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

Autor:	McAuley CM; CSIRO Food and Nutrition Flagship, Private Bag 16, Werribee, Victoria, Australia, 3030; Melbourne School of Land and Environment, University of Melbourne, Melbourne, Victoria, Australia, 3010. Electronic address: catherine.mcauley@csiro.au., Britz ML; Melbourne School of Land and Environment, University of Melbourne, Melbourne, Victoria, Australia, 3010., Gobius KS; CSIRO Food and Nutrition Flagship, Private Bag 16, Werribee, Victoria, Australia, 3030., Craven HM; CSIRO Food and Nutrition Flagship, Private Bag 16, Werribee, Victoria, Australia, 3030.
Jazyk:	angličtina
Zdroj:	Journal of dairy science [J Dairy Sci] 2015 Dec; Vol. 98 (12), pp. 8348-58. Date of Electronic Publication: 2015 Oct 21.
DOI:	10.3168/jds.2015-9335
Abstrakt:	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 7°C). 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 7°C in sterile milk, with generation times of 35 to 41h and 16 to 22h, respectively. Thermoduric enterococci were detected in pasteurized milk stored at 4°C 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 ≤5°C. (Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)
Databáze:	MEDLINE
Externí odkaz:	Zobrazit plný text záznamu