What Is Diagnostic Microbiology?

In order to obtain accurate microbiological diagnosis results, the disease material must first be collected correctly. The disease material can only be taken from animals that are dying or within a few hours of death, so that the disease material is fresh. It should be performed according to the requirements of aseptic operation. Strict disinfection can be used to determine the type of collected disease materials based on the items suspected of being diagnosed or differentially diagnosed for several diseases suspected in the preliminary clinical diagnosis.

Diagnostic microbiology

Author: Connie R. Mahon with Publisher: Oversea Publishing House
Publication year: 2006-09-01
Pages: 1211
Price: 694

Testing for HIV Infected Persons

The microbiological diagnosis of gas gangrene and human food poisoning caused by this type A of bacteria mainly depends on the isolation and identification of bacteria. The various diseases caused by other types are caused by bacteria producing toxins in the intestine. The bacteria do not necessarily invade the human body. At the same time, this bacteria is often present in the normal intestinal tract of humans and animals, and it is easy to kill animals other than the bacteria. It was infected by this bacteria after death. Therefore, the detection of the bacteria from the disease material does not indicate that it is the pathogen. Therefore, the bacteriological examination has certain reference significance only when the virulent bacteria is isolated. The main points for the identification of the bacteria are: anaerobic growth, neat colony, fast growth, Gram-positive crude bacilli, no movement, double-layer hemolytic ring, causing violent fermentation of milk, breast muscle injection pigeons die late, breast muscle smears can be seen Capsule bacterial cells.

An effective method of microbiological diagnosis is a test for intestinal contents of toxins. The method is to take the contents of the ileum. If the collected amount is not enough, the contents of the back of the jejunum or the front of the colon can be taken, diluted with an appropriate amount of sterilized physiological saline, and the supernatant is divided into two after centrifugal precipitation, and one is not heated. , One portion is heated (60 ° C for 30min), and rabbits (1 to 3m1) or mice (0.1 to 0.3m1) are injected intravenously. If toxins are present, animals in the non-heated group often die within minutes to ten hours, while animals in the heated group do not die.

To determine the types of toxins and their bacterial types in lethal animals, further tests for toxin neutralization and protection are required. The method is to divide the aforementioned supernatant into 6 parts, respectively add appropriate amounts of various antitoxins and physiological saline (control) of the bacteria, mix them for 40 minutes at 37 ° C, and then intravenously inject a group of mice or rabbits. Observe for 24 hours, record the death and survival of each group of animals, and determine the bacterial type according to Table 22-7. Due to type B and type D toxin E and type E. Toxins are precursors of toxins, and only show virulence after being activated by trypsin. Therefore, without trypsin treatment, type A serum can also protect type D and E toxins, type B serum can protect type E toxins, and type C serum can protect type B, D, and E toxins. However, after the trypsin treatment, the neutralization test may be destroyed or partially destroyed due to toxin and toxin, and the experimental results may sometimes be inaccurate. ^[2]

Collect sick materials

For accurate microbiological diagnosis, disease materials must be collected correctly first. Disease materials can only be taken from poultry that are dying or within a few hours of death, so that the disease materials are fresh and should be performed according to the requirements of aseptic operation. Strict disinfection can be used to determine the type of collected disease materials based on the items suspected of being diagnosed or differentially diagnosed for several diseases suspected in the preliminary clinical diagnosis. The more easily taken disease materials are blood, liver, spleen, lung, kidney, brain, ascites, pericardial fluid, synovial fluid, etc.

Smear microscopy

A small number of infectious diseases, such as aspergillosis, can be confirmed by collecting the material directly and smearing for microscopy.

Isolation, cultivation and identification of pathogens

The pathogen can be isolated from the disease by artificial culture. Bacteria, fungi, molds and viruses need to be separated and cultured by different methods, such as using ordinary media, special media, cells, avian embryos and sensitive animals. The isolated pathogens also need to be identified in morphology, physicochemical properties, virulence and immunology to determine the species and serotype of the pathogen.

Animal vaccination test

For some poultry diseases that have obvious clinical symptoms or pathological changes, the diseased material can be treated appropriately to inoculate sensitive animals of the same species or animals that are most sensitive to suspected diseases. Symptoms, mortality, and pathological changes after inoculation are compared with the original disease. As evidence for diagnosis, disease materials can be collected from dead and dead poultry if necessary, and smear microscopy and separation and identification are performed. The more commonly used experimental animals are chickens, geese, ducks, rabbits, mice, etc.

Immunological diagnosis

According to the principle of the specific reaction between antigen and antibody, unknown antibodies can be detected with known antigens, and unknown antigens can also be detected with known antibodies. At present, hemagglutination test and hemagglutination inhibition test, precipitation test, Neutralization test, cytolysis test, complement binding test, immunoenzyme technology, immunofluorescence technology, and radioimmunity, etc., can be tested on certain items as needed and possible. ^[3]