ABSTRACT
Resistance to antibiotics may be due to production of specific inactivating enzymes, modification of the cell surface to change the permeability, or to modification of the target. The mechanisms of resistance depend on the site of inhibition and type of resistance and may be specific, as in altered deoxyribonucleic acid gyrase produced by quinolone resistance mutants, or general as in changes in outer-membrane porins which decrease uptake of range of unrelated drugs. In hospital infection control, surveillance of drug resistance markers coupled with plasmid typing may provide a simple epidemiological tool which is applicable to range of organisms in a situation where spread of plasmid-determined resistance between organisms may be highly relevant. In some clinical situations the minimum bactericidal concentration is more relevant. The essential concept of the minimal inhibitory concentration is to expose a standard bacterial inoculum to an increasing dose of antibiotic in order to determine the minimum concentration at which bacterial growth is inhibited.
