Composting can eliminate pathogenic organisms, including salmonellae, from sewage sludge. However, if salmonellae are present in the compost at undetectable levels or are inoculated into the compost by infected animals or from other sources, they may regrow presenting a health hazard for certain uses of compost. In the study, the authors examined dilute mineral-salt extracts of three composts from widely separate composting sites in the United States and found that they supported growth of Salmonella typhimurium. From kinetic studies of the growth of the organism on these extracts, the authors concluded that each compost produced on extraction a single water-soluble substrate and that the substrates from the different composts were very similar, if not identical.