Resistance of Escherichia coli O157:H7 and Other Shiga Toxin-producing Non-O157 Escherichia Coli to Ultraviolet Treatment

Introduction: Shiga toxin-producing Escherichia coli (STEC) is one of the important foodborne pathogens that is known to cause severe life threatening health conditions like HUS (Hemolytic Uremic Syndrome). Though it is linked to a wide variety of foods, beef is a predominantly identified source of serious E. coli O157:H7 and non-O157 outbreaks.

Purpose: The purpose of the current study was to find non-thermal solutions to enhance beef safety using ultraviolet radiation. Current research aims at studying the resistance patterns of various E. coli O157:H7 strains to UV treatment. This study also compares the resistance of the cocktails of serotypes E. coli O26, O45, O103, O104, O111, O121 and O145 to UV. 

Methods: Five individual strains of E. coli O157:H7 suspended in phosphate buffered saline (PBS, pH 7) were subjected to the UV radiation (1.04 mW/cm² intensity) for different time periods ranging from 20 seconds to 180 seconds. E. coli O26, O45, O103, O104, O111, O121 and O145 cocktails of strains were also prepared and subjected to UV radiation as above. The treated solutions were appropriately diluted and plated on the tryptic soy agar (TSA) and enumerated.

Results: The results show that among the 5 E. coli O157:H7 strains tested, strain 5 (human isolate) was the most resistant and followed by E009 ≥ 932 ≥ 1 ≥ 4. E. coli O104 was the most resistant serotype among the 7 E. coli serotypes tested then followed by O45 ≥ O103 ≥ O121 ≥ O26 ≥ O111 ≥ O145.

Significance: Results revealed that while 180-second treatment was enough for reducing all five strains of E. coli O17:H7 to non-detectable levels except for E. coli O157:H7-5 which is a human isolate which required 210 seconds.