AUTHOR=Johler Sophia , Kalbhenn Eva M. , Heini Nicole , Brodmann Peter , Gautsch Sylvia , Bağcioğlu Murat , Contzen Matthias , Stephan Roger , Ehling-Schulz Monika 

TITLE=Enterotoxin Production of Bacillus thuringiensis Isolates From Biopesticides, Foods, and Outbreaks

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01915

DOI=10.3389/fmicb.2018.01915

ISSN=1664-302X

ABSTRACT=<p>While the relevance of <italic>Bacillus (B.) cereus</italic> as a major cause of gastroenteritis is undisputed, the role of the closely related <italic>B. thuringiensis</italic> in foodborne disease is unclear. <italic>B. thuringiensis</italic> strains frequently harbor enterotoxin genes. However, the organism has only very rarely been associated with foodborne outbreaks, possibly due to the fact that during outbreak investigations, <italic>B. cereus</italic> is routinely not differentiated from <italic>B. thuringiensis</italic>. A recent EFSA scientific opinion stresses the urgent need for further data allowing for improved risk assessment, in particular as <italic>B. thuringiensis</italic> is a commonly used biopesticide. Therefore, the aim of this study was to gain further insights into the hazardous potential of <italic>B. thuringiensis</italic>. To this end, 39 <italic>B. thuringiensis</italic> isolates obtained from commercially used biopesticides, various food sources, as well as from foodborne outbreaks were characterized by <italic>panC</italic> typing, <italic>panC</italic>-based SplitsTree analysis, toxin gene profiling, FTIR spectroscopic analysis, a cytotoxicity assay screening for enterotoxic activity, and a sphingomyelinase assay. The majority of the tested <italic>B. thuringiensis</italic> isolates exhibited low (23%, <italic>n</italic> = 9) or mid level enterotoxicity (74%, <italic>n</italic> = 29), and produced either no (59%, <italic>n</italic> = 23) or low levels (33%, <italic>n</italic> = 13) of sphingomyelinase, which is reported to act synergistically with enterotoxins Nhe and Hbl. One strain isolated from rosemary was however classified as highly enterotoxic surpassing the cytotoxic activity of the high-level reference strain by a factor of 1.5. This strain also produced vast amounts of sphingomyelinase. Combining all results obtained in this study into a fingerprint pattern, several enterotoxic biopesticide strains were indistinguishable from those of isolates from foods or collected in association with outbreaks. Our study shows that many <italic>B. thuringiensis</italic> biopesticide strains exhibit mid-level cytotoxicity in a Vero cell assay and that some of these strains cannot be differentiated from isolates collected from foods or in association with outbreaks. Thus, we demonstrate that the use of <italic>B. thuringiensis</italic> strains as biopesticides can represent a food safety risk, underpinning the importance of assessing the hazardous potential of each strain and formulation used.</p>