Abstract
Bacteria of the genus Listeria pose a problem in the food industry due to their wide distribution and their good survival in adverse conditions. L. monocytogenes (E. Murray et al. 1926) Pirie 1940 is human pathogen, while L. innocua Seeliger (ATCC® 33090™) as not pathogenic bacteria is the most often found listeria in food production environment. Disinfectants represents an important part of Listeria management in food processing environments and benzalkonium chloride (BAC) is used frequently. The purpose of the work was to determine whether strains of listeria can adapt to BAC. To carry out the adaptation, a precise determination of antibacterial activity of BAC was needed. Firstly minimum inhibitory concentration (MICMTP) of BAC was determined with broth microdilution method for each Listeria strain. Then, we checked whether MICMTP was indeed the lowest concentration of BAC, which had an influence on growth of strains with growth curves. We found out that growth inhibitory effect (MICGC) was achieved at concentrations of BAC that were lower than MICMTP (0.1-0.5x of MICMTP values). Adaptation of listeria to BAC was therefore performed by using 0.25x MICGC as the initial BAC concentration. Results showed that 50 % of the strains were able to adapt to BAC, and in L. monocytogenes ŽM500 this adaptation was even stable. The broth microdilution method was useful for approximate assessment of antimicrobial activity of BAC, while for the more precise determination of disinfectant activity it is necessary to determine it by using another method such as plate count method.
Highlights
Assessing of adaptation ability of Listeria to benzalkonium chloride (BAC) by determination of its minimal inhibitory concentration
Med KAC uvrščamo tudi razkužilo benzalkonijev klorid (BAC), ki se kot kationsko površinsko aktivno sredstvo pogosto uporablja za medicinsko dezinfekcijo in sanitacijo v živilsko predelovalnih okoljih zaradi svoje dvojne, tako hidrofobne kot tudi hidrofilne, narave
Da je eden izmed možnih mehanizmov za razvoj odpornosti bakterij vrste L. monocytogenes proti KAS, sprememba sestave maščobnih kislin v bakterijski membrani (Bisbiroulas in sod., 2011), kar bakterijam omogoča rast v stresnih razmerah
Summary
V raziskavo smo vključili 10 sevov bakterij rodu Listeria iz mikrobiološke zbirke Laboratorija za živilsko mikrobiologijo na Oddelku za živilstvo Biotehniške fakultete (oznaka sevov ŽM). Uporabili smo 5 sevov bakterij vrste Listeria monocytogenes Bakterije so bile shranjene pri -20 °C v suspenziji glicerola (0,15 ml) in kulture Po revitalizaciji smo sev iz gojišča TSB nacepili na selektivno gojišče ALOA Po eno kolonijo smo nacepili na gojišče TSA Tryptic Soy Agar, Biolife, 4021502) in ponovno 24 h inkubirali pri 37 °C. Pred vsakim eksperimentom smo za pripravo inokuluma z gojišča TSA vzeli eno kolonijo izbranega seva ter jo prenesli v 4 ml gojišča TSB, vsebino premešali na vrtinčnem mešalniku in 4 ure inkubirali pri 37 °C na stresalniku (75 obratov/ minuto). Za nadaljnje delo smo 150 μl tako pripravljene kulture prenesli v 10 ml gojišča TSB ter točno koncentracijo celic določili z metodo štetja kolonij na gojišču TSA
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