ANTIBIOTIC SUSCEPTIBILITY TESTING. Bacteria demonstrate two kinds of resistance to antibiotics, namely intrinsic resistance and acquired resistance. Intrinsic resistance means that the species was resistant to an antibiotic even before its introduction.
Radiation is naturally present in our environment, as it has been since before the birth of this planet. In addition, radiation can be produced artificially, as in medical x-rays and microwaves for cooking. Nonetheless, most people are not aware of all the natural and man-made sources of radiation in our environment.
Methane is released into the atmosphere by both natural and anthropogenic sources. It is released in low oxygen environments such as swamps and bogs and through the roots of some plants. Anthropogenic sources have increased methane emissions through increased use of natural gas and through mining.