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<p>Serotype Ib and sequence type 261 (Ib/ST261) of <i>Streptococcus agalactiae</i> has emerged as a specific pathogen causing high mortality of bullfrogs (<i>Rana catesbeiana</i>) in Hainan, China, since 2019. However, its virulence gene profile and antimicrobial resistance (AMR) patterns remain poorly characterized. This study is aimed to characterize the virulence gene profile, resistance-associated mutations, and dynamic changes in antimicrobial resistance of <i>S. agalactiae</i> Ib/ST261 collected from diseased bullfrogs in 2019 and 2023 in Hainan, China. By comparing with the isolates in 2019, they shared a stable virulence gene profile (<i>pav</i>A <i>+ sip+iag</i>A <i>+ cfb+hyl</i>B<i>+bib</i>A<i>+csp</i>A<i>+fbs</i>A), and same resistance-associated adaptation mutations of <i>gyr</i>A (S81L), <i>par</i>C (D83Y), <i>pbp</i>1A (Y305F, A604T, N639S), and <i>pbp</i>2B (V79A, S247F, S313P, N412D, T656I), as well as similar weak biofilm formation. Though most of them exhibited similarly high resistance to tetracycline (97%), chloramphenicol (92%), cotrimoxazole (92%), sulfamethoxazole (90%), and penicillin (90%), the acquired resistance genes of <i>tet</i>M, <i>aac</i>C2, <i>sul</i>1 and <i>sul</i>2 were almost completely lost and the resistance was significantly different with the changes of environmental stress from 2019 to 2023, especially, the emerged carbapenem resistance was substantially enhanced in 4 folds to imipenem, and aminoglycoside resistance was further boosted in 34 folds to spectinomycin, 46 folds to streptomycin and 49.7 folds to amikacin. Our findings highlight the persistent virulence and variation of multidrug resistance of <i>S. agalactiae</i> serotype Ib/ST261, underscoring its specific role in bacteremia of bullfrog and the challenges it poses for treatment.</p>

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Virulence and resistance adaptation of Streptococcus agalactiae Ib/ST261 infecting bullfrogs in Hainan, China between 2019 and 2023

  • 期刊论文

  • 发表日期：

    2026年3月15日

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  • Guiying Guo,
  • Zihao Di,
  • Sheng Huang,
  • Xuesong Li,
  • Nuo Yang,
  • Lixia Fan,
  • Jun Xie,
  • Xiuqing Cai,
  • Yuqi Meng,
  • Fei Yan,
  • Jiping Zheng

摘要

Serotype Ib and sequence type 261 (Ib/ST261) of Streptococcus agalactiae has emerged as a specific pathogen causing high mortality of bullfrogs (Rana catesbeiana) in Hainan, China, since 2019. However, its virulence gene profile and antimicrobial resistance (AMR) patterns remain poorly characterized. This study is aimed to characterize the virulence gene profile, resistance-associated mutations, and dynamic changes in antimicrobial resistance of S. agalactiae Ib/ST261 collected from diseased bullfrogs in 2019 and 2023 in Hainan, China. By comparing with the isolates in 2019, they shared a stable virulence gene profile (pavA + sip+iagA + cfb+hylB+bibA+cspA+fbsA), and same resistance-associated adaptation mutations of gyrA (S81L), parC (D83Y), pbp1A (Y305F, A604T, N639S), and pbp2B (V79A, S247F, S313P, N412D, T656I), as well as similar weak biofilm formation. Though most of them exhibited similarly high resistance to tetracycline (97%), chloramphenicol (92%), cotrimoxazole (92%), sulfamethoxazole (90%), and penicillin (90%), the acquired resistance genes of tetM, aacC2, sul1 and sul2 were almost completely lost and the resistance was significantly different with the changes of environmental stress from 2019 to 2023, especially, the emerged carbapenem resistance was substantially enhanced in 4 folds to imipenem, and aminoglycoside resistance was further boosted in 34 folds to spectinomycin, 46 folds to streptomycin and 49.7 folds to amikacin. Our findings highlight the persistent virulence and variation of multidrug resistance of S. agalactiae serotype Ib/ST261, underscoring its specific role in bacteremia of bullfrog and the challenges it poses for treatment.