Agriculture Reference
In-Depth Information
compounds hexanal and 2-(
E
)-hexenal, which when added to apple slices in MAP
demonstrated activity against
L. monocytogenes
,
E. coli
O157:H7, and
Salmonella
Enteritidis (Lanciotti and others 2003). In addition the wounding response compounds
(
E,Z
) - 2,6 - nonadienal and (
E
)-2-nonenal from cucumber were inhibitory to
B. cereus
,
E. coli
O157:H7,
L. monocytogenes
, and
Salmonella
Typhimurium when added to
growth media (Cho and others 2004).
The stress-induced compound 6,7-dimethoxycoumarin, which was isolated from
Valencia oranges (
Citrus sinesis
cv. Valencia), was shown to control the production
of afl atoxins (Mohanlall and Odhav 2006) and it was suggested that its use could be
extended to the postharvest control of mycotoxins in stored grains.
Quorum Sensing Signaling Molecules
Bacteria present in an ecosystem communicate with one another using chemical
signals (autoinducers) to regulate gene expression. This process, known as
quorum
sensing (QS)
, has been studied in depth for plant pathogens (von Bodman and others
2003). QS is used by bacteria to regulate a number of cellular responses, including
sporulation, biofi lm formation, bacteriocin production, and motility.
QS signals have been shown to be involved with the microbial spoilage of bean
sprouts (Rasch and others 2005). Autoinducers have also been detected on tomato,
cantaloupe, and carrots (Lu and others 2004), and on 11 of 12 produce items tested
in another study (Lu and others 2005). Similarly,
Yersinia enterocolitica
produced
signals in vegetable simulating agar (Medina-MartÃnez and others 2007). QS in food-
related bacteria has recently been reviewed (Gobbetti and others 2007).
The possibility of interfering with this communication for food safety purposes has
been proposed (Smith and others 2004) but is still in the early stages of development.
For example, signal antagonists might be used to interrupt QS signals to interfere with
biofi lm formation and virulence. Such QS inhibitors (possibly signal-degrading
enzymes or mimics) have been identifi ed in a number of produce extracts (Rasmussen
and others 2005) indicating that this mechanism forms part of the plant's defense
against bacterial attack.
Biocontrol agents might also be used as defense barriers in the form of biofi lms.
Biofi lm formation and production of surfactin by
B. subtilis
have been shown to be
effective in preventing the invasion of
Arabidopsis
by the plant pathogen
P. syringae
(Bais and others 2004). Such observations suggest a possible approach to prevent the
colonization of edible plants by human pathogens.
Siderophores
Siderophores are low - molecular - weight, ferric - chelating molecules that may enhance
the effectiveness of biocontrol agents on produce through competition for iron.
Many antagonistic bacteria, such as pseudomonads and aeromoads, that have the
potential to produce siderophores have been isolated from produce (Schuenzel and
Harrison 2002). Calvente and others (1999) isolated two strains of the yeast
Rhodotorula glutinis
from apples that produced the siderophore rhodotorulic acid.
Biocontrol of
Penicillium expansum
on wounded apples was found to be more effec-
tive with a combination of the yeast and siderophore than the yeast alone (6% and
34% disease prevalence, respectively). Sansone and others (2005) also evaluated
