Technique differences to enumerate and isolate E. coli O157:H7 and the use of ozonated water to eliminate E. coli
Carr, Mandy Annett
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The objectives of this study were to compare the currently suggested method by USDA and a procedure including immunomagnetic separation for sensitivity in detecting E. coli 0157:H7 on beef hide samples when time before enrichment and sample handling procedures were varied; and to determine the effect of ozonated water bath treatments on the survivability of a non-pathogenic strain of E coli (ATCC 25922) on inoculated beef fat samples. The effects of time/handling practices and detection method utilized a 2 method X 3 time/handling factorial. Three sponges were hydrated with sterile buffer and each used to aseptically sample a 7.6cm X 38cm area of beef hide. The sponges were aseptically halved and placed in sterile sampling bags. A total of 30 animals were sampled on 5 days. Samples were randomly assigned to a treatment group of Method 1 - Immediate (Ml-I), Method 1 - Delayed Chilled (Ml-DC), Method 1 - Delayed Room Temperature (Ml-DRT), Method 2 - Immediate (M2-I), Method 2 - Delayed Chilled (M2-DC), or Method 2 - Delayed Room Temperature (M2-DRT). Immediate samples began enrichment within 4 h of sampling. Delayed samples were placed in an ice chest with icepacks (DC) or without icepacks (DRT), and stored at room temperature for 28 h. Method 1 used traditional procedures accepted by the USDA utilizing the BioControl Assurance EIA EHEC test kit for screening. Method 2 utilized the Dynal anti-0157 magnetic bead technique. The Dynal anti-0157 beads in Method 2 appeared to increase the likelihood of finding samples containing microorganisms that were confirmed by O agglutination compared to the technique in Method 1 (77.8 vs. 8.9%). Immediate testing found 26 O agglutination positive samples compared to 22 positive samples by both DC and DRT. All O positive samples from Method 1 were non-identifiable with the api 20 E test. However, of the 70 positive samples after O agglutination in Method 2, 25 (35.7%) were identified as E. coli. E. coli 0157:H7 was not found in any sample. Within Method 2, if enrichment was initiated immediately, 66.7% of samples were identified with a genus name. If enrichment was delayed, storing with ice packs (DC) enabled 36.7% to be identified compared to 30.0% if the samples were stored at room temperature (DRT) before sampling. The ozone study utilized a 2 inoculation level X 3 time treatment factorial arrangement of a randomized block design, with day as the block, to determine the effect of an ozonated water bath system on the survival of £. coli (ATCC 25922). ORP readings of 650 to 700 millivolts were utilized throughout the study. Five beef fat samples were used for each treatment on each day. Samples inoculated with 10 CFU/ml E. coli exposed to 0 min were not different (P > .05) from samples in the bath for 10 or 60 seconds (5.66, 5.38, and 5.38 log10 CFU/cm^, respectively). Samples inoculated with 10^ CFU/ml exposed for 0 min were different (P < .05) from samples in the bath for 10 or 60 seconds (3.02, 2.81 and 2.53 log10 CFU/cm^, respectively), but counts from the two bath treatments were not different (P > .05). These results indicate that the current air, water and OPR settings were not effective to eliminate E. coli (ATCC 25922).