[Intestinal microbiome and its relationship with necrotizing enterocolitis in very low birth weight preterm infants]

Objective: To explore the composition of intestinal microflora prior to onset of necrotizing enterocolitis (NEC) in very low birth weight preterm infants. Methods: This was a multicenter prospective nested case-control study. A total of 46 very low birth weight preterm infants (birth weight <1 500 g and gestional age <35 weeks) within 24 h of life admitted into Neonatal Intensive Care Unit of Children's Hospital of Soochow University and Suzhou Municipal Hospital from April 20 to November 20, 2018 were enrolled. Baseline clinical data and fecal samples of these infants were collected. The subsequent sampling time points were 1st, 4th and 7th day in the first week of life then once per week consecutively. The endpoint of sampling was NEC occurrence, patient discharge or the 8th week post-discharge, whichever came first. Fecal samples were analyzed by 16 S rDNA high-throughput nucleotide sequencing. The control cases were infants without NEC who were matched to the NEC cases with a ratio of 1∶1. The operational taxonomic units (OTU), sequence number and shannon diversity index of the fecal samples were analyzed. Continuous variables were compared with t-test or non-parametric test, and χ test or Fisher's exact test was used for categorical variables. Results: There were 23 patients in each group. The gestational age was (29.4±1.8) weeks in NEC group and (29.9±1.6) weeks in control group, including 13 males (57%) and 11 males (48%) in each group, respectively. Species abundance showed that the Firmicutes in both groups decreased temporarily at 7 days of age and then increased with age in control group, but not in NEC group, the Proteobacteria in both groups increased at 7 days of age and then decreased in control group, but kept increasing in NEC group. Regarding the other levels of taxonomy, compared with that of the control group, the NEC group had lower abundance of Proteobacteria, γ-proteobacteria and Enterobacteriaceae at 7 days of age, while higer abundance of Faecalibacterium at 14 days of age, meanwhile, lower Clostridium and Streptococcus at 21 days of age, lower Firmicutes, Clostridia and Clostridium perfringens and higher Proteobacteria and γ-proteobacteria at 28 days of age, these differences were all statistically significant (U=43.00, 43.00, 45.00, 80.00, 74.00, 76.00, 19.00, 8.00, 36.00, 25.00, 25.00,all P<0.05). The shannon index of NEC group was both lower than that of the controls at 21 days of age (2.4 (1.4, 3.0) vs. 3.1 (2.6, 4.0), U=67.00, P=0.027) and 28 days of age (2.4 (1.4, 2.8) vs. 3.9 (3.3, 4.2), U=12.00, P=0.001). Conclusions: The intestinal microflora profile of very low birth weight preterm infants has already changed prior to NEC development. The emergence of differential flora and the reduction of microflora diversity may facilitate early identification and prevention of NEC.