In a study by , titled "Synergistic Combinatorial Strategy for Combating Antimicrobial Resistance (AMR) in Clinical Bacteria by Combining Antibiotics with Plant Extracts," 0.4 mL of concentrated sulphuric acid was added to 10 mL of aqueous Psidium guajava (guava) leaf extract. This mixture was boiled for 30 minutes and then centrifuged. Antimicrobial tests showed that untreated guava extract at 5.0 µg/mL had no inhibitory effect (0.0 mm inhibition zones) on Salmonella spp., Escherichia coli, Staphylococcus aureus, and Streptococcus spp. However, the reacted guava extract at 0.1 µg/mL exhibited inhibition zones ranging from 7 mm to 12 mm for all four bacterial strains.