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Questions and Answers
Which of the following bacteria are characterized as spirochetes?
What shape do aerobic/microaerophilic helical vibrioid bacteria typically have?
Which bacteria is known for relying on plants for usable nitrogen?
Which of the following bacteria can grow in both the presence and absence of oxygen?
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What is a defining characteristic of Rickettsias and Chlamydias?
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Gram-positive cocci are primarily associated with which type of infections?
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Which bacteria is known for its ability to form endospores, making it highly resistant to harsh conditions?
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Which of these bacteria causes diarrhea?
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Which type of bacteria can be classified as obligate anaerobes?
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What characterizes regular nonsporulating Gram-positive rods?
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Which organism is known for causing food poisoning and is a type of mycobacteria?
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Which of the following diseases is NOT associated with Clostridia?
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What defines the growth characteristics of Bacilli?
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Which of the following statements about Mycobacteria is true?
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What is a common characteristic of irregular nonsporing Gram-positive rods?
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What beneficial role does Lactobacillus play in food production?
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Study Notes
Bacteria Organization
- Bacteria classification is based on shape, metabolism, staining properties, and pathogenic potential.
- Some bacteria are free-living and beneficial while others are pathogenic.
Spirochetes
- Spiral-shaped bacteria with corkscrew motion.
- Difficult to see on Gram stain but are generally Gram-negative.
- Examples: Treponema (syphilis), Borrelia (Lyme disease), Leptospira interrogans (Leptospirosis)
Aerobic/Microaerophilic Helical Vibrioid Gram-Negative Bacteria
- Helical or slightly curved shaped (vibrioid).
- Require oxygen for growth (aerobic) or only a small amount (microaerophilic).
- Motile with flagella.
- Often found in water or the gastrointestinal tract.
- Examples: Campylobacter (diarrhea), Helicobacter (ulcers)
Gram-Negative Aerobic Rods and Cocci
- Rod-shaped (bacilli) or spherical (cocci).
- Need oxygen for growth (aerobic) and utilize respiratory metabolism.
- Found in soil, water, and the respiratory tract.
- Examples: Rhizobium (soil bacteria, nitrogen fixation), Legionella (pneumonia), Neisseria (gonorrhea, meningitis), Bordetella (pertussis), Francisella (tularemia), Pseudomonas (aeruginosa - infections)
Facultative Anaerobic Gram-Negative Rods
- Found in soil, water, and the gastrointestinal tract of humans and animals (enteric bacteria).
- Can grow with or without oxygen (facultative anaerobes).
- Examples: Escherichia (workhorse of molecular biology), Salmonella, Shigella, Enterobacter, Proteus, Providencia.
Rickettsias and Chlamydias
- Obligate intracellular parasites, requiring a host for replication.
- Very small gram-negative bacteria, often rod-shaped or coccoidal.
- Often cause disease.
- Rickettsias need both a vertebrate and an arthropod host.
- Example: Rickettsia rickettsii (Rocky Mountain spotted fever, transmitted by ticks)
- Chlamydias do not infect invertebrates.
- Example: Chlamydia trachomatis (urogenital infections)
Gram-Positive Cocci
- Spherical-shaped bacteria.
- Some grow in clusters or chains.
- Often involved in infections of the skin, respiratory tract, or bloodstream.
- Range from harmless to highly virulent.
- Examples: Staphylococcus (clusters), Streptococcus (chains - pyogenes, pneumoniae), Peptostreptococcus
Endospore-Forming Gram-Positive Rods and Cocci
- Form endospores (survival structures) which make them highly resistant to harsh conditions (heat, disinfectants).
- Widespread in soil.
- Common cause of food poisoning.
- Include free-living and pathogenic species.
- Examples: Bacillus anthracis (anthrax), Bacillus cereus, Clostridium (tetanus, botulism), Clostridium difficile, Clostridium perfringens.
Regular Nonsporulating Gram-Positive Rods
- Generally, do not need oxygen to live (anaerobic).
- Obligate anaerobes are harmed by oxygen.
- Facultative anaerobes can survive with or without oxygen.
- Do not form spores (nonsporulating).
- Uniform shape and predictable growth (regular).
- Examples: Carnobacterium (found in permafrost), Lactobacillus (fermentation in yogurt, cheese, sauerkraut, pickles), Listeria monocytogenes (food poisoning)
Irregular Nonsporulating Gram-Positive Rods
- Mostly facultative anaerobes, some obligate aerobes.
- Irregular shape with club shapes or varying sizes (pleomorphic).
- Examples: Actinomyces (opportunistic), Corynebacterium diphtheria (diphtheria), Propionibacterium acnes (acne), Propionibacterium shermanii (Swiss cheese production), Actinomyces israelii (periodontal disease, lung infections)
Mycobacteria
- Primarily aerobic, acid-fast rods.
- Widespread in water, soil, and food.
- Some are obligate intracellular parasites in humans and animals.
- Can colonize a host without symptoms.
- Infections are difficult to treat.
- Neither Gram-positive or negative.
- Resistant to many antibiotics.
- Examples: Mycobacterium tuberculosis (TB), Mycobacterium leprae (leprosy)
- Classified into fast-growing and slow-growing types.
- Difficult to grow in culture, resistant to Gram stain, and identified using an acid-fast stain.
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