Table 3.

Summary of studies in which DNA sequences obtained directly from stools have been used to associate bacterial risk and development of necrotizing enterocolitis (NEC), listed in ascending order according to number of pre-NEC stools sequenced.

Study	Sequencing technology	No. of subjects without NEC	No. of specimens from subjects without NEC	No. of subjects with NEC	No. of pre-NEC specimens from subjects who subsequently developed NEC	Comments
Brower-Sinning et al. [30], Pittsburgh, PA, USA	16S rRNA gene sequencing	10	10	9	9	Tissue analysis only, no pre-NEC samples; Proteobacteria, Clostridia associated with risk, as was diminished bacterial diversity
Mai et al. [31], three University of Florida-affiliated NICUs, FL, USA	16S rRNA gene sequencing	9	18	9	18	Case stools demonstrated an increase in Proteobacteria, and a decrease in Firmicutes in the second of the paired samples (i.e., week before NEC)
McMurtry et al. [32], Louisiana State University Health Sciences Center, Touro Infirmary, East Jefferson General Hospital and Children's Hospital of New Orleans, LA, USA	16S rRNA gene sequencing	74	74	21	21	Bacterial diversity and relative abundance of Clostridia was significantly lower in NEC specimens compared to controls
Raveh-Sadka et al. [33] Pittsburgh, PA, USA	Metagenomic sequencing	5	34	5	21	No clear association between bacterial content as identified by metagenomics and outcome; no microbiologic evidence of time–space clustering
Heida et al. [2], Groningen, The Netherlands	16S rRNA gene sequencing of meconium and subsequent stools	22	57	11	30	Clostridium perfringens and Bacteroides dorei associated with risk, and staphylococi associated with protection.
Torrazza et al. [34], Gainseville, FL, USA	16S rRNA gene sequencing	35	77	18	40	Novel sequence matching closest to Klebsiella pneumoniae during week 1 associated with subsequent development of NEC
Ward et al. [17], Cincinnati, OH, and Birmingham, AL, USA	Metagenomic sequencing	89	185	27	60	Specific sequence types of E. coli associated with NEC
Sim et al. [18], St Mary's Hospital, Queen Charlotte's and Chelsea Hospital, London, UK	16S rRNA gene sequencing	44	369	22	88	Klebsiella, clostridium associated with risk; no microbiologic evidence of time–space clustering
Zhou et al. [16], Brigham and Women's Hospital, Boston, MA, USA	16S rRNA gene sequencing	26	111	10	88	Age-specific differences identified, with early- and late-onset NEC having an association with Clostridia and Gammaproteobacteria, respectively
Warner et al. [23], St Louis Children's Hospital, St Louis, MO; Kosair Children's Hospital, Louisville, KY; Children's Hospital at Oklahoma University, Oklahoma City, OK, USA	16S rRNA gene sequencing	120	2720	46	866	Gammaproteobacteria associated with risk, and Negativicutes associated with protection; lack of diversity is associated with risk

NICU, neonatal intensive care unit.