Isolation and identification of contaminant microorganisms in industrial and non-industrial Iranian fermented milk (Doogh)

Abstract

Doogh is a traditional fermented milk based drink, that is a very popular product in Iran, its microbial safety is important. The purpose in this study, 16S based rDNA PCR, cloning and sequencing was to investigated the exploration microbial contaminants in commercial pasteurized Doogh specimens. To isolate and identify the contaminants in 24 different Doogh samples (17 different industrial and 6 different non-industrial samples) Polymerase chain reaction (PCR) was applied. The experimental results revealed that lactic acid bacteria (Lactobacillus brevis, L. fermentum, L. paracasei and L. gallinarum) gram-positive spore-forming bacteria (Bacillus anthracis, B. licheniformis. and B. subtilis) and acetic acid bacteria (Acetobacter indonesiensis and A. tropicalis) were identified in Doogh samples. Likewise, result obtained from sequencing of D1/D2 26S rDNA determined the presence of different yeasts including Saccaromyces sp. (S. unisporous, S. pastorianus) Kazachstaia sp. (K. servazzi, K. unispora) Pichia fermentans, Galctomyces candidum, and Cryptococcus magnus. The results demonstrated that some types of bacteria and yeasts and molds were identified as the main contaminants in Iranian Doogh.