Novel linear plasmids carrying vanA cluster drives the spread of vancomycin resistance in Enterococcus faecium in India. (June 2022) - Bakthavatchalam, Yamuna Devi
Highlights: In India, the burden of vancomycin-resistant Enterococcus faecium is growing; however, the genetic basis is largely unexplored. Sequence types (STs) of VRE were highly heterogeneous, and 24 distinct STs were identified. Novel Tn 1546 ( van A) variants carrying IS 256 and IS L3 elements. The van A gene was identified on both pRUM-like circular and pELF-like linear plasmids. Co-location of van A (encoding vancomycin resistance) and optr A (coding for resistance to linezolid) genes on transferable plasmids is worrisome. ABSTRACT: Objectives: The genetic basis for the spread of vancomycin resistance in Enterococcus faecium is largely unexplored in India. The present study aimed to investigate the plasmid diversity and variation of Tn 1546 associated with van A harbouring VREfm isolates. Methods: A total of 122 VREfm isolates collected from blood cultures were included in this study. MLST analysis was performed on all isolates, and they were also screened for the presence of van A and van B genes. Whole genome sequencing was performed for a subset of fifteen VREfm isolates belonging to ST1643. Results: All of the 122 VREfm isolates carried the van A gene. Twenty-four different sequence types were seen; of these, ST1643, ST80 and ST17 were predominant. Whole genome sequencing was performed on 15 VREfm isolates belonging to ST1643. For eight isolates the van A gene was found on pRUM-like circular plasmids, and for the remaining seven isolates, the van A gene was found on the linear plasmids. Novel Tn 1546 variants carrying van A were found on both circular and linear plasmids. Interestingly, co-presence of van A and optr A were seen in the backbone of three linear plasmids. Conclusion: Multiple van A-carrying plasmids and Tn 1546 -like elements were involved in the dissemination of vancomycin resistance in VREfm. The co-occurrence of Tn 1546 carrying van A and Tn 554 family transposon carrying optr A on the backbone of plasmids is worrisome. The dissemination of such plasmids may pose treatment and infection control challenges.