Dairy to Deliver Yeast?

September 23/Life Science Weekly -- "This study aimed to examine the diversity and ecology of yeasts associated with traditional Egyptian dairy products employing molecular techniques in yeast identification. A total of 120 samples of fresh and stored Domiati cheese, kariesh cheese, and ''Matared'' cream were collected from local markets and examined," investigators in Mansoura, Egypt, report.

"Forty yeast isolates were cultured from these samples and identified using the restriction-fragment length polymorphism (RFLPs) of 5.8S-ITS rDNA region and sequencing of the domains D1 and D2 of the 26S rRNA gene. Yeasts were identified as Issatchenkia orientalis (13 isolates), Candida albicans (4 isolates), Clavispora lusitaniae (Candida lusitaniae) (9 isolates), Kodamaea ohmeri (Pichia ohmeri) (1 isolate), Kluyveromyces marxianus (6 isolates), and Candida catenulata (7 isolates).

"With the exception of C. lusitaniae, the D1/D2 26S rRNA gene sequences were 100% identical for the yeast isolates within the same species. Phylogenetic reconstruction of C. lusitaniae isolates grouped them into three distinguished clusters. Kariesh cheese was found to be the most diverse in its yeast floras and contained the highest total yeast count compared with other examined dairy products. This was linked to the acidic pH and lower salt content of this cheese, which favor the growth and survival of yeasts in foodstuffs. Stored Domiati cheese also contained diverse yeast species involving isolates of the pathogenic yeast C. albicans," wrote W.M. Elsharoud and colleagues, Mansoura University.

The researchers concluded, "This raises the possibility of dairy products being vehicles of transmission of pathogenic yeasts."

Elsharoud and colleagues published their study in the Journal of Food Science ("Molecular Identification of Yeasts Associated with Traditional Egyptian Dairy Products." Journal of Food Science, 2009;74(7):M341-M346).

For additional information, contact W.M. Elsharoud, Mansoura University, Faculty Agriculture, Dairy Department, Food Safety & Microbial Physiol Laboratory, Mansoura, Egypt.

From the September 28, 2009, Prepared Foods E-dition