Incidence and Behavior of Salmonella and Escherichia coli on Whole and Sliced Zucchini Squash (Cucurbita pepo) Fruit

The incidence of coliform bacteria (CB), thermotolerant coliforms (TC), Escherichia coli, and Salmonella was determined for zucchini squash fruit. In addition, the behavior of four serotypes of Salmonella and a cocktail of three E. coli strains on whole and sliced zucchini squash at 25 ± 2°C and 3 to 5°C was tested. Squash fruit was collected in the markets of Pachuca city, Hidalgo State, Mexico. CB, TC, E. coli, and Salmonella were detected in 100, 70, 62, and 10% of the produce, respectively. The concentration ranged from 3.8 to 7.4 log CFU per sample for CB, and <3 to 1,100 most probable number per sample for TC and E. coli. On whole fruit stored at 25 ± 2°C or 3 to 5°C, no growth was observed for any of the tested microorganisms or cocktails thereof. After 15 days at 25 ± 2°C, the tested Salmonella serotypes had decreased from an initial inoculum level of 7 log CFU to <1 log, and at 3 to 5°C they decreased to approximately 2 log. Survival of E. coli was significantly greater than for the Salmonella strains at the same times and temperatures; after 15 days, at 25 ± 2°C E. coli cocktail strains had decreased to 3.4 log CFU per fruit and at 3 to 5°C they decreased to 3.6 log CFU per fruit. Both the Salmonella serotypes and E. coli strains grew when inoculated onto sliced squash: after 24 h at 25 ± 2°C, both bacteria had grown to approximately 6.5 log CFU per slice. At 3 to 5°C, the bacterial growth was inhibited. The squash may be an important factor contributing to the endemicity of Salmonella in Mexico.