Bacterial resistance to antimicrobial agents, also known as drug resistance.

1. Intrinsic resistance: It is the resistance determined by bacterial chromosome genes and passed down from generation to generation, such as the resistance of Enterobacter to penicillin.

2. Acquired drug resistance: refers to the decrease or disappearance of the sensitivity of bacteria to drugs after repeated contact with drugs. Most of them are mediated by plasmids, but they can also be mediated by chromosomes. The former has more clinical significance. For example, the resistance of Staphylococcus aureus to penicillin.

Note: Drug resistance: pathogens and tumor cells are less sensitive to drugs.

Tolerance: the human body's sensitivity to drugs is reduced.

(B) the mechanism of drug resistance

1. Inactivated enzyme production

Hydrolase: such as β -lactamase can open the β -lactam ring in the molecular structure of penicillins and cephalosporins and make the drugs ineffective;

Synthase (passivating enzyme): such as acetylation enzyme, phosphorylase, nucleotidase, etc. The corresponding chemical groups can be combined with drug molecules to inactivate drugs.

2. Change the target of drug action

① Drug-resistant bacteria can change the structure of target protein, so that drugs can not be combined with target protein, such as rifamycin resistance of bacteria;

② Increase the number of target proteins, such as MRSA resistant to methicillin.

③ New target protein with low affinity to antibiotics was produced, and methicillin-resistant Staphylococcus aureus was resistant to β-lactams.

3. Reduce the permeability of cell membrane

The change of bacterial outer membrane structure and pore protein configuration makes it difficult for drugs to penetrate into bacteria. Such as the resistance mechanism of bacteria to β -lactam antibiotics, tetracycline and chloramphenicol.

4. Active pump function

Some drug-resistant bacteria have active transport pumps, which can pump drugs into bacteria out of the body, which is one of the important mechanisms of acquired drug resistance.

5. Bacteria change metabolic pathways

If bacteria are resistant to sulfonamides, they can produce dihydrofolate by producing a large amount of p-aminobenzoic acid (paba) or directly using folic acid.