Division of Microbiology

BASIC BACTERIOLOGY

INTRODUCTION

  • Bacteria are:

    • Single-celled microorganisms.

    • Lack a nuclear membrane.

    • Metabolically active.

    • Divide by binary fission.

  • Medically significant as a major cause of diseases.

  • Bacteria, despite their simple appearance, are sophisticated and highly adaptable.

  • Majority of bacteria can exist and grow independently; exceptions include Chlamydia and Rickettsia, which are obligately intracellular.

GROSS MORPHOLOGY

  • Characteristic shapes of bacteria:

    • Cocci (spherical)

    • Rods (bacilli)

    • Spirals (spirilla)

  • Occurrence in aggregates (e.g. pairs, chains, clusters) is diagnostic.

CELL STRUCTURE

  • Prokaryotic features:

    • Nucleoid instead of a nucleus.

    • Lack membrane-bound organelles.

    • Plasma membrane conducts functions typical of organelles in eukaryotes.

    • Multiplication through binary fission.

SURFACE STRUCTURES

Flagella

  • Structure:

    • Distinct from eukaryotic flagella.

    • Composed of a basal body and a cylindrical protein filament.

  • Function:

    • The flagellum moves by rotation around its axis.

    • Useful for diagnosing bacteria based on flagellar number and arrangement.

Pili (Fimbriae)

  • Description:

    • Slender, hair-like appendages found in many Gram-negative bacteria.

  • Function:

    • Important for adhesion to host surfaces.

Capsules

  • Description:

    • Some bacteria create a viscous polysaccharide gel capsule.

  • Function:

    • Capsules confer resistance to phagocytosis.

IMPORTANT CHEMICAL COMPONENTS OF SURFACE STRUCTURES

Cell Wall Peptidoglycans

  • Found in both Gram-positive and Gram-negative bacteria.

  • Functions:

    • Confers characteristic shape.

    • Provides mechanical protection.

  • Composition:

    • Glycan backbone composed of muramic acid and glucosamine.

    • Highly cross-linked peptide chains.

  • Relevance:

    • Target for β-lactam antibiotics.

Teichoic Acids

  • Description:

    • Polyol phosphate polymers linked to peptidoglycan in some Gram-positive bacteria.

  • Characteristic:

    • Strongly antigenic but absent in Gram-negative bacteria.

Lipoteichoic Acids

  • Description:

    • Polymers of amphiphilic glycophosphates anchored in the cytoplasmic membrane.

  • Functions:

    • Antigenic, cytotoxic, and play a role in adhesion (e.g., Streptococcus pyogenes).

Lipopolysaccharides

  • Description:

    • Major component of the outer membrane in Gram-negative bacteria.

  • Structure:

    • Comprises a lipid A anchor, a polysaccharide core, and carbohydrate chains.

  • Relevance:

    • Sugars provide serologic specificity.

Wall-Less Forms

  • Types of bacteria: Mycoplasma and L-forms.

  • Characteristics:

    • Lack cell wall peptidoglycans.

    • Mycoplasmas have a unique surface membrane structure.

CYTOPLASMIC STRUCTURES

Plasma Membrane

  • Composition:

    • Primarily a protein and phospholipid bilayer (approximately 3:1).

  • Functions:

    • Involved in transport, biosynthesis, and energy transduction.

Organelles

  • Description:

    • Bacterial cytoplasm contains 70S ribosomes.

    • Houses metabolic reserve granules (e.g., poly-β-hydroxybutyrate).

Endospores

  • Formation:

    • Produced by Bacillus and Clostridium species.

  • Characteristics:

    • Heat-resistant, dehydrated resting cells containing DNA and essential machinery.

    • Enclosed in a complex protective coat.

BACTERIAL METABOLISM

  • Definition:

    • Involves all biochemical reactions within a cell.

  • Focus area:

    • Chemistry of substrate oxidations and dissimilation reactions to generate energy.

  • Assimilation reactions: uptake and utilization of required compounds for growth.

HETEROTROPHIC METABOLISM

Overview

  • Heterotrophic metabolism involves biologically oxidizing organic compounds (e.g., glucose) to produce ATP and other compounds needed for biosynthesis.

Types of Respiration

Respiration

  • Oxygen is consumed, yielding:

    • 38 moles of ATP from oxidation of glucose (380,000 cal), with additional heat loss.

Fermentation

  • Process where an organic compound acts as the terminal electron acceptor instead of oxygen.

  • Generates less energy, supporting anaerobic growth.

KREBS CYCLE

  • Process:

    • Oxidative decarboxylation of pyruvate via acetyl CoA to produce CO2.

  • ATP Yield:

    • 15 moles of ATP (150,000 calories).

GLYOXYLATE CYCLE

  • Modification of the Krebs cycle

  • Produces acetyl CoA from the oxidation of fatty acids and lipid compounds.

ELECTRON TRANSPORT AND OXIDATIVE PHOSPHORYLATION

  • Function:

    • ATP production through electron transfer reactions in the cytoplasmic membrane causing oxidative phosphorylation of ADP.

MITCHELL OR PROTON EXTRUSION HYPOTHESIS

  • Explanation:

    • Energy conservation based on hydrogen ion extrusion, creating a proton motive force.

    • This allows for ATP synthesis in both respiration and photosynthesis.

BACTERIAL PHOTOSYNTHESIS

  • Description:

    • Light-dependent, anaerobic mechanism.

  • Process:

    • Reduces carbon dioxide to glucose for biosynthesis and energy.

  • Variants:

    • Photolithotrophic and photoorganotrophic reactions based on hydrogen source.

AUTOTROPHY

  • Definition:

    • Metabolic process using inorganic compounds for energy without sunlight.

  • Analogous terms include:

    • Chemotrophy, chemoautotrophy, or chemolithotrophy.

ANAEROBIC RESPIRATION

  • A type of heterotrophic metabolism using a different terminal electron acceptor (e.g., nitrate, sulfate).

NITROGEN CYCLE

  • A recycling process among bacteria, plants, and animals, involving:

    • Ammonification, mineralization, nitrification, and nitrogen fixation.

BACTERIAL PATHOGENESIS

  • Infection:

    • Invasion of host tissues leading to microbial multiplication.

  • Distinction:

    • Infection vs. disease; infections may not lead to symptoms.

HOST SUSCEPTIBILITY

  • Resistance enhancement:

    • Phagocytic cells and immune systems play crucial roles.

    • Initial resistance is non-specific, while specific immunity develops.

  • Vulnerable groups:

    • Very young, elderly, and immunosuppressed individuals.

BACTERIAL INFECTIVITY

  • Definition:

    • Result of the balance between bacterial virulence and host resistance.

  • Bacterial objective:

    • Multiplication rather than causing disease.

HOST RESISTANCE

  • Components:

    • Physical and chemical defenses against infection:

      • Antibacterial factors in secretions and rapid turnover of epithelial cells.

  • Environmental challenges:

    • Limited free iron, recognition by phagocytic cells, inflammatory responses.

GENETIC AND MOLECULAR BASIS FOR VIRULENCE

  • Virulence factors:

    • Encoded on different DNA components (chromosomal, plasmid, transposon).

HOST-MEDIATED PATHOGENESIS

  • Tissue damage in some infections may stem from the immune response rather than direct bacterial effects.

INTRACELLULAR GROWTH

  • Varied requirements of bacteria (e.g., Rickettsia being obligate intracellular vs. Salmonella which invade but do not need host cells).

VIRULENCE FACTORS

  • Key functions:

    1. Invade the host

    2. Cause disease

    3. Evade host defenses

  • Types:

    • Flagella, pili, fimbriae for adherence.

ENDOTOXINS

  • Lipopolysaccharide endotoxins from Gram-negative bacteria can induce:

    • Fever, inflammatory response, and other toxic events.

EXOTOXINS

  • Various protein toxins produced and secreted from pathogenic bacteria divide into categories:

    • Cytotoxins, neurotoxins, enterotoxins.

SIDEROPHORES

  • Iron-binding factors enabling competition for iron with host proteins.

CLASSIFICATION OF BACTERIA BASED ON MORPHOLOGY

Cocci

  • Types include:

    • Coccus, diplococci, encapsulated diplococci, Staphylococci, Streptococci, Sarcina, Tetrad, Vibrio.

Bacilli

  • Types include:

    • Coccobacillus, bacillus, diplobacilli, Streptobacilli.

GRAM POSITIVE BACTERIA

  • Notable examples:

    • Clostridium botulinum, Staphylococcus aureus, Bacillus anthracis.

GRAM NEGATIVE BACTERIA

  • Notable examples:

    • Neisseria meningitidis, Escherichia coli, Vibrio cholerae.

BASIC MYCOLOGY

  • Fungi are eukaryotic microorganisms that can exist as:

    • Yeasts, molds, or combinations of both.

  • Pathological implications:

    • Can cause various superficial or systemic diseases.

PHYSIOLOGY OF FUNGI

  • Fungi are heterotrophic and primarily aerobic; some can synthesize lysine.

MORPHOLOGY OF FUNGI

  • Yeasts:

    • Single-celled, reproduce by budding.

  • Molds:

    • Multicellular, filamentous structures (hyphae).

  • Dimorphism:

    • Ability to switch forms based on environmental conditions.

CLASSIFICATION OF FUNGI

  • Asexual and sexual structures termed anamorphs and teleomorphs, respectively.

BASIC BIOLOGY OF FUNGI

Hyphal and Yeast Morphogenesis

  • Growth occurs apically via organelles and cytoskeletal elements.

Reproduction

  • Sexual reproduction involves karyogamy and meiotic division, while asexual reproduction occurs via mitosis.

Disease Mechanisms of Fungi

  • Fungi can penetrate host barriers more easily under immunocompromised states, enabling infections to arise.

SPECTRUM OF MYCOSES

  • Classification based on:

    1. Site of infection (e.g., superficial, cutaneous).

    2. Route of acquisition (e.g., exogenous, endogenous).

    3. Type of virulence exhibited.

HELMINTHS

  • Worm-like parasites:

    • Include flatworms (Platyhelminthes) and roundworms (Nematoda).

  • Size and structure: all helminths are relatively large.

PATHOGENESIS OF HELMINTHS

  • Symptoms depend on worm size and metabolic activity.

HOST DEFENSE

  • Covers diverse immune responses including antibody- and cell-mediated immunity against helminths.

ROUNDWORMS

Ascaris Lumbricoides

  • Symptoms and life cycle:

    • Worms can obstruct intestines and symptoms correlate with load.

Hookworms

  • Symptoms on skin entry and respiratory penetration, with potential associated anemia due to intestinal attachment.

CONTROL OF PARASITIC INFECTIONS

  • Sanitary practices and treatment remain crucial in maintaining human health against parasitic infections.

ECTOPARASITES

  • Pathogens infecting skin layers, relevant examples include ticks, fleas, and lice.

  • Importance in public health correlates to transmission dynamics.

PEDICULOSIS

  • Types of lice infecting humans and transmission methods.

SCABIES

  • Caused by mites; primarily transmitted through direct contact.

  • Symptoms such as intense pruritus and skin damage may lead to secondary infections.

CONCLUSION

  • The multi-faceted interactions between these microorganisms and their hosts underscore the importance of continued study in microbiology.