College of Veterinary Medicine, Shandong Agricultural University, Tai'an City, China.
Delicious Food Co. Ltd, Weifang City, China.
Transbound Emerg Dis. 2018 Dec;65(6):1605-1614. doi: 10.1111/tbed.12912. Epub 2018 May 25.
Macrococcus caseolyticus is generally considered to be a non-pathogenic bacterium that does not cause human or animal diseases. However, recently, a strain of M. caseolyticus (SDLY strain) that causes high mortality rates was isolated from commercial broiler chickens in China. The main pathological changes caused by SDLY included caseous exudation in cranial cavities, inflammatory infiltration, haemorrhages and multifocal necrosis in various organs. The whole genome of the SDLY strain was sequenced and was compared with that of the non-pathogenic JCSC5402 strain of M. caseolyticus. The results showed that the SDLY strain harboured a large quantity of mutations, antibiotic resistance genes and numerous insertions and deletions of virulence genes. In particular, among the inserted genes, there is a cluster of eight connected genes associated with the synthesis of capsular polysaccharide. This cluster encodes a transferase and capsular polysaccharide synthase, promotes the formation of capsules and causes changes in pathogenicity. Electron microscopy revealed a distinct capsule surrounding the SDLY strain. The pathogenicity test showed that the SDLY strain could cause significant clinical symptoms and pathological changes in both SPF chickens and mice. In addition, these clinical symptoms and pathological changes were the same as those observed in field cases. Furthermore, the anti-microbial susceptibility test demonstrated that the SDLY strain exhibits multiple-antibiotic resistance. The emergence of pathogenic M. caseolyticus indicates that more attention should be paid to the effects of this micro-organism on both poultry and public health.
巨大球菌通常被认为是一种非致病性细菌，不会引起人类或动物疾病。然而，最近从中国商业肉鸡中分离到一株可导致高死亡率的巨大球菌（SDLY 株）。SDLY 株引起的主要病变包括颅腔干酪样渗出物、炎症浸润、出血和多个器官的局灶性坏死。对 SDLY 株的全基因组进行了测序，并与非致病性巨大球菌 JCSC5402 株进行了比较。结果表明，SDLY 株含有大量突变、抗生素耐药基因和大量毒力基因的插入和缺失。特别是，在插入基因中，有一个与荚膜多糖合成相关的八个连续基因簇。该簇编码一种转移酶和荚膜多糖合成酶，促进荚膜的形成并导致致病性的改变。电子显微镜显示 SDLY 株周围有明显的荚膜。致病性试验表明，SDLY 株可引起 SPF 鸡和小鼠出现明显的临床症状和病理变化。此外，这些临床症状和病理变化与田间病例观察到的相同。此外，药敏试验表明 SDLY 株表现出多重耐药性。致病性巨大球菌的出现表明，应更加关注该微生物对家禽和公共卫生的影响。
