Research on neonatal microbiomes: what neonatologists need to know

Lung Microbiota and Ventilator-Associated Pneumonia in the Neonatal Period

The lung microbiota is a complex community of microorganisms that colonize the respiratory tract of individuals from, or even before, birth. Although the lungs were traditionally believed to be sterile, recent research has shown that there is a diversity of bacterial species in the respiratory system. Knowledge about the lung microbiota in newborns and its relationship with bacterial infections is of vital importance to understand the pathogenesis of respiratory diseases in neonatal patients undergoing mechanical ventilation. In this article, the current evidence on the composition of the lung microbiota in newborns will be reviewed, as well as the risks that an altered microbiota can impose on premature newborns. Although advances in neonatal intensive care units have significantly improved the survival rate of preterm infants, the diagnosis and treatment of ventilator-associated pneumonia has not progressed in recent decades. Avoiding dysbiosis caused by inappropriate use of antibiotics around birth, as well as avoiding intubation of patients or promoting early removal of endotracheal tubes, are among the most important preventive measures for ventilator-associated pneumonia. The potential benefit of probiotics and prebiotics in preventing infectious, allergic or metabolic complications in the short or long term is not clearly established and constitutes a very important field of research in perinatal medicine.

Physiology of the Neonatal Gastrointestinal System Relevant to the Disposition of Orally Administered Medications

A thorough knowledge of the newborn (age, birth to 1 month postpartum) infant's gastrointestinal tract (GIT) is critical to the evaluation of the absorption, distribution, metabolism, and excretion (ADME) of orally administered drugs in this population. Developmental changes in the GIT during the newborn period are important for nutrient uptake as well as the disposition of orally administered medications. Some aspects of gastrointestinal function do not mature until driven by increased dietary complexity and nutritional demands later in the postnatal period. The functionalities present at birth, and subsequent maturation, can also impact the ADME parameters of orally administered compounds. This review will examine some specific contributors to the ADME processes in human neonates, as well as what is currently understood about the drivers for their maturation. Key species differences will be highlighted, with a focus on laboratory animals used in juvenile toxicity studies. Because of the gaps and inconsistencies in our knowledge, we will also highlight areas where additional study is warranted to better inform the appropriate use of medicines specifically intended for neonates.

The human microbiome and metabolomics: Current concepts and applications

The mammalian gastrointestinal tract has co-developed with a large number of microbes in a symbiotic relationship over millions of years. Recent studies indicate that indigenous bacteria are intimate with the intestine and play essential roles in health and disease. In the quest to maintain a stable niche, these prokaryotes influence multiple host metabolic pathways, resulting from an interactive host-microbiota metabolic signaling and impacting strongly on the metabolic phenotypes of the host. Since dysbiosis of the gut bacteria result in alteration in the levels of certain microbial and host co-metabolites, identifying these markers could enhance early detection of diseases. Also, identification of these metabolic fingerprints could give us clues as to how to manipulate the microbiome to promote health or treat diseases. This review provides an overview of our current knowledge of the microbiome and metablomics, applications and the future perspectives.

Randomized Controlled Trial of Talactoferrin Oral Solution in Preterm Infants

OBJECTIVE

To evaluate the safety and explore the efficacy of recombinant human lactoferrin (talactoferrin [TLf]) to reduce infection.

STUDY DESIGN

We conducted a randomized, double blind, placebo-controlled trial in infants with birth weight of 750-1500 g. Infants received enteral TLf (n = 60) or placebo (n = 60) on days 1 through 28 of life; the TLf dose was 150 mg/kg every 12 hours. Primary outcomes were bacteremia, pneumonia, urinary tract infection, meningitis, and necrotizing enterocolitis (NEC). Secondary outcomes were sepsis syndrome and suspected NEC. We recorded clinical, laboratory, and radiologic findings, along with diseases and adverse events, in a database used for statistical analyses.

RESULTS

Demographic data were similar in the 2 groups of infants. We attributed no enteral or organ-specific adverse events to TLf. There were 2 deaths in the TLf group (1 each due to posterior fossa hemorrhage and postdischarge sudden infant death), and 1 death in the placebo group, due to NEC. The rate of hospital-acquired infections was 50% lower in the TLf group compared with the placebo group (P < .04), including fewer blood or line infections, urinary tract infections, and pneumonia. Fourteen infants in the TLf group weighing <1 kg at birth had no gram-negative infections, compared with only 3 of 14 such infants in the placebo group. Noninfectious outcomes were not statistically significantly different between the 2 groups, and there were no between-group differences in growth or neurodevelopment over a 1-year posthospitalization period.

CONCLUSION

We found no clinical or laboratory toxicity and a trend toward less infectious morbidity in the infants treated with TLf.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00854633.

Randomized Control Trial of Human Recombinant Lactoferrin: A Substudy Reveals Effects on the Fecal Microbiome of Very Low Birth Weight Infants

The purpose of this study is to evaluate the effects of enteral lactoferrin on the fecal microbiome and contrast those influences with the neonatal intensive care unit (NICU) environment. We theorized that lactoferrin and the NICU habitat shape the fecal microbial composition of very preterm infants. Although functions attributed to lactoferrin include intestinal immune system development and emergence of a healthy gut microbiota, evidence is limited. Twenty-one very low birth weight (VLBW <1500 g) infants received twice-daily talactoferrin (TLf, a drug designation for recombinant human lactoferrin) or its excipient by gastric gavage from day 1-28 of life. Twenty-four-hour fecal samples were collected on day 21 of life and compared with fecal operational taxonomy units (OTUs) in treated and control infants in 2 NICUs. Workflow included fecal DNA isolation, generation of amplicons for the V1-V3 region of bacterial 16S ribosomal RNA, and sequencing of a gel-purified multiplex amplicon library using a Roche 454 GS FLX Titanium (Roche, Branford, Connecticut) platform and protocols. Fecal OTUs per infant were higher in NICU 1 vs NICU 2 (P < .001), consistent with fewer antibiotic days (P < .02) and a shorter duration of parenteral nutrition (P < .007) in NICU 1. Proteobacteria and Firmicutes were the major phyla in infants treated with TLf and placebo. Among Enterobacteriaceae, TLf prophylaxis reduced Enterobacter and Klebsiella, but increased Citrobacter in feces of VLBW infants. Citrobacter caused no neonatal infections in the study population. OTUs for Clostridiaceae increased in NICU 1 among infants treated with TLf. Importantly, OTUs of staphylococci were barely detectable in both NICUs among infants fed TLf. Fewer hospital-acquired infections occurred in infants treated with TLf vs controls, although the reduction was seen mostly in coagulase-negative staphylococci-related bloodstream and central line infections (P = .06). TLf modified the fecal microbiome in VLBW infants, but care practices in the NICU habitat also contributed. Future research must establish whether elimination vs enrichment of gut-related microbiota reduces clinically significant hospital-acquired infections and promotes a healthy commensal microflora in the intestines of VLBW infants.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00854633.

Lungs, microbes and the developing neonate

Microbes are ubiquitous on the human body and comprise approximately 90% of the cells and 99% of the genes of the human supraorganism. High-throughput sequencing technology has permitted the development of culture-independent means to identify the microbiota that are unique to the various microenvironments of the body and probably contribute some function. Although the respiratory tract interfaces with the environment, the lungs were always thought to be a sterile environment - until recently, when these techniques were applied to healthy and disease states. Further, there appears to be a complex interplay between the development of the gastrointestinal and respiratory microbiota and the regulation of immune function. The contribution of this dynamic metabolic mass to respiratory disease in the newborn is unknown. This article will review emerging data from recent human and murine studies that suggest there is a microbial influence on the development of respiratory disease, but it will also highlight many of the gaps that remain in understanding the function of the respiratory microbiome.

Gut microbiota, the immune system, and diet influence the neonatal gut-brain axis

The conceptual framework for a gut-brain axis has existed for decades. The Human Microbiome Project is responsible for establishing intestinal dysbiosis as a mediator of inflammatory bowel disease, obesity, and neurodevelopmental disorders in adults. Recent advances in metagenomics implicate gut microbiota and diet as key modulators of the bidirectional signaling pathways between the gut and brain that underlie neurodevelopmental and psychiatric disorders in adults. Evidence linking intestinal dysbiosis to neurodevelopmental disease outcomes in preterm infants is emerging. Recent clinical studies show that intestinal dysbiosis precedes late-onset neonatal sepsis and necrotizing enterocolitis in intensive care nurseries. Moreover, strong epidemiologic evidence links late-onset neonatal sepsis and necrotizing enterocolitis in long-term psychomotor disabilities of very-low-birth-weight infants. The notion of the gut-brain axis thereby supports that intestinal microbiota can indirectly harm the brain of preterm infants. In this review, we highlight the anatomy and physiology of the gut-brain axis and describe transmission of stress signals caused by immune-microbial dysfunction in the gut. These messengers initiate neurologic disease in preterm infants. Understanding neural and humoral signaling through the gut-brain axis will offer insight into therapeutic and dietary approaches that may improve the outcomes of very-low-birth-weight infants.