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

The efficacy of a new generation disinfectant, octenidine dihydrochloride (OH), as wash and coating treatments for reducing Listeria monocytogenes (LM), Salmonella spp. (SAL), and Escherichia coli O157:H7 (EC) on cantaloupe was investigated. Cantaloupe rind plugs inoculated separately with the three bacterial species (∼8 log CFU/cm(2)) were washed for 1, 3, 5 min at 25 °C in water, or chlorine (200 ppm), ethanol (1%), OH (0.01, 0.05, 0.1%) and surviving populations were measured after treatment. Additionally, inoculated cantaloupe rind plugs were coated with 2% chitosan or chitosan containing OH (0.01, 0.05, 0.1%) and sampled for surviving pathogens. Subsequently, the antimicrobial efficacy of OH wash and coating (0.1, 0.2%) on whole cantaloupes was determined. All OH wash reduced LM, SAL, and EC on cantaloupe rinds by > 5 log CFU/cm(2) by 2 min, and reduced populations to undetectable levels (below 2 log CFU/cm(2)) by 5 min (P < 0.05). Similarly, OH coating on cantaloupe rinds reduced the pathogens by 3-5 log /cm(2) (P < 0.05). Washing and coating whole cantaloupes with OH reduced the three pathogens by at least 5 log and 2 log CFU/cm(2), respectively (P < 0.05). Results suggest that OH could be used as antimicrobial wash and coating to reduce LM, SAL, and EC on cantaloupes.

Physical covering for control of Escherichia coli O157:H7 and Salmonella spp. in static and windrow composting processes.

This study investigated the effect of a 30-cm covering of finished compost (FC) on survival of Escherichia coli O157:H7 and Salmonella spp. in active static and windrow composting systems. Feedstocks inoculated with E. coli O157:H7 (7.41 log CFU/g) and Salmonella (6.46 log CFU/g) were placed in biosentry tubes (7.5-cm diameter, 30-cm height) at three locations: (i and ii) two opposing sides at the interface between the FC cover layer (where present) and the feedstock material (each positioned approximately 10 cm below the pile's surface) and (iii) an internal location (top) (approximately 30 cm below the surface). On specific sampling days, surviving populations of inoculated E. coli O157:H7 and Salmonella, generic E. coli, and coliforms in compost samples were determined. Salmonella spp. were reduced significantly within 24 h in windrow piles and were below the detection limit after 3 and 7 days at internal locations of windrow and static piles containing FC covering, respectively. Likewise, E. coli O157:H7 was undetectable after 1 day in windrow piles covered with finished compost. Use of FC as a covering layer significantly increased the number of days that temperatures in the windrows remained ≥55°C at all locations and in static piles at internal locations. These time-temperature exposures resulted in rapid reduction of inoculated pathogens, and the rate of bacterial reduction was rapid in windrow piles. The sample location significantly influenced the survival of these pathogens at internal locations compared to that at interface locations of piles. Finished compost covering of compost piles aids in the reduction of pathogens during the composting process.

Effectiveness of bacteriophages in reducing Escherichia coli O157:H7 on fresh-cut cantaloupes and lettucet.

Consumption of produce contaminated with Escherichia coli O157:H7 has resulted in cases of foodborne illness. We determined the efficacy of a mixture of three E. coli O157:H7-specific bacteriophages (ECP-100) in reducing the number of viable E. coli O157:H7 on contaminated fresh-cut iceberg lettuce and cantaloupe. E. coli O157:H7 was spot inoculated on lettuce pieces (9 cm2) with a population of 3.76 log CFU/cm2, allowed to dry, and then sprayed with a control (phosphate-buffered saline) or ECP-100 to deliver 7.98 log PFU/cm2 to lettuce stored for 2 days at 4 degrees C. Cut pieces of cantaloupe were spot inoculated with E. coli O157:H7 (4.55 log CFU/ml) and treated with the control or ECP-100 (6.69 log PFU/ml), and then stored at 4 or 20 degrees C for up to 7 days. On days 0, 2, 5, and 7, cantaloupe samples were homogenized, and populations of E. coli O157:H7 were enumerated. Populations of E. coli O157:H7 on lettuce treated with ECP-100 on 0, 1, and 2 days (0.72, <0.22, and 0.58 log CFU/cm2 of lettuce) and stored at 4 degrees C were significantly (P < 0.05) lower than those treated with the control (2.64, 1.79, and 2.22 log CFU/cm2), respectively. Populations on cut cantaloupes treated with ECP-100 on days 2, 5, and 7 (0.77, 1.28, and 0.96 log CFU/ml) and stored at 4 degrees C were significantly lower than those cut cantaloupes treated with the control (3.34, 3.23, and 4.09 log CFU/ml), respectively. This study is the first to show the effectiveness of bacteriophages to reduce E. coli O157:H7 on fresh-cut lettuce and cantaloupes.

A novel approach to investigate the uptake and internalization of Escherichia coli O157:H7 in spinach cultivated in soil and hydroponic medium.

Internalization of Escherichia coli O157:H7 into spinach plants through root uptake is a potential route of contamination. A Tn7-based plasmid vector was used to insert a green fluorescent protein gene into the attTn7 site in the E. coli chromosome. Three green fluorescent protein-labeled E. coli inocula were used: produce outbreak O157:H7 strains RM4407 and RM5279 (inoculum 1), ground beef outbreak O157:H7 strain 86-24h11 (inoculum 2), and commensal strain HS (inoculum 3). These strains were cultivated in fecal slurries and applied at ca. 10(3) or 10(7) CFU/g to pasteurized soils in which baby spinach seedlings were planted. No E. coli was recovered by spiral plating from surface-sanitized internal tissues of spinach plants on days 0, 7, 14, 21, and 28. Inoculum 1 survived at significantly higher populations (P < 0.05) in the soil than did inoculum 3 after 14, 21, and 28 days, indicating that produce outbreak strains of E. coli O157:H7 may be less physiologically stressed in soils than are nonpathogenic E. coli isolates. Inoculum 2 applied at ca. 10(7) CFU/ml to hydroponic medium was consistently recovered by spiral plating from the shoot tissues of spinach plants after 14 days (3.73 log CFU per shoot) and 21 days (4.35 log CFU per shoot). Fluorescent E. coli cells were microscopically observed in root tissues in 23 (21%) of 108 spinach plants grown in inoculated soils. No internalized E. coli was microscopically observed in shoot tissue of plants grown in inoculated soil. These studies do not provide evidence for efficient uptake of E. coli O157:H7 from soil to internal plant tissue.