| Popis: |
Resistance to antibiotics is an increasing problem in the developing world. Resistance genes in the normal gut flora may act as a reservoir from which pathogens may acquire resistance. Trimethoprim is an important drug in the treatment of a wide range of infections but resistance has increased in recent years particularly in the developing world. A survey was conducted in Vellore, south India, to determine the rate of carriage of antibiotic resistant enterobacteria in the normal gut flora of a sample of the population. Very high rates of resistance were encountered to the widely used antimicrobials, ampicillin, chloramphenicol and trimethoprim. The trimethoprim resistant strains were analyzed further, 35% were capable of plasmid-mediated transfer of trimethoprim resistance by different plasmids types, as identified by restriction endonuclease digestion. Resistance to a variety of other agents was co-transferred. Transferable trimethoprim resistance was shown, by DNA hybridization, to result from the presence of three different drug resistant dihydrofolate reductase (dhfr) genes. The dhfrV was present in 50&37 of transconjugants, associated with either the transposon Tn21 or only with the integrase-like open reading frame (orf) of this transposon; 31% possessed the dhfrI, associated with the integrase orf of Tn7 and 19% had dhfrIV. The dihydrofolate reductase (DHFR) enzyme type IV has only ever been identified in this area of India, in 1984. The enzyme mediates only low level resistance, as measured by conventional tests, but it is inducible, a unique property in the DHFRs. It has persisted in this area despite a seemingly poor resistance mechanism. The DHFR type IV enzymes characterized during this survey were also inducible. |
