 For a long time no transferable resistance gene to quinolones from one bacterium to another had been observed. This phenomenon has been demonstrated in 1998 in a bacterium of the Klebsiella pneumoniae species carrying a qnrA gene which encodes a protein that protects the target of the antibiotic in the bacteria. Since several genes have been observed. These genes reduce the sensitivity of the bacteria without ever reach detectable resistance levels on the tests commonly used in the laboratory. However, these genes are often found among enterobacteria in combination with other mechanisms of resistance to other classes of antibiotics including beta-lactam antibiotics that are widely used antibiotics. 