Bacterial Morphology

Most clinically relevant bacterial species range in size from 0.25 to 1 pm in width and 1 to 3 ^m in length, thus requiring microscopy for visualization (see Chapter 6 for more information on microscopy). Just as bacterial species and genera vary in their metabolic

- Murein Periplasmic -

Gram-positive

Flagellum

Pilus

Capsule (variable)

Outer membrane"

- Murein Periplasmic -

Cytoplasmic membrane

Flagellum

Pilus

Capsule (variable)

Outer membrane"

Cytoplasmic membrane

Gram-negative

Gram-positive jnnnr HKKKKKIWI

Gram-negative

Figure 2-13 General structures of the gram-positive and gram-negative bacterial cell envelopes. The outer membrane and periplasmic space are only present in the gram-negative envelope. The murein layer is substantially more prominent in gram-positive envelopes. (Modified from Niedhardt FC, Ingraham JL, Schaechter M, editors: Physiology of the bacterial cell: a molecular approach, Sunderland, Mass, 1990, Sinauer Associates.)

processes, their cells also vary in size, morphology, cell-to-cell arrangements, and in the makeup of one of the most prominent cellular structures, the cell wall. In fact, cell wall differences provide the basis for the Gram stain, the most fundamental test used in bacterial identification schemes. This staining procedure separates almost all medically important bacteria into two general types: gram-positive bacteria, which stain a deep blue color, and gramnegative bacteria, which stain a pink to red color (see Figure 6-3). This simple but important color distinction is due to differences in the constituents of bacterial cell walls that influence the cell's ability to retain certain dyes, even after decolorization with alcohol.

Common bacterial cellular morphologies include cocci (round), coccobacilli (ovoid), and bacillus (rod-shaped), as well as fusiform (pointed-end), curved, or spiral shapes. Cellular arrangements are also noteworthy because cells may characteristically occur singly, in pairs, tetrads, clusters, or in chains (see Figure 6-4 for examples of bacterial staining and morphologies). The determination of Gram reaction coupled with cell size, morphology, and arrangement are essential aspects of bacterial identification.

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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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