Effects of porcine bile on survival of Bacillus cereus vegetative cells and Haemolysin BL enterotoxin production in reconstituted human small intestine media.
OBJECTIVE
To determine the effects of porcine bile (PB) on Bacillus cereus vegetative cells and Haemolysin BL (HBL) enterotoxin production in reconstituted small intestine media (IM).


RESULTS
The effects of PB on the growth of B. cereus vegetative cells in reconstituted IM at PB concentrations ranging between 0 and 3.0 g l(-1) were examined. Four gastric media (GM) named GM-J broth (JB), GM-chicken, GM-milk and GM-pea were prepared by mixing equal volumes of a gastric electrolyte solution containing pepsin with JB, chicken, semi-skimmed milk and pea soup, respectively. Bacillus cereus was inoculated at approx. 2 x 10(4) CFU ml(-1) into each GM at pH 5.0 for 30 min at 37 degrees C, then mixed to the same volume of double-strength JB (IM) and PB to give concentrations of between 0 and 3.0 g of PB per litre at pH 6.5 and incubated at 37 degrees C. The diarrhoeal B. cereus strain F4430/73 grew in IM-JB, IM-chicken and IM-milk at PB concentrations of up to 0.6, 1.5 and 1.2 g l(-1), respectively. Growth was observed in IM-pea at all concentrations tested. The highest PB concentrations allowing a 3 log B. cereus increase in IM-JB, IM-chicken, IM-milk and IM-pea after a 7-10 h incubation period were 0.3, 0.9, 0.9 and 3.0 g l(-1), respectively. The effect of PB on B. cereus cells was strongest in IM-JB, followed by IM-chicken, IM-milk and IM-pea. Haemolysin BL enterotoxin was detectable in IM-chicken, IM-whole milk, IM-semi-skimmed milk and IM-pea up to PB concentrations of only 0.6, 0.6, 0.3 and 0.9 g l(-1), respectively. The diarrhoeal B. cereus strain F4433/73 behaved similarly to B. cereus strain F4430/73, whereas the food strain TZ415 was markedly more susceptible to bile.


CONCLUSIONS
The tolerance of B. cereus cells to PB strongly depends on the type of food contained in the IM. Bile tolerance is also subject to strain variation.


CONCLUSIONS
The probability that B. cereus cells will grow in the small intestine, produce toxins and cause diarrhoea is likely to depend on the food they are ingested with, on the bile tolerance of the B. cereus strain, and on bile concentration.
Clavel
T
T
Université d'Avignon et des Pays de Vaucluse, UMR 408, Sécurité et Qualité des Produits d'Origine Végétale, Avignon, F-84029, France. thierry.clavel@univ-avignon.fr
Carlin
F
F
Dargaignaratz
C
C
Lairon
D
D
Nguyen-The
C
C
Schmitt
P
P
D000818:Animals; D016863:Bacillaceae Infections / Q000382:microbiology*; D001409:Bacillus cereus / Q000187:drug effects / Q000502:physiology*; D001426:Bacterial Proteins / Q000032:analysis / Q000096:biosynthesis*; D001431:Bacteriological Techniques; D001647:Bile Acids and Salts / Q000494:pharmacology*; D015169:Colony Count, Microbial; D005516:Food Microbiology; D005517:Foodborne Diseases / Q000382:microbiology*; D006460:Hemolysin Proteins / Q000032:analysis / Q000096:biosynthesis*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007421:Intestine, Small / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D013552:Swine
D001426:Bacterial Proteins; D001647:Bile Acids and Salts; D006460:Hemolysin Proteins; C083961:hemolysin BL protein, Bacillus