(P07-004-23) Staphylococcus aureus Enterotoxins in Human Milk

Objectives: Staphylococcus aureus is a gram-positive bacteria that colonizes the mucosal surfaces such as the skin in many people with no adverse effects. S. aureus can be found in healthy breast milk from non-mastitis mothers in small amounts. However, some strains of S. aureus produce enterotoxins and related compounds that cause a variety of clinical diseases. Milk donated to non-profit milk banks is not usually tested for the presence of S. aureus. This study was to test the hypothesis was that the milk from milk bank donors with and without mastitis may contain culturableS. aureus and detectable S. aureus enterotoxins (SE).

Methods: Milk samples that had been donated to the WakeMed Mothers Milk Bank by 19 non-mastitis, and 7 mastitis affected donors were cultured with total plate count (TPC) aerobic bacteria and S. aureus -specific Petrifilm™. SE concentration was measured in the same samples by ELISA (MyBioSource #MBS162591).

Results: Milk from 5 of the 7 donors with mastitis had culturable bacteria by TPC, but only one donor had consistent samples with S. aureus cultures. TPC showed 16 of the 19 non-mastitis donors had culturable bacteria and 8 of those tested S. aureus-positive. Nearly all samples turned the S. aureus plate pink, an indicator for DNase residue from various previously viable coagulase-positive Staphylococci sp. No detectable SE was measured in the milk from donors with mastitis, including the one that had S.aureus-positive Petrifilm™. ELISA showed 11 of the 19 samples from non-mastitis donors contained low concentrations ( 0.11 to 1.51 ng/mL) of SE (mean ± sd = 0.67±0.50). All of the samples from non-mastitis donors that had culturable S. aureus had detectable SE in the ELISA.

Conclusions: The data suggest that SE, which is thought to be heat stable, may be present at low concentrations in raw donor human milk. S. aureus was not a common cause of mastitis in this small sample, and the immune response to mastitis may make SE undetectable or non-reactive.

Funding Sources: NC State University Office of Undergraduate Research