Inhibition of Foodborne Pathogens by Native Microflora Recovered from Fresh Peeled Baby Carrot and Propagated in Cultures

Abstract

The inhibitory effect of fresh peeled baby carrot and associated microflora on the viability and growth of Listeria monocytogenes, Yersinia enterocolitica, Salmonella enterica, Escherichia coli O157:H7, and Pseudomonas marginalis was investigated. The population of viable L. monocytogenes was reduced by more than 2 logs following the dipping of sliced baby carrots in the bacterial suspension for 2 min. However, other pathogens subjected to the same treatment showed no reduction in the population. Surface sanitization of baby carrots reduced the number of native microflora and in turn increased the growth of each pathogen on this commodity by 2 to 3 logs. Filter-sterilized carrot homogenates exhibited no antimicrobial activity and were capable of supporting the growth of each pathogen to a density of over 2 x 10(9) CFU/mL. However, the growth of each pathogen in carrot homogenates containing microflora recovered from baby carrot and propagated in tryptic soy broth was reduced 2 to 3 logs after incubation at 28 degrees C for 2 d. On pepper disks, which have no antilisterial activity and very low levels of background microflora, the addition of carrot microflora also reduced the growth of each pathogen 2 to 4 logs after 2 d at 20 degrees C. The reduction was dependent upon the ratio between the number of carrot microflora and pathogen tested. The growth of L. monocytogenes or Y. enterocolitica on pepper disks containing carrot microflora was almost completely stopped after storage at 8 degrees C for 8 d. The inhibitory effect of baby carrots on pathogens is in part due to the antimicrobial activity of carrot tissue and in part due to the antagonistic action of associated microflora.