I'm conducting antibiograms on MH plates to check the antibacterial activity of some macroalgae extracts.
I'm using is Vibrio parahaemolyticus, two different bacterial strains. One of the strains turns the agar into a light brown color no matter if extract is added or not, the other one doesn't.
Anyone knows what could be causing this effect?
I checked and only found an article about MH Broth turning brown in the presence of peroxidase and hydrogen peroxidase.
Thank you very much.
Note: The MHA is supplemented with NaCl up to a 2.5%.
The discoloration of Mueller Hinton Agar plates to brown could be attributed to a few potential reasons. Here are some common factors that may contribute to the browning of Mueller Hinton Agar plates:
Article Role of Melanin Pigment in Expression of Vibrio cholerae Vir...
Its probably a natural feature of this Vibrio strain. Addition of trace elements could stop the pigment production as this could be a siderophore.
Some siderophores released for iron scavenging can also turn the plates brown. If you rear the strain in a fridge does it turn the plate blue?
Oxidation of component : Agar plates may turn brown due to the oxidation of the components, especially if they are exposed to air for an extended period.
Am suspecting that the agar medium has expired and also over heating during autoclaving
due to an increase in temperatures that are not optimal between 40 degrees Celsius
The brown color observed in the agar with one of the Vibrio parahaemolyticus strains could be due to various factors. Here are a few possibilities to consider:
1. Oxidation: It is possible that the extract or components within the extract are undergoing oxidation when in contact with the agar, leading to the development of a brown color. This could be due to the presence of reactive compounds or enzymes in the extract that promote oxidation.
2. Interaction with components in the agar: Certain compounds in the extract may interact with components present in the agar, resulting in a color change. For example, the extract could react with the pH indicator used in the agar, causing a color shift.
3. Reaction with the supplemented NaCl: The presence of NaCl in the agar may react with components in the extract, leading to a color change. This could occur through chemical reactions or precipitation.
4. Autolysis or cell death: It is possible that the brown color is a result of autolysis or cell death of the bacterial strain itself. This could release pigments or enzymes that cause the color change.
5. Other factors: There could be other factors specific to the bacterial strain or the extract being used that are causing the observed color change. It may require further investigation or experimentation to determine the exact cause.
Since you mentioned that you found an article about MH Broth turning brown in the presence of peroxidase and hydrogen peroxide, it is worth considering if the extract or the bacterial strain produces peroxidase or if there is any presence of hydrogen peroxide that could be causing the observed effect.
good luck,
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