Antimicrobical activity of plant extracts against selected food borne pathogens : bachelor thesis

Patogeni uzročnici kvarenja hrane predstavljaju veliki zdravstveni problem širom svijeta što je posljednjih godina eskaliralo na neviđenu razinu. Prema tome, potražnja za sigurnom i kvalitetnom hranom je sve veća. Korištenje sintetskih konzervansa je često, ali je njihova sigurnost još uvijek upitna, što je potaknulo znanstvenike da traže prirodne konzervanse. U ovom radu ispitana su antimikrobna svojstava odabranih ljekovitih biljaka protiv najčešćih patogenih uzročnika kvarenja hrane. Istraživane su četiri biljne vrste (lavanda, ružmarin, mravinac i matičnjak) kako bi se odredilo njihovo antibakterijsko djelovanje prema tri Gram pozitivne (G (+)) (Staphylococcus aureus, Enterococcus feacalis, Listeria monocytogenes) i dvije Gram negativne (G (-)) bakterijske vrste (Salmonella enterica, Escherichia coli). Biljni ekstrakti su pripremljeni korištenjem ultrazvučne kupelji (2 h, 60 °C, biljni materijal: voda = 15: 100). Antibakterijsko djelovanje određeno je korištenjem metode određivanja minimalne inhibitorne koncentracije (MIC) i metodom difuzije u jažicama (engl. Well diffusion method). Rezultati testiranja antimikrobne aktivnosti pokazali su bolju aktivnost biljnih ekstrakata prema G (+) vrstama i najučinkovitiji ekstrakti, s najnižim MIC vrijednostima (u rasponu od 217 do 707 mg GAE/L) bili su ekstrakti ružmarina i mravinca, dok je najslabiji antimikrobni učinak zapažen kod matičnjaka (> 5551,2 mg GAE/L). Suprotno tome, matičnjak i mravinac pokazali su veću zonu inhibicije (30 mm) prema G (+) vrstama, korištenjem metode difuzije u jažicama. Kod obje metode svi testirani biljni ekstrakti pokazali su slabiju aktivnost, odnosno visoke MIC vrijednosti, te malu ili nikakvu zonu inhibicije prema G (-) bakterijama.Food-borne pathogens are causing major public health problems worldwide what in recent years have escalated to unprecedented levels. Accordingly, demand for safe and high-quality food has increased. The use of synthetic preservatives is well known but still questionable due to their safety, what encouraged scientists to search for natural preservatives. The present research was conducted in order to study the antimicrobial properties of selected medicinal plants against commonly food borne pathogens. Four plant species (lavender, rosemary, oregano and lemon balm) were investigated to evaluate their antibacterial activity against three Gram positive (G (+)) (Staphylococcus aureus, Enterococcus feacalis, Listeria monocytogenes) and two Gram negative (G (-)) bacterial strains (Salmonella enterica, Escherichia coli). Plant extracts have been prepared using ultrasound bath (2 h, 60 °C, plant material: water ratio = 15:100). The antibacterial activity was quantified using well diffusion and broth microdilution methods by detection of the inhibition zone and minimal inhibitory concentrations (MICs), respectively. The analyses of antibacterial activities showed better activity of plant extracts against G (+) species and the most effective, with the lowest MIC values (range from 217 to 707 mg GAE/L), were rosemary and oregano, while the weakest antibacterial activity was observed for lemon balm (> 5551.2 mg GAE/L). On contrary, lemon balm and oregano showed larger inhibition zone (30 mm) using well diffusion method against G (+) species. Using both methods all tested plant extracts showed weaker activity, higher MIC values and no or smaller inhibition zone against G (-) bacteria