Bacteria Types and Characteristics

Biologic Relationships of Pathogenic Microorganisms

• Identifying microorganisms helps predict their pathogenicity, e.g., Staphylococcus aureus isolated from blood is more likely to cause disease than Staphylococcus epidermidis.
• Identifying organisms that spread widely in the community and cause serious disease, like Neisseria meningitidis, is crucial for taking preventative measures.

Bacteria Identification

• Bacteria are identified using phenotypic, immunological, or molecular characteristics.
• Gram staining differentiates bacteria based on the chemical and physical properties of their cell walls by detecting peptidoglycan.
• Gram-positive bacteria have large amounts of peptidoglycan in their cell wall, trapping the violet dye and staining purple.
• Gram-negative bacteria have thin peptidoglycan in their periplasmic gel, retaining carbol fuchsin and staining pink.
• Acid-fast staining is used for mycobacteria, such as Mycobacterium tuberculosis, Mycobacterium leprae, and Nocardia.

Bacterial Morphology

• Bacteria can have various shapes, including:
  • Cocci: oval or spherical; may be arranged in pairs, tetrads, chains, or clusters.
  • Bacilli: rod-shaped; may show arrangements like coccobacilli, streptobacilli, or comma-shaped.
  • Spirochetes: slender, flexuous, and spiral.
  • Actinomyces: branching filamentous.

Flagella

• Bacteria may have flagella, which are classified as:
  • Monotrichous: single polar flagellum.
  • Lophotrichous: multiple polar flagella.
  • Peritrichous: flagella distributed over the entire cell.
  • Amphitrichous: single flagellum at both ends.
• Bacteria without flagella are called Atrichous.

Endospore Position

• The presence, shape, and position of the endospore within the bacterial cell are noted, e.g., Bacillus subtilis and Clostridium tetani.

Oxygen Requirements

• Bacteria can be classified based on their oxygen requirements:
  • Aerobic: require oxygen to live.
  • Anaerobic: do not require oxygen and may be killed by exposure.
  • Facultative anaerobes: can live with or without oxygen.
  • Aerotolerant anaerobes: can tolerate oxygen and grow in its presence.

Carbon Dioxide Requirement

• Capnophilic bacteria require higher amounts of CO2 for growth (5-10% CO2 and 15% O2), e.g., H. influenzae and Brucella abortus.

Temperature, pH, and Light

• Bacteria can be classified based on their optimal temperature, pH, and light requirements:
  • Temperature: psychrophiles (0-20°C), mesophiles (25-40°C), and thermophiles (55-80°C).
  • pH: acidophiles (pH < 4.0), alkaliphiles (pH 8.2-8.9), and neutrophiles (pH 7.2-7.6).
  • Light: phototrophs (derive energy from sunlight) and chemotrophs (derive energy from chemical sources).

Osmotic Pressure and Carbon Source

• Bacteria can be classified based on their tolerance to osmotic pressure:
  • Halophiles: can survive at high salt concentrations.
  • Osmophiles: can survive at high sugar concentrations.
• Bacteria can also be classified based on their carbon source:
  • Autotrophs: reduce inorganic carbon into organic compounds, such as through photosynthesis.
  • Heterotrophs: use carbon that has been reduced by autotrophs.

Method of Obtaining Nutrition

• Bacteria can be classified based on their method of obtaining nutrition:
  • Heterotrophic bacteria: obtain food from other living organisms, such as symbiotic, pathogenic, or saprophytic bacteria.
  • Autotrophic bacteria: obtain food by synthesizing it on their own.

Additional Identification Methods

• The interaction of antibodies with surface structures can help distinguish between bacterial subtypes.
• DNA sequencing of key genes, such as 16S ribosomal RNA or DNA gyrase, can identify the organism precisely.