Question

3. (25 pts) Explain the phenomenon of drug resistance form the standpoint of microbial genetics (include a description of R factors). 4. (25 pts) a) Describe the two types of ELISA test. Be sure to include in your answer what immunological agent coats the wells of the plate and how the reaction between antibody and antigen can be measured. b) Explain which type of ELISA can be used to determine an individual's past exposure to a pathogen.

Answer 1

3. The drug resistance is developed by tolerating the mount of drug that would normally inhibit the growth of microrganism.Th development of resistance to antimicrobial drugs could be resulted due to genetic variation and adaptability of microbial populations.Drug resistance genes are often carried on plasmids or in transposons that can undergo vertical transfer easily and between microbes through horizontal gene tranfer.Problematic microbial strains showing extensive abtimicrobial resistance are emerging;many of these strain can reside as members of the normal microbiota in individual but also can cause opportunistic infection.The transmission of many of these highly resistant microbial strains often occur clinical settings,but can also community acquired.

4.a)

ELISA ,stand for enzyme-linked immnosorbent assay,is a very mature method for the detection of various targets.ELISA can be divided into four major types: direct,Indirect,sandwich and compititve.We discuss here direct and sandwich ELISA test.

Direct ELISA: in direct ELISA, only an enzyme - labeled primary antibody is used, meaning that secondary antibodies asre not needed.The enzyme -labeled primary antibody "directly" binds to the target(antigen) that is immobilized to the plate (solid surface).Next,the enzyme linked to the primary antibody reacts with its substrate to produce a visible signal that can be measured.In this way,the antigen of interest is detected.

Sandwich ELISA: In direct or indirect ELISA,it is the antigen that is immobilized to the plate.In sandwich ELISA,however, it is the antibody that is immobilized to the plate,and this antibody is called capture antibody.In addition to capture antibody, sandwich ELISA also involves the use of detection antibodies,which generally include the unlabeled primary detection antibody and the enzyme-labeled secondary detection antibody.Firstly,the antigen of interest binds to the capture antibody immobilized to the plate.Secondly,th primary detection antibody binds to the antigen.Thirdly,the secondly detection antibody binds to the primary detection antibody,and then the enzyme react with its substrate to produce a visible signal that can be measured.

b) Indirect ELISA used to determine the individual's past exposure to pathogen.