When Edward McCabe, MD, PhD, was a pediatric resident in the mid-1970s, he often treated preterm infants with necrotizing enterocolitis (NEC). “It’s a horrible disease,” he said. Forty years later, when he retired from clinical practice in 2012, few strides had been made in prevention, treatment, or mortality. The lack of significant advances to prevent or treat NEC in fragile preterm infants is frustrating to clinicians who care for them, McCabe said.

“There have been lots of studies on [causes and treatments] with essentially no change in mortality,” said McCabe, the senior vice president and chief medical officer for the March of Dimes. Currently, about 12% of preterm infants weighing less than 1500 g develop NEC, and about one-third die from sepsis or other complications (Gephart SM et al. Adv Neonatal Care. 2012;12[2]:77-87; http://1.usa.gov/21IRhiH).

However, a new prospective case-control study by researchers at Washington University School of Medicine in St Louis provides a preliminary road map for additional investigation into causes and potential treatments (Warner BB et al. Lancet. doi:10.1016/S0140-6736(16)00081-7 [published online March 8, 2016]). The research team sequenced DNA extracted from 3586 stool samples retrieved from 166 preterm infants who were hospitalized in neonatal intensive care units at 3 hospitals: St Louis (Missouri) Children’s Hospital; Kosair Children’s Hospital in Louisville, Kentucky; and Children’s Hospital at Oklahoma University in Oklahoma City. All babies weighing less than 1500 g without congenital heart disease or intestinal perforations who were expected to survive more than 1 week were eligible for the study. The babies’ stool samples were analyzed from neonatal admission to 60 days of age or until a NEC diagnosis, whichever occurred first.

Investigators discovered that the gastrointestinal bacterial microbiome of 46 preterm babies who developed NEC contained significantly more gram-negative gammaproteobacteria, such as Escherichia coli, and less anaerobic bacteria, particularly Negativicutes, compared with preterm babies who did not develop the disease.

“Neonatologists have long believed that gut bacteria could have a bearing on developing or being protected from necrotizing enterocolitis,” said Phillip I. Tarr, MD, the study’s senior author and a professor of pediatrics and microbiology at the Washington University School of Medicine in St Louis. That hypothesis, he explained, is based on several factors, including the association between greater antibiotic use and NEC and the protective factor of breastfeeding. “However, the identity of the risk-conferring microbes had not been clarified,” Tarr added.

It was the study’s scope and methodology, however, that enabled the researchers to demonstrate that the gut microbiome transition occurs before infants develop NEC, noted Scott Lorch, MD, a neonatologist and director of the Neonatal-Perinatal Medicine Fellowship at the Children’s Hospital of Philadelphia, who was not involved in the study. Because thousands of stool samples were sequenced from the time the infants were admitted to neonatal intensive care—before any were diagnosed with NEC—researchers were able to study how the infants’ gut microbiomes evolved over several weeks, Lorch explained, thus demonstrating that the microbiome changed in those infants who later developed NEC before they became ill.

Although the research results point to the gut microbiome having a role in the development of necrotizing enterocolitis, it’s unclear whether the altered gut microbiome causes NEC or it’s a marker for some other underlying trigger, such as antibiotic use, or other infections or treatments.

“To improve our understanding as to whether the microbial community is the chicken or the egg will require an improved understanding of host response,” said lead author Barbara B. Warner, MD, a pediatrics professor at Washington University School of Medicine in St Louis. “[This] will likely require a systems approach going back to a representative animal model and additional human studies.”

The infants who develop NEC might have an altered immune response, she explained, or be exposed to microbes in the neonatal intensive care unit that cause NEC and change their gut microbiome as well.

If the composition of the baby’s gut microbiome is indeed the cause, researchers need to determine whether the abundance of inflammation-causing gammaproteobacteria or the scarcity of the anaerobic bacteria, which produce anti-inflammatory short-term fatty acids, is the true culprit, Tarr noted.

The precise link between antibiotics and NEC also needs to be examined, noted David A. Relman, MD, a professor of medicine, microbiology, and immunology at Stanford University School of Medicine, who was not involved in the study. Babies are routinely given antibiotics in the neonatal intensive care unit as a precaution against infections like sepsis, and the infants who developed NEC were given antibiotics for more days, pre-NEC, than those who didn’t. However, it’s unclear whether the antibiotics made the infants more susceptible to developing NEC, he explained.

“It may simply be that the [infants who developed NEC] were sicker and the things that made them sick are more important than the antibiotics,” Relman said.

If gut microbiome dysbiosis does cause NEC, the question is whether probiotics could prevent its development. A 2014 meta-analysis concluded that probiotics had a protective effect in reducing the incidence of NEC in preterm infants (AlFaleh and Anabrees. Cochrane Lib. doi:10.1002/14651858.CD005496.pub4 [published online April 10, 2014]). However, a multicenter randomized clinical trial of 1300 preterm infants found no difference in the incidence of necrotizing enterocolitis, sepsis, or death in infants who were given a probiotic compared with those who were not (Costeloe K et al. Lancet. 2016;387[10019]:649-660).

Tarr noted that the Costeloe et al study used just 1 type of probiotic, Bifidobacterium breve BBG-001, and other types of probiotics still might be beneficial.

Future work should investigate the particular strains of gammaproteobacteria found in the gut microbiomes of babies who develop NEC, Relman explained. Adding a piece to this puzzle, a recent study by another team of researchers found that gut colonization by uropathogenic E coli, which is a primary cause of urinary tract infections, was positively associated with development of and mortality from NEC in preterm infants (Ward DV et al. Cell Rep. 2016;14[12]:2912-2924). Relman also noted that researchers should also examine viruses and proteins present in preterm infants’ gut microbiomes to determine what role they might play in the disease’s development.

Tarr and Warner said their team will next study the efficacy of targeted microbial therapies, such as prebiotics, antibiotics, or probiotics in curbing NEC among preterm infants.

“If an intervention corrects the dysbiosis, and the rate of NEC is then diminished, that would strengthen the contention that gut bacterial communities are causative,” Warner said.