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 the newborn and its relationship with bacterial infections is of vital importance to understand the pathogenesis of respiratory diseases in neona-tal patients undergoing mechanical ventilation. In this article, the current evidence on the compo-sition of the lung microbiota in the newborn will be reviewed, as well as its role in the develop-ment of bacterial infections in mechanically ventilated neonates. Although advances in many as-pects of the neonatal intensive care unit care have significantly improved the survival 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 use of probiotics and prebiotics to prevent infectious, allergic or metabolic complications in the short or long term constitutes a very important field of research in perinatal medicine.

Introduction The increase in survival of extremely preterm infants has led to increased rates of bronchopulmonary dysplasia (BPD). Therefore, a potential role of human milk feeding in protecting against this condition has been suggested. Material and methods Retrospective descriptive study based on data about morbidity in the population of infants born from 22+0 to 26+6 weeks of gestation, included in the Spanish network SEN1500 during the period 2004-2019 and who were alive at discharge. The primary outcome was moderate-severe BPD. In addition, associated conditions were studied, including breastfeeding at discharge. The temporal trends of BPD and breastfeeding rates at discharge were also studied. Results In the study population of 4341 infants who survived to discharge, the rate of moderate-severe BPD was 43,7% and increased over the period to a rate >50% in the last three years. The factors significantly associated with a higher risk of moderate-severe BPD were male sex, high-frequency oscillatory ventilation, inhaled nitric oxide, patent ductus arteriosus, and late-onset sepsis. Exclusive human milk feeding at discharge and any amount of human milk at discharge were associated with a lower incidence of moderate-severe BPD (OR 0.752, 95% CI 0.629-0.901, and OR 0.714, 95% CI 0.602-0.847, respectively). The rates of human milk at discharge in infants with moderate-severe BPD increased over the period. In the last years, more than one-third of extremely preterm infants were discharged on exclusive human milk feeds, and about two-thirds of them on any amount of human milk feeding. Conclusions
The results of the present study strongly support the role of any amount of human milk in preventing BDP in extremely preterm infants.