(The) use of dechaining enzyme on plate count of lactic acid bacteria

Abstract

An intracellular enzyme which can lyze chains of bacterial cells into shorter filaments was extracted from cells of $\mbox{\underline{Lactobacillus}}$ $\mbox{\underline{bulgaricus}}$ NLS-4 and tried to use in plate count of lactic acid bacteria growing in milk. Since the enzyme seemed to be bound to cell wall a treatment with five moles of Licl was needed for an effective extraction. The enzyme activity showed optimum pH at 6.0 and dechained the cells most effectively at this pH. It was also found that the enzyme produced by one strain of $\mbox{\underline{L}}$. $\mbox{\underline{bulgaricus}}$ could dechain the cells of not only its own strain but other strains such as $\mbox{\underline{streptococcus}}$ $\mbox{\underline{lactis}}$. When culture suspensions of lactic acid bacteria were treated with the enzyme just before the dilutions for plating out, higher number of colnies per ml of culture suspension were observed. Treating culture suspensions with 60 $\mu$g/ml of enzyme for 30 minutes under optimum growth temperature of the subjected strain gave best results in plate counts. The enzyme and technique obtained were applied in the plate counts of $\mbox{\underline{L}}$. $\mbox{\underline{bulgaricus}}$ and $\mbox{\underline{S}}$. $\mbox{\underline{lactis}}$ in milk cultures. The treatment of culture suspension with the dechaining enzyme during the process of standard plate count increased the values of cell concentration by three to four folds compared to that with the conventional plate count. It was concluded, therefore, that the dechaining enzyme extracted from $\mbox{\underline{L}}$. $\mbox{\underline{bulgaricus}}$ NLS-4 can be utilized for the standard plate count of lactic acid bacteria, specially in milk cultures where no other quantitative method for cell growth are available.