Risk assesment of staphylococcal enerotoxins occurrence in soft cheeses

Abstract

Risk assessment is a scientifically based process consisting of hazard identification, hazard characterization, exposure assessment and risk characterization. A risk in the food safety context is the probability and the consequences of adverse health effects following the ingestion of food. Cheeses represent an important part in the human diet. Approximately 10% of cheese in Europe is made from raw milk, presenting a considereble potential risk to public health. In Serbia, a large number of cheeses present at the town markets is produced in households and can be classified as soft cheeses regardless ripening. Since some soft cheeses are produced from raw milk in acorrdance with our tradition, there is a possibility that the pathogenic microorganisms, such as coagulase-positive staphylococci pass into cheese from raw milk. The main representative of coagulase-positive staphylococci is Staphylococcus aureus subsp. aureus. As a ubiquitous microorganism is often present on the skin of humans and animals, and often colonizes ductus papillaris of dairy animals. From the point of view food safety this microrganism is significant brcase it may produce thermostable enterotoxins which ingested in a certain amount via food causes intoxication in the human organism. The aim of this PhD thesiss was to assess the risk of staphylococcal enterotoxin occurrence in soft cheeses on the basis of number of coagulase-positive staphylococci in cheese, conditions for their growth, synthesis of enterotoxins, and the presence of genes for enterotoxin synthesis in coagulase positive-staphylococci isolated from cheese, as well to asses the risk of staphylococcal enterotoxins occurrence in soft cheeses. The material consisted of 555 samples of soft cheeses of different ages produced of raw, or cooked milk in individual households at different geographic localities in Serbia, and obtained from 17 markets. In order to isolate and determine the number of coagulase-positive staphylococci, the standard method (SRPS EN ISO 6888-2) was used and the number of Lactococcus spp., Lactobacillus spp. was determined by the method described in ISO 27205: 2010 (IDF 149: 2010) standard...

Procena rizika je naučno baziran proces koga čine identifikacija hazarda, karakterizacija hazarda, procena izloženosti i karakterizacija rizika. U kontekstu bezbednosti hrane rizik predstavlja verovatnoću i posledice da nastane štetno delovanje na zdravlje ljudi posle konzumiranja hrane. Sirevi kao hrana zauzimaju važno mesto u ishrani ljudi. U Evropi se danas oko 10% sireva proizvodi od sirovog mleka i ovi sirevi mogu da predstavljaju potencijalni rizik po javno zdravlje. U Republici Srbiji veliki broj sireva, prisutan na tržištu gradskih pijaca, proizvodi se u domaćinstvima i može se svrstati u grupu mekih sireva bez zrenja ili sa zrenjem. Budući da se odreĎen broj mekih sireva proizvodi od nekuvanog mleka, kao deo tradicije, postoji mogućnost da sa sirovim mlekom u sir dospeju patogeni mikroorganizmi kao što su koagulaza pozitivne stafilokoke. Glavni predstavnik koagulaza pozitivnih stafilokoka je Staphylococcus aureus subsp. aureus. Kao ubikvitarni mikroorganizam nalazi se na koži ljudi i životinja, a često kolinizuje ductus papillaris mlečne žlede muznih životinja. Sa aspekta bezbednosti hrane značaj ovog mikroorganizma se ogleda u tome što stvara termostabilne enterotoksine koji uneti u odreĎenoj količini, putem hrane, u organizam čoveka izazivaju intoksikacije. Cilj ove doktorske disertacije je bio da se, na osnovu broja koagulaza pozitivnih stafilokoka u siru, uslova za njihovo razmnožavanje i stvaranje enterotoksina, kao i prisustva gena za sintezu enterotoksina kod koagulaza pozitivnih stafilokoka izolovanih iz sira, proceni rizik od nalaza enterotoksina stafilokoka u mekim sirevima. Ispitivanjem je obuhvaćeno 555 uzoraka mekih sireva različite starosti proizvedenih od kuvanog ili nekuvanog mleka u individualnim domaćinstvima iz različitih geografskih lokaliteta u Srbiji, koji su uzeti sa 17 pijaca. Izolacija, identifikacija i odrĎivanje broja koagulaza pozitivnih stafilokoka raĎeni su standardnom metodom (SRPS EN ISO 6888-2), a broj Lactococcus spp. i Lactobacillus spp. je odreĎen metodom opisanom u standardu ISO 27205:2010 (IDF 149:2010). Identifikacija koagulaza pozitivnih stafilokoka do vrste raĎena je na osnovu biohemijskih osobina pomoću BBLCrystal Identifikacionim sistemom-BD i ID 32 Staph-Biomerieux (Francuska). Sposobnost izolata koagulaza pozitivnih stafilokoka da stvaraju klasične enterotoksine (SEA, SEB, SEC, SED, SEE), kao i prisustvo enterotoksina u siru ispitani su primenom ELFA tehnike VIDAS SET2 (BioMerieux, Francuska)...