Eggs and raw or undercooked egg-containing food items are frequently identified as the bacterial source during epidemiolocal investigation of Salmonella outbreaks. Multi-locus variable number of tandem repeats analysis (MLVA) is a widely used Salmonella typing method enabling the study of diversity within populations of the same serotype. In vivo passage, however, has been linked with changes in MLVA type and more broadly the Salmonella genome. We sought to investigate whether in vivo passage through layer hens had an effect on MLVA type as well as the bacterial genome and whether any mutations affected bacterial virulence. Layer hens were infected with either Salmonella Typhimurium DT9 (03-24-11-11-523) as part of a single infection or were co-infected with an equal amount of Salmonella Mbandaka. Salmonella shedding in both single and co-infected birds was variable over the course of the 16-week experiment. Salmonella Typhimurium and Salmonella Mbandaka were identified in feces of co-infected birds. Salmonella colonies isolated from fecal samples were subtyped using MLVA. A single change in SSTR-6 was observed in Salmonella Typhimurium strains isolated from co-infected birds. Isolates of Salmonella Typhimurium of both the parent (03-24-11-11-523) and modified (03-24-12-11-523) MLVA type were sequenced and compared with the genome of the parent strain. Sequence analysis revealed that in vivo passaging resulted in minor mutation events. Passaged isolates exhibited significantly higher invasiveness in cultured human intestinal epithelial cells than the parent strain. The microevolution observed in this study suggests that changes in MLVA may arise more commonly and may have clinical significance.

中文翻译：

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鼠伤寒沙门氏菌的体内传代导致细菌基因组中的微小突变，并增加了体外侵袭性。

在沙门氏菌爆发的流行病学调查中，经常将鸡蛋和含有生鸡蛋或未煮熟的鸡蛋食品作为细菌来源。多基因座可变数目的串联重复分析（MLVA）是一种广泛使用的沙门氏菌分型方法，可用于研究同一血清型群体内的多样性。然而，体内传代与MLVA类型的变化以及沙门氏菌基因组的变化有关。我们试图调查母鸡在体内的传代是否对MLVA类型以及细菌基因组有影响，以及是否有任何突变影响细菌的毒力。作为单次感染的一部分，母鸡用鼠伤寒沙门氏菌DT9（03-24-11-11-523）感染，或与等量的姆班达卡沙门氏菌共同感染。在为期16周的实验过程中，单个和共感染禽类中沙门氏菌的排出量是可变的。在共感染禽类的粪便中鉴定出鼠伤寒沙门氏菌和姆班达卡沙门氏菌。从粪便样本中分离出的沙门氏菌菌落使用MLVA进行亚型化。从共感染禽类分离的鼠伤寒沙门氏菌菌株中观察到SSTR-6的单一变化。对亲本（03-24-11-11-523）和改良（03-24-12-11-523）MLVA类型的鼠伤寒沙门氏菌的分离株进行测序，并与亲本菌株的基因组进行比较。序列分析显示，体内传代导致较小的突变事件。传代的分离株在培养的人肠道上皮细胞中显示出比亲本株显着更高的侵袭性。