Otpornost na antimikrobne lijekove izolata mliječnokiselinskih bakterija izoliranih tijekom proizvodnje tvrdog ovčjeg sira

master's thesis

• Title (english): The Resistance to Antimicrobial Drugs of Lactic Acid Bacteria Isolates Obtained during the Production of Hard Sheep Cheese
• Author: Ena Horvat
• Mentor: Nevijo Zdolec (mentor)
• Committee member: Tomislav Mikuš (predsjednik povjerenstva)
• Committee member: Željka Cvrtila (član povjerenstva)
• Committee member: Nevijo Zdolec (član povjerenstva)
• Granter: University of Zagreb; Faculty of Veterinary Medicine; Zagreb
• Defense date and country: 2024-11-11, Croatia
• Scientific / art field, discipline and subdiscipline: BIOMEDICINE AND HEALTHCARE; Veterinary Medicine; Veterinary Public Health and Food Safety

Abstract

Autohtona mikrobiota tradicionalnih sireva može biti izvor potencijalnih mljekarskih
kultura koje se mogu koristiti u kontroliranoj, standardiziranoj proizvodnji. Cilj ovog rada bio je
procijeniti osjetljivost bakterija mliječne kiseline izoliranih tijekom tradicionalne proizvodnje
Paškog sira na antimikrobna tvari (antibiotike). Bakterije mliječne kiseline (BMK, n=175) izolirane
su iz sirovog ovčjeg mlijeka, sirišta janjadi, gruša i sira tijekom zrenja koristeći de Man, Ragosa i
Sharpe agar (MRS) te identificirane pomoću MALDI-TOF masene spektrometrije. Nakon
identifikacije do razine vrste, izolati su testirani na osjetljivost prema antibioticima: ampicilinu,
vankomicinu, gentamicinu, kanamicinu, streptomicinu, eritromicinu, klindamicinu, tetraciklinu i
kloramfenikolu E-testom (minimalna inhibitorna koncentracija) na MRS agaru. Rezultati su
interpretirani prema mikrobiološkim graničnim vrijednostima predloženim od strane EFSA-e.
Ukupno je identificirano 16 različitih vrsta BMK, a prevladavale su vrste homofermentativnih
laktobacila, potom enterokoka, pediokoka i laktokoka. Većina je izolata bila osjetljiva na
antibiotike što ide u prilog dobre prakse u ekološkom ovčarstvu otoka Paga. Fenotipski zabilježenu
rezistenciju pojedinih izolata potrebno je dodatno istražiti u smislu potencijala prijenosa
rezistencije na izloženu indikatorsku nerezistentnu mikrobiotu. Izolati koji su pokazali potpunu
osjetljivost na antimikrobna sredstva, kao što su Lactiplantibacillus plantarum, Lactococcus lactis,
Enterococcus faecium i Enterococcus durans, predstavljaju potencijalne kandidate za daljnju
karakterizaciju i odabir za primjenu u mljekarstvu.

Abstract (english)

The indigenous microbiota of traditional cheeses may be a source of potential dairy cultures
that can be used in controlled, standardized production. The aim of this study was to evaluate the
antimicrobial susceptibility of lactic acid bacteria isolated during the traditional production of Pag
cheese. Lactic acid bacteria (LAB, n=160) were isolated from raw sheep milk curd and cheese
during ripening using de Man, Ragosa and Sharpe agar (MRS) and identified by MALDI-TOF
mass spectrometry. After identification to species level, isolates were tested for antimicrobial
susceptibility to ampicillin, vancomycin, gentamycin, kanamycin, streptomycin, erythromycin,
clindamycin, tetracycline, and chloramphenicol by E-test (Minimal Inhibitory Concentrations) on
MRS agar. The results were interpreted according to the microbiological cut- off values proposed
by EFSA. A total of 16 different species of LAB were identified, with the predominant species
being homofermentative lactobacilli, followed by enterococci, pediococci and lactococci. Most
isolates were sensitive to antibiotics, which indicates good practice in organic sheep farming on
the island of Pag. The phenotypically recorded resistance of individual isolates needs to be further
investigated with regard to the potential of resistance transfer to the exposed, non-resistant
microbiota. Isolates that showed complete sensitivity to antimicrobial agents, namely -
Lactiplantibacillus plantarum, Lactococcus lactis, Enterococcus faecium, and Enterococcus
durans, are potential candidates for further characterization to be selected for dairy applications.

• Keywords: antimikrobna rezistencija; bakterije mliječne kiseline; MALDI-TOF MS; „Paški sir“
• Keywords (english): antimicrobial resistance; lactic acid bacteria; MALDI-TOF MS; „Pag cheese“
• Language: croatian
• URN:NBN: urn:nbn:hr:178:867681
• Study programme: Title: Veterinary Medicine; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: doktor/doktorica veterinarske medicine (doktor/doktorica veterinarske medicine)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2025-01-07 13:21:25