Pritchard T J, Flanders K J, Donnelly C W
University of Vermont, Department of Animal and Food Sciences, Burlington 05405, USA.
Int J Food Microbiol. 1995 Aug;26(3):375-84. doi: 10.1016/0168-1605(94)00130-x.
This study was undertaken to compare the incidence of Listeria contamination of processing equipment with that of the general dairy processing environment. A total of 378 sponge samples obtained from 21 dairy plants were analyzed for Listeria using three different enrichment media. Use of extended microbiological analysis allowed us to identify 26 Listeria positive sites which would have not been identified had a single test format been employed. Eighty (80) of 378 sites (21.2%) were identified as Listeria positive. Listeria innocua was isolated from 59 of the 80 (73.8%) positive samples, L. monocytogenes was identified in 35 (43.8%) of the positive samples, and L. seeligeri was isolated from 5 (6.3%) of the Listeria positive samples. Positive equipment samples were obtained from 6 of the 21 (28.6%) plants and 19 of the 21 (90.5%) plants had positive environmental sites. Seventeen of the 215 (7.9%) samples from equipment were positive for Listeria species. Eleven of these sites, including 3 holding tanks, 2 table tops, 3 conveyor/chain systems, a pasta filata wheel, a pint milk filler and a brine pre-filter machine, were positive for L. monocytogenes. Nineteen of the 21 (90.5%) plants had positive environmental sites. Sixty-three of the 163 (41.1%) samples from environmental sites were Listeria positive and 24 were positive for L. monocytogenes. Two-tailed student t-test analysis of the mean frequencies indicated that the level of contamination was significantly higher (p < 0.001) in 'environmental' (49.7%) as opposed to 'equipment' samples (7.0%). Our study indicates that environmental contamination with Listeria does not necessarily translate into contamination of equipment within the same plant, and that greater emphasis needs to be placed on the cleaning and sanitizing of the plant environment.
本研究旨在比较加工设备中李斯特菌污染的发生率与一般乳制品加工环境中李斯特菌污染的发生率。从21家乳制品厂采集了378个海绵样本，使用三种不同的增菌培养基对样本进行李斯特菌分析。采用扩展微生物分析方法，使我们能够识别出26个李斯特菌阳性位点，若仅采用单一检测形式则无法识别这些位点。378个位点中有80个（21.2%）被鉴定为李斯特菌阳性。在80个阳性样本中，有59个（73.8%）分离出无害李斯特菌，35个（43.8%）阳性样本中鉴定出单核细胞增生李斯特菌，5个（6.3%）李斯特菌阳性样本中分离出斯氏李斯特菌。21家工厂中有6家（28.6%）的设备样本呈阳性，21家工厂中有19家（90.5%）的环境位点呈阳性。215个设备样本中有17个（7.9%）的李斯特菌属呈阳性。其中11个位点，包括3个储存罐、2个桌面、3个传送带/链条系统、1个意大利面拉丝轮、1个一品脱牛奶灌装机和1个盐水预滤机，单核细胞增生李斯特菌呈阳性。21家工厂中有19家（90.5%）的环境位点呈阳性。163个环境位点样本中有63个（41.1%）李斯特菌呈阳性，24个单核细胞增生李斯特菌呈阳性。对平均频率进行双尾学生t检验分析表明，“环境”样本（49.7%）的污染水平显著高于“设备”样本（7.0%）（p < 0.001）。我们的研究表明，李斯特菌对环境的污染不一定会转化为同一工厂内设备的污染，并且需要更加重视工厂环境的清洁和消毒。
