The growth rate and antibacterial activity of lactic acid bacteria GMH2 and GMH3 in various salt concentration

Abstract

Lactic acid bacteria (LAB) can be naturally found in fermented fish products that contain various salt concentrations. LAB is reported to produce proteinogenic antibacterial compounds named bacteriocin that can inhibit the growth of pathogenic and spoilage bacteria. In order to evaluate the performance of previously isolated LABs, namely GMH2 and GMH3, to inhibit the growth of these bacteria in fermented food systems, it is necessary to examine the effect of salt concentration on the growth rate and antibacterial activity. LAB GMH2 and GMH3 were inoculated on de man rogosa and sharp broth (MRSB) at various salt concentrations, including 0%, 7.5%, and 15%, followed by incubation at 37°C for 30 hours with observation every 6 hours. Bacterial growth was tested using the Total Plate Count (TPC) method, which was then further processed using the DMFit program to obtain growth rates, while antibacterial activity was tested using the macrodilution method against histamine-producing bacteria (HPB) Klebsiella pneumoniae (CK2). Both strains showed the highest growth rate at 0% NaCl, with 0.171 and 1.681 log CFU/hour for GMH2 and GMH3, respectively and remained steady until 7.5% salt concentration at 0,153 log CFU/hour for GMH2 and 0.044 log CFU/hour for GMH3. Antibacterial activity for both isolates showed the highest inhibitory value of 39.87±2.25% for GMH2 and 79.55±1.08 for GMH3. The addition of 7.5% and 15% interestingly did not show a significant reduction in antibacterial activity. The results of this study concluded that LAB GMH2 and GMH3 have the potency to be used as starters in fish fermented products, which possess up to 7.5% salt content.