The overall goal of this application is to identify and characterize milk contamination by Campylobacter jejuni clone SA, an emergent ruminant C. jejuni clone that is transmitted from ruminants to humans potentially via milk. <P>The specific objectives of this project are 1) to determine the prevalence of clone SA in unprocessed milk and in dairy cow feces, 2) to determine the mechanisms by which clone SA contaminate milk using Campylobacter-inoculated cows, and 3) to examine the survivability of clone SA in raw milk and raw milk cheese and assess the effectiveness of milk pasteurization for inactivating clone SA. <P>This research project will last for three years and work proposed for all three specific objectives will be conducted simultaneously. Once completed, the planned work will 1) generate new information on the prevalence and distribution of C. jejuni clone SA (and other C. jejuni strains) in dairy cattle feces and bulk-tank milk, 2) obtain empirical evidence that will demonstrate if C. jejuni clone SA contaminates milk via fecal contamination or udder excretion or both, and 3) ascertain the effectiveness of pasteurization on inactivation of C. jejuni clone SA in milk and the survivability of this organism in raw milk cheese. <P>These findings will significantly enhance our knowledge of the ecology and epidemiology of Campylobacter in ruminant reservoirs and provide important information for the development of pre- and post-harvest strategies to control Campylobacter transmission via milk. Therefore the outcomes of this application will have a significant impact on strengthening food safety in the U.S.
Campylobacter jejuni is a major cause of foodborne illnesses in the United States and worldwide. Previous and current research efforts on Campylobacter have been mainly focusing on poultry contamination as poultry meat is considered a major food vehicle for transmission of this pathogen. However, our recent work has identified a ruminant C. jejuni clone that is emerging as a significant foodborne hazard in the U.S. This clone (named clone SA) was first identified in sheep and has recently become the predominant cause of ovine abortion. Our recent work also revealed that C. jejuni clone SA is increasingly associated with outbreaks (related to raw milk) and sporadic cases of foodborne gastroenteritis in humans. Despite the evidence suggesting the emerging role of C. jejuni clone SA in foodborne diseases and its likely transmission through milk, virtually nothing is currently known about its prevalence in milk and how it contaminates milk. There is also a complete lack of information concerning the survivability of this pathogenic clone in raw milk and its resistance to milk processing stresses. In this project, we will determine the prevalence of clone SA in unprocessed milk and in dairy cow feces, determine the mechanisms by which clone SA contaminate milk, examine the survivability of clone SA in raw milk and raw milk cheese, and assess the effectiveness of milk pasteurization for inactivating clone SA. These studies will generate important information on this emerging threat to food safety and will facilitate the development of pre- and post-harvest measures to control its transmission via milk. The outcomes will have a significant impact on strengthening food safety in the U.S.
For objective 1, an epidemiological investigation will be conducted to determine the prevalence of C. jejuni clone SA in dairy cattle feces and raw milk. Bulk tank raw milk (as milk filters) will be cultured for Campylobacter, which will be confirmed and genotyped by PCR, pulsed field gel electrophoresis and MLST. Both absolute and relative prevalence of C. jejuni clone SA in milk will be reported. For determining the prevalence of clone SA in dairy cattle feces, the C. jejuni isolates archived from NAHMS's nationwide survey of dairy operations (2002 and 2007) will be screened using clone SA-specific primers and confirmed by PFGE and MLST.
<br/>For objective 2, milking cows will be orally inoculated with C. jejuni clone SA and a control C. jejuni strain under laboratory conditions. Blood, feces, milk, and teat swabs will be collected for culturing C. jejuni. The binary response variables for each tissue and sampling period will be analyzed using a hierarchical multi-level mixed logistical regression analysis with the primary fixed effect factor of interest being the strain of C. jejuni inoculated into the cow's intestinal tract.
<br/>For objective 3, various conditions (time and temperature combinations) used for pasteurization will be tested for inactivation of clone SA in milk. Standard culture methods will be used to determine the viability of C. jejuni before and after each pasteurization treatment. Additionally, C. jejuni clone SA will be inoculated into raw milk, which will be used to prepare cheese under laboratory conditions. The viability of the inoculated organism during the preparation of raw milk cheese will be examined using standard culture methods.