Human Bacterial Pathogens

The ability of human bacterial pathogens to attach to melon surfaces [20] and their virulence characteristics must both be considered. Results of a study examining attachment of bacteria from a mixed cocktail containing multiple suspensions of individual strains of each genus (salmonella, E. coli, and L. monocytogenes) on the surface of cantaloupes stored at 4°C for up to 7 days showed that salmonella has the strongest attachment to the cantaloupe surface followed by L. monocytogenes and E. coli, either as individual strains or as a mixed cocktail [20]. The strength of attachment increased slightly for E. coli over the 7 days of storage, but decreased for L. monocytogenes. Efficacy of sanitizer treatments applied to inoculated cantaloupes at 7 days postinoculation was greatly reduced for L. monocytogenes and E. coli but not for salmonella. Surface irregularities such as roughness, crevices, and pits have been shown to increase bacterial adherence by increasing cell attachment and reducing the ability to remove cells [21].

Salmonella is among the most frequently reported causes of foodborne outbreaks of gastroenteritis in the U.S. [22]. Salmonellosis has been steadily increasing as a public health problem in the U.S. since reporting began in 1943 [23]. Five multistate outbreaks of salmonellosis have been associated epidemiologically with cantaloupes. The first in 1990 involved S. Chester, which affected 245 individuals (two deaths) in 30 states [22]. The second in 1991 involved more than 400 laboratory-confirmed S. Poona infections and occurred in 23 states and Canada [22]. A 1997 outbreak associated with S. Saphra was reported ( htm). The most recent outbreaks (2000, 2001, and 2002) were due to S. Poona [5]. Other melons including watermelon have been associated with outbreaks of foodborne illness [5,24-26]. The implication of these outbreaks is that improvements are needed at the farm level to limit or minimize contact of melons with sources of human pathogens, and at the packinghouse level in sanitizing and processing conditions.

Other human pathogens including E. coli O157:H7 and shigella are capable of growth on melon flesh [6,7]. A 1993 outbreak of foodborne illness was attributed to cantaloupe contaminated with E. coli O157:H7 (M. Diermayer, Oregon Health Division, Portland, OR, personal communication).

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