ludwig at biology.ucsc.edu
Tue Mar 10 13:08:22 EST 1992
Since I posted this message a month ago, I have been pummeled with the
same three queries. I'm repeating that message, along with the stock,
Timentin, not carbenicillin, is the antibiotic of choice for
Agrobacterium counterselection. While it is a proprietary product of
SmithKline Beecham Pharmaceuticals and, in the U.S., is a prescription
drug, Timentin is readily available and cheap (US$ 5 per gram).
Timentin is a mixture of two antibiotics: ticarcillin, a semi-synthetic
beta-lactam (like carbenicillin) and clavulanic acid, a beta-lactamase
inhibitor. SKB mixes Timentin in two formulae, 30:1 and 15:1 (w/w)
ticarcillin:clavulanic acid. The latter is preferable. Because most wild
Agrobacterium isolates have beta-lactamase activity, clavulanic acid is
All Agrobacterium isolates we have tested, including both tumefaciens
and rhizogenes strains, are highly Timentin susceptible. Further,
Agrobacterium strains carrying the standard pBR beta-lactamase gene are
also Timentin (clavulanic acid) susceptible. Timentin killing of
Agrobacterium wild-type strains is three logs greater than with
comparable doses of carbenicillin. In plant transformation experiments,
0.1 mg/ml Timentin (15:1) is sufficient to counterselect Agrobacterium.
1. SKB have changed the Timentin formulas I posted (100:1 and 50:1) to
30:1 and 15:1. The appropriate dose in tissue culture medium is indeed
0.1 mg/ml (not 0.1 mg/liter) of 15:1 mixture or 0.2 mg/ml of 30:1
mixture. To improve efficacy (of any antimicrobial), solid media are
best slightly dried before use.
2. At these concentrations, Timentin exhibits no phytotoxicity to
Arabidopsis root cultures.
3. I don't know why you can't get Timentin from Sigma.
University of California
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