Rapid genus identification of selected lactic acid bacteria isolated from Mugil cephalis and Oreochromis niloticus organs using MALDI-TOF

Lactic acid bacteria (LAB) are traditionally used in food and feed bio-industries as they have health-promoting probiotic effect for their host and currently considered safe for human and animal consumption. Recently, we isolated 177 strains from freshwater fishes of dams of Tunisia exhibiting antimicrobial activities against various food-borne pathogens and generated a laboratory biobank to be characterized. Herein, we investigated whether MALDI-TOF could assist rapid identification of LAB genus. First, a lactic microflora-selective Man Rogosa Sharpe medium was used. Isolates were further screened according to the antimicrobial activity, using well-difusion agar. In total, four major genera have been well identified and species frequency has been estimated (74% Enterococcus, 24% Leuconostoc, 3% Lactococcus, and 2% Vagococcus). Eighteen isolates was further analyzed using MALDI-TOF. Comparative analysis of spectral fingerprints to six referenced MALDI-TOF fingerprints was carried out from the recently developed USC library ( www.spectrabank.org ). The intra- and inter-specific phyloproteomic relationships among strains were compared to available phylogenetic data based on 16S rDNA genes. This study showed that MALDI-TOF MS is a potent and reliable rapid method for both discrimination and identification of LABs. This highlights the insight of proteomic approach into the screening of food-derived beneficial microorganisms.