Acquisition of microbes by the neonate, which begins immediately during birth, is influenced by gestational age and mother’s microbiota and modified by exposure to antibiotics1. In neonates, prolonged duration of antibiotic therapy is associated with increased risk of sepsis after 4 days of life, known as late-onset sepsis (LOS)2, a disorder critically controlled by neutrophils3, but a role for the microbiota in regulating neutrophil behavior in the neonate has not been described. We exposed pregnant mouse dams to antibiotics in drinking water to limit transfer of maternal microbes to the neonates. Antibiotic exposure of dams decreased the total number of microbes in the intestine, altered the structure of intestinal microbiota and changed the pattern of microbial colonization. These changes were associated with decreased numbers of circulating and bone marrow neutrophils and granulocyte/macrophage restricted progenitor cells in the bone marrow. Antibiotic-exposure of dams attenuated the postnatal granulocytosis by reducing the number of interleukin (IL) 17-producing cells in intestine and consequent production of granulocyte colony stimulating factor (G-CSF). Relative granulocytopenia contributed to increased susceptibility of antibiotic-exposed neonatal mice to Escherichia coli K1 and Klebsiella pneumoniae sepsis, which could be partially reversed by administration of G-CSF. Restoration of normal microbiota, through TLR4- and MYD88-dependent mechanism, induced accumulation of IL17-producing type 3 innate lymphoid cells (ILC) in the intestine, promoted granulocytosis, and restored the IL17-dependent resistance to sepsis. Specific depletion of ILCs prevented the IL17- and G-CSF-dependent granulocytosis and resistance to sepsis. These data support a role for the intestinal microbiota in regulation of granulocytosis and host resistance to sepsis in the neonates.

ObjectiveNeuronal exosomes purified from peripheral blood samples have been proposed as diagnostic tool in the setting of acute brain injury but never tested clinically. We hypothesized that exosome protein biomarkers would change over time following acute hypoxic brain injury and would predict response to therapy.MethodsSynaptopodin (SYNPO), an actin‐associated protein present in postsynaptic spines, was evaluated as a potential biomarker as well as: synaptophysin, neuron‐specific enolase, and mitochondrial cytochrome c oxidase. A secondary analysis was performed on neonatal samples collected at 8, 10, and 14 h after the initiation of therapeutic‐controlled hypothermia for acute hypoxic–ischemic encephalopathy (n = 14). Neuronal exosomes were purified from serum and protein levels were quantified using standard ELISA methods. The primary study outcomes were length of stay (LOS), discharge on seizure medication (DCMED), and composite neuroimaging score (NIS).ResultsThe slope of change in neuronal exosome SYNPO between 8 and 14 h appeared to be the most promising biomarker for all three clinical study outcomes. SYNPO was highly correlated with LOS (−0.91, P < 0.001). SYNPO increased in 6/8 without DCMED and was worse or neutral in 5/5 with DCMED (P = 0.02). All four neonates with an abnormal NIS had neutral or decreasing SYNPO (P = 0.055). Other candidate biomarkers were not associated with outcomes.InterpretationThis report provides the first clinical evidence that neural exosomes turn over rapidly enough in the peripheral circulation to be used as a “troponin‐like” test following acute brain injury. Optimal sampling and biomarkers likely vary with type of brain injury.

To our knowledge, this study describes the first pharmacokinetic data of ampicillin in neonates with HIE receiving CH and demonstrates a reduced total body clearance and an increased V for ampicillin. Based on these data, modifications to the ampicillin dosing regimens seem appropriate during the period of CH. Dosing regimens of ampicillin 25 and 50 mg/kg/day were able achieve optimal probability of target attainment against all susceptible gram-negative and gram-positive bacteria in a population of neonates with HIE receiving CH for 50% and 100% fT > MIC.