The effect of iron on the toxigenicity of Vibrio cholerae

In vitro and in vivo studies were conducted to assess the response of chole ra toxin (CT) production to increasing iron concentrations in an aquatic en vironment. Production of CT by seven of eight Vibrio cholerae strains teste d, including the Bengal strain (O139), was significantly enhanced in the pr esence of iron concentrations of 1.0 and 10 g/L. The exception (El Tor Ogaw a) had a significant CT response only in the presence of 10 g of iron/L. En hancement of CT production also occurred at iron concentrations less than 1 .0 g/L, but not to a statistically significant degree. The high iron concen trations, which in this study were found to stimulate CT production, have b een described by others in association with sediments, water plants, and ch itinous fauna. Other investigators have shown a predilection by V. choler-n e to attach to these sites in the aquatic environment. The importance of ex cess in vivo iron with respect to the pathogenicity of several gram-negativ e bacilli is well recognized. However, the possible impact of environmental iron on the in vitro toxigenicity of a microorganism, in this case V. chol erae in its aquatic environment, is to the best of our knowledge a new find ing with important epidemiologic implications. These findings, coupled with the fact that iron concentration is considerably enhanced in industrially polluted waters and sediments, may reflect a causal link between the concur rent global upsurge of industrialization and pandemic occurrence of cholera during the latter half of the 20th century. Enhanced toxigenicity may also cause clinical disease following ingestion of lower than usual infective d oses of cholera vibrios, thereby increasing the incidence of symptomatic ca ses and, possibly, of severe cases.