The concentration and disinfection time
of the antibiotic used was probably not sufficient
to clean the explants. Scortichini and
Chiariotti [11] employed three antibiotics,
streptomycin sulphate (S), piperacillin (P)
and rifampicin (R) at (25 to 200) mg·L–1, in
order to test the antibacterial and phytotoxic
effects of these compounds on shoot tip
explants of Prunus persica. The authors
found that the antibiotics used, even though
presenting a broad spectrum, partially eliminated
contaminants (30.0% of explants
escaped their action) and clearly showed
phytotoxicity with rifampicin and streptomycin
sulphate. Reed et al. [12] reported that
internal bacterial contaminants in tissue-cultured
hazelnuts were eliminated by antibiotic
treatment. Single antibiotics were ineffective,
but a combination of two or more
of them eliminated most contaminants.
Streptomycin combined with timentin or
gentamicin killed all of the isolated bacteria
tested. The authors also found that, in plant
tissues, antibiotics with a concentration 3–
4 times higher than those effective on isolated
bacteria were needed to eliminate
internal bacteria.