Grant I R, Rowe M T
Department of Food Science (Food Microbiology), Queen's University of Belfast, Belfast, UK.
Lett Appl Microbiol. 2004;38(4):283-8. doi: 10.1111/j.1472-765x.2004.01498.x.
To assess the impact of chemical decontamination and refrigerated storage before culture on the recovery of Mycobacterium avium subsp. paratuberculosis from heat-treated milk.
Five-millilitre samples of ultra heat-treated (UHT) milk spiked with Myco. paratuberculosis NCTC 8578, B4 or 806R (ca 10(6) CFU ml(-1)) were heated at 63 degrees C for 20 or 30 min by submersion in a water bath. Heat-treated milk (0.5 ml) was cultured immediately into BACTEC 12B medium or refrigerated at 4 degrees C for 48 h before culture. Milk samples that received a 20-min heat treatment were also subjected to decontamination with 0.75% cetylpyridinium chloride (CPC) for 5 h at room temperature before inoculation into BACTEC 12B medium when tested immediately and after 48 h at 4 degrees C. BACTEC vials were monitored for evidence of growth over an 18-week incubation period at 37 degrees C. CPC decontamination resulted in a significant reduction in the number of culture-positive milk samples recovered immediately after heating (P < 0.05) and after refrigerated storage for 48 h (P < 0.01). Refrigerated storage for 48 h before testing did not have any significant effect, beneficial or detrimental, on Myco. paratuberculosis recovery rates.
CPC decontamination applied to milk immediately or 48 h after heating will adversely affect the recovery of viable Myco. paratuberculosis, possibly leading to nonrecovery of the organism although viable cells are present in the original milk sample.
Published pasteurization studies in which milk samples were decontaminated before culture will have underestimated the survival capability of Myco. paratuberculosis after high-temperature, short-time pasteurization. CPC decontamination should not be applied to pasteurized milk in future studies.
评估培养前化学去污和冷藏对从热处理牛奶中回收副结核分枝杆菌的影响。
将添加了副结核分枝杆菌NCTC 8578、B4或806R（约10⁶ CFU/ml⁻¹）的5毫升超高温瞬时灭菌（UHT）牛奶样品通过浸入水浴在63℃加热20或30分钟。热处理后的牛奶（0.5毫升）立即接种到BACTEC 12B培养基中，或在培养前于4℃冷藏48小时。接受20分钟热处理的牛奶样品在立即检测以及在4℃保存48小时后接种到BACTEC 12B培养基之前，还在室温下用0.75%十六烷基吡啶氯化物（CPC）去污5小时。在37℃孵育18周期间监测BACTEC瓶中生长的证据。CPC去污导致加热后立即回收的培养阳性牛奶样品数量显著减少（P<0.05），以及冷藏保存48小时后（P<0.01）。检测前48小时冷藏保存对副结核分枝杆菌的回收率没有任何显著的有益或有害影响。
加热后立即或48小时后对牛奶应用CPC去污会对存活的副结核分枝杆菌的回收产生不利影响，尽管原始牛奶样品中存在活细胞，但可能导致该菌无法回收。
已发表的在培养前对牛奶样品进行去污的巴氏杀菌研究可能低估了副结核分枝杆菌在高温短时巴氏杀菌后的存活能力。在未来的研究中不应将CPC去污应用于巴氏杀菌牛奶。
