Prevalence and Characteristics of Bacillus cereus Group Isolated from Raw and Pasteurised Milk
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Prevalence and Characteristics of Bacillus cereus Group Isolated from Raw and Pasteurised Milk Behrad Radmehr1 · Bita Zaferanloo1 · Thien Tran2 · David J. Beale3 · Enzo A. Palombo1 Received: 16 April 2020 / Accepted: 11 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The elimination of spore-forming bacteria is not guaranteed by current pasteurisation processes and is a challenging problem for the dairy industry. Given that Bacillus cereus sensu lato (B. cereus group) is an important foodborne pathogen and spoiler in the dairy industry, this study aimed at evaluating the prevalence and characteristics of B. cereus group in raw and pasteurised milk samples collected in Victoria, Australia. Isolated B. cereus group were tested for antimicrobial susceptibility, biofilm formation and virulence properties. Genetic diversity was assessed using ERIC-PCR. Proteomic profiling using MALDI-TOF MS and chemical profiling using Fourier-transform infrared (FTIR) spectroscopy were also applied for clustering of the isolates. Results showed 42.3% of milk samples contained B. cereus group, with a higher contamination level for pasteurised milk. Virulence studies identified genes nheA, nheB, hblA and nheC in most isolates and cyk gene in 46% of all isolates. Antimicrobial susceptibility testing showed a high prevalence of resistance towards ampicillin, ceftriaxone and penicillin. The biofilm-forming capacity of our isolates showed that most (53.7%) had the ability to form a biofilm. Genetic profiling using ERIC-PCR placed most B. cereus group isolates from pasteurised milk in the same cluster, indicating that they probably originated from a similar source. Raw milk isolates showed greater diversity indicating various sources. FTIR spectroscopy showed high agreement with genetic profiling. In contrast, low agreement between proteomic (MALDI-TOF MS) and genetic typing was observed. The present study showed that the FTIR spectroscopy could be adopted as a rapid tool for the typing of B. cereus group. Overall, the virulence and antimicrobial resistance characteristics, together with the ability of isolates to produce biofilm, indicate the importance of B. cereus group in the Australian dairy industry.
Introduction Bacillus cereus sensu lato, commonly known Bacillus cereus group, contains at least eight species: Bacillus cereus (sensu strico), Bacillus anthracis, Bacillus cytotoxicus, Bacillus mycoides, Bacillus pseudomycoides, Bacillus thuringiensis, Bacillus toyonensis, and Bacillus weihenstephanensis [1, 2]. Bacillus cereus group is recognised as a major foodborne pathogen. It is also an important spoilage organism in milk and dairy products because its elimination is not guaranteed by current pasteurisation and sanitation processes [3, * Enzo A. Palombo [email protected] 1
Department of Chemistry and Biotechnology, Swinburne University of Technology, Hawthorn, VIC 3122, Australia
2
Bruker Pty Ltd, Preston, VIC 3072, Australia
3
Land and Water, Commonwealth Scientific and Industri
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