(2) Gram-negative--bacteria which, when stained by the gram stain method,
do not retain the gram stain color (dark violet or purple), but retain the color of the
counter stain (red or pink).
(3) Acid-fast--bacteria that when stained with certain dyes and then treated
with an acid, followed by a counter stain, retain the color of the dye.
(4) Nonacid-fast--bacteria that when treated as in (c), above, retain the
counter stain rather than the dye.
e. Microscopic Examination.
Shape (refer back to para 2-7).
Arrangement (refer back to para 2-7).
Spore formation--spore formers or non-spore formers. (para 2-8b(3)).
Motility--motile or nonmotile. (determined from an instained wet
(1) Enzymes. Certain bacteria produce specific enzymes that enable the
bacterial infection to invade the tissues of the host. Some of these enzymes break down
cell membranes or chew up the chemicals that hold tissue together. The effect of this
enzymatic action is to enlarge the site of infection.
Production of toxins.
(a) Exotoxins--extremely potent proteins that are produced in bacterial
cells and which diffuse freely into the cells of host tissues, causing severe systemic
(b) Endotoxins--lipopolysaccharide chemicals, less potent than
exotoxins, that are part of gram-negative bacterial cells and that affect the host cells
only after the bacterial cell disintegrates.
2-10. PATHOGENIC BACTERIA
Table 2-2 presents a list of the principal pathogenic bacteria of public health
importance, organized in such a way as to illustrate the means of identification