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 <i>Streptococcus agalactiae</i> [group B <i>Streptococcus</i> (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 <i>lsa(E)</i> and <i>lnu(B)</i> 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 <i>lsa(E)</i> and <i>lnu(B)</i> were identified as prevalent lincosamide resistance determinants alongside <i>erm(B)</i>, with 18.7% of isolates co-carrying <i>lsa(E)</i> and <i>lnu(B)</i>, 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 <i>lsa(E)-lnu(B)</i> 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, ICE<i>Sag37</i> served as the primary ICE harbouring <i>lsa(E)-lnu(B)</i>, while novel genetic contexts for <i>lsa(E)-lnu(B)</i> were identified in CC19, CC23 and CC103. This study highlights the high prevalence of <i>lsa(E)-lnu(B)</i> 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.