The minimum inhibitory concentration of lactic acid (LA, L-lactic acid, Xena International Inc., IL, USA) for the antibiotic-resistant and non-resistant bacterial strains was determined using a 96 well plate broth dilution method described by Dev Kumar et al. (2020) (link) with some modifications. Briefly, lactic acid stock solutions were serially diluted in 96 well plates −180 μl in each well—and inoculated with 20 μl of 6.83 ± 0.18 log CFU/ml of bacteria. Serial dilutions were performed from initial lactic acid concentrations of 5 and 3% to obtain lactic acid concentrations of 2.5, 1.5, 1.25, 0.75, 0.62, 0.37%, 0.31%, 0.18, 0.15, 0.09, 0.07, 0.04, 0.03, and 0.02% v/v. The 96-well plates (Costar® 96 Well Flat Bottom, Corning LifeSciences Inc. ME, USA) were incubated for 24 h at 37 °C, and the growth kinetics were observed using the Bio-Tek Cytation 3 multi-mode plate reader (BioTek Instruments, Inc. USA). Conditions in the Bio-Tek Cytation 3 multi-mode plate reader were set as follows: the total runtime was set at 24 h with read intervals of 30 min, the shaker was set to an orbital shake every 10 s at a frequency of 283 cpm (3 mm), the read speed was set to Normal with a delay of 100 ms and the optical density was read at an absorbance of 600 nm. Un-inoculated blanks of TSB were used as a control for this experiment (Figure 1 ).
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