Adhezija bakterij vrst Listeria monocytogenes in Escherichia coli na zeleno solato (Lactuca sativa L.)

Svetelj, Gašper (author), Jeršek, Barbka (mentor), Vidrih, Rajko (co-mentor)

Namen dela je bil oceniti adhezijo bakterij vrst L. monocytogenes in E. coli na liste zelene solate (Lactuca sativa L.). Bakterije vrste L. monocytogenes so po kontaminaciji solatnih listov na njih dobro rastle in se adherirale pri 12 °C (4,3 ± 0,1 log cfu/g po 1 dnevu, 5,3 ± 0,2 log cfu/g po 9 dneh). Podoben trend adhezije smo zaznali pri bakterijah vrste E. coli (5,1 ± 0,1 log cfu/g po 1 dnevu, 6,4 ± 0,2 log cfu/g po 9 dneh). V nadaljnjih preiskavah so se bakterije vrste E. coli bolje adherirale na neoprane, kot na oprane solatne liste. Glede na dobljene rezultate, smo predvidevali, da ima površina solate dovolj ustreznih hranilnih snovi, ki omogočajo bakterijam vrste E. coli adhezijo in rast na solatnem listu. Dobro rast bakterij smo potrdili v vodnem izpirku solatne površine, saj so bakterije vrste E. coli iz začetnega števila 5,35 ± 0,02 log cfu/ml v 2 dneh dosegle koncentracijo 7,15 ± 0,03 log cfu/ml. Kemijske analize sladkorjev (glukoza, fruktoza, saharoza) sveže solate in solate med skladiščenjem pri 12 °C so pokazale, da se vsebnosti le-teh zmanjšujejo. Sladkorje smo določili tudi na sami površini solatnih listov, to je v vodnem izpirku solatne površine (glukoza 0,215 ± 0,131 mg/100 ± 5 cm2; fruktoza 0,121 ± 0,086 mg/100 ± 5 cm2; saharoza: 0,430 ± 0,130 mg/100 ± 5 cm2). Na površini solatnih listov smo določili tudi za bakterije izkoristljive vire dušika (nitratni dušik: 0,019 mg/100 ± 5 cm2 in amonijev dušik: 0,003 mg/100 ± 5 cm2). Rezultati naših raziskav kažejo, da so solatni listi ugodno okolje za adhezijo, kolonizacijo in rast bakterij vrst E. coli in L. monocytogenes. Pranje solatnih listov v vodi vpliva na zmanjšanje hranilnih snovi, potrebnih za bakterijsko rast in tako na zmanjšanje njihove adhezije in rasti.

• Language: Slovenian
• Keywords: patogene bakterije, Listeria monocytogenes, Escherichia coli, adhezija bakterij, mikrobiota, zelena solata, Lactuca sativa L., kemijske analize, inokulacija, kontaminacija površin, izpiranje
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: BF - Biotechnical Faculty
• Publisher: [G. Svetelj]
• Year: 2017
• PID: 20.500.12556/RUL-96660
• UDC: 579.67:635.52:614.31
• COBISS.SI-ID: 4822648
• Publication date in RUL: 08.10.2017

Secondary language

• Language: English
• Title: Adhesion of Listeria monocytogenes and Escherichia coli on green lettuce (Lactuca sativa L.)

Abstract

The purpose of this research was to assess the adhesion of L. monocytogenes and E. coli on lettuce leaves (Lactuca sativa L.). After artificial inoculation of salad leaves with L. monocytogenes these bacteria have adhered well and grown at 12°C (4.3 ± 0.1 log cfu/g, 5.3 ± 0.2 log cfu/g after 1 and 9 days, respectively). Similar adhesion trend was observed for E. coli (5.1 ± 0.1 log cfu/g, 6.5 ± 0.1 log cfu/g after 1 and 9 days, respectively). Further experiments with E. coli indicated that these bacteria adhered better on unwashed lettuce leaves than on washed one. That indicates that the surface of salad leaves have enough nutrients to allow adhesion and growth of E. coli. Therefore, we have checked the growth of E. coli in lettuce washing solution. The results revealed that E. coli grew well in lettuce washing solution as from initial concentration of 5.35 ± 0.02 log cfu/ml they reached 7.15 ± 0.03 log cfu/ml in 2 days. Chemical analysis of fresh lettuce leaves and lettuce leaves during storage showed that they contained fructose 0.71 ± 0.08 g/100g (2 days), 0.36 ± 0.15 g/100g (9 days), glucose 0.55 ± 0.10 g/100g (2 days) in 0.27 ± 0.10 g/100g (9 days) and sucrose 0.19 ± 0.04 g/100g (2 days), 0.08 ± 0.06 g/100g (9 days). All three sugars were also detected on the surface of fresh lettuce leaves (in lettuce leaves washing solution) and average amounts were: fructose 0.121 ± 0.086 mg/100 ± 5 cm2, glucose 0.215 ± 0.131 mg/100 ± 5 cm2, and sucrose 0.430 ± 0.130 mg/100 ± 5 cm2. Nitrogen compounds present on surface of lettuce leaves were determined as nitrate 0.019 mg/100 ± 5 cm2 and ammonium 0.003 mg/100 ± 5 cm2. Our results indicate that lettuce leaves represent favourable environment for adhesion, colonisation and growth of E. coli and L. monocytogenes. Washing of lettuce reduces nutrients for bacterial growth and consequently diminish the adhesion and growth of E. coli.

• Keywords: pathogens, Listeria monocytogenes, Escherichia coli, bacterial adhesion, microbiota, green lettuce, Lactuca sativa L., chemical analysis, inoculation, surface contamination, washing