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.
Natural sources of background radiation include: 1  Cosmic rays-radiation that reaches the Earth from space. 2  Rocks and soil-some rocks are radioactive and give off radioactive radon gas.atural sources. Natural sources of background radiation include: 1  Cosmic rays-radiation that reaches the Earth from space. 2  Rocks and soil-some rocks are radioactive and give off radioactive radon gas. 3  Living things-plants absorb radioactive materials from the soil and these pass up the food chain.