Resistance to antibiotics in the normal flora of animals

The normal bacterial flora contains antibiotic resistance genes to various degrees, even in individuals with no history of exposure to commercially pr epared antibiotics. Several factors seem to increase the number of antibiot ic-resistant bacteria in feces. One important factor is the exposure of the intestinal flora to antibacterial drugs. Antibiotics used as feed additive s seem to play an important role in the development of antibiotic resistanc e in normal flora bacteria. The use of avoparcin as a feed additive has dem onstrated that an antibiotic considered "safe" is responsible for increased levels of antibiotic resistance in the normal flora enterococci of animals fed with avoparcin and possibly in humans consuming products from these an imals. However, other factors like stress from temperature, crowding, and m anagement also seem to contribute to the occurrence of antibiotic resistanc e in normal flora bacteria. The normal flora of animals has been studied wi th respect to the development of antibiotic resistance over four decades, b ut there are few studies with the intestinal flora as the main focus. The r esults of earlier studies are valuable when focused against the recent unde rstanding of mobile genetics responsible for bacterial antibiotic resistanc e. New studies should be undertaken to assess whether the development of an tibiotic resistance in the normal flora is directly linked to the dramatic increase in antibiotic resistance of bacterial pathogens. Bacteria of the n ormal flora, often disregarded scientifically, should be studied with the i ntention of using them as active protection against infectious diseases and thereby contributing to the overall reduction of use of antibiotics in bot h animals and humans.