O38 – NEC as an infectious disease: Identifying strains of opportunistic pathogens
Author(s):
Background: Despite significant improvements in neonatal intensive care, necrotizing enterocolitis (NEC) continues to be a significant cause of morbidity and mortality in premature infants. The pathophysiology of NEC remains poorly understood. Formula feeding, bacterial colonization and hypoxic/ischemic conditions are major risk factors. The role of bacterial pathogens as causative agents of NEC is suggested by hospital outbreaks of the disease secondary to contaminated formula.
Hypothesis: While the premature gut is colonized with a variety of microbial species, we hypothesize that predominant species and strains acting as opportunistic pathogens are key in the pathogenesis of NEC.
Methods: To test this hypothesis, we isolated bacteria from NEC animals, and assessed the ability of these bacteria to promote NEC upon introduction to naïve rat pups. NEC was induced in neonatal rats by formula feeding, hypoxia (5% O2 for 10 min) and hypothermia (8°C for 10 min), three times daily for four days. On day of life four, the rats were euthanized and a segment of the terminal ileum was resected for analysis. NEC was graded histologically. Intestinal microbiota were characterized by plating serially diluted homogenates of terminal ileum on blood agar. Bacterial colonies emerging after 48 h incubation at 37°C were classified based on their appearance, and each class was enumerated. Bacterial species were identified by sequencing the variable region of the 16S rRNA gene and querying a nucleotide database. Suspected NEC pathogens were identified (designated numbers 4, 9, 22, 44, and 69) and introduced to rat pups subjected to the same NEC protocol. Formula was prepared daily with bacterial concentrations of 106 colony forming units per milliliter (cfu/ml) and 108 cfu/ml. After sacrifice on day of life 4, NEC was graded.
Results: Bacterial strain 22 did not induce NEC. Bacterial strain 69 induced low-grade NEC at 106 cfu/ml. Strain 4 induced low-grade NEC at 108 cfu/ml. Strain 9 induced low-grade NEC at 106 cfu/ml and high-grade NEC at 108 cfu/ml. Strain 44 induced high-grade NEC at both doses.
Conclusions: Our findings suggest that specific bacterial strains are implicated in the pathogenesis of NEC. Strain 22 did not promote NEC and thus may have been protective. Strain 44 strongly promoted NEC – an example of a true NEC pathogen. Further examination of these strains may provide useful insights into the pathogenesis, treatment, and prevention of NEC.