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Prevalence, seasonality, and growth of enterococci in raw and pasteurized milk in Victoria, Australia


McAuley, CM and Britz, ML and Gobius, KS and Craven, HM, Prevalence, seasonality, and growth of enterococci in raw and pasteurized milk in Victoria, Australia, Journal of Dairy Science, 98, (12) pp. 8348-8358. ISSN 0022-0302 (2015) [Refereed Article]

Copyright Statement

Copyright 2015 American Dairy Science Association

DOI: doi:10.3168/jds.2015-9335


This study investigated the prevalence, seasonality, and species variety of enterococci present in raw milk factory silos and pasteurized milk in 3 dairying regions in Victoria, Australia, over a 1-yr period. Additionally, the growth ability of thermoduric enterococci isolated in this study (Enterococcus faecalis, E. faecium, E. hirae, and E. durans) was determined in milk at temperatures likely to occur during storage, transport, and distribution, and before domestic consumption (4 and 7C). Enterococci were detected in 96% of 211 raw milk samples, with an average count of 2.48 log10 cfu/mL. Counts were significantly lower in winter than summer (average 1.84 log10 cfu/mL) and were different between factories but not regions. Enterococcus faecalis was the most prevalent species isolated from raw milk in every factory, comprising between 61.5 and 83.5% of enterococcal species across each season. Enterococci were detected in lower numbers in pasteurized milk than in raw milk and were below the limit of detection on spread plates (<10 cfu/mL) after factory pasteurization. Residual viable cells were only detected following enrichment using 100-mL samples of milk, with 20.8% of the samples testing positive; this equated to a decrease in the average raw milk enterococci count of >4 log10 cfu/mL following pasteurization. Although E. faecalis predominated in raw milk and E. durans was found in only 2.9% of raw milk samples, E. durans was the most prevalent species detected in pasteurized milk. The detection of enterococci in the pasteurized milk did not correlate with higher enterococci counts in the raw milk. This suggested that the main enterococci populations in raw milk were heat-sensitive and that thermoduric enterococci survived pasteurization in a small numbers of instances. All of the thermoduric enterococci that were assessed for growth at likely refrigeration temperatures were able to grow at both 4 and 7C in sterile milk, with generation times of 35 to 41h and 16 to 22h, respectively. Thermoduric enterococci were detected in pasteurized milk stored at 4C for 2 wk (typically 1 to 9 cells/100mL, up to 2.82 log10 cfu/mL), demonstrating the potential of enterococci to survive pasteurization and contribute to milk spoilage at refrigeration temperatures. This is particularly relevant for milk that is aseptically packaged to exclude gram-negative psychrotrophic bacteria and kept above the recommended storage temperature of ≤5C.

Item Details

Item Type:Refereed Article
Keywords:Enterococcus, raw and pasteurized milk, dairy, season, growth
Research Division:Biological Sciences
Research Group:Microbiology
Research Field:Bacteriology
Objective Division:Health
Objective Group:Public health (excl. specific population health)
Objective Field:Food safety
UTAS Author:Britz, ML (Professor Margaret Britz)
ID Code:106725
Year Published:2015
Web of Science® Times Cited:19
Deposited By:Tasmanian Institute of Agriculture
Deposited On:2016-02-18
Last Modified:2017-11-08

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