Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 14, 2008
Publication Date: March 25, 2009
Citation: Renye Jr, J.A., Somkuti, G.A., Paul, M., Van Hekken, D.L. 2009. CHARACTERIZATION OF ANTILISTERIAL BACTERIOCINS PRODUCED BY E. FAECIUM AND E. DURANS ISOLATES FROM HISPANIC-STYLE CHEESES. Journal of Industrial Microbiology and Biotechnology. 36(3):261-268. Interpretive Summary: Enterococci are bacteria often identified in raw-milk Hispanic-style cheeses and are thought to contribute to their unique qualities. In addition, they may help protect the cheese from the growth of food-borne pathogens by producing antimicrobial peptides called bacteriocins. Enterococci have been shown to inhibit the growth of several food-borne pathogens, including Listeria monocytogenes. In this study, enterococci isolated from Hispanic-style cheeses from Mexico were tested for the ability to inhibit the growth of several food-borne pathogens. Six of the bacteria screened were shown to inhibit the growth of Listeria. Genetic screens identified known bacteriocins in four of the enterococci, meaning the remaining two may produce novel compounds. Some of the isolated enterococci were also shown to be highly resistant to several antibiotics. Their role in the transfer of antibiotic resistance to other bacteria, along with their ability to cause human infections prohibits them from being considered “safe” bacteria for use in food production. Yet they remain a viable source for natural antibacterial compounds that may serve as alternatives to antibiotics for controlling the growth of bacterial pathogens.
Technical Abstract: Enterococci are often identified as constituents of the indigenous microflora from raw milk artisanal cheeses and are believed to contribute to the unique organoleptic qualities of these products. Many strains of enterococci are also known to produce antimicrobial peptides, enterocins, which may prevent the growth of certain food-born pathogens. In this study 33 enterococcal isolates from Hispanic-style cheeses were screened for the production of bacteriocins. Of the 33 isolates, 5 E. faecium and 1 E. durans isolates inhibited the growth of Listeria spp. The antilisterial activity was lost after treatment with pepsin, trypsin, pronase, proteinase K and a-chymotrypsin suggesting the active component was a protein or peptide. The active compounds were heat-stable and had molecular weights between 4 and 8 kDa, which is characteristic of Class II enterocins. A PCR screen showed that four E. faecium isolates contained nucleic acid sequences for multiple enterocins. Isolate H41K contained entA and entP; and isolates H51Ca, H51Cb and H41B contained entA, entP and entL50AB, with H41B also containing entB. All PCR tests performed were negative for E. faecium isolate H41D, suggesting the production of a novel enterocin. The isolates were also screened for susceptibility to antibiotics, with only two showing low-level resistance to vancomycin (8 µg ml-l). However, three isolates were highly resistant to both tetracycline and kanamycin, with two of the isolates also showing high resistance to erythromycin.