Staphylococcus epidermidis Sensitizes Perinatal Hypoxic-Ischemic Brain Injury in Male but Not Female Mice.

Background:Staphylococcus epidermidis is the most common nosocomial infection and the predominant pathogen in late-onset sepsis in preterm infants. Infection and inflammation are linked to neurological and developmental sequelae and bacterial infections increase the vulnerability of the brain to hypoxia-ischemia (HI). We thus tested the hypothesis that S. epidermidis exacerbates HI neuropathology in neonatal mice. Methods: Male and female C57Bl/6 mice were injected intraperitoneally with sterile saline or 3.5 × 107 colony-forming units of S. epidermidis on postnatal day (PND) 4 and then subjected to HI on PND5 (24 h after injection) or PND9 (5 d after injection) by left carotid artery ligation and exposure to 10% O2. White and gray matter injury was assessed on PND14-16. In an additional group of animals, the plasma, brain, and liver were collected on PND5 or PND9 after infection to evaluate cytokine and chemokine profiles, C5a levels and C5 signaling. Results: HI induced 24 h after injection of S. epidermidis resulted in greater gray and white matter injury compared to saline injected controls in males, but not in females. Specifically, males demonstrated increased gray matter injury in the cortex and striatum, and white matter loss in the subcortical region, hippocampal fimbria and striatum. In contrast, there was no potentiation of brain injury when HI occurred 5 d after infection in either sex. In the plasma, S. epidermidis-injected mice demonstrated increased levels of pro- and anti-inflammatory cytokines and chemokines and a reduction of C5a at 24 h, but not 5 d after infection. Brain CCL2 levels were increased in both sexes 24 h after infection, but increased only in males at 5 d post infection. Conclusion: Ongoing S. epidermidis infection combined with neonatal HI increases the vulnerability of the developing brain in male but not in female mice. These sex-dependent effects were to a large extent independent of expression of systemic cytokines or brain CCL2 expression. Overall, we provide new insights into how systemic S. epidermidis infection affects the developing brain and show that the time interval between infection and HI is a critical sensitizing factor in males.

Effect of Neotype Rectal Mild Hypothermia Therapy on Intestinal Bacterial Translocation in Rats with Hypoxic-Ischemic Brain Damage.

BACKGROUND Previous studies have shown that a neotype rectal cooling device can induce mild hypothermia (MH) in Sprague-Dawley rats with ischemic-hypoxic brain damage (HIBD) and inhibit cell apoptosis in the hippocampal CAl region, and does not cause damage to rectal tissues. The present study aimed to investigate the effect of rectal MH on bacterial translocation (BT) in Sprague-Dawley rats with HIBD. MATERIAL AND METHODS A total of 60 Sprague-Dawley rats were randomly divided into 4 groups: a control group (group C), a normothermia group (group NT), a cooling blanket group (group CB), and a rectal cooling group (group RC). Rats in group CB and group RC received MH using a cooling blanket and rectal cooling device after HIBD model establishment. Then, we measured diamine oxidase (DAO) and D-lactate level separately in groups NT, CB, and RC. Finally, the spleen, liver, and mesenteric lymph nodes were collected for bacterial culture, and rectal tissues were collected for H&E staining. RESULTS The therapeutic outcome was better in Sprague-Dawley rats receiving rectal MH without rectal injury compared to rats in group CB. Escherichia coli (E. coli) was found in MLNs in group RC. E. coli, Proteus vulgaris, Stenotrophomonas maltophilia, and Acinetobacter lwoffii were detected in the rats of groups CB and NT. At 12 h following rectal MH, DAO and D-lactate levels were lower than in group NT. CONCLUSIONS The neotype rectal MH cooling method could be a potential strategy to induce rapid, controllable hypothermia, thus reducing the possibility of inflammatory cell infiltration and BT incidence.

Vancomycin Is Protective in a Neonatal Mouse Model of Staphylococcus epidermidis-Potentiated Hypoxic-Ischemic Brain Injury.

Infection is correlated with increased risk of neurodevelopmental sequelae in preterm infants. In modeling neonatal brain injury, Toll-like receptor agonists have often been used to mimic infections and induce inflammation. Using the most common cause of bacteremia in preterm infants, Staphylococcus epidermidis, we present a more clinically relevant neonatal mouse model that addresses the combined effects of bacterial infection together with subsequent hypoxic-ischemic brain insult. Currently, there is no neuroprotective treatment for the preterm population. Hence, we tested the neuroprotective effects of vancomycin with and without adjunct therapy using the anti-inflammatory agent pentoxifylline. We characterized the effects of S. epidermidis infection on the inflammatory response in the periphery and the brain, as well as the physiological changes in the central nervous system that might affect neurodevelopmental outcomes. Intraperitoneal injection of postnatal day 4 mice with a live clinical isolate of S. epidermidis led to bacteremia and induction of proinflammatory cytokines in the blood, as well as transient elevations of neutrophil and monocyte chemotactic cytokines and caspase 3 activity in the brain. When hypoxia-ischemia was induced postinfection, more severe brain damage was observed in infected animals than in saline-injected controls. This infection-induced inflammation and potentiated brain injury was inoculum dose dependent and was alleviated by the antibiotic vancomycin. Pentoxifylline did not provide any additional neuroprotective effect. Thus, we show for the first time that live S. epidermidis potentiates hypoxic-ischemic preterm brain injury and that peripheral inhibition of inflammation with antibiotics, such as vancomycin, reduces the extent of brain injury.

Effects of therapeutic hypothermia on the gut microbiota and metabolome of infants suffering hypoxic-ischemic encephalopathy at birth.

Neonatal hypoxic ischemic encephalopathy (HIE) in the perinatal period can lead to significant neurological deficits in later life. Total body cooling (TBC) is a neuroprotective strategy used in the treatment of HIE and has been shown to reduce seizures and improve neurodevelopmental outcomes in treated infants. Little is known, however, about the effects of HIE/TBC on the developing gut microbiota composition and subsequent metabolic profile. Ten term infants with HIE who received TBC at 33.5°C for 72h were recruited. A control group consisted of nine healthy full term infants. Faecal samples were collected from both groups at 2 years of age and stored at -20°C. 16S rRNA amplicon Illumina sequencing was carried out to determine gut microbiota composition and 1H NMR analysis was performed to determine the metabolic profile of faecal water. The gut microbiota composition of the HIE/TBC infants were found to have significantly lower proportions of Bacteroides compared to the non-cooled healthy control group. Alpha diversity measures detected significantly lower diversity in microbial richness in the HIE/TBC infant group compared to the control infants (Shannon index, <0.05). High inter-individual variation was found in gut microbiota composition and metabolic profile of both groups. Initial principal coordinate analysis and hierarchal clustering of compounds on MetaboAnalyst 3.0 indicated no clear separation in the metabolic profile of these two infant groups. These results suggest that there is no significant impact on the gut microbial development of HIE/TBC infants compared to healthy infants at 2years of life. To our knowledge this is the first study to report the gut microbiota composition and metabolic profile of infants who have experienced HIE/TBC at birth.

Hypothermic Neuronal Rescue from Infection-Sensitised Hypoxic-Ischaemic Brain Injury Is Pathogen Dependent.

Perinatal infection increases the vulnerability of the neonatal brain to hypoxic-ischaemic (HI) injury. Hypothermia treatment (HT) does not provide neuroprotection after pre-insult inflammatory sensitisation by lipopolysaccharide (LPS), a gram-negative bacterial wall constituent. However, early-onset sepsis in term babies is caused by gram-positive species in more than 90% of cases, and neuro-inflammatory responses triggered through the gram-negative route (Toll-like receptor 4, TLR-4) are different from those induced through the gram-positive route via TLR-2. Whether gram-positive septicaemia sensitises the neonatal brain to hypoxia and inhibits the neuroprotective effect of HT is unknown. Seven-day-old Wistar rats (n = 178) were subjected to intraperitoneal injections of PAM3CSK4 (1 mg/kg, a synthetic TLR-2 agonist) or vehicle (0.9% NaCl). After an 8-h delay, the left carotid artery was ligated followed by 50 min of hypoxia (8% O2) at a rectal temperature of 36°C. Pups received a 5-h treatment of normothermia (NT, 37°C) or HT (32°C) immediately after the insult. Brains were harvested after 7 days' survival for hemispheric and hippocampal area loss analyses and immunolabelling of microglia (Iba1) and hippocampal neurons (NeuN). Normothermic PAM3CSK4-injected animals showed significantly more brain injury than vehicle animals (p = 0.014). Compared to NT, HT significantly reduced injury in the PAM3CSK4-injected animals, with reduced area loss (p < 0.001), reduced microglial activation (p = 0.006), and increased neuronal rescue in the CA1 region (p < 0.001). Experimental induction of a sepsis-like condition through the gram-positive pathway sensitises the brain to HI injury. HT was highly neuroprotective after the PAM3CSK4-triggered injury, suggesting HT may be neuroprotective in the presence of a gram-positive infection. These results are in strong contrast to LPS studies where HT is not neuroprotective.

Perinatal infection and hypoxic-ischemic encephalopathy: a pilot study.

Recent studies suggest a synergic effect of infection and hypoxia-ischemia in the causation of perinatal brain damage. We conducted a prospective pilot study on the presence of infection in hypoxic-ischemic encephalopathy (HIE), focusing on neurotropic viruses. Sixteen newborns with HIE were included in the study. There were no confirmed cases of viral infection. There was a case of bacterial early onset sepsis and four cases of suspected sepsis due to clinical and/or analytical signs, but with negative cultures. Our results do not support universal screening for viral infection in cases of HIE.

Chorioamnionitis and brain injury.

The limited available evidence supports a strong association of chorioamnionitis with neonatal encephalopathy and CP in the term infant. The association of chorioamnionitis with depressed Apgar scores or neonatal seizures and with CP is equivocal in the preterm infant. Different study results may be related to differences in study populations, perhaps specifically to differences in susceptibility by stages of neurologic development as well as differences in gene frequencies associated with inflammation and thrombophilia. We require further understanding of the normal roles of cytokines in brain development, pregnancy, and inflammatory homeostasis before clinical interventions directed at cytokines, their receptors, or the inflammatory process are considered.

Short report: Hyperammonaemia in critically ill septic infants.

Three infants with subphrenic abscess, pyonephrosis, and obstructive ureterocoele respectively had grossly increased concentrations of plasma ammonia. This was considered to be a result of infections with urea splitting organisms. All died in spite of intensive care support, including specific measures to reduce plasma ammonia.