Clostridium perfringens type A produces an enterotoxin that induces diarrhoea experimentally in man and animals. The enterotoxin causes increased membrane permeability in susceptible cells which is ...thought to be due to pore formation in the host cell membrane. The effect of purified C. perfringens enterotoxin on intact intestinal CaCO-2 monolayers was examined in Ussing chambers and on single cells by whole-cell patch clamp. Mucosal application of C. perfringens enterotoxin resulted in prompt increases in short-circuit current coupled with a reduction in transepithelial resistance consistent with movement of sodium and other cations smaller than diethanolamine from mucosa to serosa. These changes were independent of extracellular calcium. Increases in short-circuit current were also observed in the apical membranes of CaCO-2 monolayers permeabilised across the basolateral membrane with nystatin. Currents were blocked by subsequent exposure to mucosal barium and zinc. Zinc also prevented the development of the current increases in apical membranes. Cationic currents were also observed following exposure of single CaCO-2 cells in whole-cell patch clamp recordings. These data indicate that C. perfringens enterotoxin is able to form cation permeant pores in the apical membrane of human intestinal CaCO-2 epithelia and the increases in short-circuit current can be prevented by pre-exposure to zinc ions.
Bacillus cereus is an important cause of bacterial food poisoning. It is a spore former and the spores attach easily to stainless steel surfaces. The spores have long appendages and it is believed ...that these play an important role in the attachment to surfaces. In this study, spores of three different strains (NVH 74, NVH 1230-88 and IAM 1110) where the appendages had been removed by ultrasonication, were compared with the native spores with respect to the ability to attach to stainless steel and polypropylene surfaces. Both static conditions and fluid flow conditions were studied. Under static conditions, the attachment of the native spores to the surface was slightly, but significantly, higher than the attachment of the same spores without appendages. Under fluid flow conditions, however, for NVH 74 and IAM 1110 spores without appendages seemed to adhere slightly better to the surface than native spores. For NVH 1230-88, spores without appendages adhered very poorly to the surface compared with native spores. The results indicate that the importance of the appendages in the attachment of
Bacillus cereus spores to surfaces may depend both upon the strain and the hydrodynamic conditions under which the attachment takes place.
The location of the cpe gene, encoding the enterotoxin responsible for food poisoning in humans, has been studied in a series of enterotoxigenic Clostridium perfringens strains by means of pulsed ...field gel electrophoresis of genomic DNA. The cpe gene was found at the same chromosomal locus in strains associated with food poisoning in humans and was shown to be linked to a repetitive sequence, the HindIII repeat, and an open reading frame, ORF3, that may be part of an insertion sequence. In contrast, when the strains originated from domesticated livestock cpe was located on a large episome where it was often close to a copy of the transposable element IS1151. In these cases, the HindIII repeat was not linked to the cpe gene although this was generally preceded by ORF3.
Out of 321 strains of Bacillus cereus from several sources and isolated in four different countries, 239 (74%) produced cytotoxins. Only 127 (53%) of the cytotoxic strains were positive for the ...B-component gene of the haemolysin BL (enterotoxin) by polymerase chain reaction (PCR). Western blots using antiserum produced against enterotoxin(s) gave positive results for 199 (83%) of the cytotoxic B. cereus strains. On closer examination of seven of the strains, involved in food poisoning, we found that two strains completely lacked the L2- and B-components (of the haemolysin BL), and two strains were negative for the B-component gene by PCR, but were positive for the L2-component. From our experiments we concluded that there is at least one enterotoxin complex in addition to the haemolysin BL enterotoxin and enterotoxin T.
H-NS is a major component of chromatin in enteric bacteria. H-NS plays a structural role in organising the chromosome, and influences DNA rearrangements as well as the expression of many genes. The ...biochemical and functional characteristics of H-NS are distinct from those of 'typical' DNA-binding proteins and much remains to be learned about the mechanism(s) by which H-NS acts. In this article we review our current understanding of the role of H-NS, and describe possible models by which H-NS might influence DNA structure and gene expression.
The non-haemolytic enterotoxin from Bacillus cereus has been sequenced. It is composed of three components, nonhaemolytic enterotoxin A, B and C of 41.0, 39.8 and 36.5 kDa respectively. Transcription ...of the operon seems to be positively regulated by plcR, a gene that also regulates phospholipase C expression. There is substantial similarity between the three proteins of non-haemolytic enterotoxin and between the non-haemolytic enterotoxin and haemolytic enterotoxin proteins.
Four strains of Bacillus thuringiensis were isolated from infections in burn wounds and from water used in the treatment of burn wounds. The strains produced large parasporal inclusion bodies ...composed of 141, 83, and 81 kDa protoxins. The four strains were tested for insecticidal activity against larvae of Pieris brassicae and Aedes aegypti but showed no activity; Vero cell assays for the production of enterotoxins were also negative. Attempts to classify the strains according to flagellar H-serotype showed them all to be non-flagellated. Apart from two occupational health accidents that occurred during the handling of highly concentrated B. thuringiensis fluids, this is the first report of B. thuringiensis causing non-gastrointestinal clinical infection in immunosuppressed patients.
Clostridium perfringens enterotoxin (CPE) is an important cause of food poisoning with no significant homology to other enterotoxins and its mechanism of action remains uncertain. Although CPE has ...recently been shown to complex with tight junction proteins, we have previously demonstrated that CPE increases ionic permeability in single Caco-2 cells using the whole-cell patch-clamp technique, thereby excluding any paracellular permeability. In this paper we demonstrate that CPE forms pores in synthetic phospholipid membranes in the absence of receptor proteins. The properties of the pores are consistent with CPE-induced permeability changes in Caco-2 cells suggesting that CPE has innate pore-forming ability.
PDF
