title: Longevity of Mycobacterium bovis in Raw and Traditional Souring Milk as a Function of Storage Temperature and Dose.
abstract: BACKGROUND
  Unpasteurised fresh and souring dairy products form an essential component of household diets throughout many rural communities in southern Africa. The presence of milk-borne zoonotic pathogens such as Mycobacterium bovis (M. bovis), the causative agent of bovine tuberculosis and zoonotic tuberculosis in humans, constitute a public health threat, especially in remote areas with poor disease surveillance in livestock and highly compromised human health due to HIV/AIDS.
  
  
  METHODS
  In this study we used culture to determine the longevity of M. bovis in experimentally inoculated fresh and naturally souring milk obtained from communal cattle in the KwaZulu-Natal province of South Africa. The effect of bacterial load and storage temperature on the survival of M. bovis was evaluated by spiking mixtures of fresh milk and starter soured milk (aMasi) culture with three concentrations of bacteria (10(2), 10(4), 10(7) colony forming units/ml), followed by incubation under controlled laboratory conditions that mimicked ambient indoor (20°C) and outdoor (33°C) temperatures and periodic sampling and testing over time (0-56 days).
  
  
  RESULTS
  M. bovis cultured from samples of the fresh and souring milk was identified by PCR analysis. At the highest spiking concentration (10(7) cfu/ml), M. bovis survived for at least 2 weeks at 20°C; but, at all concentrations in the 33°C treatment, M. bovis was absent by three days after inoculation. Logistic regression analysis was used to assess the effects of bacterial concentration and time since inoculation, as well as determine the potential half-life of M. bovis in raw souring milk. Given the most favourable tested conditions for bacterial survival (20°C), approximately 25% of mycobacteria were alive after one day of storage (95% CI: 9-53%), giving an estimated half-life of M. bovis in raw souring milk of approximately 12 hours (95% CI: 7-27 hours).
  
  
  CONCLUSIONS
  This study demonstrates that M. bovis may survive in fresh and souring milk for periods of time that represent a risk of exposure to people consuming these products, as well as domestic or wild animal populations that have reported opportunities to consume homemade unpasteurised dairy products. The temperature at which the milk is soured and stored substantially affects the survival time of M. bovis.
authors.affiliation: Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa; ARC-Onderstepoort Veterinary Institute, Zoonotic Diseases Section, Onderstepoort, South Africa.
authors.forename: Anita L
authors.initials: AL
authors.lastname: Michel
authors.affiliation: Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.
authors.forename: Claire
authors.initials: C
authors.lastname: Geoghegan
authors.affiliation: ARC-Onderstepoort Veterinary Institute, Zoonotic Diseases Section, Onderstepoort, South Africa.
authors.forename: Tiny
authors.initials: T
authors.lastname: Hlokwe
authors.affiliation: ARC-Onderstepoort Veterinary Institute, Zoonotic Diseases Section, Onderstepoort, South Africa.
authors.forename: Keneilwe
authors.initials: K
authors.lastname: Raseleka
authors.affiliation: Department of Environmental Science, Policy and Management, University of California, Berkeley, CA, United States of America; School of Mathematical Sciences, University of KwaZulu-Natal, Durban, South Africa.
authors.forename: Wayne M
authors.initials: WM
authors.lastname: Getz
authors.affiliation: Institute of Tropical Medicine, Antwerp, Belgium.
authors.forename: Tanguy
authors.initials: T
authors.lastname: Marcotty
mesh_terms: D000818:Animals; D002417:Cattle; D004269:DNA, Bacterial / Q000032:analysis; D005511:Food Handling; D005516:Food Microbiology; D008892:Milk / Q000382:microbiology*; D009163:Mycobacterium bovis; D016133:Polymerase Chain Reaction; D012044:Regression Analysis; D013019:South Africa; D013696:Temperature; D014380:Tuberculosis, Bovine / Q000453:epidemiology* / Q000382:microbiology*
chemical_list: D004269:DNA, Bacterial