Nisin Production by Enterococcus hirae DF105Mi Isolated from Brazilian Goat Milk.

The purpose of this study was to select the promising biopreservation bacteriocin producer strain from goat milk and characterize the expressed bacteriocin, related to its physiological and biochemical properties and specificity of operon encoding production and expression of antimicrobial peptide. Brazilian goat milk was used as the source for the selection of bacteriocin-producing lactic acid bacteria. One strain (DF105Mi) stood out for its strong activity against several Listeria monocytogenes strains. Selected strain was identified based on the biochemical and physiological characteristics and 16s rRNA analysis. The bacteriocin production and inhibitory spectrum of strain DF105Mi were studied, together with the evaluation of the effect of temperature, pH, and chemicals on bacteriocin stability and production, activity, and adsorption to target cells as well as to the cell surface of bacteriocin producers. Physiological and bio-molecular analyses based on targeting of different genes, parts of nisin operon were performed in order to investigate the hypothesis that the studied strain can produce and express nisin. Based on biochemical, physiological, and 16s rRNA analysis, the strain DF105Mi was classified as Enterococcus hirae. The selected strain produces a bacteriocin which is stable in a wide range of pH (2.0-12.0), temperature (up to 120 °C), presence of selected chemicals and presents adsorption affinity to different test organisms, process influenced by environmental conditions. Higher bacteriocin production by Ent. hirae DF105Mi was recorded during stationary growth phase, but only when the strain was cultured at 37 °C. The strain's genetic analysis indicated presence of the genes coding for the production of the bacteriocin nisin. This result was confirmed by cross-checking the sensitivity of the produced strain to commercial nisin A. The strong anti-Listeria activity, bacteriocin adsorption, and stability of produced bacteriocin indicate that Ent. hirae DF105Mi presents a differentiated potential application for biopreservation of fermented dairy products.

Bacteriocin production and resistance to drugs are advantageous features for Lactobacillus acidophilus La-14, a potential probiotic strain.

L. acidophilus La-14 produces bacteriocin active against L. monocytogenes ScottA (1600 AU/ml) in MRS broth at 30°C or 37°C. The bacteriocin proved inhibitory to different serological types of Listeria spp. Antimicrobial activity was completely lost after treatment of the cell-free supernatant with proteolytic enzymes. Addition of bacteriocin produced by L. acidophilus La-14 to a 3 h-old culture of L. monocytogenes ScottA repressed cell growth in the following 8h. Treatment of stationary phase cells of L. monocytogenes ScottA (107-108 CFU/ml) by the bacteriocin resulted in growth inhibition. Growth of L. acidophilus La-14 was not inhibited by commercial drugs from different generic groups, including nonsteroidal anti-inflammatory drugs (NSAID) containing diclofenac potassium or ibuprofen arginine. Only one non-antibiotic drug tested, Atlansil (an antiarrhythmic agent), had an inhibitory effect on L. acidophilus La-14 with MIC of 2.5 mg/ml. L. acidophilus La-14 was not affected by drugs containing sodium or potassium diclofenac. L. acidophilus La-14 shows a good resistance to several drugs and may be applied in combination for therapeutic use.