Probiotics Overview

Probiotics

• Probiotics are live, non-pathogenic microorganisms used to improve microbial balance in the gastrointestinal tract or vagina.
• Popular probiotic strains include Lactobacillus spp., Bifidobacterium spp., and Saccharomyces boulardii.
• They are ingested through food, capsules, tablets, or powder.
• They improve antibiotic therapy by reducing microbial adhesion and growth.
• They possess immunomodulatory properties and strengthen the intestinal barrier.
• Probiotics can shorten the duration of rotavirus diarrhea in children.

Spore Forming Probiotics

• Products with Bacillus endospores are commercially available as probiotics.
• They are more stable than Lactobacillus and Bifidobacterium in challenging atmospheric conditions like heat, gastric conditions, and moisture.
• Bacillus clausii strains are used as probiotics due to their immune-modulatory and antimicrobial properties.
• OTC B. clausii strains are available for acute diarrhea treatment.

Bacterial Growth

• Bacterial growth refers to an orderly increase in all components of a bacterium.
• Bacteria reproduce through binary fission, where one cell divides into two progeny cells.
• This leads to exponential growth, creating colonies of hundreds of cells from a single cell.
• Generation time is the time required for a cell to divide.
• For many bacteria, under ideal conditions, the doubling time can be as short as 20 minutes.
• E. coli, for example, has a generation time of 20 minutes, leading to one cell becoming one million cells after 20 generations (approximately 7 hours).

Structure of Bacteria

• Cytoplasm: A gel-like substance containing water, enzymes, nutrients, wastes, gases, ribosomes, a chromosome, and plasmids.
• Metabolism and replication occur in the cytoplasm.

Ribosomes

• Bacterial ribosomes are the sites of protein synthesis.
• They are smaller than eukaryotic ribosomes (70S vs. 80S) with different subunit sizes (50S & 30S vs. 60S & 40S).
• The differences between bacterial and human ribosomes explain the selective action of antibiotics on bacterial protein synthesis.

Nucleoid

• The nucleoid is the region where the chromosomal DNA is found in the cytoplasm.
• Most bacteria have a single, folded chromosome responsible for replication.
• There is no nuclear membrane.

Flagella

• These are long, whip-like appendages that enable bacterial movement toward nutrients and attractants.
• Swarming motility involves bacteria moving over a solid surface by rotating flagella, allowing them to spread across petri dishes.

Medical Importance Of Flagella

• Flagella play a role in urinary tract infections by propelling bacteria up the urethra.
• Specific antibodies against flagellar proteins aid in identifying bacteria in clinical labs.

Pili

• Short, protein appendages, smaller than flagella.
• They attach to specific receptors on human cell surfaces, crucial for the initiation of infection for some organisms like E. coli.
• Sex pili, a specialized type of pili, form the attachment between male and female bacteria during conjugation (called F-pilus).

Plasmid

• Extranuclear genetic elements composed of DNA.
• Transmitted to daughter cells during binary fission.
• Important for:
  • Antibiotic resistance through enzymes.
  • Heavy metal resistance (e.g., mercury).
  • Ultraviolet light resistance through DNA repair enzymes.
  • Exotoxins, including several enterotoxins.

Capsule

• A glycocalyx or slime layer – a viscous layer secreted around the cell wall, antigenic in nature.
• Advantages:
  • Adheres bacteria to surfaces.
  • Prevents phagocytosis.
  • Protects bacteria from lytic enzymes.
  • Key component for bacterial biofilm formation.

Biofilm

• A community of interactive bacteria attached to a solid surface or to each other, encased in an exopolysaccharide matrix.
• Common cause of hospital-acquired infection on medical devices.
• Bacteria within biofilms often exhibit resistance to antimicrobials.
• Streptococcus mutans, causing dental caries, uses sugar to build its capsule, forming a biofilm example.

Endospores

• Endospores are dehydrated, tough, non-reproductive bacterial stages allowing survival in unfavorable conditions like:
  • Low nutrient conditions.
  • Radiation.
  • High temperatures.
  • Disinfectants.
• They form when growth requirements are depleted or when conditions are unfavorable for growth.
• Sporulation is an adaptive response enabling survival through spore formation from vegetative cells.
• Endospores can survive for long periods until suitable conditions return, then germinate into vegetative forms.
• Gram-positive bacteria usually produce endospores.
• Examples include Clostridium (gangrene) and Bacillus (anthrax).

Endospore Structure

• Coat: A keratin-like structure.
• Cortex: A thick peptidoglycan layer.
• Core: Contains the bacterial chromosome.

Factors Affecting Bacterial Growth

• Physical factors:
  • Temperature: Influences growth, multiplication, survival, and death. High temperatures denature bacterial proteins. Cold temperatures slow growth, used for food preservation. Freezing doesn't kill but preserves microbes. Freeze-drying (lyophilization) is used to preserve cultures for extended periods., a process removing water under low temperature and pressure.
  • pH: The pH of the medium significantly affects microbial growth. Optimal acidity for most bacteria is around pH 6-8.
  • Osmotic pressure: Cells shrink in hypertonic solutions (high solute concentration) and expand/burst in hypotonic solutions (low solute concentration). Salt and sugar are used as food preservatives.
• Chemical Requirements:
  • Water: Essential for all microbial metabolism.
  • Elements: Carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), iron (Fe), sodium (Na), magnesium (Mg), chlorine (Cl), manganese (Mn), copper (Cu), zinc (Zn), cobalt (Co), molybdenum (Mo), and selenium (Se) are essential for microbial growth.
  • Carbon Source:
    • Organic compounds (e.g., glucose, sugars, amino acids).
    • Inorganic carbon (e.g., carbon dioxide (CO2)).

Capnophiles

• Microorganisms that thrive in high concentrations of carbon dioxide (CO2) (usually about 5% in cell cultures).
• They may require CO2 for their metabolism.

Oxygen Requirements

• Bacteria are classified based on their oxygen requirements:
  • Obligate aerobes: Require oxygen for growth (e.g., Mycobacterium tuberculosis).
  • Facultative anaerobes: Can utilize oxygen for respiration but can also grow without it through fermentation (e.g., E. coli).
  • Microaerophilic: Thrive in low oxygen levels.
  • Obligate anaerobes: Cannot grow in the presence of oxygen due to the lack of superoxide dismutase or catalase (e.g., Clostridium tetani).
  • Some obligate anaerobes can survive but not grow in oxygen, while others are quickly killed.

This quiz covers the essentials of probiotics, including their health benefits, popular strains, and applications. It also explores spore-forming probiotics like Bacillus clausii and their advantages in various conditions. Test your knowledge about these vital microorganisms and their role in gut health.