Submitted to: International Journal of Food Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/6/2006
Publication Date: 1/1/2007
Citation: Zhang, Y., Emily, Y., Cripe, J., Hall, G., Bhagwat, A.A., Meng, J. 2007. Characterization of listeria monocytogenes isolated from retail food. International Journal of Food Microbiology. 113:47-53. Interpretive Summary: Listeria monocytogenes is an important food-borne pathogen that can have a high mortality rate if consumed in high numbers. The severity of the illness also varies among various strains of this pathogen. Only limited information exists related to growth, biochemical and genetic characteristics of L. monocytogenes strains isolated from ready-to-eat foods. We used DNA-based analysis in combination with antibiotic resistance profiles to classify 167 different L. monocytogenes isolates obtained from retail foods. The characterization of L. monocytogenes isolates with the proposed scheme enabled us to determine the potential risk associated with individual strains. Both the food-preparation industry and consumers will benefit from the results of this research.
Technical Abstract: Listeria monocytogenes isolates (n = 167) recovered from retail deli meats, raw chickens and fresh produce samples were characterized by serogroup identification using PCR, genotyping using pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility testing. Five L. monocytogenes serogroups were identified among the 167 isolates: 68 isolates (41%) belonged to serogroup 1/2b, 3b, 53 isolates (32%) to serogroup 4b, 4d, 4e, 43 isolates (26%) to serogroup 1/2a, 3a, 2 isolates (1.2%) from serogroup 1/2c, 3c and only 1 isolate (0.6%) to serogroup 4a, 4c. PFGE generated 120 patterns and correlated well with PCR serogrouping. Most L. monocytogenes isolates were resistant to sulfonamide (73%) and some were resistant to tetracycline (8.4%) and ciprofloxacin (1.8%). Tetracycline resistance was conjugatively transferable and the tet(M) gene was identified from 14 tetracycline resistant isolates as well as their transconjugants. These findings indicate that L. monocytogenes strains present in food were diverse and resistance to one or more antibiotics among these isolates was common. In addition, the potential presence of serotype 4b in all food categories raised a public health concern as serotype 4b has been the number one serotype associated with human listeriosis.