Bacterial septicemia commonly occurs and usually cause huge losses in sericulture industry. Here, two pathogenic bacterial strains were isolated from dead silkworm and named as ZJ-1 and ZJ-2. Phenotypic and genotypic analysis results revealed that both of these two strains are closely related to Serratia marcescens (S. marcescens). The morphological as well as physiological and biochemical characteristics of ZJ-1 were accordant with S. marcescens mentioned in Bergey’s manual of determinative bacteriology, whereas ZJ-2 showed some discrepancies such as the utilization of malonate and starch, fermentation of maltose and sucrose, and tests of urease, etc. Surprisingly, ZJ-2 could produce red pigment at high temperature (37°) but ZJ-1 could not. Besides, by analyzing the lethal concentration 50 (LC₅₀) of ZJ-1 and ZJ-2, it was found that the virulence of ZJ-2 was lower than that of ZJ-1. These results revealed that ZJ-1 and ZJ-2 were two different strains of S. marcescens and that ZJ-2 was expected to be a safe (low-toxicity) and efficient strain for the production of red pigment. Nonetheless, further research in molecular level is needed to understand the regulation mechanism of pigment production and infection of ZJ-2.

细菌性败血症通常发生，通常在蚕桑业中造成巨大损失。在这里，从死蚕中分离出两个致病细菌菌株，分别命名为ZJ-1和ZJ-2。表型和基因型分析结果表明，这两个菌株都与粘质沙雷氏菌（S. marcescens）密切相关。ZJ-1的形态，生理生化特性均与粘质沙雷氏菌一致。在Bergey的《确定性细菌学手册》中提到过，而ZJ-2表现出一些差异，例如丙二酸和淀粉的利用，麦芽糖和蔗糖的发酵以及脲酶的测试等。令人惊讶的是，ZJ-2在高温下会产生红色色素（ 37°），但ZJ-1不能。此外，通过分析ZJ-1和ZJ-2的致死浓度50（LC ₅₀），发现ZJ-2的毒力低于ZJ-1。这些结果表明ZJ-1和ZJ-2是marcescens的两种不同菌株，并且预期ZJ-2是生产红色颜料的安全（低毒性）和有效菌株。尽管如此，还需要在分子水平上进行进一步的研究，以了解ZJ-2色素产生和感染的调控机制。