A closed genome of Streptococcus agalactiae ST347/II reveals a composite integrative element coupling nisin P biosynthesis to erm(B) and tet(O) in Dominican group B Streptococcus

A closed Streptococcus agalactiae ST347/CC19 serotype II genome (2,066,859 bp) links nisin P biosynthesis to clindamycin resistance via contiguous erm(B) and tet(O) on a composite integrative element.

• Why it matters: Clindamycin prophylaxis for penicillin-allergic women depends on which group B Streptococcus lineages carry resistance and on the mobile elements that disseminate it. No Dominican group B Streptococcus genome had been closed to resolve these element relationships.
• What they did: The isolate was sequenced twice on Oxford Nanopore, assembled as one circular chromosome, and screened against 83 Dominican maternal colonization genomes. Two integrative conjugative elements (~34 kb and ~35 kb) were delimited, with an eleven-gene class I lanthipeptide cluster 96 bp from the first element encoding a 31-residue nisin P core.
• The result: The complete operon appeared in 12/83 genomes and 13/84 (15.5%) with the isolate; tet(O) and erm(B) co-occurred in all 12 carriers (Fisher p = 1.03 x 10^-14 and 4.70 x 10^-12). In drafts, co-occurrence was statistical rather than linkage, while ST1 genomes lacked the operon and predicted lineage-wide susceptibility.

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