Fungicides are the most common agents used in postharvest treatment of fruit and are the most effective against blue mould, primarily caused by Penicillium expansum. Alternatively, blue mould can be treated with antagonistic microorganisms naturally occurring on fruit, such as the bacterium Gluconobacter oxydans. The aim of this study was to establish the antifungal potential of the G. oxydans 1J strain isolated from apple surface against Penicillium expansum in culture and apple juice and to compare it with the efficiency of a reference strain G. oxydans ATCC 621H. The highest antifungal activity of G. oxydans 1J was observed between days 3 and 9 with no colony growth, while on day 12, P. expansum colony diameter was reduced to 42.3 % of the control diameter. Although G. oxydans 1J did not fully inhibit mould growth, it showed a high level of efficiency and completely prevented patulin accumulation in apple juice. Tretiranje voća fungicidima, nakon berbe, uobičajeni je način suzbijanja plave plijesni. Međutim, propadanje voća može se spriječiti i upotrebom antagonističkih mikroorganizama, kao što je bakterija Gluconobacter oxydans. Svrha ovoga rada bila je izolirati prirodnu mikrobnu populaciju s površine jabuka i istražiti moguće inhibitorno djelovanje Gluconobacter oxydans 1J na plavu plijesan, Penicillium expansum, najvažnijeg uzročnika kvarenja jabuka u skladištu. Najveća antifungalna aktivnost bakterije primijećena je između 3. i 9. dana, kada nije zabilježen porast kolonija, a nakon 12. dana promjer kolonije plijesni bio je manji za 42,3 %. Iako istraživana bakterija Gluconobacter oxydans 1J nije u potpunosti inhibirala rast plijesni u jabučnom soku pokazala je visoku razinu učinkovitosti (od 86 % do 95 %). Gluconobacter oxydans 1J djelomično inhibira rast plijesni i u potpunosti biosintezu patulina, ovisno o vremenu i uvjetima uzgoja.