Escherichia coli O157:H7 control in nonintact meat products and inhibition of Listeria monocytogenes biofilms on kitchen surfaces.

摘要

In the first study, beef knuckles (approximately 4--5 kg) were surface-inoculated (4.7+/-0.3 log CFU/g) with nonpathogenic rifampicin-resistant Escherichia coli O157:H7 (4-strain composite) in the first contamination scenario, and were injected with a hand-operated single needle brine injector, either with sterile distilled water (control) or brine solution of sodium chloride [NaCl; 5.5%] and sodium tripolyphosphate [STP; 2.75%] at seven locations per knuckle. In the second contamination scenario, the enhancement solutions (i. e., water and brine) inoculated (3.7+/-0.1 and 3.4+/-0.2 log CFU/ml, respectively) with the 4-strain E. coli O157:H7 composite were used for needle injection. The results of this study indicated that E. coli O157:H7 levels were translocated to the entire depth of beef knuckles after injection with water and brine injection solutions under both contamination scenarios.;In the second study, surface-inoculated 3-cm thick beef steaks (8-strain rifampicin-resistant E. coli O157:H7 composite, at contamination levels; high: 7.0 log CFU/g and low: 4.2 log CFU/g) were subjected to single-pass blade tenderization (hand-operated tenderizer with 48 blades) without or with prior tenderizer sanitation. The results of this study showed that single-pass tenderization vertically transferred surface contamination of E. coli O157:H7 throughout the 3.0 cm thick inoculated steak (high: 3.5--5.4 log CFU/g and low: 1.3--2.9 log CFU/g), and horizontally transferred to the surface (high: 5.8 log CFU/g and low: 2.9 log CFU/g) and interior (high: 2.2--4.2 log CFU/g and low: 0.7--1.5 log CFU/g) of the subsequently tenderized uninoculated steak.;In the third study, restructured beef steaks (2.5-cm thick) were inoculated (6 log CFU/g) with rifampicin-resistant E. coli O157:H7 (8-strain composite) and moisture-enhanced (110%, wt/wt) with four brine formulations: sodium chloride (NaCl, 0.5%)+sodium tripolyphosphate (STP, 0.25%), NaCl+STP+cetylpyridinium chloride (CPC, 0.2%), NaCl+STP+lactic acid (0.3%), or NaCl+STP+sodium metasilicate (0.2%). Beef steaks were stored in vacuum-packaged frozen (-20°C) for 30 days. Beef steaks were cooked to internal temperatures of 60°C by pan-broiling (PrestoRTM electric skillet), double pan-broiling (George ForemanRTM grill) or roasting (Magic ChefRTM standard kitchen oven) on day-0 and day-30. The results of this study indicated that only cetylpyridinium chloride was effective as an antimicrobial agent when included in the brining formulation at 0.2% concentration (wt/wt in final product) along with salt and phosphate, reducing E. coli O157:H7 populations by 0.5 logs in beef steaks stored under frozen conditions for 30 days. Double-panbroiling was more the effective compared to panbroiling and roasting, with E. coli O157:H7 reductions ranging from 2.5 to 4.5, 1.3 to 1.9 and 0.8 to 2.0 log CFU/g, respectively, in 2.5 cm beef steaks when cooked to the internal temperature of 60°C.;In the fourth study, beef roasts (2 kg) were inoculated (6--7 log CFU/g), moisture-enhanced with four brine formulations, and stored under frozen conditions, as described for the beef steaks study. E. coli O157:H7 counts in uncooked roasts treated with CPC were 0.7--2.4 log CFU/g lower than those of the roast samples treated with control (i e., NaCl+STP) brining formulation. E. coli O157:H7 counts were undetectable (0.5 log CFU/g) in 50.0 and 40.6 % of samples, from a total 32 roasts cooked to 60 or 55°C, respectively. Survivors of 0.5--5.4 log CFU/g and 0.5--5.2 log CFU/g were obtained from subsamples of the remaining roasts cooked to 60 or 55°C, respectively.;In the last study, samples of laminate (2.5x4 cm) and corian (4.5x4.5 cm) kitchen countertop top surfaces were inoculated (5 log CFU/cm2) with a 5-strain mixture of L. monocytogenes and incubated (25+/-2°C; 96 h) at 50 and 90% relative humidity (RH). L. monocytogenes cells survived on laminate and corian kitchen counter surfaces (0.5--1.1 and 0.1--0.9 log CFU/cm2) for 4 days (96 h) under both environmental (dry 50% and humid 90% RH) conditions. All four wipes were able to remove L. monocytogenes cells from the laminate surfaces for the entire length of storage (96 h), and were most efficient (5.0--6.2 log CFU/cm2) for pathogen removal immediately after contamination (0 h), under both environmental conditions. Highest levels of left over L. monocytogenes (2.7--3.8 log CFU/cm2) cells were recovered from these surfaces after cleaning with each wipe type, immediately after contamination, under both environmental conditions. (Abstract shortened by UMI.)