The evolution of in-vitro antimicrobial susceptibility techniques.

(1988). Host range of conjugative 25-2-Megadalton tetracydine resistance plasmid from Neisseria gonorrhoeae and related species.resistant Mycoplasma homlnls strains contain streptococcal tetM sequences. (1988). telM-and 0-lactamse-contaming Neuseria gonorrhoeae (tetracydine resistant and penicillanie producing) in The Netherlands. Spread of Neisseria gonorrhoeae resistant to tetra-cydine outside the United States of America. Antimicrobial susceptibility testing (AST) is performed by laboratories every day on clinical isolates often with new antimicrobial agents. The techniques employed are often taken for granted and are frequently abused. This review traces the evolution of the generally used routine methods. The first recorded observations of antibiosis in vitro were made by van Leeuwenhoek in 1676 (Balows, 1974). At a presentation to the Royal Society of London he described how his 'living animalcules' disappeared after he placed them in some 'pepper water'. Agar diffusion methods were first utilized by Beijerinck in 1889 (Dufrenoy, 1947), for studying the effect of different auxins on bacterial growth. They have only been generally used for AST following the discovery of penicillin, and varying diffusion sources of the antibacterial agent have been used. These include the 'ditch' plate (Fleming, 1924); cutting wells into the agar (Reddish, 1929); and the cylinder-plate synonymous with 'Oxford cup', 'fish spine', or 'Heatley cup' (Abraham et al., 1941). The use of absorbent paper as a means of carrying antibacterial solutions was first suggested by Pope in 1940 (Heatley, 1944). Filter paper discs incorporating penicillin were utilized by Vincent & Vincent (1944) for assaying this newly discovered compound. Mohs (1945) described a 'radial streak' technique with 15-mm diameter discs and interpretation of results for the first time was judged by comparison with a sensitive control. Further paper disc diffusion methods were (1947) described a technique using tablets incorporating penicillin instead of impregnated filter paper. The filter paper disc that is commonly utilized today has a diameter of 6-5 mm, and was first described by Bondi et al. (1947). It was soon apparent to the early groups describing diffusion methods, that there was a need for standardization of methodology. This was achieved for single disc diffusion techniques by Bauer, Kirby and colleagues (Bauer etal., 1966) in the USA. The Bauer-Kirby method provided important advances in methodological standardization and zone diameter interpretation against a quantitative minimum inhibitory concentration (MIC) value. Earlier, workers in the UK had recognized the need for standardized susceptibility techniques (Gould & Bowie, 1952). Gould & Bowie devised a disc diffusion technique …