Metabiotic associations of molds and Salmonella Poona on intact and wounded cantaloupe rind

Salmonella Poona, a serotype rarely implicated in human infections, has recently caused several cantaloupe-associated outbreaks of salmonellosis. Metabiotic associations of molds and foodborne pathogens on produce have been reported. We tested proteolytic activity and measured changes in the pH of cantaloupe rind caused by growth of Alternaria alternata, Cladosporium cladosporioides, Epicoccum nigrum, Geotrichum candidum, and Penicillium expansum. Survival and growth characteristics of Salmonella Poona co-infected with each mold on the surface rind and in wounded rind tissue as affected by temperature were determined. C. cladosporioides, G. candidum, and P. expansum, but not A. alternata and E. nigrum, showed proteolytic activity on agar media containing gelatin and/or casein, with concurrent increases in pH, thus favoring survival and growth of salmonellae. Intact and mechanically wounded tissue of cantaloupe rinds were inoculated with a five-strain mixture of S. Poona and/or test mold. Five inoculation schemes were used: mold only, S. Poona only, mold and S. Poona simultaneously, mold then S. Poona 3 days later, and S. Poona then mold 3 days later. The pH of cantaloupe rinds inoculated with molds and stored at 20 °C for 14 days was significantly higher (P≤0.05) than on day 0. Only the pH of rinds inoculated with C. cladosporioides or G. candidum was significantly higher (P≤0.05) on day 21 than on day 0, when cantaloupes were stored at 4 °C. An initial population of S. Poona increased from 3.3 log10 cfu/sample (ca. 7 cm2) of cantaloupe rind to populations as high as 9.5 log10 cfu/sample during storage at 20 °C for up 14 days, regardless of co-inoculation with molds. Populations of S. Poona decreased or remained constant at 4 °C for up to 21 days. Results demonstrate that persistence and growth of S. Poona on intact, wounded, and decaying cantaloupe rind are not markedly affected by the presence of molds.