Micro W8 Part 1: Bacteria

Study Notes

Bacteria classification is based on shape, metabolism, staining properties, and pathogenic potential.
Some bacteria are free-living and beneficial while others are pathogenic.

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)

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)

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.

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)

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

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.

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)

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)

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.