Bacterial Infiltration and Internalization in Fruits and Vegetables 447
14.4.1.3 Damage by Insects and Birds
Insects and birds are a source of microorganisms (including pathogenic bacteria) in
fresh fruits and vegetables. Microorganisms transferred to fresh produce during
contact with insects or birds can enter areas of preexisting damage (Beuchat, 1996).
In addition, these pests may facilitate entry of microorganisms into fresh produce
via damage caused when they feed on leaves or fruits. Insects and birds have been
reported to be carriers of E. coli O157:H7 (Wallace et al., 1997; Shere et al., 1998;
Iwasa et al., 1999; Janisiewicz et al., 1999; Rahn et al., 1997). Vinegar flies and
nitidulid beetles contaminated 75 to 100% of damaged peaches and nectarines with
plant pathogens (Michailides and Spotts, 1999). Houseflies can carry about 100
different pathogenic microorganisms and transmit about 65% of these pathogens
(Kettle, 1982). Human enteric pathogens found in houseflies include Shigella spp.,
Salmonella Typhimurium, Campylobacter jejuni, Entamoeba histolytica, Vibrio
cholerae O139, and pathogenic Escherichia coli (Olsen, 1998). Iwasa et al. (1999)
reported that wild house flies on a cattle farm were persistently contaminated with
E. coli O157:H7. The presence of this pathogen on these flies was most likely linked
to the flies’ frequent contact with cow manure. A high incidence of E. coli O157:H7
in cuts and bruises in whole apples was linked to microbial contamination from fruit
flies (Janisiewicz et al., 1999).
14.4.1.4 Physical Damage
14.4.1.4.1 Environmental Factors
Environmental factors such as strong winds, hail, and frost can cause physical
damage to fresh produce in the form of bruises, cuts, punctures, and splits. The
action of strong winds and hail can result in damage to the protective cuticle of
leaves (Van Gardingen et al., 1991; Rogge et al., 1993), including rupture or removal
of cuticular waxes by bending, rubbing, particle impaction, or flexing action. Gen-
erally, the cuticular layer of plant leaves offers protection from invasion by bacteria
and other microorganisms by helping the leaves to repel water. Water repellency is
a common property of leaves and is linked to an intact layer of epicuticular waxes
(Neinhuis and Barthlott, 1997). Bermandinger-Stabentheiner (1994) suggested that
the action of strong winds may even melt waxes via frictional heat. The removal of
cuticular waxes certainly decreases the water repellency of leaves and increases their
wettability, predisposing them to invasion by microorganisms. Damage to the cutic-
ular layer can permit microbial proliferation in cellular fluids and moisture released
from the damaged sites. Sugars in released juices from damaged tissue attract insects,
which can further injure fresh produce and facilitate entry of microorganisms (Heard,
2002).
14.4.1.4.2 Maturation of Fruits
Maturation of certain fruits increases their susceptibility to mechanical damage.
During maturation, some fruits such as citrus endure folding or creasing of the rind
and degradation in the rind at the stem end (Ryall and Pentzer, 1982). Such types
of age-induced changes in the rind of citrus fruits can cause damage, including
splitting during harvesting, washing, or packaging, and permit the entry of bacteria