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Questions and Answers
What is the typical size range of most bacteria?
Which shape corresponds to spherical bacteria?
What type of bacteria retain the crystal violet stain and appear purple?
What structural component is found only in bacterial cells?
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How are Gram-negative bacteria characterized in their cell wall structure?
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Which arrangement of cocci bacteria is described as clusters?
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What happens to Gram-negative bacteria when treated with alcohol during the Gram stain process?
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Which of the following correctly describes the composition of peptidoglycan?
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What is the function of endotoxin in gram-negative bacteria?
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Where are β-lactamases located in gram-negative bacteria?
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What distinguishes mycobacteria in staining procedures?
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What is the main role of capsules in bacteria?
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What type of DNA are plasmids typically associated with?
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What is the primary component of the bacterial cytoplasmic membrane?
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Which of the following describes transposons in bacteria?
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What does opsonization refer to in the context of immune response?
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Study Notes
Bacterial Structure and Morphology
- Microbiology is the study of microorganisms, which are microscopic, unicellular, and cell-cluster organisms.
- Study of microorganisms causing diseases in humans is called medical microbiology.
- Bacteria range in size from 1 to 3 μm with the smallest bacteria being Mycoplasma at 0.2 μm.
- Bacteria exist in three basic shapes:
- Cocci (spheres)
- Bacilli (rods)
- Spirochetes (spirals)
- Cocci are arranged in three patterns:
- Pairs (diplococci)
- Chains (streptococci)
- Clusters (staphylococci)
- Bacterial shape is determined by the rigid cell wall.
- Shape is a key identifier in bacterial identification.
Bacterial Cell Wall
- All bacteria have a cell wall composed of peptidoglycan except Mycoplasma, which only has a cell membrane.
- Peptidoglycan is found only in bacteria, covering the entire organism.
- Peptidoglycan functions:
- It determines the shape of the bacterium.
- It's the target of penicillin and cephalosporin antibiotics which inhibit transpeptidase, an enzyme involved in peptidoglycan synthesis.
- Peptidoglycan is composed of a sugar backbone (glycan) and peptide side chains (peptides).
- Gram-negative bacteria have a thin layer of peptidoglycan covered by an outer lipid-containing membrane.
- Gram-positive bacteria have a thick layer of peptidoglycan and no outer membrane.
Gram Staining
- Gram-positive bacteria retain the stain and appear purple.
- Gram-negative bacteria lose the stain when exposed to lipid solvents and appear pink.
- This difference is due to the differences in the cell wall structure.
Outer Membrane of Gram-negative Bacteria
- Endotoxin (lipopolysaccharide, LPS) is a major inducer of septic shock.
- Endotoxin is composed of:
- Lipid A: responsible for fever and hypotension during septic shock
- Polysaccharide (O antigen): used in laboratory identification
- Periplasmic space lies between the inner cell membrane and the outer membrane of Gram-negative bacteria.
- The periplasmic space is the location of β-lactamases, enzymes that degrade β-lactam antibiotics, such as penicillins and cephalosporins.
Bacterial Membrane
- The cytoplasmic membrane of bacteria consists of a phospholipid bilayer located just inside the peptidoglycan.
- Functions of the bacterial membrane:
- Active transport of nutrients into cells
- Secretion of toxins out of the cells
Cell Walls of Acid-Fast Bacteria
- Mycobacteria are acid-fast because they resist decolorization with acid-alcohol after staining with carbolfuchsin.
- This is due to the high concentration of lipids in the cell wall.
- The dyes used in the Gram stain do not stain mycobacteria. However, they are stained by Ziehl-Neelsen (ZN).
Bacterial DNA
- The bacterial genome consists of a single chromosome of circular DNA located in a nucleoid.
- It carries genetic material.
- Plasmids are extrachromosomal pieces of circular DNA.
- They encode exotoxins, enzymes, and antibiotic resistance.
- Transposons (Jumping genes) are small pieces of DNA that move between chromosomal DNA and plasmid DNA.
- They carry antibiotic-resistant genes.
Structures External to the Cell Wall
- Capsules are composed of polysaccharides (except for the polypeptide capsule of anthrax bacillus).
- Functions of the capsule:
- They are antiphagocytic, meaning they prevent neutrophils from engulfing bacteria.
- Antibodies against the capsule neutralize the antiphagocytic effect and allow bacteria to be engulfed by neutrophils.
- This process is called opsonization.
- Capsules are antigens in several vaccines, such as the pneumococcal vaccine.
- Specific identification is made by using antiserum against the capsular polysaccharide.
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Description
Explore the fascinating world of bacteria through this quiz focused on their structure and morphology. Learn about the different shapes of bacteria, the composition of their cell walls, and how these features play a crucial role in their identification. Test your knowledge on medical microbiology and the unique characteristics of various bacterial forms.
