Detection of antibiotic resistance in vitro

Testing the susceptibility of bacteria to antimicrobial agents is fundament al to the study of resistance. The qualitative methods that were originally devised evolved separately in different countries and as the need for more precise quantitative information became clear, different solutions to the problem emerged. Consequently. the methods now recommended vary widely betw een countries acid achieving a consensus on standardisation has proved diff icult. Sensitivity testing serves two purposes to provide meaningful result s to the prescriber and to monitor changes in susceptibility of microbial p opulations. The diagnostic purpose is adequately served by the diversity of methods used, provided they are performed and controlled efficiently. High ly standardised methods are however needed for surveillance in the national and international context and to provide meaningful comparisons to be made between individual centres. These needs are best met by the use of agreed methods and interpretative criteria in sentinel laboratories. No sensitivit y test method can provide the 'correct' answer all the time, if only becaus e the 'correct' answer in therapeutic terms is wt known with ally certainty . Laboratories providing a sensitivity testing service can influence prescr ibing and hence the development of resistance - in a number of different wa ys and the quest for standardisation at all costs should not obscure these important functions. (C) 2000 Elsevier Science B.V. and International Socie ty of Chemotherapy. All rights reserved.