Scientists of the Department of Food Science and Technology at Agricultural University of Athens (Greece), within the QUAFETY European project (2011-2014), determined the prevalence of Listeria monocytogenes and Escherichia coli O157:H7 in fresh-cut rocket, cucumbers and strawberries. The detection of both pathogens was based on the respective ISO methods with a parallel study for the comparison of two chromogenic culture media: ALOA and RAPID'L. mono in the former case, CT - SMAC and Fluorocult in the latter.
Confirmation of the suspect colonies was performed by hemolysis, rhamnose and xylose fermentation as well as specific PCR for L. monocytogenes; Latex Test and specific PCR for E. coli O157:H7.
The results of biochemical tests and molecular analyses showed that the prevalence of L. monocytogenes was 7% in rocket, 6% in cucumbers and 3.8% in strawberries, while prevalence of E. coli O157: H7 was 7% in rocket, 3% in cucumbers and 3.8% in strawberries. Furthermore, it was concluded that parallel use of more than one chromogenic media is necessary for accurate estimation of L. monocytogenes and E. coli O157:H7 prevalence.
The same scientists have also assessed the biodiversity of 22 L. monocytogenes and 12 Escherichia coli Ο157:Η7 strains isolated from rocket, cucumber and strawberry samples, as well as the detection of virulence - associated genes. Genotypic diversity of both pathogens was assessed by RAPD - PCR using M13, UBC155 and HLWL85 as primers and by rep - PCR using (GTG)5 as primer. Results showed that all L. monocytogenes strains belonged to 4b serotype. Many virulence associated genes such as plcB, plcA, actA, hlyA regarding L. monocytogenes and stx2, eae and some of their variants regarding E. coli O157:H7 have been detected. However, none of the isolates contained all necessary genes required for pathogenicity, as detected by published specific - PCR protocols, most probably due to variations in the primer hybridization sequences.
Source: Hadjilouka A., Madjourani K.S., Katsarou A., Koubou V., Paramithiotis S., Mataragas M., Drosinos, E.H., Laboratory of Food Quality Control and Hygiene, Department of Food Science and Technology, Agricultural University of Athens, Greece. www.quafety.eu