Agarose gel electrophoresis of fifteen drug-resistant genes for Citrobacter freundii. M: DL2000 maker, 1: blaTEM, 2: blaPER, 3: blaCTX, 4: blaSHV, 5: blaDHA, 6: blaACC, 7: blaFOX, 8: qepA, 9: blaEBC, 10: qnrA, 11: qnrC, 12: TetA, 13: TetB, 14 TetC, 15: TetG.