In this chapter we will discuss the classification of bacteria, some of the more common pathogens, and the preparation, staining, and examination of specimens. Also included are basic serologic tests, such as the rapid plasma reagin (RPR) card test for syphilis and the Monosticon slide test for infectious mononucleosis, the potassium hydroxide (KOH) preparation for the identification of fungi, and the principles and procedures for blood grouping and typing.
Bacteria are prokaryotic microorganisms of the kingdom Protista. They reproduce asexually by transverse binary fission in which the cell divides into two new cells. They are found almost everywhere, with the human body harboring vast numbers. Many bacteria are beneficial and essential to human life, only a few are harmful to man.
Since there are thousands of different bacteria, a method of classification is essential. Bacteria are classified according to their (1) disease-producing ability, (2) growth requirements, (3) morphologic characteristics, (4) colonial morphology, (5) biochemical activity, (6) toxins, and (7) Grams stain reaction.
The disease producing ability is termed as either pathogenic or nonpathogenic. Pathogens are bacteria that cause diseases and nonpathogens are the harmless bacteria. Many bacteria that are essential to our body are called common or normal flora in their proper environment. For example, alpha streptococcus in the throat is common flora, but when it is found elsewhere, such as in the blood stream, possibly as a result of tooth extraction, it may cause septicemia and endocarditis.
The four growth requirements are (1) temperature, (2) oxygen, (3) nutrition, and (4) moisture. Temperature requirements are divided into three categories.
The oxygen requirements vary according to the amount of oxygen needed for an organism to grow or reproduce. Aerobes are those organisms that reproduce in the presence of oxygen. Obligate aerobes are those that grow only in the presence of free oxygen. Anaerobes are organisms that do not reproduce in the presence of oxygen, and obligate anaerobes are those that grow only in the absence of free oxygen and are killed if exposed to free oxygen. Facultative organisms are those that grow both in the presence of free oxygen and in an oxygen-free atmosphere. Microaerophilic organisms are those that grow only in reduced amounts of free oxygen.
Nutritionally, different bacteria require different foods that their particular environment must provide. Autotrophic bacteria are selfnourishing and heterotrophic bacteria are not self-sustaining. Moisture is indispensable for bacterial growth.
Morphologic characteristics are based on three distinct shapes or categories: