Cocci Shaped Bacteria

4 Key excerpts on "Cocci Shaped Bacteria"

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  eBook - ePub

  Bacteria and Viruses

  • Britannica Educational Publishing, Kara Rogers(Authors)
  • 2010(Publication Date)
  • Britannica Educational Publishing

    (Publisher)

  Vibrio cholerae , which causes cholera. Other shapes of bacteria include the spirilla, which are bent and rebent, and the spirochetes, which form a helix similar to a corkscrew, in which the cell body is wrapped around a central fibre called the axial filament.

  The bacterium Streptococcus mutans is an example of a spherical (coccus) bacterium. This species of bacteria commonly aggregates into pairs and short chains . David M. Phillips/Visuals Unlimited

  Bacteria are the smallest living creatures. An average-size bacterium, such as the rod-shaped Escherichia coli , a normal inhabitant of the intestinal tract of humans and animals, is about 2 micrometres (μm; millionths of a metre) long and 0.5 μm in diameter, and the spherical cells of Staphylococcus aureus are up to 1 μm in diameter. A few bacterial types are even smaller, such as Mycoplasma pneumoniae , which is one of the smallest bacteria, ranging from about 0.1 to 0.25 μm in diameter; the rod-shaped Bordetella pertussis , which is the causative agent of whooping cough, ranging from 0.2 to 0.5 μm in diameter and 0.5 to 1 μm in length; and the corkscrew-shaped Treponema pallidum , which is the causative agent of syphilis, averaging only 0.15 μm in diameter but 10 to 13 μm in length. Some bacteria are relatively large, such as Azotobacter , which has diameters of 2 to 5 μm or more; the cyanobacterium Synechococcus , which averages 6 μm by 12 μm; and Achromatium , which has a minimum width of 5 μm and a maximum length of 100 μm, depending on the species. Giant bacteria can be visible with the unaided eye, such as Titanospirillum namibiensis , which averages 750 μm in diameter, and the rod-shaped Epulopsicium fishelsoni

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  eBook - ePub

  Problem-Based Microbiology E-Book

  Problem-Based Microbiology E-Book

  • Swapan K. Nath, Sanjay G. Revankar(Authors)
  • 2005(Publication Date)
  • Saunders

    (Publisher)

  APPENDIX B Pathogenic Bacteria: Concepts

  Kevin McIver, PhD

  BACTERIAL STRUCTURE

  Bacteria are prokaryotes ’simple, single-cell organisms. They lack a distinct nucleus (i.e., no nucleolus, no nuclear membrane), and they often possess a single , circular chromosome . Transcription (mRNA synthesis) and translation (protein synthesis) occur simultaneously in the cytoplasm. In comparison, higher organisms (eukaryotes) have a true nucleus with a nuclear membrane containing multiple chromosomes; transcription of mRNA occurs in the nucleus and must be translocated to the cytoplasm to be translated by ribosomes.

  Bacterial Morphology

  Bacteria are microscopic in size, ranging from about 0.2 to 2.0 μm in diameter. Bacteria have distinct shapes (Table B-1 ;

  Fig. B-1A-F

  ). For cocci (spheres), cell division can occur in various planes, resulting in several arrangements: diplococci , chains , and clusters . The bacilli (rods) are most frequently found among the medically important bacteria, and they vary in length and detailed shapes: short rods , coccobacilli , fusiform , and curved (comma-shaped, spiral) rods .

  TABLE B-1 Bacterial Morphologies

  Shapes/Arrangement	Mechanism of Division or Detailed Shapes	Examples
  Cocci (Spheres)
  Diplococci	Pairs dividing in one plane ( Fig. B-1A )	Streptococcus pneumoniae, Neisseria gonorrhoeae
  Chains	Divide in one plane, no separation ( Fig. B-1B )	Streptococcus pyogenes
  Clusters	Divide in three planes ( Fig. B-1C )	Staphylococcus aureus
  Bacilli (Rods)
  Short rods	Rounded ends ( Fig. B-1D )	Pseudomonas aeruginosa
  Coccobacilli	Short, rounded	Francisella tularensis
  Fusiform	Tapered ends	Fusobacterium necrophorum
  Curved Rods
  Vibrios	Hook or comma shaped ( Fig. B-1E

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  eBook - ePub

  Microbiology For Dummies

  • Jennifer Stearns, Michael Surette, Jennifer Stearns, Michael Surette(Authors)
  • 2019(Publication Date)
  • For Dummies

    (Publisher)

  In this chapter, we give a bird’s-eye view of the structure of microbial cells. Then we go into some of the most important structures in detail. We discuss major differences between microbes — for instance, what differs between eukaryotic and prokaryotic microorganisms, as well as things that all cells have in common.

  Seeing the Shapes of Cells

  We know that prokaryotic cells come in many different shapes and sizes because we can look at them under a microscope. A description of the shape of a cell is called the cell morphology. The most common cell morphologies are cocci (spherical) and bacilli (rods). Coccibacillus are a mix of both, while vibrio are shaped like a comma, spirilla are shaped like a helix (a spiral, sort of like a stretched-out Slinky), and spirochetes are twisted like a screw. Figure 4-1 shows these common cell morphologies.

  FIGURE 4-1: Cell morphologies.

  Although prokaryotes are unicellular organisms, their cells can be arranged in a few different ways, like chains or clusters, depending on how the cells divide:

  • Cocci bacteria that divide along a single plane form small chains of two cells called diplococci or long chains of multiple cells called streptococci.
  • Cocci bacteria can also divide along multiple planes to form tetrads (two planes), cubelike sarcinae (three planes), or grapelike clusters called staphylococci (multiple planes).
  • Similarly to the cocci, rod-shaped bacteria can divide to form double-celled diplobacilli or longer chains called streptobacilli.

  The shape of a cell is encoded in its genes. Although we generally know how cell shape is controlled, the reason behind the many different shapes remains a mystery.

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  eBook - PDF

  Medical Microbiology

  • F. H. Kayser, K. A. Bienz, J. Eckert(Authors)
  • 2011(Publication Date)
  • Thieme

    (Publisher)

  The Morphology and Fine Structure of Bacteria 149 Cocci Fig. 3. 2 Cocci are spherical bacteria. Those found in grapelike clusters as in this picture are staphylococci (Scanning electron micros-copy (SEM)). Rod Bacteria Fig. 3. 3 The straight rod bacteria with rounded ends shown here are coli bacteria (SEM). Spirilla Fig. 3. 4 Spirilla, in this case borrelia are spiral bacteria (light microscopy (LM), Giemsa stain). 3 150 3 General Bacteriology DNA Topology in Bacterial Cells The DNA double helix (one winding/10 base pairs) is also wound counterclockwise about its helical axis (one winding/15 helical windings). This so-called supercoiling is necessary to save space and energy. Only supercoiled DNA can be replicated and transcribed. Topoisomerases steer the supercoiling process. DNA gyrase and topo-isomerase IV are topoisomerases that occur only in bacteria. The 4-quinolones, an important group of anti-infection substances, inactivate these enzymes irreversibly. Bacteria During Cell Division Fig. 3. 5 The nucleoid (nucleus equivalent) of bacteria consists of a tangled circular DNA molecule without a nuclear membrane. Transmission electron microscopy (TEM) image of staphylococci. Plasmids Fig. 3. 6 a Open circular form (OC). The result of a rupture in one of the two nucleic acid strands. b Twisted (CCC = covalently closed circular), native form (TEM image). a b 3 The Morphology and Fine Structure of Bacteria 151 Cytoplasm The cytoplasm contains a large number of solute low-and high-molecular-weight substances, RNA and approximately 20 000 ribosomes per cell. Bacteria have 70S ribosomes comprising 30S and 50S subunits. Bacterial ribosomes function as the organelles for protein synthesis. The cytoplasm is also frequently used to store reserve substances (glycogen depots, poly-merized metaphosphates, lipids). The Most Important Bacterial Cytoplasmic Membrane Proteins Permeases Active transport of nutrients from outside to inside against a concentration gradient.

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