Streptococcus suis is a previously neglected, newly emerging multidrug-resistant zoonotic pathogen. Mobile genetic elements (MGEs) play a key role in intra- and interspecies horizontal transfer of antimicrobial resistance (AMR) determinants. Although previous studies showed the presence of several MGEs, a comprehensive analysis of AMR-associated mobilome as well as their interaction and evolution has not been performed. In this study, we presented the AMR-associated mobilome and their insertion hotspots in S. suis. Integrative conjugative elements (ICEs), prophages and tandem MGEs were located at different insertion sites, while 86% of the AMR-associated MGEs were inserted at rplL and rum loci. Comprehensive analysis of insertions at rplL and rum loci among four pathogenic Streptococcus species (Streptococcus agalactiae, Streptococcus pneumoniae, Streptococcus pyogenes, and S. suis) revealed the existence of different groups of MGEs, including Tn5252, ICESp1108, and TnGBS2 groups ICEs, Φm46.1 group prophage, ICE_ICE and ICE_prophage tandem MGEs. Comparative ICE genomics of ICESa2603 family revealed that module exchange and acquisition/deletion were the main mechanisms in MGEs’ expansion and evolution. Furthermore, the observation of tandem MGEs reflected a novel mechanism for MGE diversity. Moreover, an in vitro competition assay showed no visible fitness cost was observed between different MGE-carrying isolates and a conjugation assay revealed the transferability of ICESa2603 family of ICEs. Our statistics further indicated that the prevalence and diversity of MGEs in S. suis is much greater than in other three species which prompted our hypothesis that S. suis is probably a MGEs reservoir for other streptococci. In conclusion, our results showed that acquisition of MGEs confers S. suis not only its capability as a multidrug resistance pathogen, but also represents a paradigm to study the modular evolution and matryoshkas of MGEs.

Prophages play important roles in the transduction of various functional traits, including virulence factors, but remain debatable in harboring and transmitting antimicrobial resistance genes (ARGs). Herein we characterize a prevalent family of prophages in Streptococcus, designated SMphages, which harbor twenty-five ARGs that collectively confer resistance to ten antimicrobial classes, including vanG-type vancomycin resistance locus and oxazolidinone resistance gene optrA. SMphages integrate into four chromosome attachment sites by utilizing three types of integration modules and undergo excision in response to phage induction. Moreover, we characterize four subtypes of Alp-related surface proteins within SMphages, the lethal effects of which are extensively validated in cell and animal models. SMphages transfer via high-frequency conjugation that is facilitated by integrative and conjugative elements from either donors or recipients. Our findings explain the widespread of SMphages and the rapid dissemination of ARGs observed in members of the Streptococcus genus.

Sir, Oxazolidinones, including linezolid and tedizolid, are highly effective against infections of enterococci, staphylococci and streptococci, which are clinically important Gram-positive pathogens. 1 cfr is the first gene that is transferable and causes resistance to oxazolidinones; cfr also mediates resistance to phenicols, lincosamides, pleuromutilins and streptogramin A. 2 Recently, Wang et al. 3 first reported a novel transferable resistance gene, optrA, which confers resistance to oxazolidinones and phenicols in enterococcal isolates in China. Shortly after, the optrA gene was detected in clinical enterococcal isolates in Italy 4 and in Staphylococcus sciuri in China. 5 WGS is now routine and thousands of bacterial genomes are available in public databases. To investigate the prevalence of optrA in the sequenced genomes, we retrieved the optrA sequence and traced this gene in the GenBank database (Table S1, available as Supplementary data at JAC Online). We found that optrA presented in two enterococcal isolates from human blood in the USA, two environmental samples from swine manure metagenome in China and six Streptococcus suis isolates from healthy pigs in China. These results are the first reported presence of optrA in clinical enterococci in the USA, and in environmental microorganisms and streptococci in China. optrA genes in those isolates showed 99% nucleotide identity with the original optrA from Enterococcus faecalis pE349. Comparison of the OptrA amino acid sequences revealed seven variants with alterations at nine positions (Table S1). Further analysis showed that the genetic context of optrA in two US isolates, especially that from E. faecalis 599, was similar to that in the chromosome of E. faecalis E016 though seemingly lacking

To avoid potential systematical toxicity, solid lipid nanoparticles (SLNs) were prepared as a vehicle for transdermal delivery of ivermectin (IVM) using hot homogenisation followed by ultrasonic method. The as-prepared SLNs were approximately spherical shape with good stability. IVM was encapsulated in amorphous form within SLNs and displayed prolonged release from SLNs without burst release due to high encapsulation efficiency (EE). The cumulative permeation of IVM across excised rat skin from SLNs was significantly increased compared to the ivermection suspension. These results indicated that the proposed SLNs can be considered as an efficient carrier for dermal delivery of IVM to effectively treat scabies.