Co-Existence of Oxazolidinone Resistance Genes cfr (D) and optrA on Two Streptococcus parasuis Isolates from Swine

This study was performed to investigate the presence and characteristics of the oxazolidinone resistance genes optrA and cfr (D) in Streptococcus parasuis . In total, 36 Streptococcus isolates (30 Streptococcus suis isolates, 6 Streptococcus parasuis isolates) were collected from pig farms in China in 2020–2021, using PCR to determine the presence of optrA and cfr . Then, 2 of the 36 Streptococcus isolates were further processed as follows. Whole-genome sequencing and de novo assembly were employed to analyze the genetic environment of the optrA and cfr (D) genes. Conjugation and inverse PCR were employed to verify the transferability of optrA and cfr (D). The optrA and cfr (D) genes were identified in two S. parasuis strains named SS17 and SS20, respectively. The optrA of the two isolates was located on chromosomes invariably associated with the araC gene and Tn 554 , which carry the resistance genes erm (A) and ant (9). The two plasmids that carry cfr (D), pSS17 (7550 bp) and pSS20-1 (7550 bp) have 100% nucleotide sequence identity. The cfr (D) was flanked by GMP synthase and IS1202. The findings of this study extend the current knowledge of the genetic background of optrA and cfr (D) and indicate that Tn 554 and IS1202 may play an important role in the transmission of optrA and cfr (D), respectively.