Discs carrying 10-fold serial dilutions of antibiotic are placed on a lawn of bacteria to find the lowest concentration that will inhibit growth of the bacteria. bacterial growth appeared up the edge of the first (1/10) and second dilution disc (1/100), but a 20-mm zone of clearance appeared around the third dilution disc (1/1,000). if resistance is defined as no zone of clearance, what is the resistance titer of the antibiotic for this organism?

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.