Incubating confluent cell culture HeLa cells for 18 h with increasing concentrations of estrogens progressively enhanced the subsequent attachment of a variety of radiolabeled bacteria to the HeLa cells. This effect was not caused by other hormones and was not produced by 1-h incubations of HeLa cells or bacteria with hormones. Estrogens did not similarly affect two other receptor cell lines studied. The addition of metabolic inhibitors showed that this effect of estrogens on HeLa cells was energy dependent and involved protein synthesis. Concurrent incubation of the HeLa cells and estrogens with the antiestrogen nafoxidine blocked the subsequent increase in adherence. These data suggest that estrogen receptors are present in HeLa cells and that hormonally-induced alterations in the synthesis of bacterial receptor sites may modify the capacity of certain cells to bind bacteria.

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Zinc significantly enhances the ability of piliated Gram-negative and Grampositive bacteria to attach to HeLa cells. This effect is related to the concentration of zinc and degree of bacterial piliation, and is not present with unpiliated organisms. Bacterial viability is not necessary for this effect, and sulfhydryl blockers decrease the response. These data suggest that zinc can bind to bacterial pili and augment bacterial adherence; in this manner, zinc may act as a virulence factor.

SUMMARY. Enterotoxigenic Escherichia coli is a major cause of diarrhoea in man. When zinc in concentrations of 1 0 -6~ or 1 0 -5~ was added to the growth medium, there was a significant increase in heat-labile enterotoxin production by each of six toxigenic strains. Zinc in these concentrations did not alter bacterial growth or the activity of preformed toxin. Other heavy metals did not enhance toxin production and o-phenanthroline, a relatively specific zinc-chelating compound, blocked the enhancing effect. The significance of these findings is discussed in relation to the use of supplemental dietary zinc.