Lactic Acid Bacteria Antagonism of Acid-tolerant and Antibiotic-resistant Non-staphylococcal Pathogenic Species Isolated from a Fermented Cereal Beverage using Baird-Parker Agar

Fermented foods may contain acid-tolerant and antibiotic-resistant pathogenic microorganisms. Pathogens can be antagonized by lactic acid bacteria, resulting in improved microbiological safety. This study assessed the antagonistic effects of selected lactic acid bacteria against pathogenic bacteria isolated from a cereal fermented food.

Eight presumptive staphylococci isolated from a commercially produced cereal fermented beverage on Baird-Parker agar supplemented with tellurite were identified using 16S rRNA sequencing. Acid resistance of the isolates was assessed using acidified media (brain heart infusion broth of pH 3.6 and 1.5% acidity) for 48 h followed by taking plate counts. Antibiotic resistance (19 antibiotics) was assessed using the disk diffusion assay. A spot-on-the-lawn method was used to assess antagonistic effects of Lactobacillus plantarum MNC 21, Lactococcus lactis MNC 24, Weissella confusa MNC 20 and Lactobacillus rhamnosus yoba 2012 against Lysinibacillus macroides, Bacillus subtilis, Enterococcus faecalis and Escherichia coli.

Presumptive staphylococci were identified as Lysinibacillus macroides (n = 1), Bacillus subtilis (n = 2), Enterococcus faecalis (n = 4) and Escherichia coli (n = 1). These isolates were acid-tolerant (from 6.3 ±0.9 log cfu/mL at 0 h to 3.6 ±0.9 log cfu/mL at 48 h), antibiotic-resistant (multiple antibiotic resistance index of 0.1–0.5) and their growth was inhibited by the lactic acid bacteria (inhibition zone diameters of 14–24 mm).

The lactic acid bacteria cultures of MNC 20, MNC 21, MNC 24 and Lactobacillus rhamnosus yoba 2012 can be used in various food fermentations to inhibit growth of bacterial pathogens; thus, improving product safety.