Viable Coxiella burnetii in hard cheeses made with unpasteurized milk

Abstract

Q fever is a bacterial zoonosis caused by Coxiella burnetii whose main reservoir are small ruminants. Infected animals shed the bacteria into the environment through the products of abortion as well as through feces, urine, and milk. Susceptible people are mainly infected by the inhalation of contaminated aerosols, while food-borne infection is unclear. High prevalence of C. burnetii DNA in cheeses from cattle, sheep or goat has been reported, but studies on viability of C. burnetii in hard cheeses are scarce. In this study, 67 sheep handicraft hard cheeses of different geographic origins made with unpasteurized milk were analyzed for the presence of C. burnetii DNA. To investigate viability of C. burnetii in cheese, 5 cheeses were selected among the 20 that tested DNA positive. Presence of viable C. burnetii was demonstrated in one cheese by experimental inoculation in BALB/c mice and culture in Vero cells. To further investigate the effect of cheese ripening in C. burnetii viability, another 12 cheeses elaborated in the same farm and season, and ripened for between 2.0 and 10.1 months were investigated. Results showed presence of C. burnetii DNA in all of them and viable C. burnetii in 5, indicating that C. burnetii can remain viable after at least 8 months of ripening in hard cheeses made with unpasteurized milk under the acid pH (4.96–5.41) and low water activity (0.9065–0.9533) conditions observed.