Optimizing methods of identifying Escherichia coli strains from ice cream on 16S rDNA

Subject Areas : Food Microbiology

Maryam Ranjbar ¹ , Mohammad Goli ² , Gholamreza Ghalamkari ³ , Mostafa Manian ⁴ , Mohammad Reza Meracy ⁵ , Reza Nedaeinia ⁶

1 - M.Sc., Department of Food Science and Technology, Isfahan (Khorasgan) branch, Islamic Azad University, Isfahan, Iran.
2 - Assistant Professor, Department of Food Science and Technology, Isfahan (Khorasgan) branch, Islamic Azad University, Isfahan, Iran.
3 - Assistant Professor, Department of Animal Science, Isfahan (Khorasgan) branch, Islamic Azad University, Isfahan, Iran.
4 - M.Sc., Department of Immunology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
5 - Associate Professor, Department of Epidemiology and Biostatistics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
6 - M.Sc., Department of Microbiology, Laboratory control, Deputy of Food and Drug, Isfahan University of Medical Sciences, Isfahan, Iran.

Received: 2015-01-31 Accepted : 2015-04-29 Published : 2015-12-01

Keywords: Ice cream, Escherichia coli, 16S rDNA, Chromogenic substances, Optimizing,

Abstract :

Background & Objectives: Milk and its products support the growth of infectious germs such as Escherichia coli, the most important agent of food contamination, in special conditions. This study was aimed to optimize the methods of identification of E. coli strains from ice cream based on 16S rDNA. Materials & Methods: In this cross-sectional study, 82 bacterial strain were isolated from 200 ice cream samples collected from different regions of Isfahan. Of these, 48 positive indole strains were isolated. The isolation was carried out based on Iran’s national standards (No. 2946) and using chromogenic media on a comparative basis. After numerical analysis, the 16SrRNA was amplified by PCR and the amplified genes were sequenced. Results: We observed that the method used in the national standard is 88 % reliable with 12 % error. Moreover, the positive indole strain such as Escherichia hermannii, Providencia rettgeri, Klebsiella oxytoca, Morganella morganii showed errors in the final result. Conclusion: We demonstrated that culture media containing chromogenic materials could identify Escherichia coli with a more accurate, simple, quick and inexpensive procedure.