This research aimed to study the effect of citric acid and Glucono-δ-lactone(GDL) on some selected pathogenic bacteria (Salmonella enteritidis, Staphylococcus aureus, Bacillus cereus, Escherichia coli O157:H7 and Pseudomonas aeruginosa) and lactic acid bacteria LAB (Lactobacillus acidophilus, Streptococcus thermophilus, Lactobacillus bulgaricus and Lactobacillus paracasei). The pH of LB medium was adjusted by citric or GDL at (4.4, 4.8, 5.2, 5.6, 6.2, 6.8 and 7.0) to test pathogens. However, the pH of MRS or M17 media were adjusted by citric or GDL at (4.4, 4.8, 5.2, 5.6, 6.2 and 6.8) to test LAB. Final pH, biomass concentration (C^B), Total viable count (TVC) and microbial growth rate % (MGR) of all studied bacteria were determined after 24 hrs of incubation. Citric acid and GDL had a high antimicrobial effect on pathogens. But they had no effect on LAB. GDL had the higher inhibition effect than citric acid against pathogenic strains. The inhibition effect of citric acid and GDL started to appear at low pH ≤ 5.2. While Staphylococcus aureus and Salmonella enteritidis were totally inhibited by GDL at pH 5.2. In addition, citric acid was more effective for enhancing the growth of LAB followed by GDL.