areas, revealing great genetic diversity of this zoonotic pathogen. In this study, whole-genome sequences of antibiotic-resistant S. suis strains isolated from human patients (2 strains), diseased pigs (4 strains), and asymptomatic pigs (3 strains) in Thailand were compared with known genomes of 1186 S. suis strains. Single-nucleotide polymorphism-based phylogenetic analysis indicated that the Thai-isolated S. suis strains have close genetic relatedness to S. suis strains isolated from Canada, China, Denmark, Netherlands, United Kingdom, and United States of America. The genome analysis revealed genes conferring antibiotic resistance (aad(6), ant(6)-Ia, ermB, tet(O), patB, and sat4) and gene clusters (aph(3')-IIIa and aac(6')-Ie-aph(2″)-Ia) associated with aminoglycoside, macrolide, and fluoroquinolone resistance in S. suis in Thailand. This work provides additional resources for future genomic epidemiology investigation of S. suis.

Antimicrobial susceptibility of Streptococcus suis isolated from diseased pigs, asymptomatic pigs, and human patients in Thailand.

BACKGROUND: Prophylaxis and treatment of emerging zoonotic Streptococcus suis infection in agricultural and healthcare settings mainly rely on antibiotics. However, continued use of antibiotics contributing to emergence and widespread of antibiotic resistant S. suis becomes a significant challenge in many endemic countries, including Thailand. Meanwhile, the knowledge of antibiotic susceptibility patterns of bacterial pathogens is required for overcoming the antimicrobial resistance problem, the information of antibiotic susceptibility of S. suis strains isolated in Thailand remains limited. This study aims to assess the susceptibility of Thai-isolated S. suis strains to different antibiotic classes in order to gain an insight into the distribution of antibiotic-resistant patterns of S. suis strains in different regions of Thailand. RESULTS: This study revealed the antimicrobial resistance and multidrug resistance of 262 S. suis strains isolated in different regions of Thailand. Susceptibility testing indicated widespread resistance to macrolides and tetracyclines of S. suis strains in the country. Beta-lactam antibiotic drugs (including cefotaxime and ceftiofur), vancomycin, chloramphenicol, as well as florfenicol were potentially the most effective therapeutic drugs for the treatment of S. suis infection in both pigs and humans. High prevalence of intermediate susceptibility of S. suis isolated from asymptomatic pigs for penicillin G, gentamicin, enrofloxacin, and norfloxacin could be the premise of the emergence of S. suis antibiotic resistance. Resistance was also found in S. suis strains isolated from asymptomatic pigs indicating that they could act as reservoirs of antibiotic resistance genes. CONCLUSIONS: To the best of our knowledge, this is the first report on antimicrobial resistance of a large collection of S. suis strains isolated from pigs and humans in Thailand. It revealed the multidrug resistance of S. suis strains in pigs and humans. The information gained from this study raises an awareness and encourage best practices of appropriate antibiotic drug prescribing and use among human health and agriculture sectors.

Expression and Characterization of Serotype 2 Streptococcus suis Arginine Deiminase.

BACKGROUND: Arginine deiminase (ArcA) has been speculated to facilitate the intracellular survival of Streptococcus suis under acidic conditions. However, the physical and biological properties and function of SS2-ArcA have not yet been elucidated. METHODS: Recombinant SS2-ArcA (rSS2-ArcA) was expressed and purified using Ni-NTA affinity chromatography. Under various pH and temperature conditions, the enzymatic properties of purified rSS2-ArcA and crude native SS2-ArcA were determined. RESULTS: The SS2-arcA-deduced amino acid sequence contained a conserved catalytic triad (Cys399-His273-Glu218). The optimum temperature and pH of 47-kDa rSS2-ArcA and crude native SS2-ArcA were 42°C and pH 7.2. The rSS2-ArcA and crude native SS2-ArcA were stable for 3 h at 4 and 25°C, respectively. The pH stability and dependency tests suggested that rSS2-ArcA and crude native SS2-ArcA were functionally active in acidic conditions. The L-arginine substrate binding affinity (Km) values of rSS2-ArcA (specific activity 16.00 U/mg) and crude native SS2-ArcA (specific activity 0.23 U/mg) were 0.058 and 0.157 mM, respectively. rSS2-ArcA exhibited a weak binding affinity with the common ArcA inhibitors L-canavanine and L-NIO. Furthermore, the partial inactivation of SS2-ArcA significantly impaired the viability and growth of SS2 at pH 4.0, 6.0, and 7.5. CONCLUSIONS: This study profoundly demonstrated the involvement of ArcA enzymatic activity in S. suis survival under acidic conditions.