Chemical substances, often natural, that inhibit the growth of bacteria or kill bacteria. Antibiotics normally have specific targets, such as the ribosome of the bacterial replication machinery. Virtually all of modern medicine rests on the efficiency of antibiotics. Antibiotics not only cure bacterial infections, but also decrease the infectious disease risk of surgery, cancer, chemotherapy and transplants to a level low enough to make these procedures medically feasible.
Antibiotics
Antibiotic Resistance
The ability of bacteria to thwart the action of an antibiotic, so that the antibiotic no longer inhibits the growth of or kills the bacteria. Resistance may be linked to enzymes that destroy the antibiotic, alter targets of the antibiotic and alter transfer of the antibiotic; thus preventing it from reaching its target.
Commensal
This normally means a microorganism that lives in close contact with a human or animal, doing neither harm nor good. Some of the bacteria covered in this website are commensals in one animal and pathogens in another. For example: Salmonella is a commensal in the intestine of an adult cow but a pathogen in the intestine of a human. Other bacteria such as the anaerobic bacteria of the rumen and colon can be beneficial to the host. Thus, we are using the term commensal rather loosely to mean bacteria that normally do not cause disease in their primary host.
Horizontal Gene Transfer
The transfer of one or more genes from one bacterium to another in a single process that can take as little as an hour to complete. This process has also been called bacterial sex. Bacteria are capable of transferring genes to or acquiring genes from bacteria of a different species or genus. Horizontal gene transfer allows bacteria to become resistant to antibiotics by acquiring DNA from a bacterium that already has acquired resistance to the antibiotic, rather than by sustaining a mutation to resistance - a long and hazardous process for a bacterium.
Non-clinical Bacteria or Non-clinical Isolates
Bacteria which are normally present in or on the bodies of humans or animals and seldom cause disease. These bacteria are also referred to as commensals. They also include bacteria from soil and water that do not normally cause disease. Sometime this definition is stretched because one animal's commensal can be another animal's disease-causing bacteria (pathogen). Thus, for example: Salmonella Typhimuyrium is a commensal in animals but causes disease in humans.
Reservoir of Resistance
A bacterium that has acquired resistance genes and has the capability of transferring them horizontally to other bacteria, especially human pathogens. A bacterium acts as a storage chamber or reservoir that keeps the resistance gene in the environment ready to be transferred to other bacteria.
Transmission of Antibiotic Resistant Pathogen DNA
The oft-expressed view that the main resistance problem arising from agricultural use of antibiotics is transmission of antibiotic-resistant zoonotic pathogens to humans far under estimates the complexity, magnitude and potential impacts of antibiotic use in agriculture. A far great danger is that antibiotic resistant bacteria from animals, whether pathogen or commensal, will be transmitted to humans through the food supply and will transfer resistant genes to human intestinal bacteria and through them to serious human pathogens. That is, the spread of genes is the problem, not just the spread of bacteria. Evidence is mounting that transfer of antibiotic resistant genes between bacteria normally found in the animal intestinal tract or in food and bacteria found in the human intestine occurs far more frequently than would have been expected from laboratory experiments. The direction of transfer is uncertain in most cases, but the fact that a genetic conduit of some sort is open between animal and human bacteria increases the possibility of resistance gene flow from animal bacteria to human bacteria via the food supply. The possibility of gene transfer should be considered seriously in any deliberations over safety issues. Another factor that has received insufficient attention is the stability of resistant genes in most hosts. Contrary to earlier beliefs, antibiotic resistant genes do not take a fitness toll in most cases. This is probably the case because under selective pressure, bacteria make genetic changes that improve the fit between a newly acquired resistant gene and its bacterial host. Resistant genes are not only easy to get, but also hard to lose (Salyers and Amabile-Cuevas, 1997.) Thus, the spread of a particular type of resistant gene may be difficult or impossible to reverse. It is of primary importance to prevent the spread of resistant genes in the first place.
CHISHOLM TRAIL LOFT
DEFINITIONS
DEFINITIONS
