Editing Infection (section)

===Biochemical tests===
Biochemical tests used in the identification of infectious agents include the detection of [[metabolic]] or [[enzymatic]] products characteristic of a particular infectious agent. Since bacteria ferment [[carbohydrate]]s in patterns characteristic of their [[genus]] and [[species]], the detection of [[Fermentation (biochemistry)|fermentation]] products is commonly used in bacterial identification. [[Acids]], [[alcohols]] and [[gases]] are usually detected in these tests when bacteria are grown in [[Growth medium#Selective media|selective]] liquid or solid media.<ref>{{Cite journal |last1=Flint |first1=Harry J. |last2=Scott |first2=Karen P. |last3=Duncan |first3=Sylvia H. |last4=Louis |first4=Petra |last5=Forano |first5=Evelyne |date=2012-07-01 |title=Microbial degradation of complex carbohydrates in the gut |journal=Gut Microbes |volume=3 |issue=4 |pages=289–306 |doi=10.4161/gmic.19897 |issn=1949-0976 |pmc=3463488 |pmid=22572875}}</ref>

The isolation of [[enzymes]] from infected tissue can also provide the basis of a biochemical diagnosis of an infectious disease. For example, humans can make neither [[RNA replicase]]s nor [[reverse transcriptase]], and the presence of these enzymes are characteristic., of specific types of viral infections. The ability of the viral protein [[hemagglutinin]] to bind [[red blood cells]] together into a detectable matrix may also be characterized as a biochemical test for viral infection, although strictly speaking hemagglutinin is not an ''enzyme'' and has no metabolic function.<ref>{{Cite journal |last1=Makkoch |first1=Jarika |last2=Prachayangprecha |first2=Slinporn |last3=Payungporn |first3=Sunchai |last4=Chieochansin |first4=Thaweesak |last5=Songserm |first5=Thaweesak |last6=Amonsin |first6=Alongkorn |last7=Poovorawan |first7=Yong |date=2012 |title=Erythrocyte Binding Preference of Human Pandemic Influenza Virus A and Its Effect on Antibody Response Detection |journal=Annals of Laboratory Medicine |volume=32 |issue=4 |pages=276–282 |doi=10.3343/alm.2012.32.4.276 |issn=2234-3806 |pmc=3384809 |pmid=22779069}}</ref>

[[Serological]] methods are highly sensitive, specific and often extremely rapid tests used to identify microorganisms. These tests are based upon the ability of an antibody to bind specifically to an antigen. The antigen, usually a protein or carbohydrate made by an infectious agent, is bound by the antibody. This binding then sets off a chain of events that can be visibly obvious in various ways, dependent upon the test. For example, "[[Strep throat]]" is often diagnosed within minutes, and is based on the appearance of antigens made by the causative agent, ''[[S. pyogenes]]'', that is retrieved from a patient's throat with a cotton swab. Serological tests, if available, are usually the preferred route of identification, however the tests are costly to develop and the reagents used in the test often require [[refrigeration]]. Some serological methods are extremely costly, although when commonly used, such as with the "strep test", they can be inexpensive.<ref name=Sherris/>

Complex serological techniques have been developed into what are known as [[immunoassays]]. Immunoassays can use the basic antibody – antigen binding as the basis to produce an electro-magnetic or particle radiation signal, which can be detected by some form of instrumentation. Signal of unknowns can be compared to that of standards allowing quantitation of the target antigen. To aid in the diagnosis of infectious diseases, immunoassays can detect or measure antigens from either infectious agents or proteins generated by an infected organism in response to a foreign agent. For example, immunoassay A may detect the presence of a surface protein from a virus particle. Immunoassay B on the other hand may detect or measure antibodies produced by an organism's immune system that are made to neutralize and allow the destruction of the virus.

Instrumentation can be used to read extremely small signals created by secondary reactions linked to the antibody – antigen binding. Instrumentation can control sampling, reagent use, reaction times, signal detection, calculation of results, and data management to yield a cost-effective automated process for diagnosis of infectious disease.