Principles of diagnosis of infectious diseases

===Lecture Details===
Priscilla Johanesen; Week 11 MED1011; Microbiology
===Lecture Content===
Transport as quickly as possible, in transport media, at correct temperature, remember anaerobes (thioglycollate). Microscopy can be used for wet mount, staining, culture, molecular diagnosis and serology can be used. Indian ink and dark field microscopy is used for direct examination. 
Gram positive organsisms are Staph aureus, bacillus anthracis. Gram negative are Neisseria gonorrhoeae, pus cells, E coli, Vibrio cholerae. Flourescent dye can be used for Chlamydia. Acid-fast stain is used for TB. Microscopy is good for pre-culture diagnosis, is fast.
Culture is used for bacteria, fungi and viruses. Growth conditions are important for bacteria (temperature, atmosphere). There are many media types. Viral culture requires living cells. Advantages of culture are live organisms, isolation from normal flora, cultured from almost any site, many types of microorganisms. Disadvantages are maintaining viability, time taken (hours to days for bacteria, days to weeks for viruses).
Molecular diagnosis can be done with DNA, RNA or proteins, electrophoretic analysis, nucleic acid probes, PCR or real time PCR. Advantages are detection from any specimen or culture, no strict transport, allows gene analysis, identification of one or more organisms from sample, fast and more sensitive than many other techniques. Disadvantages are expense, highly trained personnel, cost, contamination problems, lab space, no distinction between viable and non-viable organisms.
Serologic analysis where pathogen culture is difficult, can be identified from host response and antigen-antibody reactions. Concerned with antibody-antigen reactions in vitro. Agglutination, precipitation, complement fixation, immunofluorescence and ELISA are used.
ELISA can have double antibody sandwich assay to detect antigens or indirect immunosorbent assay to detect antibodies. Sandwich detects antigen by having antibody plate, antigen binds, flourescent antibody sandwiches. Direct has antigen on plate, antibody binds and second enzyme antibody is added, product proportional to primary antibody.
Antibiotic susceptibility can be tested.
===Readings===
====Mims Ch 32====