SECTION B
Note: Criteria for the separation of the small colorless protozoan forms from bacteria are very limited. Cells in which the chromatinic material is clearly organized into chromosomes which divide and separate during mitosis are probably protozoa. Robinow (Bacteriol. Rev., 20, 1956, 207-242) states that he "knows of no other protists, besides the blue-green algae, with nuclei resembling the chromatin bodies of bacteria though it is probable that they exist". The reader is referred to this review for a detailed statement on the position.
It is suggested that all microbial forms which come under this Section be followed through the key. This practice may assist materially in clarifying the situation.
1. Ultra-microscopic and filterable forms; strict intracellular parasites of animals and plants not cultivable on artificial media but transferable by contact or by arthropod vectors Virales p. 985 2. Strict parasites occurring within tissue cells of animal hosts or on or in erythrocytes. With few exceptions, which have been treated under Section H, they cannot be or have not been cultivated in artificial media. Some can be cultivated in chick embryos or in tissue cultures. In the tissues or blood stream they occur either as spherical ele- mentary bodies and initial bodies from 0.2 to 2.0 microns in diameter or slightly larger (usually 0.20 to 0.35 micron), singly or in aggregations in plaques several microns in diameter or as bacillary, triangular, ring-shaped horseshoe-shaped and other pleo- morphic forms. Bacillary forms may be as long as 3 microns. Stain with Giemsa's or Macchiavello's stain without differentiation into cytoplasmic and nuclear structures, a condition which would be suggestive of protozoa. See Manual keys for the class Microtatobiotes p. 933 3. Small, spherical bodies, 150 to 300 millimicrons in diameter, which germinate to produce filaments approximately 0.2 micron wide and from 2 to 50 microns long, sparcely or richly branching. At a later stage of growth small endomycelial corpuscles develop in the filaments by a process of successive condensation and constriction. As a result the homogeneous filaments are retransformed into chains of close-set spherical bodies which are released by fragmentation; highly resistant to penicillin and sulfathiazole; colonies on agar have a dense granulated central area which penetrates into the agar and which is surrounded by a translucent flat peripheral zone or consist of a pearly film containing numerous spots due to calcium or magnesium soaps; do not ferment lactose, sucrose, mannitol or dulcitol Mycoplasma p. 914 Note: L-phase colonies of some bacteria bear a strong resemblance to the colonies of Mycoplasma. They are generally more opaque, more heavily marked on the surface, tend to revert to the normal bacillary form in penicillin-free semi-solid media, are more difficult to subculture, do not require cholesterol for growth and ferment the same carbohydrates as the parent organism. 4. Spiral cells ; proceed to Section C p. 998 This section does not include: (a) all forms like Vitreoscilla, which, through their great length and extreme flexibility, are apt to coil in one plane in watch-spring fash- ion; (b) spiral cells of the streptomyces type which arise from branching Gram-posi- tive filaments; and (c) chains of vibrios. The latter do not possess the true helical twist of the spiral organisms. 5. Spherical to ovoid cells which reproduce by production of a tubular outgrowth, 0.2 to 0.3 micron wide, from the cell on the end of which a daughter cell is formed. The tubular outgrowths may be simple or branched. Daughter cells are initially spherical but are later ovoid to rod-shaped; colorless or contain photosynthetic pigments. 996
