浙江某市屠宰场猪链球菌血清型、耐药及致病特征

Serotypes, antimicrobial resistance, and pathogenic characteristics of Streptococcus suis isolated from a slaughterhouse in an area of Zhejiang Province

摘要:

【目的】猪链球菌(Streptococcus suis)是猪的重要病原菌，同时也是人畜共患病原。猪的扁桃体是猪链球菌主要定殖部位之一，是易感猪和人的重要传染源。因此，对屠宰场健康猪进行猪链球菌流行病学调查，具有重要的公共卫生学意义。【方法】本研究自2020年至2021年，从浙江某市屠宰场采集健康猪扁桃体样品，分离鉴定猪链球菌，采用血清型特异性PCR法分型，通过耐药基因检测、药敏试验、斑马鱼毒力实验分析其耐药及致病特征。【结果】131份健康猪扁桃体样品猪链球菌阳性率为62.59%(82/131)，共分离猪链球菌68株，其中16型分离率最高，占比16.18%(11/68)，其次为31型(11.76%，8/68)、9型(7.35%，5/68)、3型(7.35%，5/68)等。含2种及以上血清型的扁桃体样品占15.85%(13/82)。药敏试验表明，分离株主要对林可酰胺类(100%，68/68)、大环内酯类(98.53%，67/68)、四环素类(100%，68/68)抗生素耐药，所有菌株均属于多药耐药。值得关注的是，有18株菌对青霉素耐药、3株菌对头孢噻肟耐药、2株菌对利福平耐药、11株菌对利奈唑胺耐药。大环内酯类/林可酰胺类耐药基因、四环素类耐药基因检出率均为82.35%(56/68)，这是猪链球菌对这些抗生素耐药的主要原因。按不同批次分离的菌株，选择25株代表株进行斑马鱼毒力实验，结果显示：5株菌对斑马鱼致病力强，攻毒剂量为3×10⁶CFU/尾时死亡率为80%–100%。【结论】该地区健康猪不仅猪链球菌携带率高，而且存在多药耐药和致病性强的菌株，这为了解该地区猪链球菌病的发病规律和制定相关的防控策略提供参考。

Abstract:

[Objective] Streptococcus suis is a major swine pathogen and a zoonotic agent. Swine tonsil is a natural habitat of S. suis, and the tonsillar S. suis from healthy pigs is considered as an important source of infection for susceptible pigs and humans. Thus, the epidemiological investigation of S. suis from healthy pigs in slaughterhouses is of great significance for public health. [Methods] We collected healthy pigs' tonsils from a slaughterhouse in Zhejiang in 2020-2021, isolated and identified S. suis, and serotyped the strains by the serotype-specific PCR assay. Through the resistance gene detection, antimicrobial susceptibility testing, and zebrafish infection experiment, we examined the antimicrobial resistance and pathogenic characteristics of these isolates. [Results] The positive rate of S. suis in 131 tonsil samples of healthy pigs was 62.59% (82/131), and we isolated a total of 68 strains. The strains were dominated by serotype 16 (16.18%, 11/68), followed by serotype 31 (11.76%, 8/68), serotype 9 (7.35%, 5/68), and serotype 3 (7.35%, 5/68). In addition, tonsil samples containing 2 or more serotypes of S. suis accounted for 15.85% (13/82). The antimicrobial susceptibility testing showed that the isolates were mainly resistant to lincosamides (100%, 68/68), macrolides (98.53%, 67/68), and tetracyclines (100%, 68/68), and all isolates were multidrug-resistant. It is worth noting that 18 isolates were resistant to penicillin, 3 resistant to cefotaxime, 2 resistant to rifampicin, and 11 resistant to linezolid. The detection rate of both macrolides/lincosamides resistance genes and tetracycline resistance genes was 82.35% (56/68), which was the main reason why these isolates were resistant to the above antimicrobials. We selected 25 representative strains for the zebrafish infection experiment, and the results showed that 5 strains were highly virulent with mortality of 80%-100% when challenged with the dose of 3×10⁶ CFU/fish. [Conclusion] Healthy pigs in this area had a high detection rate of S. suis. All isolates were multidrug-resistant, and some were highly virulent. These results contribute to understanding the incidence of S. suis and formulating relevant prevention and control strategies in this area.