Hi everyone, we are making some experiments with Salmonella species in a microplate reader. We are basically characterizing its growth curve in 18 hour time of incubation. However, only one Salmonella strain seems to get the TSB medium darker (very dark colour), affecting the reads, and we don't understand this behavior. Maybe it's H2S production but TSB doesn't have iron in its formula...any experience with this?
Thank you for answering
Hi,
I think , producing H2S from bacteria reacts with Cystine and cysteine from peptone to give black color.
Thank yo so much for your answer! I'll check some papers about this .
It should be noted that not all Salmonella spp produced considerable H2S that will make TSB dark. Salmonella enterica has been found to produce the highest level of H2S, and thereby seen as thick dark colonies.
I believe that you have a very significant research direction in your hands. The presence of iron compounds in the medium cannot be the only source of darkening in medium. You should review the mechanism of darkening by bacteria in particular and microorganisms in general. The pancreatic digest in the medium provides the sulfur-containing amino acids, methionine and cysteine. Your special bacterium might posses very useful enzymes relevant in sulfur sequestration and re-directing further reactions of sulfur with other medium components. You never truly know with bacteria. I must encourage you to follow this lead. We could be looking at some very novel reactions.
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