Agriculture Reference
In-Depth Information
and programmable instrument (e.g., KingFisher apparatus of ThermoFisher Scientifi c,
Waltham, MA).
Several companies produce a variety of IMB, such as Dynal beads and Quantum
Dots from Invitrogen Corp. (Carlsbad, CA), BioMag beads from Polysciences Inc.
(Warrington, PA), ProMag beads from Bangs Laboratories (Fishers, IN), MACS
Microbeads from Miltenyi Biotech Inc. (Auburn, CA), and MagSpheres from Luminex
Corporation (Austin, TX). Our previous work has shown that based on hydrodynamic
considerations, larger and denser beads have greater capturing effi ciencies than lighter
and smaller beads (Tu and others 2003a). These beads are used to capture bacteria or
toxins from briefl y enriched food samples, washed and then incubated with another
antibody conjugated with a signaling tag that might generate easily detectable signals
(e.g., absorption and fl uorescence changes) through either enzymatic or chemical
reactions (Tu and others 2001b; Li and others 2004).
Detection of Pathogens on Cantaloupe
Cantaloupes grow in contact with the earth, which increases their potential for contact
with soilborne bacteria, fungi, insects, and animals. The possibility of a product
becoming infected is compounded by contaminated irrigation water, improperly
applied fertilizers, ineffective washing techniques, and poor hygiene practices of fi eld
workers. It has been shown that
E. coli
O157:H7 can survive up to 100 days in soil
(Ingham and others 2004). Several outbreaks and recalls of cantaloupe have occurred,
in particular a multistate outbreak strain of
Salmonella
on cantaloupes from Mexico
that caused 133 cases from 2000-2002 (CDC 2002). In November 2006, more than
62,000 cases of cantaloupes from the western U.S. were recalled by Rio Vista, Ltd.
of Rio Rico, Arizona, because routine sampling by the FDA tested positive for
Salmonella
(FDA 2006). Other microbes have been cited in outbreaks on cantaloupe,
including
Campylobacter
and
Norovirus
(Bowen and others 2006). Because of its
rough surface and porous veins, bacteria can attach to cantaloupe surfaces rather
tightly, as evidenced by the diffi culty in removing the bacteria through simple aqueous
washings (Ukuku and others 2001). The bacteria may become incorporated into bio-
fi lms with existing microfl ora, which can further shield from the effects of washing
or chemical treatments (Annous and others 2005). This noncompetitive relationship
has been demonstrated by inoculating the surface with phytopathogenic mold, which
does not inhibit the growth of subsequently inoculated
Salmonella
(Richards and
Beuchat 2005). The waxy surface of the fruit can repel aqueous sanitizers (Beuchat
and Ryu 1997). This strong attachment and hydrophobicity may add further complica-
tions to the detection, quantifi cation, and reduction of suspected pathogens on the
surfaces of cantaloupes. Sanitizing methods have included the use of hydrogen per-
oxide, chlorine, 94 °C water, (Ukuku 2006) as well as ozone, peroxyacetic acid, and
chlorinated trisodium phosphate (Rogers and others 2004). Bacteria can be transferred
to the fl esh of the melons by cutting, which provides a surface that supports the growth
of pathogenic bacteria (Del Rosario and Beuchat 1995). The possibility of cross-
contamination from food service workers or other foods led to the proposal of a Hazard
Analysis and Critical Control Point (HACCP) plan for handling of fresh produce
(Beuchat 1995). Twenty cases of
E. coli
O157:H7 cross-contamination of cantaloupe
were documented in Oregon in 1993 (Jackson and others 2000).
