Fecal analysis. Groups of six BALB/c female mice that were 6 weeks old were
inoculated by using a plastic gavage with approximately 109 spores suspended in
200 l of sterile H2O. The mice were housed individually in cages with grid floors
to prevent coprophagia. Fresh fecal pellets were collected at appropriate times,
weighed, and homogenized in PBS before serial dilutions were inoculated onto
DSM agar (28) plates and incubated at 37°C for 2 days. Identification of probiotic
strains from the normal flora was based on colony morphology and microscopic
examination of spore size and shape as described previously (5). A control
group of uninoculated mice was also included.
Simulated GIT conditions. Spores were suspended in simulated gastric juice (1
mg of pepsin [porcine stomach mucosa; Sigma] per ml; pH 2.0) or small intestine
fluid (1 mg of pancreatin [porcine pancreas; Sigma] per ml and 0.2% bile salts
[50% sodium cholate–50% sodium deoxycholate; Sigma]; pH 7.4) and incubated
at 37°C. Samples were removed, serially diluted, and plated to determine the
number of CFU per milliliter on DSM agar plates.
Enterotoxin genes. Chromosomal DNA was isolated from strains and tested
for the presence of B. cereus enterotoxin genes by using PCR as described
previously to profile food-poisoning Bacillus strains (14, 30).
Enterotoxin detection. Enterotoxins were detected by using two commercial
immunoassay kits. A BCET-RPLA kit (Oxoid) was used to detect the HblC
subunit of the Hbl enterotoxin in enrichment cultures, while a Tecra BDE kit
(Tecra Diagnostics) was used to detect the NheA subunit of the Nhe enterotoxin.