Agglutinating Sera

AGGLUTINATING SERA, sera of various animals, capable of causing agglutination reactions (see Agglutination). They are obtained by parenteral administration of bacterial cultures to animals. The serum of an animal treated in this way undergoes agglutination reaction specifically with the type of microbe with which the animal was treated, and does not react (or reacts very weakly) with other related species. This property of A. s. allows one to determine the affiliation of a particular microbe to a given species. During an infectious disease, just as during immunization, the microbe acts on the body, which is why the serum of a patient also acquires agglutinating properties. Using this, it is possible to determine the nature of the infection by testing the agglutinating action of the serum of a suspected patient on a known type of microbe whose participation as the causative agent is suspected in this infectious process. A. s. can be of different strengths and act in different dilutions. The minimum amount of serum at which its action can still be detected is called the serum titer. The titer of sera obtained by artificial immunization is usually significantly higher than the titer of sera from patients. The former is measured in thousandths and ten-thousandths of a cubic cm of serum, while the titer of patient sera is only in tenths and hundredths of a cubic cm. To obtain A. s., rabbits are usually used, and among large animals - horses, donkeys, sheep, and goats. Rabbits are the most suitable animals for this purpose, since the serum of normal rabbits shows very weak agglutinating properties, and in the sera of immunized rabbits, phenomena of group agglutination are expressed much less than in horse serum and sera of other animals. Immunization to obtain A. s. can be carried out with both living and dead cultures. The dosage during immunization depends on the type of microbe and the individual properties of the culture taken. When setting up the agglutination reaction for diagnostic purposes, it is necessary to take into account that 1) there exist cultures that easily precipitate from suspension on their own (spontaneous agglutination) and 2) that immune serum, acting especially energetically on its specific microbe, is often able to agglutinate related species of microbes (group agglutination). Therefore, to avoid errors in evaluating the results of the agglutination reaction, it is necessary to ensure the absence of spontaneous agglutination in the cultures used in the experiment by setting up a control, which is a suspension of the given culture in a physiological saline solution (0.85% NaCl) without the addition of A. s. In group agglutination, the microbe specific to the serum being tested will reveal itself by agglutinating in a significantly higher titer than related species of microbes. In addition, there is a special method called the Castellani test, which allows distinguishing the causative microbe from related species and from microbes of secondary or mixed infections using the agglutination reaction. The Castellani test is based on the fact that if an excessive amount of culture is introduced into A. s., the serum completely loses its agglutinating properties in the case when the culture taken for testing is specific for this serum. If the culture introduced into the test belongs to a related species of microbes or to microbes of mixed and secondary infections, it is unable to completely exhaust the agglutinating properties of the serum with respect to the causative microbe of the main infection and specific to this serum. * Not all microbes give equally good A. s. The best and therefore firmly established in laboratory practice are typhoid, paratyphoid, cholera, and dysentery sera, alongside which plague serum, serum for the Malta micrococcus, and others are also used.