Antibiotic resistance in bacteria is a global problem that has caused scientists to research into antibacterial substances other than antibiotics. Honey has properties that make it a good antibacterial substance. For example, honey contains hydrogen peroxide, which is known to kill bacteria. The most effective honey tested so far for antibacterial activity is Manuka honey. It contains less hydrogen peroxide than many other types of honey, but it does contain an antibacterial compound, methylglyoxal (MGO), which is not found in other types of honey. A student decided to investigate the effect of two antibacterial substances on the bacterium Bacillus subtilis, which respires aerobically: • MGO in Manuka honey • an antibiotic solution used in cell cultures to prevent contamination. The student wanted to find the lowest concentration of each antibacterial substance that would kill or inhibit the growth of B. subtilis.