Cefotaxime causing dark pink colouration of plant tissue culture medium - (Sep/13/2021 )

I am a trying transformation of banana via co-culture of banana apical meristems. After 3 days of co-culture in the dark, i transfer the banana meristems to medium with 500mg/L cefotaxime to kill the Agrobacterium. However, after about 2 weeks. The medium starts to to go pink starting -  see picture below. Any idea what causes this and how to fix it?

Can you provide details of your experiment please. Most of the people left on here are not working in your field, but may be in related fields (e.g. mammalian cell culture) so will need some specifics to answer your question.

In particular, which medium are you using? Has this happened before when you have attempted this experiment? Have you asked your supervisor and/or technicians or other people who work in your lab?