Qualitative, Quantitative and Semi-quantitative Testing in Microbiology

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In microbiology different tests are performed like Microbial limit tests (MLT), Sterility, Bacterial endotoxin testing (BET) and LBPC etc. In these tests some are qualitative, some are quantitative and some are semi quantitative tests.

Qualitative tests: Qualitative tests are those tests in which results are only given in form or either pass or fail or present or absent. In these type of tests results are not given in form of counting or calculations. Sterility test is one of example of qualitative test because in sterility test, results would be either pass or fail. In sterility testing we could check either contamination is present or absent in the sample.

Quantitative tests: Quantitative tests are those tests in which results are given in form of counting or calculations. MLT is one of the example of quantitative test in which results are given in form of number of cfu’s for total aerobic microbial count or total yeast and mold count. But when we perform pathogen testing in MLT, that pathogen identification part is qualitative testing because in pathogen testing we couldn’t determine number of cfu’s of pathogens but we give the results in form of pass or fail whether pathogens are present or absent. Colony counting is another example of quantitative testing in which results are given in form of number of cfu’s.

Semi quantitative tests: BET is one of the example of semi-quantitative test. In BET if it is performed by gel clot method then it is semi quantitative because by this method we could either give results in form of less than or greater than the specified limits. For example if product A is having BET limit of not more than 0.20 EU/mg then results would be either less than 0.20 EU/mg or greater than 0.20 EU/mg. In this, less than 0.20 EU/mg would be pass result and more than 0.20 EU/mg would be fail result. That’s why it is called semi quantitative test. But now a days different advance methods are being used for BET in which actual level of endotoxin in the product  could be determined very easily. If BET is performed by these advance methods then exact level of endotoxin could be determined in the products hence it would be included in quantitative tests.

In simple language if I ask you Do you have oranges? Your answer would be either yes or no this is called qualitative and if I ask how many oranges you have? then your answer would be either 1,2,3,4…. that could be any number, this is called quantitative. But if I ask you whether you have less than or more than 5 oranges then your answer would be either less then 5 oranges or more than 5 oranges, then this is called semi quantitative.

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