I added Cysteine-HCl to MRS and Colombia Blood Agar to reduce O2 of the media. could any body tell me should I store the media under anaerobic chamber because of Cysteine-HCl or it does not make any difference if I store them at 4 degree under aerobic condition(before inoculating).
Hi Ezgi,
the active compound of cysteine-HCl is cysteine and at neutral pH values the thiols of two cysteines react with oxygen resulting in the disulfide cystine and water. Cysteine-HCl is used to prepare stock solutions, because its dissolution results in very low pH values at which cysteine is quite stable and insensitive to the oxidation by oxygen.
Hi Mansooreh,
I recommend to store the medium in an anaerobic chamber. Cysteine will react slowly with oxygen from air atmosphere and after several hours or days your medium will be oxidized again. The duration of this process depends also on the medium viscosity. Oxygen diffuses more slowly in agar plates than in liquid medium.
I wonder using cysteine instead of cysteine HCl to make anaerobic medium will act as reducing agent.
Hi Ezgi,
the active compound of cysteine-HCl is cysteine and at neutral pH values the thiols of two cysteines react with oxygen resulting in the disulfide cystine and water. Cysteine-HCl is used to prepare stock solutions, because its dissolution results in very low pH values at which cysteine is quite stable and insensitive to the oxidation by oxygen.
thank you for you answers. would I ask you to help me figure out for how long could I store them under anaerobic chamber at 22 degree. Once I put MRS Plates under anaerobic chamber at 30 degree before inoculation for 2 weeks but the colour of the plates changed to brown. could it be possible due to the oxidation of Cysteine Hcl on the media?
Under anoxic conditions cysteine should be stable in this medium. MRS agar is very rich in nutrients, so that cysteine is additionally protected against oxidation. More likely would be an aging of the medium by reaction of medium compounds. The Maillard reaction (between carbohydrates and amino acids) could cause a darkening of the medium especially under elevated temperatures.
Hello Stefan Spring
I have a problem. When I use MRS 0.05% cysteine plates Bifidobacterium animalis subp. lactis BB12 does not grow. And with MRS 0.5% cysteine plates BB12 grows, but additionally form a precipitate as colonies, initially I thought they were contamination, but I prooved they were not. What can I do? I really need some help please.
May be your strain use cysteine as energy and carbon source and has need a great concentration to do that. Other hypothesis : pH, so you need ti ckek your final pH with the two concentration before inoculation !
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