Impact of vaccination during pregnancy and staphylococci concentration on the presence of Bacillus cereus in raw human milk

Abstract

Objective: This study aimed to determine whether vaccination during pregnancy, prematurity, and staphylococci concentration influenced the presence of B. cereus or staphylococcal enterotoxins (SEs) in raw human milk from healthy mothers.

Study design: Human milk samples were collected from 152 healthy women. B. cereus, S. aureus and coagulase-negative staphylococci (CNS) were enumerated using selective agar culture media. The detection of B. cereus spores and SEs were determined using ELISA.

Results: CNS and B. cereus concentrations in milk from non-vaccinated mothers were higher than that from mothers vaccinated during pregnancy, but S. aureus did not differ. Prematurity did not affect B. cereus or staphylococci in human milk. S. aureus and CNS concentrations in human milk with the presence of B. cereus were higher than that with the absence of B. cereus. Viable B. cereus was present in 9.2% of raw human milk samples whereas SEs were not detected in any samples.

Conclusions: Vaccination during pregnancy and low concentration of staphylococci could reduce the risk of B. cereus in raw human milk. The screening of B. cereus in raw human milk must be performed before pasteurization to reduce the risk of B. cereus infection in preterm infants.

Fig. 1

Concentrations of viable a Bacillus cereus, b coagulase-negative staphylococci (CNS) and c Staphylococcus aureus in raw human milk between mothers vaccinated during pregnancy (n = 98) and unvaccinated mothers (n = 54). Values are mean ± SEM. Asterisks show statistically significant differences between variables (**p < 0.01; *p < 0.05) using unpaired t-tests. Colony-forming units: CFU/mL. Pregnancy vaccination was the flu vaccine and/or tetanus, diphtheria and acellular pertussis (Tdap) vaccine.

Fig. 2

Comparison of counts (colony forming units, Log CFU/mL) for Staphylococcus aureus and coagulase-negative staphylococcal between milk containing B. cereus (presence, n = 14) and milk without B. cereus (absence, n = 125). Values are mean ± SEM. Asterisks show statistically significant differences between variables (**p < 0.01; *p < 0.05) using unpaired t-tests.