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close this bookBasic Laboratory Procedures in Clinical Bacteriology (WHO; 1991; 128 pages)
View the documentPreface
View the documentIntroduction
open this folder and view contentsQuality assurance in microbiology
close this folderPart I. Bacteriological investigations
open this folder and view contentsBlood
open this folder and view contentsCerebrospinal fluid
open this folder and view contentsUrine
open this folder and view contentsStool
open this folder and view contentsLower respiratory tract infections
open this folder and view contentsUpper respiratory tract infections
open this folder and view contentsSexually transmitted diseases
open this folder and view contentsPurulent exudates, wounds, and abscesses
open this folder and view contentsAnaerobic bacteriology
close this folderAntimicrobial susceptibility testing
View the documentIntroduction
View the documentGeneral principles of antimicrobial susceptibility testing
View the documentClinical definition of terms “resistant” and “susceptible”: the three-category system
View the documentIndications for routine susceptibility tests
View the documentChoice of drugs for routine susceptibility tests in the clinical laboratory
View the documentThe modified Kirby-Bauer method
View the documentDirect versus indirect susceptibility tests
View the documentTechnical factors influencing the size of the zone in the disc diffusion method
View the documentQuality control
open this folder and view contentsPart II. Essential media and reagents for isolation and identification of clinical pathogens
View the documentSelected further reading
View the documentSelected WHO publications of related interest
View the documentBack Cover


At a meeting organized by WHO in Geneva in 1977,1 concern was expressed about the worldwide increase in antibiotic resistance associated with the growing, and frequently indiscriminate, use of antibiotics in both man and animals. In recent years, drug-resistant bacteria have given rise to several serious outbreaks of infection, with many deaths. This has led to a need for national and international surveillance programmes to monitor antibiotic resistance in bacteria by susceptibility testing using reliable methods that generate comparable data. The availability of microbiological and epidemiological information would help clinicians in selecting the most appropriate antimicrobial agent for the treatment of a microbial infection.

If predictions are to be valid, the susceptibility test must be performed by an accurate and reproducible method, the results of which should be directly applicable to the clinical situation. The ultimate criterion of the reliability of any susceptibility testing method is its correlation with the response of the patient to antimicrobial therapy.

The WHO meeting considered that the modified disc technique of Kirby-Bauer, for which requirements had been established by WHO in I976,2 could be recommended for clinical and surveillance purposes in view of its technical simplicity and reproducibility. The method is particularly suitable for use with bacteria belonging to the family Enterobacteriaceae, but it can also be recommended as a general purpose method for all rapidly growing pathogens, except strict anaerobes. It was therefore recommended that the details of this test be made available for laboratory workers.3


1 WHO Technical Report Series, No. 624, 1978 (Surveillance for the prevention and control of health hazards due to antibiotic-resistant enterobacteria: report of a WHO Meeting).

2 WHO Technical Report Series, No. 610, 1977 (Twenty-eighth report of the WHO Expert Committee on Biological Standardization), Annex 5.

3 A comparable method, based on the same principles and quality control requirements as the Kirby-Bauer method, is the NEO-SENSITABS method, produced by ROSCO Diagnostica, Taastrup, Denmark. This method uses 9-mm colour-coded, antibiotic tablets, instead of paper discs. The tablet form results in an extraordinary stability with a shelf-life of four years, even at room temperature. This increased stability is very important for laboratories in tropical countries.

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