Bacillus cereus strains from donor human milk and hospital environment: uncovering a putative common origin using comparative analysis of toxin and infra-red spectroscopy profiles

Abstract

Bacillus cereus is reported as a common cause of toxin-induced food poisoning and of contamination in pasteurized human milk donations. As various toxins can be produced by B. cereus, the aim of this work was first to investigate the toxigenic potential and profiles of 63 B. cereus isolates from Amiens Picardie human milk bank. A comparison to the toxigenic profiles of 27 environmental B. cereus isolates harvested in the hospital in which this human milk bank is situated was performed. Toxin gene prevalences were the highest for nhe (ABC) and entFM followed by cytK and hbl(ACD). A 27% prevalence was found for ces human milk isolates, which is higher than previous works reporting on pasteurized milk and dairy products. No significant differences could be found between human milk and environmental isolates regarding toxin gene prevalences and/or toxin gene profiles. The second aim was to establish whether a B. cereus cross-contamination between human milk and the environment could occur. This was achieved with the help of Fourrier-transform infra-red spectroscopy which enabled the discrimination of 2 main clusters of 11 and 8 isolates, each containing human milk and Amiens Picardie human milk bank environmental isolates. For these two clusters, the time sequence showed that human milk isolates were the first to occur and might have contaminated the milk bank environment as well as other human milk donations. Routinely used on B. cereus isolates, Fourrier-transform infra-red spectroscopy could help in rapidly detecting such clusters and in limiting the spread of a B. cereus strain that might generate rejection of pasteurized donation by the human milk bank.

Keywords: Bacillus cereus; Fourier-transform infra-red spectroscopy; cereulide toxin; cytotoxin K; enterotoxins; human milk; human milk bank; pore-forming toxins.

Figure 1.. Toxin profiles of Bacillus cereus strains included in this study. Toxin profiles are defined as follows: A = nhe+, hbl+, cytK+; B = nhe+, cytK+, ces+; C = nhe+, hbl+; D = nhe+, cytK+; E = nhe+, ces+; F = nhe+; G = cytK+ and Other = combination of genes different from those described for A to G profiles.

Figure 2.. 2D plot of the first two components arising from the primary component analysis comparing the 90 B. cereus strains included in this study (3 FITR spectra acquired per strain). Color coding for B. cereus isolates as follows: Raw Human Milk; Pasteurized Human Milk; Endoscope; Linen; Human Milk Bank Room 1; Human Milk Bank Room 2; Human Milk Bank Room 3; Other hospital wards. Shape coding of the 7 B. cereus main (5 isolates and more) clusters as follows: Lower ○ Cluster 1 (5 isolates); Upper ○ Cluster 2 (8 isolates); + Cluster 3 (7 isolates); Upper▼Cluster 4 (7 isolates); Lower ▼Cluster 5 (7 isolates); ▲Cluster 6 (8 isolates); ● Cluster 7 (11 isolates).