Search

A bacterium cannot be clinically categorized as susceptible to an antibiotic in one hospital or country and resistant in another. The need for standardization of in vitro antibiotic susceptibility tests (the antibiogramme) appeared very soon, in the early 1950s. The World Health Organization convened in Geneva a first Expert Committee on Antibiotics in 1959 and a second in 1961 (WHO Technical Report Series 1959 No. 710 and 1961 No. 210). It immediately appeared that the Committee had to work in two fields: the methods and the interpretation of the data. However, it was also clear that the need for reference methods was a priority. In fact, the efforts devoted to define all the details of a reference method at WHO meetings and later were continuous until 1970. The problem of the clinical interpretation (determination of the breakpoints) seemed too controversial at the international level, and the second WHO Committee suggested that this area should be the concern of a ‘National Authority’. Consequently, the role of a National Committee is mainly in the field of interpretation. Nevertheless, in the past 20 years an important number of new techniques, devices and machines (more or less automated) have been proposed to simplify and accelerate the work of clinical laboratories. All these approaches cannot be accepted without a control. A national network of medical microbiology laboratories specializing in antibiotic evaluation has to play a role in this control under the supervision of a National Reference Center for Antibiotics. Evaluation of a new technique is not always easy. Some methods provide values that can be directly compared with the MIC determined by the reference methods defined at the international level. However, many others, automated or not, are intended to directly characterize clinically the strains studied. In certain instances, it is possible, using the basic principle of the proposed new technique, to perform a quantitative study in an attempt to correlate its results with those of the reference method. When this is not possible, the study of reference strains from the National Reference Center may provide a good approximation to decide if the technique is valuable or not, or has to be adjusted. Many of these evaluations can be performed in agreement with the manufacturer, who provides supplementary information and materials. The results are often confidential or not sufficient to justify a scientific publication. Since the clinical laboratories of a country need to be informed of the exact value of a new technique, the role of the National Committee is important in discussion and in informing all the medical microbiology laboratories. Such a Committee is even worthwhile for the adequate use of the new methods nationwide. As already pointed out, the major role of a National Committee is to decide on values of the breakpoints that delineate the clinical categories. The subject is controversial, as pointed out by Garrod at the first W H O meeting, because of the two definitions of resistance. The first is related to the pharmacologic data on the antibiotic concentrations achieved at the site of infection. The second is related to genetic alterations of the bacteria which, consequently, allow growth in the presence of an antibiotic concentration higher than that inhibiting the so-called susceptible bacteria. This latter notion has been exemplified since 1947 by the p-lactamase-producing strains of staphylococci. Depending on the relative importance attributed to one or the other factor, the value of the breakpoint relies heavily on judgment and experience. It is important to specify the various factors that have to be taken into account at a national level to adopt a particular breakpoint. All antibiotics are not widely used at the same time in all countries, in particular the recent molecules. The need for breakpoints is especially urgent when a new drug appears on the market. The breakpoints cannot be selected irrespective of those already chosen for the other members of the antibiotic family. A National Committee has to balance the intrinsic activity and the pharmacology of the new drug comparatively with the other members of the same family. Under certain circumstances, a particular