Buehner Kimberly P, Anand Sanjeev, Djira Gemechis D, Garcia Alvaro
Midwest Dairy Foods Research Center, Dairy Science Department, South Dakota State University, Brookings 57007.
Midwest Dairy Foods Research Center, Dairy Science Department, South Dakota State University, Brookings 57007.
J Dairy Sci. 2014 Nov;97(11):6777-84. doi: 10.3168/jds.2014-8342. Epub 2014 Sep 6.
Thermoduric bacteria (TDB), including sporeformers and their spores, can be present in milk and dairy products even after pasteurization. They have the potential to adversely affect the quality and shelf life of products. The objectives of this study were to identify the origin and common species of heat-resistant bacteria occurring during summer and winter on Midwest dairy farms. Bulk tank milk samples were taken from 10 dairy farms located along the South Dakota section of Interstate 29, with herd sizes ranging from 650 to 3,500 lactating dairy cows. Milk samples were profiled for the prevalence of TDB and spore counts (SC). Corn silage samples and swabs of the milking clusters were also taken at the dairies to further profile the potential sources of TDB and SC. The samples were taken 3 times during 2 seasons [winter (January-March) and summer (June-August)] to track seasonal changes in the farm bacterial flora. During winter, the average TDB counts in bulk tank milk were 2.61 log compared with 2.76 log TDB counts in the summer. The SC was 1.08 log in the winter, which was half the 2.06 log SC present in the summer season. Corn silage sampled in winter contained a 7.57 log TDB count compared with an increased 10.77 log TDB count during summer sampling. Concentrations of SC in corn silage reached an average of 6.3 log in winter compared with 11.81 log for summer. The seasonal effect was evident with an increase in summer counts across the board for TDB and SC, both in the feed and bulk tank milk samples. Bacillus licheniformis was the predominant species identified in 62.4% of winter (85 total) and 49.4% of summer (83 total) samples. Bacillus subtilis made up 9.4% of the remaining winter isolates, followed by Bacillus sonorensis at 8.2%. Conversely, B. sonorensis made up 12% of the summer isolates followed by Bacillus pumilus at 10.8%. Bacillus licheniformis is a ubiquitous microbe and was isolated from both TDB and sporeformer categories in all 3 sample types. There were larger increases in SC than TDB, indicating that summer temperatures and conditions may favor proliferation of sporeforming bacteria over that of TDB. In conclusion, samples from bulk tank milk, milking cluster swabs, and corn silage samples at each of the 10 sites indicated that B. licheniformis was the major contaminant species, regardless of season. In this experiment, corn silage was the major environmental source of both TDB and SC with higher concentrations in summer when compared with winter.
耐热菌（TDB），包括产芽孢菌及其芽孢，即使在巴氏杀菌后仍可能存在于牛奶和乳制品中。它们有可能对产品质量和保质期产生不利影响。本研究的目的是确定中西部奶牛场夏季和冬季出现的耐热细菌的来源和常见种类。从位于29号州际公路南达科他州段的10个奶牛场采集了大罐牛奶样本，牛群规模从650头到3500头泌乳奶牛不等。对牛奶样本进行了耐热菌流行率和芽孢计数（SC）分析。还在奶牛场采集了玉米青贮样本和挤奶设备的拭子，以进一步分析耐热菌和芽孢计数的潜在来源。在两个季节[冬季（1月至3月）和夏季（6月至8月）]期间采集了3次样本，以追踪农场细菌菌群的季节性变化。冬季，大罐牛奶中的耐热菌平均计数为2.61对数，而夏季为2.76对数。冬季的芽孢计数为1.08对数，是夏季2.06对数的一半。冬季采集的玉米青贮样本中的耐热菌计数为7.57对数，而夏季采样时增加到10.77对数。冬季玉米青贮中的芽孢计数平均达到6.3对数，而夏季为11.81对数。季节性影响很明显，耐热菌和芽孢计数在夏季均全面增加，无论是在饲料还是大罐牛奶样本中。地衣芽孢杆菌是在62.4%的冬季样本（共85个）和49.4%的夏季样本（共83个）中鉴定出的主要菌种。枯草芽孢杆菌占冬季其余分离株的9.4%，其次是索诺拉芽孢杆菌，占8.2%。相反，索诺拉芽孢杆菌占夏季分离株的12%，其次是短小芽孢杆菌，占10.8%。地衣芽孢杆菌是一种普遍存在的微生物，在所有3种样本类型的耐热菌和产芽孢菌类别中均有分离。芽孢计数的增加幅度大于耐热菌计数，表明夏季温度和条件可能更有利于产芽孢细菌的增殖，而非耐热菌。总之，10个地点的大罐牛奶、挤奶设备拭子和玉米青贮样本表明，无论季节如何，地衣芽孢杆菌都是主要的污染菌种。在本实验中，玉米青贮是耐热菌和芽孢计数的主要环境来源，夏季的浓度高于冬季。
