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Ebook Antibacterial chemotherapy theory, problems, and practice: Part 2

Part 2 book "Antibacterial chemotherapy theory, problems, and practice" presentation of content: Sensitivity and identification tests, genetics of antibiotic resistance, multi-drug resistant (MDR) bacteria and healthcare-acquired infections, anti-mycobacterium therapy, clinical use of antibiotics to prevent or control resistance. | Chapter 4 Sensitivity and identification tests Key points - Sensitivity tests on live bacteria versus tests performed using just the bacterial DNA. - Determination of the ‘gold-standard’ for bacterial - sensitivity, the minimum inhibitory concentration (MIC) and recent introduction of the εtest. Bacterial breakpoints and how should they be set. The introduction of automated tests. The importance of National and International Guidelines. Why it is crucial to distinguish between surveillance and epidemiology and why surveillance usually overestimates the proportion of resistant bacteria in the population. In vitro tests are an invaluable guide in choosing therapy, although they cannot always predict in vivo responses accurately; however, if an organism is found to be resistant to an antibiotic in vitro it is most unlikely that normal therapeutic doses of that antibiotic will be of value in eliminating the infection. The tests can be based on either the phenotypic (based on the expression of specific characteristics of the cell) or the genotypic (based usually on the DNA complement) properties. Although the latter is currently gaining more attention, there remains a need for both. Phenotypic tests Traditionally, there have been two major methods for nonautomated sensitivity in the laboratory—dilution tests and disk tests. Dilution tests These are performed with doubling dilutions of antibiotic solution in the bacterial culture medium. Tube dilution tests use a liquid culture medium; a known concentration of the drug is diluted in a series of doubling dilutions so that the range of concentrations of antibiotic 29 Sensitivity and identification tests CHAPTER 4 30 obtained will cover the likely bactericidal and bacteriostatic levels of that antibiotic for the organism under test. Each tube is then seeded with a standard number of organisms and the tubes are incubated, usually overnight at 37oC. Control series of tubes should also be set up with standard .