Abstract
Streptococcus suis is a zoonotic pathogen suspected to be a reservoir of antimicrobial resistance (AMR) genes. The genomes of 214 strains of 27 serotypes were screened for AMR genes and chromosomal Mobile Genetic Elements (MGEs), in particular Integrative Conjugative Elements (ICEs) and Integrative Mobilizable Elements (IMEs). The functionality of two ICEs that host IMEs carrying AMR genes was investigated by excision tests and conjugation experiments. In silico search revealed 416 ICE-related and 457 IME-related elements. These MGEs exhibit an impressive diversity and plasticity with tandem accretions, integration of ICEs or IMEs inside ICEs and recombination between the elements. All of the detected 393 AMR genes are carried by MGEs. As previously described, ICEs are major vehicles of AMR genes in S. suis. Tn5252-related ICEs also appear to carry bacteriocin clusters. Furthermore, whereas the association of IME-AMR genes has never been described in S. suis, we found that most AMR genes are actually carried by IMEs. The autonomous transfer of an ICE to another bacterial species (Streptococcus thermophilus)—leading to the cis-mobilization of an IME carrying tet(O)—was obtained. These results show that besides ICEs, IMEs likely play a major role in the dissemination of AMR genes in S. suis.
Highlights
Streptococcus suis—a normal inhabitant of the upper respiratory tract of pigs—is an important cause of post-weaning infections in pigs and a zoonotic agent afflicting people in close contact with infected pigs or eating insufficiently cooked pork meat [1,2]
Analysis of 214 genomes of S. suis strains belonging to 27 different serotypes revealed 232 Integrative Conjugative Elements (ICEs) with a full sequence, 49 ICEs with a partial sequence (due to sequencings gap(s) in the de novo assembled genome) and 135 elements deriving from ICEs
Integrative Mobilizable Elements (IMEs)-related elements appeared more prevalent than ICEs since 406 IMEs and 51 elements deriving from IMEs were detected
Summary
Streptococcus suis—a normal inhabitant of the upper respiratory tract of pigs—is an important cause of post-weaning infections in pigs and a zoonotic agent afflicting people in close contact with infected pigs or eating insufficiently cooked pork meat [1,2]. It is a major agent of human meningitis in Asia [2]. Serotype 14 strains are frequently associated with human infections [2,5]. A case of human infection due to serotype 9, which is increasingly reported in pig invasive disease worldwide, was reported in Thailand [6]
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