The excessive and permanent usage of biocide mixtures in plant tissue culture can be a potential source of resistant strains. Especially strains which already have a low resistance can adapt to higher levels of preservative tolerance, if cultured in sublethal preservative concentrations.
A very popular and patented formulation contains beside some other components a mixture of CMIT (Methylchloroisothiazolinone) and MIT (Methylisothiazolinone). Despite the producer claims that a resistance for this mixture is unlikely, there have been evidents published in the past which show resistance is possible. Stable adaptive resistance to M-CMIT, MIT, BIT, and BC preservatives was promoted on Burkholderia lata strain 383 via progressive subculture on agar containing increasing concentrations of the preservative agent, which resulted in preservative cross-resistance and altered antibiotic susceptibility, motility, and biofilm formation (Rushton et al. 2013).
- use biocide mixtures for washing steps only
- do not add biocide mixtures into media to keep the medium "clean"
- never underestimate the adaption skills of a microorganism
Rushton, Laura, et al. "Key role for efflux in the preservative susceptibility and adaptive resistance of Burkholderia cepacia complex bacteria." Antimicrobial agents and chemotherapy 57.7 (2013): 2972-2980.