Antimicrobial Activity And Safety Evaluation Of Enterococcus Faecium KQ2.6

Enterococci, belong to lactic acid bacteria, are not only widespread in vegetables, cheese, milk, sausage etc., but also present in the intestine of humans and animals. They not only can inhibit the growth of intestinal spoilage and pathogenic microorganisms, but also contribute to the intestinal absorption of nutrients and the excretion of harmful substances, which exhibit good probiotic characteristics. However, in contrast to other lactic acid bacteria, the safety of enterococci is always a controversial issue. Studies show that some enterococci from clinical sources can lead to bacteremia, urinary tract infections and endocarditis diseases etc. Therefore, screen, identify enterococci from the animal feces with a good antimicrobial activity, and the safety evaluation of enterococci, were investigated in this study The purpose of this study is to discover the safe enterococcal strain with potential application, and provide a new material for the development of enterococci-related product. The results from this study were as follows:1 st:One strain of lactic acid bacteria showing a good antimicrobial activity, was screened from the different animal feces. After Gram staining and the diversity analysis of 16SrDNA, the strain was identified as Enterococcus faecium. It was obtained from the peacock feces, so the strain was named Enterococcus faecium KQ 2.6. (KQ is the abbreviation of peacock in Chinese)2nd:The results of Oxford plate assay showed that the cell free supernatant of Enterococcus faecium KQ 2.6 not only had antimicrobial activity against gram-positive bacteria, but also had inhibitory effect on gram-negative bacteria. However, the cell free supernatant had no obvious antimicrobial activity to the fungus. Moreover, Maximum value (1600 AU/mL) of antimicrobial activity was reached when Enterococcus faecium KQ 2.6 was cultured in MRS broth for 16 h, and remained un-change in the following 8 h. According to the results of the biological characteristics, antimicrobial substances were resistant to temperature, catalase, pepsin and trypsin, but were sensitive to the change of pH values. Therefore, we could speculate that antimicrobial substances may be organic acid or acid-dependence substances. In addition, the results of antimicrobial mechanism studies showed that antimicrobial substances of Enterococcus faecium KQ 2.6 could exert adverse effect on the cell membrane of Escherichia coli, and thus led to increase the permeability of the cell membrane. What’s more, it could combine with or damage DNA of Escherichia coli, which affected the normal metabolic function of DNA and caused the death of Escherichia coli.3rd:The In vitro results showed that Enterococcus faecium KQ 2.6 was safety in a certain extent. It was sensitive to penicillin, chloramphenicol, tetracycline, ofloxacin, erythromycin, rifampicin and ciprofloxacin antibiotics etc. Meanwhile, the common virulence genes in Enterococcus faecium KQ 2.6, such as gelE, esp, asal, cylA, efaA and hyl, were not found. The In vivo results indicated that the different doses of Enterococcus faecium KQ 2.6 had no adverse effect on the weight of mice, the count of red blood cell, the content of hemoglobin, the mount of platelet, the count of white blood cell, liver, kidney and spleen index etc.,so Enterococcus faecium KQ 2.6 could be regarded as a safe strain.