Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2002
Publication Date: N/A
Interpretive Summary: Fresh-cut cantaloupe has been implicated in several outbreaks of foodborne illness in the past few years due to contamination of rind with bacterial human pathogens. In this study we wished to determine bacterial pathogen cell surface characteristics that may be important in the strength of attachment of pathogens to the cantaloupe rind. Cell surface hydrophobicity y(lack of affinity for water) and charge (both positive and negative) as well as the ability to strongly attach to the cantaloupe rind was determined for 10 strains of the bacterial pathogens Salmonella, Escherichia coli and Listeria monocytogenes. A strong correlation between both bacterial cell surface hydrophobicity and positive and negative charge with strength of bacterial attachment to the cantaloupe rind was established. This information will be used to devise more effective means of sanitizing whole cantaloupe to prevent transfer of pathogen from the rind to the interior flesh during cutting. Such methods will help to reduc the incidence of foodborne illness associated with fresh-cut cantaloupe.
Technical Abstract: Cantaloupe melon has been associated with outbreaks of Salmonella infections. It is suspected that bacterial surface charge and hydrophobicity may affect attachment and complicate detachment from cantaloupe surfaces. The surface charge and hydrophobicity of strains of Salmonella, Escherichia coli and Listeria monocytogenes were determined using electrostatic and hydrophobic interaction chromatography, respectively. Initial bacterial attachment to cantaloupe surfaces and ability to resist removal by washing with water were compared with surface charge and hydrophobicity. Whole cantaloupes were submerged in inocula containing individual strains or in cocktails containing Salmonella, E. coli and L. monocytogenes either as a mixture of strains containing all three genera or as a mixture of strains belonging to a single genus for 10 min. Inoculated cantaloupes were dried for 1 h inside a biosafety cabinet and then stored for up to 7 days at 4C. Inoculated melons were washed with water, and bacteria still attached to the melon surface as well as those in the wash water were enumerated. Initial bacterial attachment was highest for individual strains of E. coli and lowest for L. monocytogenes, but Salmonella exhibited the strongest attachment at day 0, 3 and 7. When mixed genera cocktails were used the relative degree of attachment of the three genera was altered. Salmonella strains attached the strongest, but the attachment of E. coli was greater than L. monocytogenes at day 0, 3 and 7. There was a linear correlation between bacterial cell surface hydrophobicity (r2 = 0.767), relative negative charge (r2 = 0.738), and relative positive charge (r2 = 0.724) and their strength of attachment to cantaloupe surfaces.