Phenotypic isolation and screening dominant bacteria causing spoilage in dairy products

BACKGROUND AND OBJECTIVESMicrobial contamination by food products could cause serious digestive and enteric diseases.Various methods exists for the identification and characterization of microorganisms. In this study we aimed to screen and isolate different types of bacteria that grow in dairy products for detecting the dominant spoiling agents.MATERIALS AND METHODSThe samples including milk and drinkable yogurt (Dough) were provided by one of the diary companies. Enriched cultivation environment was applied using tryptic soy broth (TSB) to isolate all the bacteria in the products. After overnight incubation, we transferred the bacteria from broth culture to the tryptic soy agar (TSA) using pour plate method. Then streak plate method was used to obtain single colonies. The colonies were characterized individually using morphological analysis and phenotypic examination of the bacteria by Gram staining and microscopic investigation. Universal primers were designed and synthesized for ۱۶S rDNA molecular PCR-based analysis.RESULTS AND DISCUSSIONEight distinct dominant single colonies were obtained from milk and three from drinkable yogurt samples. The morphology of two colonies out of three in Dough sample were rod-shaped bacili and one was round-shaped cocci. Six out of eight isolated colonies in milk were rod-shaped bacili while two colonies were round-shaped cocci. All of the dominant colonies from Dough sample seems to be gram negative. Gram staining can show us that ۷۵% of colonies in milk were gram negative and ۲۵% of them were gram positive. The genomic DNA of the respective colonies were extracted and subjected to amplification. A distinct band of arounf ۱۵۵۰ bp was observed in all samples. Furthure molecular analysis to detect the genus and species of the bacteria is in progress.CONCLUSIONThe main concept of this study was to identify the core bacteria causing the dairy to spoil before being used in the industry for making further products. By means of the information on dominant pathogenic bacteria, the company could prepare diagnostic kits and treatments to avoid early contamination and spoilage of products.

کلیدواژه ها:

Food microbiology ، dairy products ، molecular identification ، spoiling agents ، ۱۶S rDNA