THEORETICAL AND PRACTICAL REGARDS OF ANTIBIOTIC-SENSITIVITY TESTS CARRIED OUT ACCORDING TO THE RECOMMENDATION OF NCCLS

The authors divided into groups the active ingredients of drugs used f or veterinary purposes on the basis of their mechanism of action, disc ussing and indicating which resistances are indicative of resistances against some or all components of the group. They describe the three b asic types of the mechanism of resistance known at the present accordi ng to which the bacteria can prevent the attack of antibiotics: I. At the target site of the drug the configuration of the bacterial protein s alters (alteration of receptors) II. Because of the selective permea bility of the external and internal membranes the active ingredients n o not reach the target site(the most types of natural resistances are based on this mechanism) or in case they reach it, the proteins synthe tised by the bacteria remove them, preventing the development of the e ffective concentration. III. The bacteria synthetise enzymes which inh ibit the antibiotics used against them. To minimise the emergence of r esistance the antibiotics should be used following the necessary consi deration and only when it is reasonable and in an appropriate dose. It is possible to prevent the development of resistance or delay the eme rgence of it in the following ways: I. Application of appropriate comb ination of antibiotics. II. Alteration of the chemical structure of th e active ingredients in a direction which allows them to resist the en zymes synthetised by the bacteria against them. They present disk-sets arranged by taking into account the mechanism of natural, acquired an d cross resistance. During the selection they took into account as wel l the species of the animals for which the drug containing the active ingredient in question can be administered. During the tests and givin g the results the name of the active ingredient of the antibiotic is u sed, fantasy name is used only in case when there is reliable disk of the combination in question. The susceptibility tests are carried out using standard disk-diffusion method processed and recommended by NCCL S, which assures that the susceptibility tests, carried out anywhere a nd repeatedly, give exact, reliable and identical results. The NCCLS g ives to the method adequate zone-diameters indicating the susceptibili ty.