Production, characterization, and antimicrobial activity of a bacteriocin from newly isolated Enterococcus faecium IJ-31.

This work aimed to isolate and characterize Enterococcus spp. from indigenous dairy products in Islamabad, Pakistan. By classical microbiological techniques, one strain from a butter sample was identified to be Enterococcus faecium, and we designated it E. faecium IJ-31. The precise identity of this strain was then established by determining the sequence of its 16S and 23S rRNA genes. The sequence homology searches revealed matches with a number of previously reported strains, such as E. faecium HN-N3 and HN-N29, both isolated from swine intestines in China. The newly isolated strain was tested for hemolysis and antibiotic sensitivity; it was nonhemolytic on sheep and human blood and sensitive to vancomycin. Consistent with its vancomycin sensitivity, repeated attempts to amplify the vancomycin resistance genes vanA and vanB failed. Similar attempts to amplify the virulence genes gelE, agg, and cyl also failed, suggesting the absence of these genes. In contrast, the enterocin-P gene, entP, readily amplified with primers based on the previously reported sequences, and the deduced sequence showed near identity with a number of reported sequences from E. faecium. Further, the 71-residue enterocin-P sequence from strain IJ-31 is only the second complete sequence reported. The enterocin was partially purified and tested for antibacterial activity. It showed potent inhibitory activity against many bacteria, including Listeria monocytogenes, a routinely used test strain. Further, the enterocin showed potent activity against Bacillus subtilis and Bacillus cereus. The enterocin retained antibacterial activity even following heating to 121 degrees Celsius for 15 min. Further, it also retained activity after exposure to pH values ranging from 4 to 10. However, proteinase K treatment rendered the peptide nonfunctional.