Effects of artificially introduced Enterococcus faecalis strains in experimental necrotizing enterocolitis

Enterococcus faecalis is a ubiquitous intestinal symbiont and common early colonizer of the neonatal gut. Although colonization with E. faecalis has been previously associated with decreased pathology of necrotizing enterocolitis (NEC), these bacteria have been also implicated as opportunistic pathogens. Here we characterized 21 strains of E. faecalis, naturally occurring in 4-day-old rats, for potentially pathogenic properties and ability to colonize the neonatal gut. The strains differed in hemolysis, gelatin liquefaction, antibiotic resistance, biofilm formation, and ability to activate the pro-inflammatory transcription factor NF-κB in cultured enterocytes. Only 3 strains, BB70, 224, and BB24 appreciably colonized the neonatal intestine on day 4 after artificial introduction with the first feeding. The best colonizer, strain BB70, effectively displaced E. faecalis of maternal origin. Whereas BB70 and BB24 significantly increased NEC pathology, strain 224 significantly protected from NEC. Our results show that different strains of E. faecalis may be pathogenic or protective in experimental NEC.粪肠球菌（Enterococcus faecalis）是一种广泛存在的肠道共生菌，也是新生儿肠道常见的早期定植菌。尽管此前已有研究表明粪肠球菌定植可降低坏死性小肠结肠炎（necrotizing enterocolitis, NEC）的病理损伤，但这类细菌也被认为是条件致病菌。本研究对21株分离自4日龄大鼠的粪肠球菌进行了表征，分析其潜在致病特性以及定植新生儿肠道的能力。这些菌株在溶血活性、明胶液化能力、抗生素耐药性、生物膜形成能力以及激活培养肠上皮细胞中促炎性转录因子NF-κB的能力方面存在差异。仅3株菌株——BB70、224和BB24——在首次人工灌胃喂食后第4天可有效定植于新生大鼠肠道。定植能力最强的菌株BB70可有效竞争性排除母源来源的粪肠球菌。而BB70与BB24可显著加重NEC病理损伤，菌株224则可显著减轻NEC病理损伤，对机体起到保护作用。本研究结果表明，在实验性NEC模型中，不同粪肠球菌菌株可分别表现出致病或保护作用。