Novel Method for Recovery of Escherichia coli O157:H7 from Beef Surfaces

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.