Evaluating UV-C sensitivity of Coxiella burnetii in Skim Milk using a Bench-Scale Collimated Beam System and Comparative Study with High-Temperature Short-Time Pasteurization
Coxiella burnetii is a zoonotic Gram-negative obligate intracellular bacterial pathogen and the causative agent of Query (Q) fever in humans. Contamination of milk by C. burnetii as a consequence of livestock infection is a significant public health concern. Effective methods to inactivate C. burnetii in milk is a critical aspect of food safety. In this study, we measured optical light attenuation factors; absorption, scattering, and reflection of skim milk (SM) and considered for evaluation of delivered UV dose under stirred conditions. The accuracy of the method followed for the estimation of delivered UV dose in SM was verified by comparative studies of Escherichia coli ATCC 25922 inactivation in phosphate buffer (transparent fluid), and humic acid (opaque fluid). Absorption, scattering coefficient, and the reflectance of SM at 254 nm was measured as 19 {+/-} 0.3/cm. 26 {+/-} 0.5/cm and 10.6 %, respectively. SM inoculated with C. burnetii was irradiated using a collimated beam device equipped with a low-pressure UV-C254 nm lamp at doses from 0 - 12 mJ{middle dot}cm-2. Results showed a log-linear inactivation of C. burnetii in SM with UV-C sensitivity (D10) value of 4.1 {+/-} 0.04 mJ{middle dot}cm-2. Similar inactivation kinetics was observed with Salmonella enterica serovar Muenchen ATCC BAA 1674 in SM and thereby suggested as a suitable surrogate to C. burnetii for pilot scale UV-C processing studies of SM.