This is a real A-level school project and as such is intended for educational or research purposes only. Extracts of this project must not be included in any projects that you submit for marking. Doing this could lead to being disqualified from all the subjects that you are taking. You have been warned. If you want more help with doing your biology practicals then have a look at 'Advanced Level Practical Work for Biology' by Sally Morgan . If you want more detailed biology information then I'd recommend the book 'Advanced Biology' by M. Kent .
Neutrophils and other phagocytes use peroxide to kill bacteria. The enzyme NADPH oxidase generates superoxide within the phagosome , which is converted via hydrogen peroxide to other oxidising substances like hypochlorous acid which kill phagocytosed pathogens.  In individuals with chronic granulomatous disease (CGD) there is a defect in producing peroxide via mutations in phagocyte oxidases such as myeloperoxidase .  Normal cellular metabolism will still produce a small amount of peroxide and this peroxide can be used to produce hypochlorous acid to eradicate the bacterial infection. However, if individuals with CGD are infected with catalase-positive bacteria, the bacterial catalase can destroy the excess peroxide before it can be used to produce other oxidising substances. In these individuals the pathogen survives and becomes a chronic infection. This chronic infection is typically surrounded by macrophages in an attempt to isolate the infection. This wall of macrophages surrounding a pathogen is called a granuloma . Many bacteria are catalase positive, but some are better catalase-producers than others. The mnemonic "cats Need PLACESS to Belch their Hairballs" can be used to memorise the catalase-positive bacteria: nocardia , pseudomonas , listeria , aspergillus , candida , E. coli , staphylococcus , serratia , B. cepacia and H. pylori .