Methods And Methods Of Antibiotic Sensitivity Testing

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Describe briefly how antibiotic sensitivity testing is carried out in the clinical laboratory providing examples of both manual methods and automated methods (include advantages and disadvantages of methods discussed) Introduction An antibiotic is a chemical produced by a microorganism that kills or inhibits the growth of another microorganism. Therefore, the big task of microbiology laboratory is to determine how effective an antibiotic is through antimicrobial susceptibility testing of bacterial isolates. Bacterial resistance to the antibiotics can be natural or acquired. For instance, pseudomonas species, staphylococcus species, streptococcus pneumonia and members of the Enterobacteriaceae acquire a certain resistance mechanism.…show more content…
(Ataee, 2012). The important fact that needs to be kept in mind is that the effect of antibiotics is studied only IN VITRO and usually under standardised conditions. Broth Dilution Methods It is a method of diluting a stock solution where concentration decreases by the same quantity in each successive step. The method requires preparing two-fold dilutions of antibiotics in a liquid growth medium distributes in test tubes. A standardized bacterial suspension of 1–5 x 105 CFU/mL is introduced into the tubes which contained the antibiotic. After incubation at 35°C, the visible bacterial growth is checked through the tubes’ turbidity. Consequently, the lowest concentration of the antibiotic that will inhibit the growth is registered as the minimal inhibitory concentration (MIC). (Jorgensen, Ferraro 2009) This method has become popular due to the miniaturization and mechanisation of the test. The use of small, disposable, plastic microdilution trays generates an economy of reagents used. A standard tray contains 96 wells, each containing a volume of 0.1mL. On the other hand, macrodilution method use broth volumes of about 1.0ml. Approximately 12 antibiotics can be tested in a range of 8 two- fold dilutions in a single tray. The disadvantage of the broth dilution test is the repetitious manual job which is to prepare serial dilutions of the antibiotics for each test, the huge amount of reagents required for each test and
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