Environmental and Microbial Food Safety Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705-2350, USA.
Foodborne Pathog Dis. 2011 Apr;8(4):541-6. doi: 10.1089/fpd.2010.0734.
Outbreaks associated with leafy greens have focused attention on the transfer of human pathogens to these commodities during harvest with commercial equipment. Attachment of Escherichia coli O157:H7 on new or rusty spinach harvester blades immersed in spinach extract or 10% tryptic soy broth (TSB) was investigated. Bacteriophages specific for E. coli O157:H7 were evaluated to kill cells attached to blade. A cocktail of five nalidixic acid-resistant E. coli O157:H7 isolates was transferred to 25 mL of spinach extract or 10% TSB. A piece of sterilized spinach harvester blade (2×1") was placed in above spinach extract or 10% TSB and incubated at room (22 °C) or dynamic (30 °C day, 20 °C night) temperatures. E. coli O157:H7 populations attached to blade during incubation in spinach extract or 10% TSB were determined. When inoculated at 1 log CFU/mL, E. coli O157:H7 attachment to blades after 24 and 48 h incubation at dynamic temperature (6.09 and 6.37 log CFU/mL) was significantly higher than when incubated at 22 °C (4.84 and 5.68 log CFU/mL), respectively. After 48 h incubation, two blades were sprayed on each side with a cocktail of E. coli O157-specific bacteriophages before scraping the blade, and subsequent plating on Sorbitol MacConkey media-nalidixic acid. Application of bacteriophages reduced E. coli O157:H7 populations by 4.5 log CFU on blades after 2 h of phage treatment. Our study demonstrates that E. coli O157:H7 can attach to and proliferate on spinach harvester blades under static and dynamic temperature conditions, and bacteriophages are able to reduce E. coli O157:H7 populations adhered to blades.
叶类蔬菜相关的疫情暴发使人们关注到商业设备在收获过程中会将人类病原体转移到这些商品上。本研究调查了新的或生锈的菠菜收割机叶片在菠菜提取物或 10%胰蛋白酶大豆肉汤 (TSB) 中浸泡时对大肠杆菌 O157:H7 的附着情况。评估了针对大肠杆菌 O157:H7 的噬菌体以杀死附着在叶片上的细胞。将 5 株耐萘啶酸的大肠杆菌 O157:H7 分离株的混合物转移到 25 mL 的菠菜提取物或 10% TSB 中。将一块灭菌的菠菜收割机叶片(2×1")放入上述菠菜提取物或 10% TSB 中,并在室温(22°C)或动态(白天 30°C,晚上 20°C)温度下孵育。在孵育过程中,用菠菜提取物或 10% TSB 测定叶片上附着的大肠杆菌 O157:H7 数量。当以 1 log CFU/mL 的浓度接种时,在动态温度下孵育 24 和 48 小时后,大肠杆菌 O157:H7 附着在叶片上的数量(6.09 和 6.37 log CFU/mL)明显高于在 22°C 下孵育的数量(4.84 和 5.68 log CFU/mL)。孵育 48 小时后,将两片叶片的每一面都用大肠杆菌 O157 特异性噬菌体混合物喷雾,然后刮擦叶片,随后在 Sorbitol MacConkey 培养基-萘啶酸上进行平板培养。噬菌体处理 2 小时后,噬菌体处理可使叶片上的大肠杆菌 O157:H7 数量减少 4.5 log CFU。本研究表明,大肠杆菌 O157:H7 可以在静态和动态温度条件下附着在菠菜收割机叶片上并增殖,噬菌体能够减少附着在叶片上的大肠杆菌 O157:H7 数量。
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