Carbenicillin passe'

Bob Ludwig ludwig at
Wed Jan 22 18:00:41 EST 1992

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, 100:1 and 50:1 (w/w) ticarcillin:clavulanic
acid. The latter is preferable. Because most wild Agrobacterium isolates have
beta-lactamase activity, clavulanic acid is particularly efficacious. 

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/liter Timentin is sufficient to
counterselect Agrobacterium.

Bob Ludwig
University of California
Santa Cruz

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