Effect of Surface Roughness on Retention and Removal of Escherichia coli O157:H7 on Surfaces of Selected Fruits

Abstract

This study was undertaken to evaluate the effect of surface roughness on the attachment and removal of Escherichia coli O157:H7 on selected fruit and metal surfaces. A new method to determine surface roughness was developed using confocal laser scanning microscopy (CLSM). A series of 2-D layered images were taken by CLSM optical slicing of the surfaces of Golden Delicious apples, navel oranges, avocadoes, and cantaloupes. The average roughness (R a ) of the fruit surfaces was assessed by reconstructing a series of 2-D images into 3-D images. A cocktail of 5 E. coli O157:H7 strains were spot inoculated onto fruit skin surfaces with different R a . The fruits were then treated with acidic electrolyzed water (AEW), peroxyacetic acid (POAA), and sterilized deionized water. Aluminum stubs with different R a values as a model system were also spot inoculated with E. coli O157:H7 and subjected to a sonication treatment. Test results indicated that there was a positive linear correlation between R a and adhesion rate of E. coli O157:H7, and a negative correlation between R a and the efficacy of inactivation by AEW and POAA, respectively, on fruit surfaces. A linear increase of residual bacteria population with increased surface roughness of aluminum stubs was also observed. The relationship between surface roughness and surface hydrophobicity was negative linear for the aluminum stubs, but was quadratic for the 4 fruits. The environmental scanning electron microscopy images showed that bacteria tended to attach to or be entrapped in the grooves or cavities of fruits, which provided protection to the cells against washing treatments.

Enzymatic Digestion for Improved Bacteria Separation from Leafy Green Vegetables

“…Additionally, many bacteria such as Salmonella, can become internalized within the plant tissue which not only makes them less susceptible to chemical and physical removal methods, but also more difficult to detect (16,49). Factors such as bacteria type and plant surface roughness will have an influence over the physical adhesion between the bacteria and food matrix (40,56). …”

Salmonella and Tomatoes

“…Cantaloupes were also the source of a large outbreak of Listeriosis (CDC, 2011b). Cantaloupe is inherently difficult to disinfect because of the roughness of its surface, which provides many protected sites for attachment (Wang et al, 2009). It is believed that contamination of fresh-cut melon results from transfer of human pathogens on the surface to the interior flesh during cutting .…”

“…In a comparison of the inactivation of E. coli O157:H7 on freshcut apples and cantaloupe rinds by acidic electrolyzed water, peroxyacetic acid and chlorine, Wang et al (2006) observed dual phase kinetics for each of these treatments which they attributed to fruit surface topography, a determinant of bacterial distribution. Wang et al (2009) quantified the relationship between surface roughness and retention and removal of E. coli O157:H7 on selected fruits that were spot inoculated and then washed with water or sanitizing agents. Additionally, bacterial incorporation within biofilms will confer greater resistance to microcidal agents (see Chapter 2 for more information on microbial attachment).…”

Inactivation of Listeria monocytogenes, Salmonella spp. and Escherichia coli O157:H7 on cantaloupes by octenidine dihydrochloride

“…Chlorine (200 ppm) has been commonly used for washing cantaloupes, but results in only minimal reductions (~1e1.5 log/cm 2 ) in pathogen counts (Richards and Beuchat, 2004;Rodgers et al, 2004;Ukuku et al, 2006;Wei et al, 1995). The inefficiency of chlorine could be attributed to the rough surface of the cantaloupes covered by the microscopic lenticellar netting that facilitates bacterial attachment and protection from aqueous disinfectants (Annous et al, 2004;Wang et al, 2009). Moreover, formation of harmful chemical byproducts such as chloramines, trihalomethanes and other organochlorine compounds when chlorine and organic materials interact is a concern due to potential health risks, including cancer (Donato and Zani, 2010;Richardson et al, 1998;Zhang and Farber, 1996).…”