Location of Escherichia coli O157:H7 on and in Apples as Affected by Bruising, Washing, and Rubbing

Abstract

Confocal scanning laser microscopy (CSLM) was used to determine the location of Escherichia coli O157:H7 cells on the surface and in tissue of bruised Red Delicious cv. apples. Undamaged and bruised apples were inoculated by immersing in a suspension of E. coli O157:H7 cells transformed with a plasmid that encodes for the production of a green fluorescent protein. Apples were then washed in 0.1% (wt/vol) peptone water and/or rubbed with a polyester cloth and examined to determine if these treatments removed or introduced cells into lenticels, cutin, and cracks on the skin surface. Optical slices of the apples obtained using CSLM were examined to determine the depth at which colonization or attachment of cells occurred. Populations of E. coli O157:H7 on the surface of apples were determined to assess the effectiveness of washing and rubbing in physically removing cells. The location of cells on or in undamaged and bruised areas of apples that were not washed or rubbed did not differ significantly. However, washing apples resulted in an approximate 2-log reduction in CFU of E. coli O157:H7 per cm2 of apple surface. On unwashed apples, cells were detected at depths up to 30 microm below the surface. No E. coli O157:H7 cells were detected at locations more than 6 microm below the surface of washed apples. Cells that remained on the surface of rubbed apples appeared to be sealed within naturally occurring cracks and crevices in waxy cutin platelets. These cells may be protected from disinfection and subsequently released when apples are eaten or pressed for cider production.

BIOFILM FORMATION BY SALMONELLA SPP. ON CANTALOUPE MELONS**

“…Disruptions in this cuticle have been shown to enhance the ability of foodborne pathogens to attach to plant tissue (Han et al. 2000; Kenney et al. 2001).…”

Efficacy of Plant‐Derived Antimicrobials as Antimicrobial Wash Treatments for Reducing Enterohemorrhagic Escherichia Coli O157:H7 on Apples

“…Commercially available chlorine‐based sanitizers commonly used for washing apples generally result in 2‐ to 3‐log reductions of E. coli O157:H7 on apples (Beuchat and others ; Wisniewsky and others ). The surviving bacteria from chlorine treatment are reported to be found on the stem and calyx regions (Kenney and others ), and waxy cuticle cracks of apples (Kenney and others ). Moreover, chlorine reacts with the organic matter and results in the production of organochlorine compounds, which are potentially carcinogenic (Rodgers and Ryser ).…”

Kinetics and Strain Specificity of Rhizosphere and Endophytic Colonization by Enteric Bacteria on Seedlings of Medicago sativa and Medicago truncatula

“…Various approaches to surface sterilize vegetables do not eliminate the enteric pathogens (2,24,25,26). This result led to the discovery that these enteric pathogens reside within the interiors of apples, lettuce, and alfalfa sprouts (4,11,16,26). Gandhi et al (11) showed that a Salmonella Stanley strain could reside within the interiors of alfalfa sprouts to a depth of 18 m from the surface.…”