Abstract
Linezolid and vancomycin are among the last-resort antimicrobial agents in the treatment of multidrug-resistant Gram-positive bacterial infections. Linezolid- and vancomycin-resistant (LVR) Gram-positive bacteria may pose severe threats to public health. In this study, three optrA- and vanG-positive Streptococcus suis strains were isolated from two farms of different cities. There were only 1 and 343 single-nucleotide polymorphisms in coding region (cSNPs) of HCB4 and YSJ7 to YSJ17, respectively. Mobilome analysis revealed the presence of vanG, erm(B), tet(O/W/32/O), and aadE-apt-sat4-aphA3 cluster on an integrative and conjugative element, ICESsuYSJ17, and erm(B), aphA3, aac(6′)-aph(2″), catpC194, and optrA on a prophage, ΦSsuYSJ17-3. ICESsuYSJ17 exhibited a mosaic structure and belongs to a highly prevalent and transferable ICESa2603 family of Streptococcus species. ΦSsuYSJ17-3 shared conserved backbone to a transferable prophage Φm46.1. A novel composite transposon, IS1216E-araC-optrA-hp-catpC194-IS1216E, which can be circulated as translocatable unit (TU) by IS1216E, was integrated on ΦSsuYSJ17-3. Vancomycin resistance phenotype and vanG transcription assays revealed that the vanG operon was inducible. The LVR strain YSJ17 exhibited moderate virulence in a zebrafish infection model. To our knowledge, this is the first report of LVR isolate, which is mediated by acquired resistance genes optrA and vanG operons in Gram-positive bacteria. Since S. suis has been recognized as an antimicrobial resistance reservoir in the spread of resistance genes to major streptococcal pathogens, the potential risks of disseminating of optrA and vanG from S. suis to other Streptococcus spp. are worrisome and routine surveillance should be strengthened.
Highlights
Streptococcus suis is one of the most important bacterial causes of meningitis and contributes substantially to antimicrobial use in swine industry worldwide (Goyette-Desjardins et al, 2014)
Among 189 S. suis isolates collected from Jiangsu, China, 3 strains of different pig origin were positive for vanG, but exhibited variable phenotype to vancomycin
It is of special concern to animal and human health, as resistant bacteria are likely to be transmitted within farm animals and from farm animals to humans through close contact or food chain, as well as antimicrobial resistance (AMR) genes may be transferred from commensal bacteria to zoonotic pathogens (Mcewen and Fedorka-Cray, 2002; Marshall and Levy, 2011; Thanner et al, 2016)
Summary
Streptococcus suis is one of the most important bacterial causes of meningitis and contributes substantially to antimicrobial use in swine industry worldwide (Goyette-Desjardins et al, 2014). S. suis is thought to be an important antimicrobial resistance (AMR) reservoir contributing to the spread of AMR genes to major streptococcal pathogens (Palmieri et al, 2011; Huang et al, 2016b). The misuse of avoparcin had been reported to be associated with the occurrence of vancomycin-resistant enterococcus (VRE) in most parts of Europe (Bager et al, 1997; Hao et al, 2016). For this reason, avoparcin has been banned in food-producing animals in Denmark, 1995, and subsequently in China, 2002. We reported the vanG-type vancomycin resistance in zoonotic pathogen S. suis (Huang et al, 2018)
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