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Applied and Environmental Microbiology, September 2002, p. 4216-4224, Vol. 68, No. 9
0099-2240/02/$04.00+0 DOI: 10.1128/AEM.68.9.4216-4224.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Nestlé Research Center, Lausanne, Switzerland,1 Centre for Agricultural ResearchGhent, Department of Animal Product Quality, B-9090 Melle, Belgium2
Received 6 December 2001/ Accepted 30 May 2002
Thirty-eight strains of Bacillus sporothermodurans isolated from ultra-high-temperature (UHT)-treated milk or sterilized milk (UHT isolates) and from animal feed or raw milk (farm isolates) were characterized by automated ribotyping and by repetitive extragenic palindromic (REP)-PCR fingerprinting. By investigating the genetic relationships among isolates from these various sources, the relative importance of different contamination sources could be evaluated. The results of the separate clustering analyses of the PvuII and EcoRI ribopatterns and the REP-PCR patterns were largely consistent with each other and revealed the existence of two main clusters; there was one homogeneous group containing all (REP-PCR) or most (ribotyping) of the UHT isolates, and there was a second more diverse group comprising the farm isolates. A combined three-dimensional analysis of all data showed that three German UHT isolates did not belong to the compact group containing the majority of the UHT isolates. These results demonstrate that B. sporothermodurans is more heterogeneous than previously assumed and that most of the UHT isolates form a genetically distinct subgroup and are capable of producing highly heat-resistant spores. The close genetic relationship of these UHT isolates suggests a clonal origin of a few predominant strains of B. sporothermodurans that can be found in UHT-treated or sterilized milk products.
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