Vancomycin Is Protective in a Neonatal Mouse Model ofStaphylococcus epidermidis-Potentiated Hypoxic-Ischemic Brain Injury

Abstract

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.

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

“…We and others have demonstrated that synthetic compounds, such as Pam 3 CSK 4 , a Toll-like receptor (TLR) 2 agonist that mimics aspects of inflammation driven by Grampositive bacteria, increases the vulnerability of the brain to subsequent HI in neonatal mice (12,13). Recently we extended these findings to show that live S. epidermidis bacterial infection induced 14 h prior to HI also sensitizes the brain to increased injury (14). However, the time interval between infection and subsequent HI is known to be important in experimental studies (15).…”

“…We have previously shown that S epidermidis infection can increase the vulnerability of the developing brain to HI (14). To evaluate the potentiation of brain injury after S. epidermidis infection over time, mice were subjected to a combination of S. epidermidis infection and HI.…”

“…To evaluate the potentiation of brain injury after S. epidermidis infection over time, mice were subjected to a combination of S. epidermidis infection and HI. For exposure to neonatal infection, mice were intraperitoneally injected with sterile saline or 3.5 × 10 7 colony-forming units (CFU) of S. epidermidis at postnatal day (PND) 4 as previously described (14). HI was induced at 24 h (PND5) or 5 d (PND9) after S. epidermidis injection.…”

“…HI was induced at 24 h (PND5) or 5 d (PND9) after S. epidermidis injection. The timing of HI was based on our previous study which showed that infection was ongoing at 24 h but largely cleared at 5 d (14). Animals were sacrificed on PND14-PND16 for neuropathological examination (Figure 1A).…”

“…To assess the window of increased vulnerability to HI after S. epidermidis bacteraemia, we induced HI either at 24 h post infection, when bacteraemia was high, or at 5 d after infection, when bacteria was significantly reduced in the blood (14). We assessed changes in the white and gray matter at PND14-PND16, corresponding to an age when myelination is established and detectable by immunohistochemical staining in mice (24).…”