Siderophore production by enterotoxigenic Salmonella.

Eleven Salmonella strains of diverse origin studied previously for enterotoxigenicity, cell surface hydrophobicity (HIC) and haemagglutination (HA) were studied for the production of a siderophore precursor 2,3-dihydroxybenzoic acid (DHB) by colorimetry. The Salmonella strains were similarly grown aerobically and anaerobically in a deferrated (DF) medium containing 0.05 micrograms/ml iron at 22 degrees C and 37 degrees C. Salmonella strains positive for both heat-labile (LT) and heat-stable (ST) enterotoxins, i.e. ST+ LT+ strains produced 25-70 mg/l, DHB, bound to hydrophobic phenyl sepharose gel and exhibited mannose-resistant haemagglutination (MRHA) of bovine, chicken and human group A erythrocytes. Conversely, heat-labile enterotoxin-positive, only i.e. ST- LT+ strains produced less than 25 mg/l DHB and were negative for the three aforementioned parameters. This dichotomy was shown by strains grown aerobically at 22 degrees C. Strains grown at 37 degrees C gave disparate results while Salmonella anaerobically grown at both growth temperatures did not produce DHB. These studies demonstrate production of a siderophore during iron stress.