The use of essential oils for prevention of Salmonella adhesion on the surface of green lettuce (Lactuca sativa L.)

Jenič, Teja (author), Smole Možina, Sonja (mentor), Paparella, Antonello (comentor)

Green lettuce is often involved in food-borne associated outbreaks, particularly due to the presence of Salmonella. This is connected with bacterial ability to adhere to vegetable surfaces and to form biofilms. We focused on the possible application of essential oils (EOs) as alternative strategy for prevention of Salmonella adhesion on green lettuce. In the first, in vitro part, biofilm formation capability of 6 S. enterica serovars and their cell surface hydrophobicity were analysed. All strains did not or weakly produced biofilms at 8 °C, only S. Kasenyi and S. Napoli were moderate producers at 37 °C. Growth inhibition of 8 EOs on the Salmonella strains was evaluated. Based on the minimal inhibitory concentration (MIC) values, cinnamon (Cinnamomum zeylanicum) essential oil (EOC) was the most effective (MIC 1.25-1.87 µL/mL), confirmed by the growth inhibition dynamics of six Salmonella strains. In the second, in situ part, we focused on the effect of EOC on the ability of Salmonella strains to strongly or loosely adhere on lettuce surface, and on the colour properties of the treated product. Inoculated (with 5 x 105 CFU/mL of S. Kasenyi, S. Veneziana and S. Napoli) and un-inoculated lettuce leaves were treated with a suspension of 5.0 μL/mL EOC. A reduction of 0.78 log for loosely attached and 0.63 log for strongly attached cells was immediately observed. Strongly significant effect was confirmed after 120 hours at 8 °C, with a reduction greater than 1.5 log with respect to controls. The use of EOC could represent a safe alternative to conventional lettuce washing treatment with chlorinated solution, reducing microbial load and also improving product appearance during time.

• Language: English
• Keywords: Salmonella enterica, pathogens, bacterial biofilms, adhesion, essential oils, Cinnamomum zeylanicum, cell surface hydrophobicity, colour
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: BF - Biotechnical Faculty
• Publisher: [T. Jenič]
• Year: 2019
• PID: 20.500.12556/RUL-108646
• UDC: 579.67:635.52:547.913:664.8.037
• COBISS.SI-ID: 5075576
• Publication date in RUL: 11.07.2019

Secondary language

• Language: Slovenian
• Title: Uporaba eteričnih olj za preprečevanje adhezije bakterij rodu Salmonella na površini zelene solate (Lactuca sativa L.)

Abstract

Zelena solata je pogosto vpletena v izbruhe okužb s hrano, še zlasti zaradi prisotnosti bakterij rodu Salmonella. To je med drugim posledica njihove dobre sposobnosti pritrjevanja na rastlinska tkiva ter tvorbe biofilma. V naši nalogi smo raziskovali možnost uporabe eteričnih olj (EOs) kot alternativne strategije preprečevanja pritrjevanja bakterij rodu Salmonella na liste zelene solate. Prvi, in vitro del, je vključeval analizo filmotvornosti 6 sevov bakterij Salmonella ter njihove površinske hidrofobnosti. Vsi testirani sevi so slabo tvorili biofilm ali ga sploh niso tvorili pri 8 °C. Le seva S. Kasenyi in S. Napoli sta bila zmerno filmotvorna pri 37 °C. Nato smo ovrednotili protimikrobno aktivnost 8 EOs na seve bakterij Salmonella, vključno z vplivom na njihovo dinamiko rasti. Na podlagi minimalnih inhibitornih koncentracij (MIK) je bilo najučinkovitejše eterično olje cimeta (Cinnamomum zeylanicum, EOC) (MIK 1,25-1,87 μL/mL), kar je potrdila tudi dinamika inhibicije rasti bakterij. V drugem, in situ delu, smo raziskali zaviralni učinek EOC na seve bakterij Salmonella po močni ali šibki pritrditvi na površino solate, ter na spremembo barve proizvoda. V ta namen smo inokulirane (s 5 x 105 CFU/mL S. Kasenyi, S. Veneziana in S. Napoli) in neinokulirane liste solate obdelali s suspenzijo 5,0 μL/mL EOC. Zmanjšanje 0,78 log šibko pritrjenih in 0,63 log močno pritrjenih celic smo opazili takoj. Dober učinek smo dokazali tudi po 120 h pri 8 °C, z več kot 1,5 log zmanjšanjem števila celic glede na kontrolo. Uporaba EOC predstavlja varno alternativo splošno uporabni obdelavi solate z raztopino klora za zmanjšanje število prisotnih mikroorganizmov na površini, ter prispeva k izboljšanemu videzu izdelka.

• Keywords: Salmonella enterica, patogeni mikroorganizmi, bakterijski biofilmi, adhezija, eterična olja, Cinnamomum zeylanicum, površinska hidrofobnost, barva