In this work we briefl y present the mechanisms of resistance to tetracyclines. Tetracycline’s were introduced in clinical practice in 1948, and are used for the therapy in human and veterinary medicine or as growth promoters in livestock industry. Th ere are three major mechanisms of resistance to tetracyclines. Gram negative bacteria utilize effl ux pump system of proteinaceous transporters in eliminating the drug from the cell. This mechanism of resistance is encoded by tet genes that belong to the group 1. Gram positive bacteria promote resistance to tetracyclines by producing soluble cytoplasmatic ribosomal protection proteins and the most frequent once are TetM and TetO proteins. Enzymatic inactivation is not widespread mechanism and the responsible gene is termed tetX. Epidemiological importance of tetracyclines is well documented in number of research papers. We described few works showing that tetracycline’s are provoking resistance to other classes of antibiotics or vice versa. Th is phenomenon is probably due to the fact that resistance determinants are oft en situated on mobile genetic elements. Withdrawal of the therapy does not exclude resistance in short time frame due to the various environmental factors and animal feeding habits. Most oft en resistance to tetracycline is reported in Escherichia coli isolates from pigs, chickens and turkeys. The TetM and TetK proteins are most oft en found in methicillin resistant Staphylococcus aureus.
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