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BackgroundProphylaxis 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.ResultsThis 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.ConclusionsTo 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.Electronic supplementary materialThe online version of this article (10.1186/s12917-018-1732-5) contains supplementary material, which is available to authorized users.

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Forkhead-associated (FHA) domains are phosphothreonine-binding modules prevalent in proteins with important cell cycle and DNA damage response functions. The yeast checkpoint kinase Rad53 is unique in containing two FHA domains. We have generated novel recessive rad53 alleles with abolished FHA domain functions resulting from Ala substitution of the critical phosphothreonine-binding residues Arg 70 and Arg 605 . In asynchronous cells, inactivation of the N-terminal FHA1 domain did not impair Rad53 activation and downstream functions, whereas inactivation of the C-terminal FHA2 domain led to reduced Rad53 activation and significantly increased DNA damage sensitivity. Simultaneous inactivation of both FHA domains abolished Rad53 activation and all downstream functions and dramatically increased the sensitivity to DNA damage and replication blocks similar to kinase-defective and rad53 null alleles, but did not compromise the essential viability function of Rad53. Interestingly, in G 2 /M synchronized cells, mutation of either FHA domain prevented Rad53 activation and impaired the cell cycle arrest checkpoint. Our data demonstrate that both FHA domains are required for normal Rad53 functions and indicate that the two FHA domains have differential but partially overlapping roles in Rad53 activation and downstream signaling. FHA1 domains contain ϳ100 -180 amino acid residues forming an 11-stranded ␤-sandwich and act as protein-protein interaction modules by binding to phosphothreonine (Thr(P)) residues in target ligands (1). FHA domains are present in a large number of proteins in all phyla from bacteria to mammals and seem to be prevalent among proteins with cell cycle and DNA damage response functions. Important human FHA domaincontaining checkpoint proteins include NBS1 that is mutated in the Nijmegen breakage syndrome (2), CHK2 that is mutated in a subset of cases of the Li-Fraumeni multicancer syndrome (3), the spindle checkpoint protein CHFR (4), and the recently identified NFBD1/MDC1 (5).The yeast homolog of the CHK2 kinase, Rad53, is the only known protein to contain two FHA domains (6). Rad53 plays central roles in yeast DNA damage and replication block checkpoints (7). The finding that the C-terminal FHA2 domain plays an important role in the DNA damage-dependent activation of Rad53 by binding to the phosphorylated upstream protein Rad9 was instrumental in defining FHA domains as Thr(P)-binding modules (8). Phosphorylated Rad9 can also bind to the N-terminal FHA1 domain, but the in vivo relevance of this interaction is unknown (9 -11). Other proposed Rad53 FHA domain ligands include Dbf4 that can interact in yeast twohybrid and in vitro assays with both the FHA1 and FHA2 domain (12) and the protein phosphatases Ptc2 and Ptc3 that can interact with the FHA1 domain and then down-regulate Rad53 activity in the recovery from DNA damage (13). An important question considering the presence of two FHA domains in Rad53 compared with a single N-terminal FHA domain in other related kinases is: do the two FHA domains ...

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