2023年江苏地区屠宰场健康猪源猪链球菌致病与耐药特征

The pathogenic and antimicrobial resistance characteristics of Streptococcus suis isolates from healthy pigs at slaughterhouses in Jiangsu Province, 2023

摘要:

【目的】猪链球菌(Streptococcus suis,SS)是猪的常见致病菌，也是一种人畜共患病原。江苏曾于1998年暴发猪链球菌疫情，大量生猪死亡的同时，也导致14人感染死亡。因此，对江苏地区屠宰场健康猪进行猪链球菌感染调查，具有公共卫生意义。【方法】于2023年采集江苏两地屠宰场健康猪扁桃体，进行猪链球菌分离鉴定和血清分型，通过所分离菌株对斑马鱼和小鼠毒力测定、药敏试验及耐药基因检测，探究猪链球菌分离菌株的致病和耐药特征。【结果】2023年7月采集江苏昆山地区扁桃体样本，阳性率为50.85%(30/59)，分离鉴定出62株猪链球菌，其中分离率最高为31型(12.90%，8/62)，其次为19型(11.29%，7/62)、NCL2型(8.06%，5/62)等；2023年7月、11月采集江苏丹阳地区扁桃体样本，阳性率为60.71%(34/56)，分离鉴定出77株猪链球菌，其中分离率最高为16型(11.69%，9/77)，其次为9型(10.39%，8/77)、21型(10.39%，8/77)、31型(10.39%，8/77)等。两地分离株对林可酰胺类(98.56%，137/139)、大环内酯类(95.68%，133/139)、四环素类(96.40%，134/139)抗生素耐药率较高；97.84%(136/139)的菌株属于多重耐药菌株。所有菌株对头孢噻肟、万古霉素敏感。根据分离株来源及血清型选择42株(昆山市18株，丹阳市24株)代表菌株进行斑马鱼毒力测定，攻毒剂量为3×10⁶ CFU/尾时，有7株菌对斑马鱼致病力强，致死率≥80.00%。选择致死率≥80.00%且死亡趋势与强度对照无显著差异的3株代表菌株(分别为血清1型、3型、23型)进行小鼠试验，致死率均≥80.00%。【结论】江苏地区健康猪扁桃体的猪链球菌携带率较高(55.65%，64/115)，97.84%(136/139)的分离株为多重耐药菌株，血清1型、3型、23型分离株致病力强，值得关注。

Abstract:

[Objective] Streptococcus suis is a prevalent pathogen attacking pigs and a zoonotic agent. In 1998, an outbreak of S. suis infection in Jiangsu caused numerous pig deaths and 14 human deaths. Therefore, investigating S. suis infections in healthy pigs from slaughterhouses in Jiangsu is crucial for public health. [Methods] Tonsils were collected from healthy pigs in slaughterhouses of Jiangsu in 2023, and S. suis was isolated, identified, and serotyped. The pathogenicity of S. suis isolates to zebrafish and mouse models was examined. Furthermore, the antibiotic resistance characteristics and genes and the antimicrobial susceptibility of the isolates were identified and evaluated. [Results] The positive rate of S. suis in the samples collected from Kunshan in July 2023 was 50.85% (30/59). A total of 62 strains were isolated from the samples collected from Kunshan, and serotype 31 (12.90%, 8/62) had the highest isolation rate, followed by serotype 19 (11.29%, 7/62) and serotype NCL2 (8.06%, 5/62). In the samples collected from Danyang in July and November 2023, the positive rate of S. suis was 60.71% (34/56), and 77 strains were isolated. Serotype 16 had the highest isolation rate of 11.69% (9/77), followed by serotype 9 (10.39%, 8/77), serotype 21 (10.39%, 8/77), and serotype 31 (10.39%, 8/77). The isolates from both regions exhibited high resistance to lincosamides (98.56%, 137/139), macrolides (95.68%, 133/139), and tetracyclines (96.40%, 134/139). Furthermore, 97.84% (136/139) of strains were multi-drug resistant. All the strains were sensitive to cefotaxime and vancomycin. According to the sources and serotypes, we selected 42 representative strains (18 from Kunshan and 24 from Danyang) to perform zebrafish infection experiments. At a dose of 3×10⁶ CFU/fish, seven strains exhibited high pathogenicity to zebrafish, causing the mortality rates ≥80.00%. Three strains (serotypes 1, 3, and 23) causing mortality rates ≥80.00% in zebrafish and comparable to the virulent strain SC070731 were selected for mouse infection experiments. All the three strains led to the mortality rates ≥80.00% in mice. [Conclusion] The healthy pigs in Jiangsu have a high carrying rate of S. suis (55.65%, 64/115), and 97.84% (136/139) of the isolates are multi-drug resistant. Strains of serotypes 1, 3, and 23 exhibited strong pathogenicity.