Isolation of a Salmonella Kentucky ST-198 strain and its H2S-negative variant from the same patient.

Hydrogen sulfide production is a characteristic feature in the laboratory identification of Salmonella species. Ciprofloxacin-resistant Salmonella Kentucky ST-198 arose in Egypt and spread worldwide. We isolated a H2S-negative and a H2S- positive variants of the strain from the sacral wound and stool respectively of the same patient in Kuwait. Whole genome sequencing of the isolates showed that the H2S-negative variant differed in having an insertion of a base in the gene encoding molybdenum cofactor biosynthesis protein c leading to a frame-shift mutation. This gene is linked to the thiosulfate reductase gene involved in the production of H2S. This seems to be a novel mechanism in H2S-negative variant generation in salmonella. Lack of production of H2S can potentially lead to failure of detection of salmonella in the laboratory.