Escherichia coli is a bacterium often found in the intestines of humans and warm-blooded animals. While many E. coli strains are harmless, certain types, particularly E. coli O157:H7, can cause severe foodborne illness if ingested through contaminated food or water. Understanding how to eliminate these harmful bacteria is important for ensuring food safety and protecting public health.
The Lethal Temperature
To effectively neutralize E. coli, food must reach a specific internal temperature. E. coli is a mesophilic bacterium. Temperatures above its moderate thriving range cause damage to bacterial cells. Research indicates that E. coli cannot survive temperatures exceeding 131°F (55°C).
The destruction of E. coli at these temperatures occurs through a process called protein denaturation. This involves the unfolding and breakdown of essential proteins within the bacterial cell, which are essential for cell function. The World Health Organization notes that bacteria are rapidly killed at temperatures above 149°F (65°C). For consumers, the United States Department of Agriculture (USDA) recommends cooking ground beef, a common source of E. coli, to a minimum internal temperature of 160°F (71°C) to rapidly destroy these harmful bacteria.
Beyond Temperature: Factors for Effective Elimination
While reaching a sufficient temperature is important, other factors work alongside heat to ensure E. coli is eliminated from food. The duration for which a food maintains a lethal temperature, known as holding time, is crucial. Effective heat treatment combines both temperature and time: higher temperatures require less time, while lower lethal temperatures require longer holding periods for the same bacterial kill. For instance, E. coli can be inactivated at 194°F (90°C) held for at least 10 seconds, or 212°F (100°C) for at least 5 seconds.
The type of food also influences the risk and required cooking approach. Ground meats, such as ground beef, pose a higher risk because the grinding process can distribute bacteria throughout the entire product, unlike whole cuts where bacteria typically remain on the surface. Another consideration is the initial bacterial load present in the food. While many bacteria require a significant number to cause illness, virulent strains like E. coli O157 can cause serious health issues with as few as 10 bacterial cells.
The rate of heating also impacts bacterial elimination. If E. coli is exposed to sublethal temperatures for an extended period, it can undergo a “heat shock” response, becoming more resistant to subsequent heating. This means that slowly heating foods to their final cooking temperature might not be as effective at eliminating bacteria as faster heating methods.
Practical Steps for Safe Food Preparation
Applying knowledge of lethal temperatures and contributing factors is important for safe food preparation at home. Using a food thermometer is the most reliable way to confirm that food has reached a safe internal temperature throughout. Insert the thermometer into the thickest part of the food, avoiding bones or fat, and wait for the reading to stabilize.
For ground beef, the recommended safe internal temperature is 160°F (71°C). Poultry, including ground poultry, should reach 165°F (74°C). Whole cuts of beef, pork, veal, and lamb, such as steaks and roasts, are safe at 145°F (63°C), followed by a three-minute rest time after cooking.
Preventing cross-contamination is important. Always wash hands with soap and water before and after handling raw meat. Clean and sanitize surfaces, cutting boards, and utensils that have come into contact with raw ingredients. Store raw meats on the lowest shelf in the refrigerator to prevent their juices from dripping onto ready-to-eat foods. Never place cooked food back onto a plate or surface that previously held raw meat.