Comparative study of impedance and reference methods to detect contamination to enterococci in food

Enterococci are important agents from the aspect of food safety. As some bacteria in this group are resistance to enviromental conditions, so presence of enterococci in excessive amount in foods, means undesirable sanitary situation during production and distribution of foods. Enterococci are known as indicator microorganism in many countries and excessive number of this group in foods means fecal contamination. So its detection in foods is a good guide for hygienic quality of food products. According to this matter, reference and impedance methods were used for the detection of enterococci and the results compared to obtain a rapid and sensitive method for evaluation of food samples. In present study, totally 77 samples include: 36 samples of raw milk, 21 samples herbal extract and 20 samples of dry vegetable were collected and tested for detection of enterococci with two above mentioned methods. The reference method was based on IRAN's national standard method No.2198. The impedance method was done by measuring the variation of electrical resistance of broth media (M-value) which used in this method. Then the results of two methods were compared and the overall agreement was determined with using SPSS software. The results showed that the sensitivity and specificity of the impedance method were 81.2 % and 75.9% respectively and the observed overall agreement was 79.2% with reference method. The Statistical analysis between two methods showed that there is a significant difference between two methods. In other meaning the studied methods have not shown the same performance. But in the other hand as a homogenous matrix of raw milks, the impedance method have 83.3% overall agreement with reference method. So this method could be used as alternative techniques instead of reference method for detecting enterococci in raw milk.