Izvor in analiza sevov bakterije Escherichia coli, izoliranih iz pritokov, iztoka in vode Blejskega jezera

Košmrlj, Nuša (author), Ambrožič Avguštin, Jerneja (mentor), Čremožnik Zupančič, Jerneja (comentor)

Escherichia coli (E. coli) je genetsko raznolika bakterijska vrsta, običajno povezana s črevesnim mikrobiomom toplokrvnih živali, čeprav rezultati nedavnih študij nakazujejo, da lahko nekateri sevi preživijo in se razmnožujejo tudi v okolju. Znotraj vrste se sevi razlikujejo po prisotnosti genov za dejavnike virulence, zaradi česar lahko predstavljajo različno zdravstveno tveganje za ljudi in živali. Blejsko jezero, eno najbolj obiskanih alpskih jezer v Sloveniji, je zaradi turizma, kmetijske dejavnosti in poselitve v prispevnem območju, izpostavljeno vnosu različnih mikroorganizmov, tudi E. coli. V magistrskem delu smo preučili raznolikost in potencialno patogenost izolatov E. coli, osamljenih iz vode Blejskega jezera, njegovih pritokov in iztoka. Skupno smo osamili 1543 izolatov E. coli, pri katerih smo z metodo ERIC-PCR in filogenetskim razvrščanjem po prenovljeni metodi Clermont in sod. (2013) določili klonalnost ter filogenetsko pripadnost. Za nadaljnjo analizo smo izbrali 745 neklonalnih izolatov, pri katerih smo z metodo PCR preverili prisotnost izbranih genov za dejavnike virulence, ter ugotavljali hemolitično aktivnost in sposobnost razgradnje laktoze. Največ neklonalnih izolatov je bilo osamljenih iz pritokov (79,73 %) v času nekopalne sezone (75,30 %) ter uvrščenih v filogenetski skupini B1 (27,92 %) in A (25,50 %). Pri vseh izolatih smo potrdili vsaj en gen za dejavnik virulence, med vsemi analiziranimi geni pa je bil najpogosteje zaznan gen fimH (93,56 %), sledili pa so mu geni irp2, fluA, traT in kpsMTII. Večina genov, povezanih z dejavniki virulence, je bila pogosteje prisotna pri izolatih iz pritokov, kar kaže na pomemben vpliv zunanjih virov onesnaženja. Prisotnost potencialnega fekalnega onesnaženja v pritokih smo dodatno potrdili z uporabo označevalca GenBac3 in metodo qPCR. Skupni rezultati raziskave kažejo, da pritoki predstavljajo pomemben vir vnosa potencialno virulentnih sevov E. coli v Blejsko jezero skozi celo leto, pri čemer na njihovo pojavnost pomembno vplivajo različni antropogeni dejavniki, predvsem kmetijska dejavnost, neurejenost odvajanja komunalne vode ter sezonsko pogojene človekove aktivnosti.

• Language: Slovenian
• Keywords: E. coli, Blejsko jezero, geni za dejavnike virulence, sezonska dinamika, qPCR
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: BF - Biotechnical Faculty
• Publisher: [N. Košmrlj]
• Year: 2026
• PID: 20.500.12556/RUL-187070
• UDC: 579.68(285Blejsko jezero)(043.2)
• COBISS.SI-ID: 290478851
• Publication date in RUL: 09.09.2026

Secondary language

• Language: English
• Title: Origin and analysis of Escherichia coli strains isolated from tributaries, outflow and water of Lake Bled

Abstract

Escherichia coli (E. coli) is a genetically diverse bacterial species typically associated with the intestinal microbiome of warm-blooded animals, although recent studies suggest that some strains can also survive and multiply in the environment. Strains within the species differ in the virulence factor genes they carry and can therefore pose varying health risks to humans and animals. Lake Bled, one of the most visited alpine lakes in Slovenia, receives inputs of various microorganisms, including E. coli, as a result of tourism, agricultural activity, and settlement within its catchment area. In this master's thesis, we examined the diversity and potential pathogenicity of E. coli isolates from the water of Lake Bled, its tributaries, and its outflow. A total of 1543 E. coli isolates were obtained, and their clonality and phylogenetic group were determined using ERIC-PCR and the revised phylogenetic typing method of Clermont et al. (2013). For further analysis, 745 non-clonal isolates were selected and screened by PCR for a panel virulence factor genes, and tested for hemolytic activity and the ability to ferment lactose. Most non-clonal isolates originated from tributaries (79.73%) were collected during the non-bathing season (75.30%) and belonged to phylogenetic groups B1 (27.92%) and A (25.50%). At least one virulence factor gene was confirmed in all isolates, with fimH being the most frequently detected gene (93.56%), followed by irp2, fluA, traT, and kpsMTII. Most virulence-associated genes were detected more frequently in isolates from tributaries, indicating a significant influence of external pollution sources. Potential fecal contamination in the tributaries was further supported using the GenBac3 marker and qPCR. Overall, the results indicate that tributaries are an important source of potentially virulent E. coli strains entering Lake Bled throughout the year, and that their occurrence is strongly influenced anthropogenic factors, primarily agricultural activity, inadequate wastewater management, and seasonally driven human activities.

• Keywords: E. coli, Lake Bled, virulence-associated genes, seasonal dynamics, qPCR