REGULATION OF STAPHYLOCOCCAL ENTEROTOXINA SYNTHESIS, SECRETION AND LOCATION

Bassam  A. HALLIS

Staphylococcal food poisoning continues to be a major public health concern constituting a large proportion of reported bacterial food poisoning cases in Europe and the United States. Staphylococcal strains producing enterotoxin A (SEA) have been most frequently implicated in food poisoning outbreaks. The mechanism of synthesis and release of SEA have not been fully elucidated.

This study is concerned with the regulation of SEA synthesis, release and cellular location by the organism staphylococcus aureus. A double antibody sandwich enzyme linked immunosorbent assay (ELISA) was first developed for the quantitative detection of SEA. This assay had a detection limit of 1.4 ngml^-1 and was specific for sea. In order to increase both sensitivity and specificity of the assay, a number of monoclonal antibodies (MnAbs) specific against the toxin were produced. The sensitivity of the ELISA was increased to 0.15 ngml^-1.

In common with previous work using batch cultures, results in this study indicate that the regulation of SEA synthesis is growth related. Nutritive factors, pH, temperature and water activity were found to have relatively little effect on the quantity of toxin produced by the bacterial cells.

Using continuous culture  techniques SEA production was shown to be controlled by a cyclic AMP mediated glucose catabolite repression. Glucose was shown also to have a second remarkable effect on SEA. Addition of glucose to derepressed steady‑state cultures resulted in rapid disappearance of the toxin from the medium. Using iodinated pure toxin as a tracer it was established that the toxin became cell associated.

Thus, although glucose apparently represses synthesis of enterotoxin A, it is clear from the data in this study that the dominant effect of glucose is to control the distribution of toxin between the medium and the bacterial cells.