Capsular Bacteria

CAPSULAR BACTERIA (microbes), a group of bacilli characterized by the ability to form capsules. Morphologically, capsular bacilli are rather thick rods with rounded ends, but they are often very short and more closely resemble large cocci than rods. Frequently, the bacilli form short chains of two or more individuals, with the entire chain surrounded by a common capsule. The rods are non-motile, do not form spores, do not liquefy gelatin, and grow easily and rapidly on ordinary nutrient media; they decolorize when stained by Gram's method. An essential characteristic of capsular bacteria is their ability to form a mucous substance, from which their capsules are composed; in most cases, the latter are broad and clearly expressed. The ability to form mucous substance results in the bacterial mass having a viscous, slimy consistency on artificial nutrient media and stretching into threads when picked up with a platinum loop. In some cases, the mucous mass is so liquid that the culture drains from the surface of the solid nutrient medium to the bottom of the test tube. When inoculated into broth, a uniform turbidity and more or less abundant precipitate, sometimes distinguished by great viscosity, is obtained the next day; a film often forms on the surface of the medium. The group of capsular bacteria includes Bac. pneumoniae Friedlander's, the rod of rhinoscleroma Frisch's, Bac. ozaenae Abegg, Bac. mucosus capsulatus, Bac. lact. aerogenes, Bac. capsul. Pfeiffer's, etc. (see separate table, figures 1-5). Attempts have been made to divide capsular bacteria into certain groups. Strong distinguishes the Friedlander group (Bac. pneumoniae, Bac. mucos. capsulatus, the rod of scleroma, etc.) and the Aerogenes group (Bac. lact. aerogenes, Bac. capsul. Pfeiffer's). The first group is characterized by the formation of capsules not only in the body but also on artificial nutrient media, the absence of milk sugar decomposition, and the absence of milk coagulation. The second group coagulates milk, decomposes lactose, glucose, and sucrose with gas formation, does not form capsules on artificial nutrient media at all or forms weakly expressed capsules, etc. There are other attempts to divide capsular bacteria into groups. For differential diagnosis of capsular bacteria, Elbert proposed using morphological differences of colonies on agar (agar-microscopy). The rod of rhinoscleroma gives flat round groups on agar, usually of straight diplobacilli arranged in concentric rows; Bac. mucosus Pfeiffer's gives star-shaped colonies, the rod of ozena gives colonies consisting of diplobacilli located far apart from each other; B. pneumoniae Friedlander's forms loop-festooned colonies; Bac. aerogenes gives terraced colonies with a dense center and descending periphery. According to the classification of bacteria adopted by the Committee on Characterization and Classification of the American Society of Bacteriologists (Bergey), capsular bacteria form the genus Encapsulateae, which includes the species Encapsulatus pneumoniae, Encapsulatus rhinoscleromatis, Encapsulatus Pfeiffer's, Encapsulatus ozaenae, etc. The bacterial capsule is a mucous layer surrounding the microbe body on all sides; in a preparation stained by ordinary methods, it appears as a light or weakly stained rim around the microbe. The capsule consists of two layers: an inner layer, which is part of the ectoplasm, and an outer layer, which is a product of secretion. There is no 'capsular membrane' that would delimit the capsule from the outside. A false or pseudocapsule, which lacks the characteristic structure of a true capsule, is distinguished from a true capsule; a zoogloea is a false capsule surrounding an entire group of microbes and having the appearance of a slimy mass. The capsule is most clearly expressed in capsular bacteria, but in a poorly developed form it probably exists in almost all bacteria. The capsule is an structure that develops in microbes as a reaction to harmful influences from the environment; for this reason, most microbes that have capsules form them in the animal body and are devoid of them on artificial nutrient media. Recent research indicates that immunobiologically, the capsule and the bacterial body are not identical to each other and possess different antigenic properties. Special methods for staining capsules are as follows: Johne's method - 2% aqueous solution of gentian or methyl violet for 1-2 minutes with heating, washing with water, 1-2% acetic acid for 5-10 seconds, washing with water, examination in water; Nicolle's method - staining in a mixture of 10 cm³ of saturated solution of gentian violet and 100 cm³ of 1% carbolic acid, washing in a mixture of 3 parts of absolute alcohol and 1 part of acetone, washing in water, etc.