Bacterial Forms

Bacteria differ from other single-cell microorganisms in both their cell structure and size, which varies from 0.3-5 im. Magnifications of 500-1000x—close to the resolution limits of light microscopy—are required to obtain useful images of bacteria. Another problem is that the structures of objects the size of bacteria offer little visual contrast. Techniques like phase contrast and dark field microscopy, both of which allow for live cell observation, are used to overcome this difficulty. Chemical-staining techniques are also used, but the prepared specimens are dead.

— Bacterial Morphology

— Bacterial Morphology

Bacteria Morphology
Fig. B.1

1.

Gram-positive cocci in grapelike

10.

Peritrichous flagellation

clusters (staphylococci)

11.

Lophotrichous flagellation

2.

Gram-positive cocci in chains

12.

Monotrichous flagellation

(streptococci)

1B.

Formation of endospores

B.

Gram-positive cocci with capsules

(sporulation) in cells of the

(pneumococci)

genera Bacillus and

4.

Gram-positive, clubshaped,

Clostridium (spore stain)

pleomorphic rods (corynebacteria)

a) Central spore, vegetative

S.

Gram-negative rods with pointed

cell shows no swelling

ends (fusobacteria)

b) Terminal spore, vegetative

S.

Gram-negative curved rods

cell shows no swelling

(here commashaped vibrios)

c) Terminal spore ("tennis

7.

Gram-negative diplococci, adjacent

racquet")

sides flattened (neisseria)

d) Central spore, vegetative

S.

Gram-negative straight rods with

cell shows swelling

rounded ends (coli bacteria)

e) Terminal spore

9.

Spiral rods (spirilla) and Gram-negative

("drumstick")

curved rods (Helicobacter)

14.

Free spores (spore stain)

Table 3.1 Morphological Characteristics of Bacteria (see Fig. 3.1 for examples)

Bacterial form

Remarks

Cocci

Straight rods

Curved rods

Mycoplasmas

Chlamydiae

Rickettsiae

Occur in clusters (Fig. 3.2), chains, pairs (diplococci), packets

Uniform thickness, rounded ends (Fig. 3.3), pointed ends, club form

Commashaped, spiral (Fig. 3.4), screwshaped

Bacteria without a rigid cell wall; coccoid cells, long threads

Two forms: spherical/oval elementary bodies (300 nm); spherical/oval reticulate bodies (1000 nm)

Short coccoid rods (0.3-1 im)

■ Simple staining. In this technique, a single staining substance, e.g., methylene blue, is used.

■ Differential staining. Two stains with differing affinities to different bacteria are used in differential staining techniques, the most important of which is gram staining. Gram-positive bacteria stain blue-violet, Gram-negative bacteria stain red (see p. 211 for method).

Three basic forms are observed in bacteria: spherical, straight rods, and curved rods (see Figs. 3.1-3.4).

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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  • Josefiina Loikkanen
    What bacteria forms terminal spores?
    8 years ago
  • Hildigard
    What is the morphology of bacterial cells?
    7 years ago

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