title: Quantitation of viable Coxiella burnetii in milk using an integrated cell culture-polymerase chain reaction (ICC-PCR) assay.
abstract: The obligate intracellular pathogen Coxiella burnetii has long been considered the most heat resistant pathogen in raw milk, making it the reference pathogen for determining pasteurisation conditions for milk products. New milk formulations and novel non-thermal processes require validation of effectiveness which requires a more practical method for analysis than using the currently used animal model for assessing Coxiella survival. Also, there is an interest in better characterising thermal inactivation of Coxiella in various milk formulations. To avoid the use of the guinea pig model for evaluating Coxiella survival, an Integrated Cell Culture-PCR (ICC-PCR) method was developed for determining Coxiella viability in milk. Vero cell cultures were directly infected from Coxiella-contaminated milk in duplicate 24-well plates. Viability of the Coxiella in milk was shown by a ≥ 0.5 log genome equivalent (ge)/ml increase in the quantity of IS111a gene from the baseline post-infection (day 0) level after 9-11 d propagation. Coxiella in skim, 2%, and whole milk, and half and half successfully infected Vero cells and increased in number by at least 2 logs using a 48-h infection period followed by 9-d propagation time. As few as 125 Coxiella ge/ml in whole milk was shown to infect and propagate at least 2 logs in the optimised ICC-PCR assay, though variable confirmation of propagation was shown for as low as 25 Coxiella ge/ml. Applicability of the ICC-PCR method was further proven in an MPN format to quantitate the number of viable Coxiella remaining in whole milk after 60 °C thermal treatment at 0, 20, 40, 60 and 90 min.
authors.affiliation: US Food and Drug Administration,Division of Food Processing Science & Technology,Bedford Park,IL 60501,USA.
authors.forename: Diana
authors.initials: D
authors.lastname: Stewart
authors.affiliation: US Food and Drug Administration,Division of Food Processing Science & Technology,Bedford Park,IL 60501,USA.
authors.forename: Y-Carol
authors.initials: YC
authors.lastname: Shieh
authors.affiliation: US Food and Drug Administration,Division of Food Processing Science & Technology,Bedford Park,IL 60501,USA.
authors.forename: Mary
authors.initials: M
authors.lastname: Tortorello
authors.affiliation: Illinois Institute of Technology, Institute for Food Science & Health,Bedford Park,IL 60501,USA.
authors.forename: Ankush
authors.initials: A
authors.lastname: Kukreja
authors.affiliation: US Food and Drug Administration,Division of Food Processing Science & Technology,Bedford Park,IL 60501,USA.
authors.forename: Arlette
authors.initials: A
authors.lastname: Shazer
authors.affiliation: US Food and Drug Administration,Division of Food Processing Science & Technology,Bedford Park,IL 60501,USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Schlesser
mesh_terms: D000818:Animals; D001431:Bacteriological Techniques / Q000662:veterinary*; D002417:Cattle; D002418:Cattle Diseases / Q000175:diagnosis*; D002522:Chlorocebus aethiops; D016997:Coxiella burnetii / Q000302:isolation & purification*; D008892:Milk / Q000382:microbiology*; D016133:Polymerase Chain Reaction / Q000662:veterinary*; D011778:Q Fever / Q000382:microbiology / Q000662:veterinary*; D014709:Vero Cells
keywords: Coxiella burnetii; ICC-PCR; milk; quantitation