Sensitivity of a Shiga Toxin-Producing and an Uropathogenic Escherichia coli to UV Irradiation After Freeze-Thaw

This study aims to investigate the effect of freeze-thaw on the sensitivity of two different strains of Escherichia coli bacteria, O157:H7 strain 961019 and E. coli ATCC 25922 strain, to UV irradiation. The O157:H7 strain was a toxin-producing E. coli, and the ATCC 25922 strain is an opportunistic pathogen that can cause urinary tract infection. Cells of the two E. coli strains were frozen at -7, -15, and -30 degrees C with one, three, and five freeze-thaw cycles prior to UV irradiation. The UV inactivation levels of the freezing-treated E. coli cells were compared with those without freezing (the controls). Freezing affected the sensitivity of the test microbes to UV light, and the effect was strain dependent. A significant increase in resistance to UV light was observed in the freezing-treated cells as compared to the control samples. The ATCC 25922 strain showed more resistance to UV irradiation than the O157:H7 strain 961019 in most cases. The O157:H7 strain 961019, on the other hand, became more resistant to UV with increased freeze-thaw cycles.