Date of Award

12-2008

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

David A. Golden

Committee Members

P. Michael Davidson, Doris H. D’Souza, Arnold M. Saxton

Abstract

A study was conducted to compare the efficiency of detection of Escherichia coli O157:H7 EDL 933 on external beef trim by commercial recovery systems based upon of the Microbial-Vac System (M-Vac) and excision sampling. Escherichia coli O157:H7 EDL 933 was cultured in tryptic soy broth for 24 hr at 37°C and transferred for three consecutive days before diluting and spot inoculating onto a 684 cm2 piece of beef trim (10 CFU/684 cm2). Beef trim was sampled with the M-Vac by passing the sampling head over the entire surface area in a vertical sampling pattern. The sampling head sprayed sterile buffer over the beef surface and instantly vacuumed the contents into a sample collection bottle. For the excision method, samples were cut from the beef trim using a coring knife. Sixty cores (3.8 cm diameter) were used per sample with one core directly inoculated by the E. coli O157:H7. Samples (M-Vac collection fluid and 60 excised cores) were held overnight at 4°C to simulate processing conditions, enriched in mEHEC broth at 42°C for up to 18 h, and confirmed positive using the BioControl Assurance Genetic Detection System (polymerase chain reaction based).

Of 75 inoculated beef trim surfaces, 96 (± 3.86) and 76% (± 3.86) of samples tested positive for E. coli O157:H7 by the M-Vac and excision methods, respectively. The ability of the M-Vac to detect E. coli O157:H7 significantly better (P<0.05) than excision, combined with the nondestructive nature of the MVac demonstrates that it is a suitable choice for sampling beef surfaces.

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