BMS Bacteria Characteristics and Structures

Bacteria Features

• Bacteria are single-celled microorganisms, ancient life forms with basic functions like other cells
• Lack chlorophyll, have a single circular DNA chromosome and no membrane-bound organelles

Size of Bacteria

• Vary in size, measured in micrometers (µm)

Shape of Bacteria

• Cocci: Spherical or round
• Bacilli: Rod-shaped
• Spirilla: Spiral or corkscrew-shaped

Arrangement of Bacteria

• Cocci:
  • Diplococci: Pairs
  • Streptococci: Chains
  • Staphylococci: Clusters
• Bacilli:
  • Diplobacilli: Pairs
  • Streptobacilli: Chains

Structure of Bacteria

• Flagellum: For movement
• Ribosomes: Protein synthesis
• Cytoplasm: Fluid inside the cell
• Nucleoid: Contains the DNA
• Plasma membrane: Controls what enters and leaves the cell
• Cell wall: Provides structure and support
• Capsule: Outer layer for protection
• Pilus: Hair-like structures for attachment

Gram Staining

• A technique to distinguish between bacterial species
• Gram-positive: Thick peptidoglycan cell wall
• Gram-negative: Thin peptidoglycan cell wall, thick lipopolysaccharide layer

Environmental Requirements

• Moisture: Essential for survival
• Oxygen:
  • Aerobes: Require oxygen
  • Anaerobes: Cannot tolerate oxygen
  • Facultative anaerobes: Can survive with or without oxygen
• Carbon dioxide: Used for growth
• Temperature: Each bacteria has an optimal temperature range
• pH: Bacteria prefer specific pH levels
• Light: Some bacteria require light for photosynthesis
• Osmotic effect: Bacteria are affected by the concentration of solute in their environment
• Mechanical stress: Physical forces can affect bacterial survival

Naming Bacteria

• Taxonomy is the classification of organisms into groups
• Bacterial names are a combination of the last two ranks: Genus and Species
• Genus is capitalized, Species is lowercase
• Usually written in italics
• Generic names can be abbreviated (e.g., S. for Streptococcus)

Classification of Organisms

• Kingdom: Procaryote
• Division: Firmicutes
• Subdivision: Low DNA content
• Family: Streptococcaceae
• Genus: Streptococcus
• Species: Streptococcus salivarius

Bacteria: The Basics

• Bacteria are single-celled organisms that differ from viruses, fungi, and eukaryotes.
• Lack a true nucleus, their DNA is in a circular chromosome within the nucleoid region.
• No membrane-bound organelles like mitochondria or endoplasmic reticulum.

Cell Wall

• Most bacteria have a rigid cell wall for shape and protection.
• Peptidoglycan composition differentiates bacteria:
  • Gram-positive: thick peptidoglycan layers
  • Gram-negative: thinner peptidoglycan layers with an outer membrane.

Shapes

• Cocci: Spherical
• Bacilli: Rod-shaped
• Spirilla/Spirochetes: Spiral-shaped
• Vibrios: Comma-shaped

Reproduction

• Binary fission: Asexual reproduction where one bacterium divides into two identical daughter cells.

Genetic Material

• Single circular chromosome contains most of their genetic information.
• Plasmids: Small, circular DNA pieces carrying beneficial genes, like antibiotic resistance.

Motility

• Flagella: Whip-like structures for propulsion
• Pili: Hair-like projections for movement
• Gliding: Movement on solid surfaces

Metabolic Diversity

• Aerobic: Require oxygen
• Anaerobic: Grow without oxygen
• Facultative anaerobes: Grow with or without oxygen
• Microaerophiles: Need low oxygen levels

Capsules

• Protective, gelatinous outer layer for evading immune systems and increasing pathogenicity.

Endospores

• Formed by Bacillus and Clostridium species in harsh conditions.
• Highly resistant structures protecting genetic material from extreme temperatures, desiccation, and disinfectants.

Biofilm Formation

• Communities of bacteria encased in a slimy matrix adhering to surfaces.
• Protect bacteria from environmental threats and increase antibiotic resistance.

Gene Transfer

• Horizontal gene transfer: Exchange genetic material for diversity and resistance.
  • Conjugation: DNA transfer through direct cell-to-cell contact.
  • Transformation: Uptake of free DNA from the environment.
  • Transduction: Bacterial DNA transfer by viruses (bacteriophages).

Antibiotic Sensitivity/Resistance

• Some bacteria are sensitive to antibiotics, others develop resistance:
  • MSSA: Sensitive
  • MRSA: Resistant

Pathogenicity

• Some bacteria cause diseases (pathogens):
  • Produce toxins, invade tissues, or evade the immune system.
• Others are harmless or beneficial, living symbiotically with humans, like gut bacteria.

Gram Staining

• Gram-positive: Appear purple due to thick peptidoglycan retaining the crystal violet dye after alcohol treatment.
  • Example: Staphylococcus aureus, Streptococcus pneumoniae.
• Gram-negative: Appear pink or red after alcohol decolorizes them and they take up the safranin counterstain.
  • Example: Escherichia coli, Neisseria gonorrhoeae.

Importance of Gram Staining

• Quick classification of bacteria into two main groups.
• Guides appropriate antibiotic therapy.
• Identifies bacterial infections in blood, urine, or sputum samples.

Oxygen Relationships

• Obligate Aerobes: Require oxygen for aerobic respiration. Found in oxygen rich environments.
  • Example: Mycobacterium tuberculosis.
• Obligate Anaerobes: Cannot survive in oxygen, lack enzymes to neutralize oxygen by-products.
  • Example: Clostridium botulinum.
• Facultative Anaerobes: Grow with or without oxygen, prefer oxygen for more energy production.
  • Example: Escherichia coli.
• Microaerophiles: Need low oxygen levels.
  • Example: Helicobacter pylori.
• Aerotolerant Anaerobes: Don't use oxygen but tolerate its presence, rely on fermentation.
  • Example: Lactobacillus.

Summary of Oxygen Relationships

Bacteria: Key Characteristics & Dental Implications

• Prokaryotic Structure: Lack a true nucleus; genetic material is in a singular circular chromosome in the nucleoid region; lack membrane-bound organelles like mitochondria and endoplasmic reticulum.
• Cell Wall: Most have a rigid cell wall providing shape and protection; peptidoglycan content differentiates types (Gram-positive: thick peptidoglycan, Gram-negative: thin peptidoglycan, outer membrane).
• Shapes: Cocci (round), Bacilli (rod), Spirilla or Spirochetes (spiral), Vibrios (comma).
• Reproduction: Asexual binary fission: one cell divides into two identical daughter cells.
• Genetic Material: Circular chromosome with most genetic information; plasmids (small circular DNA) can provide advantages like antibiotic resistance.
• Motility: Flagella (whip-like structures) for propulsion; pili (hair-like projections) for movement; gliding on solid surfaces.
• Metabolic Diversity: Aerobic (oxygen required); anaerobic (oxygen absent); facultative anaerobes (grow with or without oxygen); microaerophiles (low oxygen levels).
• Capsules: Protective gelatinous outer layer; evades host immune system; increases pathogenicity.
• Endospores: Highly resistant structures formed by bacteria like Bacillus and Clostridium; survive extreme temperatures, desiccation, and disinfectants.
• Biofilm Formation: Communities of bacteria encased in a slimy matrix, adhering to surfaces; protect bacteria from threats, increase resistance to antibiotics.
• Gene Transfer: Horizontal gene transfer contributes to genetic diversity and antibiotic resistance; conjugation (direct cell-to-cell), transformation (uptake of free DNA), transduction (viruses).
• Antibiotic Sensitivity/Resistance: Some are sensitive to antibiotics (e.g., MSSA), others develop resistance (e.g., MRSA).

Gram Staining: Differentiating Bacteria

• Key Technique: Distinguishes bacteria based on cell wall structure.
• Process: Crystal violet stain, iodine treatment, alcohol decolorization, safranin counterstain.
• Results: Gram-positive: retains crystal violet, appears purple; Gram-negative: loses crystal violet, takes up safranin, appears pink/red.
• Importance: Classifies bacteria, guides antibiotic therapy, helps diagnose infections.

Oxygen Relationships: Bacterial Survival

• Obligate Aerobes: Require oxygen for survival and growth; use it for aerobic respiration.
• Obligate Anaerobes: Cannot survive in oxygen; oxygen is toxic; use anaerobic respiration or fermentation.
• Facultative Anaerobes: Grow in both oxygen presence and absence; prefer aerobic respiration but can switch to anaerobic methods.
• Microaerophiles: Need low oxygen levels; high concentrations are toxic.
• Aerotolerant Anaerobes: Don't use oxygen but tolerate its presence; rely on fermentation.

Oral Microbiome: Beneficial and Harmful Bacteria

• Normal Oral Flora: Beneficial bacteria like Streptococcus salivarius and Lactobacillus protect tissues and maintain oral balance.
• Harmful Bacteria: Contribute to tooth decay (Streptococcus mutans, Lactobacillus) and gum disease (Streptococcus sanguinis, Fusobacterium nucleatum, Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia).
• Tooth Decay (Dental Caries): Bacteria metabolize sugars, producing acid that demineralizes enamel; plaque formation traps sugars, further contributing to acid production.
• Gum Disease (Periodontal Disease): Gingivitis (inflammation of gums); periodontitis (more severe, bone loss); biofilms and toxins damage tissue.
• Endodontic Infections: Bacteria invade tooth pulp (due to deep decay or trauma); Enterococcus faecalis, Fusobacterium, and Prevotella species are common.
• Oral Infections and Systemic Health: Bacteria can enter the bloodstream, leading to conditions like infective endocarditis and respiratory infections.

Dental Implications: Prevention, Treatment, and Resistance

• Oral Hygiene: Regular brushing, flossing, and professional cleanings control bacterial growth.
• Fluoride: Strengthens enamel, resists bacterial acid attack.
• Antibacterial Mouthwashes: Reduce harmful bacteria, prevent gum disease.
• Probiotics: May help balance the oral microbiome, reducing harmful bacteria.
• Dental Materials and Bacteria: Biofilm formation on implants can lead to peri-implantitis; research on Streptococcus mutans vaccines to prevent tooth decay.
• Bacterial Resistance in Dentistry: Overuse of antibiotics can lead to resistance (e.g., MRSA), making treatment difficult.

Summary: Dual Role of Bacteria in Dentistry

• Bacteria are essential for oral health but can cause diseases when unbalanced.
• Understanding their characteristics and behavior is vital for prevention and treatment strategies.