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Antimicrobial resistance has become a major public health threat. Food-related Staphylococcus species have received much attention due to their multidrug resistance. The cfr gene associated with multidrug resistance has been consistently detected in food-derived Staphylococcus species. In this retrospective study, we examined the prevalence of cfr-positive Staphylococcus strains isolated from poultry meat in different geographical areas of China from 2011 to 2016. Two cfr-positive Staphylococcus delphini strains were identified from poultry meat in China. Comparative and whole-genome analyses were performed to characterize the genetic features and overall antimicrobial resistance genes in the two S. delphini isolates 245-1 and 2794-1. Whole-genome sequencing showed that they both harbored a novel 20,258-bp cfr-carrying Tn558 transposon derivative on their chromosomes. The Tn558 derivative harbors multiple antimicrobial resistance genes, including the transferable multiresistance gene cfr, chloramphenicol resistance gene fexA, aminoglycoside resistance genes aacA-aphD and aadD, and bleomycin resistance gene ble. Surprisingly, within the Tn558 derivative, an active unconventional circularizable structure containing various resistance genes and a copy of a direct repeat sequence was identified by two-step PCR. Furthermore, core genome phylogenetic analysis revealed that the cfr-positive S. delphini strains were most closely related to S. delphini 14S03313-1 isolated from Japan in 2017 and 14S03319-1 isolated from Switzerland in 2017. This study is the first report of S. delphini harboring a novel cfr-carrying Tn558 derivative isolated from retail food. This finding raises further concerns regarding the potential threat to food safety and public health safety. The occurrence and dissemination of similar cfr-carrying transposons from diverse Staphylococcus species need further surveillance.

Antimicrobial resistance has become a major public health threat. Food-related Staphylococcus species have received much attention due to their multidrug resistance. The cfr gene associated with multidrug resistance has been consistently detected in food-derived Staphylococcus species. In this retrospective study, we examined the prevalence of cfr -positive Staphylococcus strains isolated from poultry meat in different geographical areas of China from 2011 to 2016. Two cfr -positive Staphylococcus delphini strains were identified from poultry meat in China. Comparative and whole-genome analyses were performed to characterize the genetic features and overall antimicrobial resistance genes in the two S. delphini isolates 245-1 and 2794-1. Whole-genome sequencing showed that they both harbored a novel 20,258-bp cfr -carrying Tn 558 transposon derivative on their chromosomes. The Tn 558 derivative harbors multiple antimicrobial resistance genes, including the transferable multiresistance gene cfr , chloramphenicol resistance gene fexA , aminoglycoside resistance genes aacA-aphD and aadD , and bleomycin resistance gene ble. Surprisingly, within the Tn 558 derivative, an active unconventional circularizable structure containing various resistance genes and a copy of a direct repeat sequence was identified by two-step PCR. Furthermore, core genome phylogenetic analysis revealed that the cfr -positive S. delphini strains were most closely related to S. delphini 14S03313-1 isolated from Japan in 2017 and 14S03319-1 isolated from Switzerland in 2017. This study is the first report of S. delphini harboring a novel cfr -carrying Tn558 derivative isolated from retail food. This finding raises further concerns regarding the potential threat to food safety and public health safety. The occurrence and dissemination of similar cfr -carrying transposons from diverse Staphylococcus species need further surveillance. [ABSTRACT FROM AUTHOR]

Traditionally, insertion sequences (ISs) play a major role in disseminating antimicrobial resistance genes (ARGs) in bacteria through transposition and translocation, forming regions that contain multiple ARGs flanked by single or multiple copies of IS. In addition, unconventional circularizable structures (UCSs), lacking recombinase genes but being surrounded by directly repeated sequences (DRs) of various sizes which do not contain transposase genes, were reported to be involved in the dissemination of ARGs. In this study, a novel UCS was identified on plasmid pE508–2 in E. faecalis E508, which carried a 24,411 bp multiresistance gene cluster, consisting of the resistance genes aphA3 , lnu (B), lsa (E), spw , aac (A) -aph (D) , lnu (B), dfrG , and two copies of aadE flanked by copies of erm (B). PCR assays revealed that three types of UCSs with lengths of 7235, 16,437, and 23,673 bp were formed, each of which contained the respective resistance genes and one copy of erm (B). Using erm (B)-negative and -positive strains, we demonstrated that erm (B)-carrying UCSs failed to transfer into an erm (B)-negative strain, but could integrate into an erm (B)-positive strain in a new site adjacent to a pre-existing erm (B) gene by natural transformation. Database searches revealed that erm (B)-flanked multiresistance gene regions, which might be able to form the respective UCSs, are present among various bacteria from different sources in various countries. In summary, this study experimentally demonstrated the excision and integration of UCS involving structures that include erm (B). The widespread presence of these UCSs in various Gram-positive bacteria highlights its role in the dissemination of ARGs among bacterial pathogens. • A structure containing multiple resistance genes flanked by three direct repeats containing the erm (B) gene was identified. • Direct repeats containing the erm (B) gene could form three unconventional circularizable structures (UCSs). • The erm (B)-carrying UCSs integrate into an erm (B)-positive strain at a new site adjacent to a pre-existing erm (B) gene. • The structures containing two or more erm (B) copies are widespread present in various Gram-positive bacteria. [ABSTRACT FROM AUTHOR]