The University of Georgia
Professor Yen-Con Hung
UV radiation is one of the widely used forms of light to kill pathogens. UV light has three different bands (UV-A, UV-B, UV-C) depending on the wavelength. The short length UV or UV-C (254 nm) is known to be germicidal and is commonly used for disinfection. Current study aims at comparing the germicidal effect of UV on the pure cultures of different Shiga toxin producing E. coli (STEC) strains and serotypes. The results indicate that the bacterial reduction increased with increasing UV exposure time and intensity. For E. coli O104 serotype, it took about 6 minutes for the pathogens to be inactivated to non-detectable levels at 1.04 mW/cm2 intensity. When the intensity was increased to 1.92 mW/cm2, the complete inactivation time was reduced to 3 minutes. One common method to compare thermal inactivation is to calculate the D values (time needed for one log reduction) from the survival curves. At an UV intensity of 1.04 mW/cm2, E. coli strain 5 had the highest D value of 87 sec and strain E009 was the least resistant strain to UV with a D value of 63 sec. At 1.92 mW/cm2 UV intensity, strain 5, was still the most resistant strain with D value of 69 sec and E009 was the least resistant strain with a D value of 43 sec. When the intensity was further increased to 3.02 mW/cm2, strain 5 was still the most resistant strain with a D value of 34 sec but the strain 1 became the least resistant strain with a D value of 11 sec. The resistance of all O157:H7 strains is follows strain 5 ≥ strain 4 ≥ strain 1 ≥ strain E009 ≥ strain E932. An overall comparison of all the strains and serotypes tested here shows that E. coli O104 was the most resistant serotype followed by E. coli strain 5 ≥ O103 ≥ O111 ≥ O26 ≥O45 ≥ O121 ≥ O145 ≥ Surrogates. The data from the current study re-confirms that there are significant differences in the sensitivities of serotypes and strains tested (p < 0.05). Among all the serotypes tested E. coli O157:H7 strain 5 and O104 was the most resistant serotype. Though bacterial inactivation is directly proportional to the UV dosage, intensity of the radiation might also play a role in efficacy of the treatment.