Bacillus cereus bacteremia in a preterm infant caused by consumption of contaminated breastmilk

Abstract

A 1490-g female infant, twin A, was born at 33 + 2 gestational weeks by cesarean delivery and was admitted to the neonatal intensive care unit (NICU) due to respiratory distress. By day 4, she was fed with expressed breast milk from her mother through a gastric tube. After three days of feeding, she presented with tachycardia, abdominal distension, bilious vomiting, hyperglycemia, and elevated C-reactive protein (36.9 mg/L). Subsequent blood culture yielded Bacillus cereus with negative lumbar puncture results. Vancomycin and amikacin were completed for 10 days. Given the absence of other possible contaminants, infant's maternal breast milk was suspected to be the source of infection. The batch of milk fed to the infant was sent for bacteria culture, which showed moderate growth for B. cereus strain. Clonal relationship between the B. cereus strain isolated from the infant's blood and the breast milk was further analyzed with pulsed-field gel electrophoresis (PFGE).1Liu P.Y. Ke S.C. Chen S.L. Use of pulsed-field gel electrophoresis to investigate a pseudo-outbreak of Bacillus cereus in a pediatric unit.J Clin Microbiol. 1997; 35: 1533-1535Crossref PubMed Google Scholar The result of the PFGE analysis showed that the B. cereus strain isolated from the infant's blood matched the strain isolated from the batch of breast milk fed to the infant (Fig. 1). Recent reports have suggested that human milk contaminated with B. cereus is the source of several infectious disease outbreaks in the NICU. However, a causal link between contaminated breast milk and neonatal bacteremia was speculated but never established. To our knowledge, this is the first study to present molecular evidence that breast milk served as the source of transmission of B. cereus from a healthy mother to her preterm infant. By using PFGE analysis, strains found in the breast milk and infected blood of the neonate had shown high similarity, therefore confirming that the mother's expressed milk was likely the source of contamination in this infant. PFGE has become the gold standard in epidemiological studies for several pathogenic bacteria, such as Bacillus species, and was proven to be a reliable tool for the differentiation of strains and species.1Liu P.Y. Ke S.C. Chen S.L. Use of pulsed-field gel electrophoresis to investigate a pseudo-outbreak of Bacillus cereus in a pediatric unit.J Clin Microbiol. 1997; 35: 1533-1535Crossref PubMed Google Scholar B. cereus was initially characterized as a causal agent of self-limited food-borne illnesses and has rarely been implicated to cause severe human diseases. However, in the past two decades, invasive infection with B. cereus have been reported in patients with immunosuppression and premature infants.2Wendelboe A.M. Smelser C. Lucero C.A. McDonald L.C. Cluster of necrotizing enterocolitis in a neonatal intensive care unit: New Mexico, 2007.Am J Infect Control. 2010; 38: 144-148Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar,3Ramarao N. Belotti L. Deboscker S. Ennahar-Vuillemin M. de Launay J. Lavigne T. et al.Two unrelated episodes of Bacillus cereus bacteremia in a neonatal intensive care unit.Am J Infect Control. 2014; 42: 694-695Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar In the review by Lewin et al., approximately 50 cases of B. cereus infection in preterm infants have been reported to date. Possible sources of infection were hospital linens, ventilator circuits, catheters, or feeding tubes, etc. Among them, banked human milk was suspected to be the origin of contamination in eight cases; however, the direct link has never been established.4Lewin A. Quach C. Rigourd V. Picaud J.C. Perreault T. Frange P. et al.Bacillus cereus infection in neonates and the absence of evidence for the role of banked human milk: case reports and literature review.Infect Control Hosp Epidemiol. 2019; 40: 787-793Crossref PubMed Scopus (9) Google Scholar Breast milk is not sterile; however, majority of infants fed with expressed breast milk do not encounter any problem, despite being exposed to bacteria in the breast milk.5Ojo-Okunola A. Nicol M. du Toit E. Human breast milk bacteriome in health and disease.Nutrients. 2018; 10: 1643Crossref Scopus (29) Google Scholar However, based on recent reports about bacterial contaminants ingested from breast milk that resulted in severe illness in preterm infants, unusual testing results of expressed human milk can alert neonatologists, as expressed milk is a potential source of infection in cases of unexplained sepsis or feeding intolerance in this population. No potential conflict of interest was reported by the authors.

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