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The emergence of the mobile colistin-resistance genes mcr-1 has attracted significant attention worldwide. This study aimed to investigate the genetic features of mcr-1 -carrying plasmid among carbapenem-resistant Enterobacterales (CRE) isolates and the potential genetic basis governing transmission. Seventeen mcr -harboring isolates were analyzed based on whole genome sequencing using short-read and long-read platforms. All the mcr-1 -carrying isolates could be conjugatively transferred into a recipient Escherichia coli UB1637. Among these 17 isolates, mcr-1 was located on diverse plasmid Inc types, consisting of IncX4 (11/17; 64.7%), IncI2 (4/17; 23.53%), and IncHI/IncN (2/17; 11.76%). Each of these exhibited remarkable similarity in the backbone set that is responsible for plasmid replication, maintenance, and transfer, with differences being in the upstream and downstream regions containing mcr-1 . The IncHI/IncN type also carried other resistance genes ( bla TEM-1B or bla TEM-135 ). The mcr-1 -harboring IncX4 plasmids were carried in E. coli ST410 (7/11; 63.6%) and ST10 (1/11; 9.1%) and Klebsiella pneumoniae ST15 (1/11; 9.1%), ST336 (1/11; 9.1%), and ST340 (1/11; 9.1%). The IncI2-type plasmid was harbored in E. coli ST3052 (1/4; 25%) and ST1287 (1/4; 25%) and in K. pneumoniae ST336 (2/4; 50%), whereas IncHI/IncN were carried in E. coli ST6721 (1/2; 50%) and new ST (1/2; 50%). The diverse promiscuous plasmids may facilitate the spread of mcr-1 among commensal E. coli or K. pneumoniae strains in patients. These results can provide information for a surveillance system and infection control for dynamic tracing.

Streptococcus suis serotype 14 is the second most prevalent serotype after serotype 2, and is highly prevalent in Southeast Asia. Among the serotype 14 strains, sequence type (ST) 105 is found in humans and pigs. We analysed the genome sequences of S. suis ST105 to identify unique sequences to develop a multiplex PCR (mPCR) -gel electrophoresis and mPCR-lateral flows trip (LFS) for epidemiological purposes. The ST105 genome was closely related to the ST1 genomes. All ST105 of Thai and Vietnamese strains were highly homologous. Of the 1818 genes found in all compared genomes, 36 unique sequences were detected only in the ST105 strain. Of these, two unique sequences encoding hypothetical proteins were selected as PCR targets. Only S. suis ST105 strains were positive for both mPCRs. mPCR-LFS had fewer complications, lower costs, and less time for testing, than those of mPCR-gel electrophoresis. This comparative genomic study demonstrates the usefulness of identifying unique sequences of ST105 S. suis . These unique sequences could be used to develop diagnostic or screening tools, such as PCR, for the detection of specific strains or clones for epidemiological purposes.

Streptococcus suis is a zoonotic pathogen that causes invasive infections in humans and pigs. Although S. suis serotype 2 strains are most prevalent worldwide, other serotypes are also occasionally detected. Herein, we investigated the genomes of two S. suis serotype 1 strains belonging to the clonal complex 1, which were recovered from a human patient and an asymptomatic pig, respectively. The genomes differed in pathotype, virulence-associated gene (VAG) profile, minimum core genome (MCG) typing, and antimicrobial resistance gene content. The porcine serotype 1 strain was sequence type (ST) 237 and MCG1, whereas the human serotype 1 strain was ST105 and MCG ungroupable. Both strains were susceptible to several antibiotics consisting of β-lactams, fluoroquinolones, and chloramphenicol. Resistance to tetracycline, macrolides, and clindamycin was observed, which was attributed to the genes tet(O) and erm(B) . Analysis of 99 VAG revealed Hhly3 , NisK, NisR, salK/salR, srtG, virB4 , and virD4 were absent in both serotype 1. However, the porcine strain lacked sadP (Streptococcal adhesin P), whereas the human strain harbored sadP1 . Phylogenetic analysis revealed that human S. suis ST105 strains from Vietnam were genetically the closest to the human serotype 1 strain, whereas porcine S. suis ST11 strains from China and Thailand were genetically the closest to the porcine strain.

Streptococcus suis is a zoonotic pathogen that causes invasive infections in individuals who are in close contact with infected pigs or contaminated pork-derived products. An unencapsulated S. suis serotype 31 strain 43640 (sequence type 221) was first isolated from a human in Thailand in 2015; however, the mechanisms underlying host-cell interactions and virulence in animal models of this serotype are still limited. This study aimed to determine the virulence of the human unencapsulated S. suis serotype 31 strain 43640 using in vitro (A549 epithelial cells) and in vivo (C57BL/6 mouse) models. The adhesion rate of the unencapsulated strain 43640 to A549 cells was significantly lower than that of the highly pathogenic S. suis serotype 2 strain P1/7 after infection at multiplicity of infection (MOI) 1 ( p  < 0.01) and MOI 10 ( p  < 0.05). The invasion of epithelial cells by S. suis serotype 31 strain 43640 was significantly higher than that of serotype 2 strain P1/7 and the reference strain 92-4172 4 h after infection. S. suis serotypes 31 and 2 significantly induced cytotoxicity in epithelial cells by more than 50% and 90%, respectively, after 4 h and 18 h of infection. S. suis serotype 31 strain 43640 induced apoptosis in A549 cells via a caspase 9-dependent pathway. Using an in vivo mouse model, we demonstrated that S. suis serotype 31 strain 43640 induced 13.33% and 46.67% mortality due to septicemia after 24 h and 48 h, respectively. Bacterial counts in the blood of mice infected with strain 43640 were significantly lower than those in mice infected with the reference strain 12 h and 24 h after infection ( p  < 0.05). This study provides information on serotype 31-ST221 virulence in in vitro and in vivo models and proves that ST221 (CC221/234), an emerging human S. suis clone in Thailand, is potentially virulent.

The surge in mobile colistin-resistant genes ( mcr ) has become an increasing public health concern, especially in carbapenem-resistant Enterobacterales (CRE). Prospective surveillance was conducted to explore the genomic characteristics of clinical CRE isolates harbouring mcr in 2015–2020. In this study, we aimed to examine the genomic characteristics and phonotypes of mcr-8 and mcr-9 harbouring carbapenem-resistant K. pneumoniae complex (CRKpnC). Polymerase chain reaction test and genome analysis identified CRKpnC strain AMR20201034 as K. pneumoniae (CRKP) ST147 and strain AMR20200784 as K. quasipneumoniae (CRKQ) ST476, harbouring mcr-8 and mcr-9 , respectively. CRKQ exhibited substitutions in chromosomal-mediated colistin resistance genes ( pmrB, pmrC, ramA, and lpxM ), while CRKP showed two substitutions in crrB , pmrB, pmrC, lpxM and lapB . Both species showed resistance to colistin, with minimal inhibitory concentrations of 8 µg/ml for mcr-8 -carrying CRKP isolate and 32 µg/ml for mcr-9 -carrying CRKQ isolate. In addition, CRKP harbouring mcr-8 carried bla NDM , while CRKQ harbouring mcr-9 carried bla IMP , conferring carbapenem resistance. Analysis of plasmid replicon types carrying mcr-8 and mcr-9 showed FIA-FII (96,575 bp) and FIB-HI1B (287,118 bp), respectively. In contrast with the plasmid carrying the carbapenemase genes, the CRKQ carried bla IMP-14 on an IncC plasmid, while the CRKP harboured bla NDM-1 on an FIB plasmid. This finding provides a comprehensive insight into another mcr -carrying CRE from patients in Thailand. The other antimicrobial-resistant genes in the CRKP were bla CTX-M-15 , bla SHV-11 , bla OXA-1 , aac(6′)-Ib-cr, aph(3′)-VI, ARR-3, qnrS1, oqxA, oqxB, sul1, catB3, fosA, and qacE , while those detected in CRKQ were bla OKP-B-15 , qnrA1, oqxA, oqxB, sul1, fosA, and qacE . This observation highlights the importance of strengthening official active surveillance efforts to detect, control, and prevent mcr -harbouring CRE and the need for rational drug use in all sectors.

Background Streptococcus suis is a zoonotic pathogen that causes substantial economic losses in the pig industry and contributes to human infections worldwide, especially in Southeast Asia. Recently, a multiplex polymerase chain reaction (PCR) process was developed to distinguish disease-associated and non-disease-associated pathotypes of S. suis European strains. Herein, we evaluated the ability of this multiplex PCR approach to distinguish pathotypes of S. suis in Thailand. Results This study was conducted on 278 human S. suis isolates and 173 clinically healthy pig S. suis isolates. PCR identified 99.3% of disease-associated strains in the human isolates and 11.6% of non-disease-associated strains in the clinically healthy pig isolates. Of the clinically healthy pig S. suis isolates, 71.1% were classified as disease-associated. We also detected undetermined pathotype forms in humans (0.7%) and pigs (17.3%). The PCR assay classified the disease-associated isolates into four types. Statistical analysis revealed that human S. suis clonal complex (CC) 1 isolates were significantly associated with the disease-associated type I, whereas CC104 and CC25 were significantly associated with the disease-associated type IV. Conclusion Multiplex PCR cannot differentiate non-disease-associated from disease-associated isolates in Thai clinically healthy pig S. suis strains, although the method works well for human S. suis strains. This assay should be applied to pig S. suis strains with caution. It is highly important that multiplex PCR be validated using more diverse S. suis strains from different geographic areas and origins of isolation.

Carbapenem-resistant Enterobacterales (CRE) species are top priority pathogens according to the World Health Organization. Rapid detection is necessary and useful for their surveillance and control globally. This study developed a multiplex polymerase chain reaction (mPCR) detection of the common carbapenemase genes NDM, KPC, and OXA-48-like, together with identification of Escherichia coli, and distinguished a Klebsiella pneumoniae complex to be K. pneumoniae, K. quasipneumoniae, and K. variicola. Of 840 target Enterobacterales species, 190 E. coli, 598 K. pneumoniae, 28 K. quasipneumoniae, and 23 K. variicola. with and without NDM, KPC, or OXA-48-like were correctly detected for their species and carbapenemase genes. In contrast, for the Enterobacterales species other than E. coli or K. pneumoniae complex with carbapenemase genes, the mPCR assay could detect only NDM, KPC, or OXA-48-like. This PCR method should be useful in clinical microbiology laboratories requiring rapid detection of CRE for epidemiological investigation and for tracking the trends of carbapenemase gene dynamics.

Streptococcus suis is a swine pathogen that also causes invasive infections in humans, leading to significant economic losses in pig production worldwide. Serotype 2 is the most pathogenic S. suis strain associated with human infections. However, non-serotype 2 strains isolated from humans have been reported globally. Here, we conducted a comparative genomic analysis of S. suis serotype 7-ST373 strains belonging to clonal complex 94, isolated from both humans and pigs, and assessed their virulence through mouse infection experiments. Genomic analysis revealed that S. suis serotype 7-ST373 strains harbor genomic islands 1–3 of the pathogenic S. suis clade. They also possess a high number of virulence-associated genes, similar to those of virulent serotype 2 strains, suggesting a high virulence potential. The antimicrobial resistance gene tet(O) , which confers tetracycline resistance, was found in all ST373 strains, while erm(B) , which confers macrolide resistance, was detected in most ST373 strains. However, the macrolide and lincosamide resistance genes lnu(B) and lsa(E) were found exclusively in a Thai human strain. Comparative genomics of ST373 strains with the virulent serotype 2 strain P1/7 identified 76 unique genes in ST373 strains, including 30 genes exclusively present in human ST373 strains. Mouse virulence experiments with two human ST373 strains (GX69 and STC2826) and one strain from a healthy pig (WUSS318) resulted in 100% mortality, classifying them as highly virulent. These findings indicate that serotype 7-ST373 strains demonstrate pathogenic potential and should be closely monitored.

Diseases caused by Streptococcus suis are a significant economic and welfare concern in pigs as well as in humans. Several molecular methods have been applied to investigate S. suis strain diversity and identify phylogenetic groups. Multilocus sequence typing (MLST), commonly used to differentiate between S. suis strains, has been instrumental in identifying that the species is genetically highly diverse. Recent advances in whole-genome analysis have resulted in schemes permitting the classification of S. suis populations as pathogenic or non-pathogenic, or disease-associated or non-disease associated. Here, we review these and other molecular approaches that can be used for surveillance, outbreak tracking, preventative health management, effective treatment and control, as well as vaccine development, including PCR based-assays that are easy to apply in modest diagnostic settings and which allow for the rapid screening of a large number of isolates at relatively low cost, granting the identification of several major clonal complexes of the S. suis population.