P2.243: Neonatal Meningitis in a Full-term Neonate Due to Streptococcus mitis oralis: A Case Report

Introduction: The incidence of neonatal sepsis in the United States is 1-2 cases per 1,000 live births. The majority are bacterial infections due to Escherichia coli and Group B Streptococcus (GBS). Only a few reported cases due to Streptococcus mitis oralis exist in the literature with limited information regarding management and treatment. We discuss our step-by-step approach in treating early-onset sepsis following published guidelines, with additional consideration of antibiotic resistance and side effects in a full-term neonate.

Case Description: We report a case of Streptococcus mitis oralis bacteremia and meningitis in a full-term 38-week and 6-day-old female neonate born to a 37-year-old G2P2 mother initially treated with ampicillin and gentamicin for presumed GBS sepsis and meningitis, then completing a 14-day treatment course with cefepime.

Discussion: Streptococcus mitis oralis is found in normal flora of the oral cavity and is typically not pathogenic. However, the S. mitis family has zinc metalloproteases, which allow the bacteria to evade host immunity and, for example, break down host proteins such as IgA1. Similar enzymes and capsule expression have been found in other pathogens, including Streptococcus pneumoniae and Neisseria meningitidis. S. mitis oralis has been reported as an etiology of meningitis in children with leukemia or lymphoma, endocarditis, brain abscesses, pneumonia, and peritonitis, and can cause sepsis in a similar fashion to GBS.

Studies have demonstrated infants have the majority of maternal oral and gut flora by day 1 of life, with S. mitis oralis found consistently on day of life 1-3. Additionally, intrapartum maternal prophylaxis may contribute to the development of antimicrobial resistance in newborns, including to ampicillin. There are multiple reports of penicillin-resistant Streptococcus mitis due to penicillin-binding protein 2 genes, identical to those found in resistant S. pneumoniae isolates. Studies suggest the following antimicrobial susceptibility of S. mitis oralis isolates to penicillin: 23% susceptible, 50% intermediate, and 27% resistant.

In our neonate, Streptococcus mitis oralis was intermediate to penicillin [MIC = 0.38], warranting an alternative antibiotic. While both ceftriaxone and vancomycin demonstrated full sensitivity, we deferred vancomycin as repeat blood cultures were negative and the patient demonstrated clinical improvement on meningitic dosing of ampicillin [likely overcoming intermediate penicillin sensitivity]. We elected to complete treatment with cefepime, a fourth-generation cephalosporin, as ceftriaxone is contraindicated in infants younger than 28 days due to risk of hyperbilirubinemia, including kernicterus, and cardiopulmonary events.

Conclusion: Clinicians should be aware of S. mitis oralis as it can cause significant illness in both pre-term and term neonates, a population more susceptible to infection. Due to the low incidence of cases, there are no proposed guidelines for management of Streptococcus mitis sepsis or meningitis in the newborn. We highlight our clinical decision-making regarding antibiotic selection and treatment duration while enhancing efficacy based on antimicrobial susceptibilities.