The bioautography assay was applied to strains of P.
larvae. The bioautography technique allows to evaluate
the minimum concentrations of the compound responsible
for the biological activity being observed the growth
inhibition areas at first sight (Marquez et al., 2003).
This experiment showed clear inhibition zones corresponding
to cinnamaldehyde (3-phenyl-2-propenal) and
eugenol (2-methoxy-4-propenyl-phenol) after separation
on TLC. On silica gel thin-layer chromatograms, cinnamon
essential oil was separated into two bioautographic
spots with different Rfs (0.67; 0.35) which
showed activity against P. larvae. No active bands corresponding
to Rfs between 0.05 and 0.21 related to the
region of terpenic alcohols were observed. Figure 2 displays
chromatogram bands and coinciding zones of
growth inhibition on the bioautography plate. Moreover,
table 2 shows the results obtained for these two components
in the tests of antimicrobial activity against P. larvae
strains from three different geographical origins.
For cinnamaldehyde compound, significant differences
were detected for Chapadmalal strain in relation to
Mechongué and Cobo strains (P