Determination of the toxic potential ofBacillus cereusisolates by quantitative enterotoxin analyses

Abstract

Haemolysin BL (HBL) and non-haemolytic enterotoxin (Nhe), each consisting of three components, represent the major enterotoxins produced by Bacillus cereus. To evaluate the expression of these toxins, a set of 100 B. cereus strains was examined. Molecular biological characterization showed that 42% of the strains harboured the genes for HBL and 99% for Nhe. The production of all Nhe and HBL components were analyzed using specific antibodies and, in culture supernatants, detectable levels of HBL and Nhe were found for 100% of hbl-positive and 96% of nhe-positive strains. The concentrations of the HBL-L(2) and NheB component ranged from 0.02 to 5.6 microg mL(-1) and from 0.03 to 14.2 microg mL(-1), respectively. Comparison of the amount of NheB produced by food poisoning and food/environmental strains revealed that the median value for all food poisoning strains was significantly higher than for the food/environmental isolates. The data presented in this study provide evidence that specific and quantitative determination of the enterotoxins is necessary to evaluate the toxic potential of B. cereus. In particular, the level of Nhe seems to explain most of the cytotoxic activity of B. cereus isolates and may indicate a highly diarrheic potential.

Bacillus cereus Nhe is a pore-forming toxin with structural and functional properties similar to the ClyA (HlyE, SheA) family of haemolysins, able to induce osmotic lysis in epithelia

“…In a study of over 100 B. cereus strains, cytotoxicity correlated well with the amount of Nhe produced but poorly with the concentration of Hbl (Moravek et al, 2006). The same group (Dietrich et al, 2005) found that mAb 1E11 raised against NheB prevented cytotoxicity in 20 out of 20 strains of B. cereus isolated from food.…”

Ability of Bacillus cereus Group Strains To Cause Food Poisoning Varies According to Phylogenetic Affiliation (Groups I to VII) Rather than Species Affiliation

“…To date, the ces gene is the most relevant marker for the emetic syndrome. The toxins Nhe and HlyII have been directly or indirectly linked to the diarrheal syndrome (3,19), but they do not yet explain the pathogenicity of all strains. Some new associated virulence factors (5) have not been evaluated yet as pathogenic makers, and others are doubtlessly still unknown.…”

A quadruple-enterotoxin-deficient mutant of Bacillus thuringiensis remains insecticidal

“…In contrast, we obtained the hbl a2 deletion with the pBKJ236/pBKJ223 system. Our work illustrates an (Hansen & Hendriksen, 2001;Guinebretière et al, 2002;Moravek et al, 2006;Fagerlund et al, 2007), and the pathogenic potential of a particular strain probably results from many factors, including the number of bacterial cells ingested, the number and type of enterotoxins present, the levels of enterotoxin expression, the type of food in which they are ingested, the degree of stomach acidity, the concentration of bile and the composition of the gut microbiota (Clavel et al, 2004(Clavel et al, , 2007.…”

“…Many strains of B. cereus and B. thuringiensis isolated from diverse origins contain some combination of genes encoding NHE, HBL and CytK (Gaviria Rivera et al, 2000;Hansen & Hendriksen, 2001;Guinebretière et al, 2002;Ehling-Schulz et al, 2005;Thaenthanee et al, 2005;Ehling-Schulz et al, 2006;Moravek et al, 2006;Ngamwongsatit et al, 2008). The nhe operon is nearly universal among B. cereus and B. thuringiensis strains, whereas the hbl operon and cytK gene are less common.…”