Autori: L-D.Dinu, S. Bach.

Editorial: Applied and Environmental Microbiology, 77(23), p.8295-8302, 2011.

Rezumat:

Escherichia coli O157:H7 continues to be an important human pathogen and has been increasingly linked to foodborne illness associated with fresh produce, particularly leafy greens. The aim of this work was to investigate the fate of E. coli O157:H7 on the phyllosphere of lettuce under low temperature and to evaluate the potential hazard of viable but non-culturable (VBNC) cells induced under such stressful conditions. First we studied the survival of six bacterial strains following prolonged storage in water at low temperature (4°C) and selected two strains with different nonculturable response for the construction of E. coli O157:H7 Tn7gfp transformants in order to quantitatively assess the occurrence of human pathogens on the plant surface. Under the suboptimal growth temperature (16° C) both E. coli O157:H7 strains on lettuce leaves did not lose culturability but under more stressful conditions (8°C) the bacterial populations evolved towards VBNC. The strain-dependent nonculturable response was more evident in the experiments with different inoculum doses (109 and 106 E. coli O157:H7 per g leaf) when strain BRMSID 188 lost culturability after 15 days and strain ATCC 43895 within 7 days, regardless of the inoculum dose. However, the number of cells entering the VBNC state in high-cell density inoculum (approx. 55%) is lower than in low-cell density inoculum (approx. 70%). We recorded the presence of Verotoxin for three days in samples that contained a VBNC population of 4-5 log10 but did not detect culturable cells. These findings indicate that E. coli O157:H7 VBNC cells are induced on lettuce plants and this may have implications regarding food safety

Cuvinte cheie: food safety, E. coli O157:H7, viable but nonculturable, verotoxin production, lettuce