托福听力背景知识:生物膜

　　It has been proposed that competence development and biofilm formation is an adaptation of S. pneumoniae to survive the defenses of the host.[64] In particular, the host’s polymorphonuclear leukocytes produce an oxidative burst to defend against the invading bacteria, and this response can kill bacteria by damaging their DNA. Competent S. pneumoniae in a biofilm have the survival advantage that they can more easily take up transforming DNA from nearby cells in the biofilm to use for recombinational repair of oxidative damages in their DNA. Competent S. pneumoniae can also secrete an enzyme (murein hydrolase) that destroys non-competent cells (fratricide) causing DNA to be released into the surrounding medium for potential use by the competent cells.[66]

　　Biofilms in medicine[edit]The rapidly expanding worldwide industry for biomedical devices and tissue engineering related products is already at $180 billion per year, yet this industry continues to suffer from microbial colonization. No matter the sophistication, microbial infections can develop on all medical devices and tissue engineering constructs.[67]

　　60-70% of nosocomial or hospital acquired infections are associated with the implantation of a biomedical device.[67] This leads to 2 million cases annually in the U.S., costing the healthcare system over $5 billion in additional healthcare expenses.[67]

　　If an infection develops a biofilm, it becomes even harder to treat. As the bacteria change, they becomes more resistant to antibiotics and the body's own host defenses.[67]

　　Biofilms in the food industry[edit]Biofilms have become problematic in several food industries due to the ability to form on plants and during industrial processes.[68] Bacteria can survive long periods of time in water, animal manure, and soil, causing biofilm formation on plants or in the processing equipment.[69] The buildup of biofilms can affect the heat flow across a surface and increase surface corrosion and frictional resistance of fluids.[70] These can lead to a loss of energy in a system and overall loss of products.[70] Along with economic problems biofilm formation on food poses a health risk to consumers due to the ability to make the food more resistant to disinfectants[68] As a result, from 1996 to 2010 the Center for Disease Control and Prevention estimated 48 million foodborne illnesses per year.[68] Biofilms have been connected to about 80% of bacterial infections in the United States.[68]

　　In produce, microorganisms attach to the surfaces and biofilms develop internally.[68] During the washing process, biofilms resist sanitization and allow bacteria to spread across the produce.[68] This problem is also found in ready to eat foods because the foods go through limited cleaning procedures before consumption[68] Due to the perishability of dairy products and limitations in cleaning procedures, resulting in the buildup of bacteria, dairy is susceptible to biofilm formation and contamination.[68][70] The bacteria can spoil the products more readily and contaminated products pose a health risk to consumers. One bacteria that can be found in various industries and is a major cause of foodborne disease is Salmonella.[71] Large amounts of salmonella contamination can be found in the poultry processing industry as about 50% of salmonella strains can produce biofilms on poultry farms.[68] Salmonella increases the risk of foodborne illnesses when the poultry products are not cleaned and cooked correctly. Salmonella is also found in the seafood industry where biofilms form from seafood borne pathogens on the seafood itself as well as in water.[71] Shrimp products are commonly affected by salmonella because of unhygienic processing and handling techniques[71] The preparation practices of shrimp and other seafood products can allow for bacteria buildup on the products.[71]

　　New forms of cleaning procedures are being tested in order to reduce biofilm formation in these processes which will lead to safer and more productive food processing industries. These new forms of cleaning procedures also have a profound effect on the environment, often releasing toxic gases into the groundwater reservoirs.[70]