Rapid identification of Tetragenococcus halophilus and Tetragenococcus muriaticus, important species in the production of salted and fermented foods, by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS)

Tetragenococcus halophilus and Tetragenococcus muriaticus are moderately halophilic lactic acid bacteria, characteristically grouped as tetrads arrangement of cocci, are found in fermentation period of various salted and fermented foods, such as soy sauce and fish sauce. T. halophilus may be one of the most important contributor to the salted and fermented products. In this study, a MALDI-TOF MS method was developed for the rapid identification of T. halophilus and T. muriaticus. Before the MS analysis, the cells were washed with ethanol and treated with formic acid, then ionized with a matrix: α-cyano-4-hydroxycinnamic acid. The MS peak similarity in each of eleven stock strains of the same species was higher than 78%, and the similarity of the two different species was about 36%. The similarity between the two Tetragenococcus and other lactic acid cocci (LAC) including Tetragenococcus koreensis and Tetragenococcus solitarius, was only 24% and less. The MALDI-TOF MS results were obtained in 30 min, from colonies grown on agar plates for viable counts. The MALDI-TOF MS method is a very rapid, simple and accurate method for discrimination of T. halophilus from T. muriaticus and other LAC, and therefore will be useful for quality control in production of salted and fermented food.