Behavior of Listeria monocytogenes on the Surface of Yellow Peaches Stored at Refrigeration Temperatures

Introduction: Listeria monocytogenes has been associated mostly with dairy and Ready-to-Eat meat but in recent years fresh fruits have emerged as a major concern and have been linked to outbreaks, sporadic cases and recalls. In the summer of 2014, a nationwide recall of stone fruits (yellow peach, white peach, nectarines) was issued due to the contamination of L. monocytogenes. Therefore, an understanding of the potential risk of L. monocytogenes on in-stone fruits is needed.

Purpose: Investigation of the fate of L. monocytogenes in yellow peaches stored at refrigeration temperature for 4 weeks.

Methods: Yellow peaches purchased from a local grocery store were used in the study. Fruits were inoculated by submersion into water containing a L. monocytogenes strain isolated from a nationwide stone fruits recall in 2014. Two inoculation levels were used. Peaches were air dried for 30 min at room temperature and then stored at 4°C for 4 weeks. Peaches were enumerated over a 4-week period by a rinsing and direct plating method developed in our FDA laboratories. Counts were obtained by plating onto ALOA and RAPID’ L. mono agars.

Results: L. monocytogenes was not able to grow in the surface of the peaches but able to survive for the duration of the experiments. Averaged counts for peaches inoculated at high levels declined from 3.2 x 10³ CFU/peach to 45 CFU/peach after 26 days of storage and for peaches inoculated at low levels, averaged counts declined from 340 CFU/peach to 68 CFU/peach. We have estimated that the average recovery rate of the rinsing method is 50%.

Significance: L. monocytogenes did not grow on yellow peaches under dry refrigerated storage conditions, but survived for an extended period of time, demonstrating that yellow peaches can carry a potential risk for causing Listeriosis in susceptible populations.