Prevalence and genetic characteristics of lincosamide resistance genes lsa(E) and lnu(B) in group B Streptococcus from southern China

Lincosamides serve as alternative therapeutic agents for penicillin-allergic patients with Streptococcus agalactiae [group B Streptococcus (GBS)] infections, but the escalating antibiotic resistance has severely compromised their clinical efficacy. This study investigated the epidemiological characteristics of antibiotic resistance and the co-transfer mechanisms of lincosamide resistance genes lsa(E) and lnu(B) in 631 clinical GBS isolates from southern China. The results showed that 98.3% of isolates carried at least one antibiotic resistance gene, with lincosamide resistance genes detected in 76.1% of isolates. The lsa(E) and lnu(B) were identified as prevalent lincosamide resistance determinants alongside erm(B), with 18.7% of isolates co-carrying lsa(E) and lnu(B), and double-positive isolates predominantly distributed in high-risk clonal complexes (CCs): CC10 (15.4%), CC17 (21.7%), CC19 (17.9%) and CC103 (35.5%). Genomic analyses revealed that lsa(E)-lnu(B) formed composite resistance modules by integrating into resistance gene clusters within integrative and conjugative elements (ICEs), with insertion sequence-mediated mobilization increasing their dissemination risk. In CC10 and CC17, ICESag37 served as the primary ICE harbouring lsa(E)-lnu(B), while novel genetic contexts for lsa(E)-lnu(B) were identified in CC19, CC23 and CC103. This study highlights the high prevalence of lsa(E)-lnu(B) resistance clusters in GBS clinical isolates from southern China and their ICE-mediated dissemination mechanisms, providing critical molecular epidemiological evidence for resistance surveillance and precision therapeutic strategies.