Veterinary Bacteriology Overview

Veterinary Bacteriology Road Map

• Aim: Provide a basic roadmap for veterinary students to understand, identify, and diagnose bacterial infectious diseases.
• Overview: Covers basics of infectious disease and bacterial structure, applying it to bacterial infectious diseases.

What is an Infectious Disease?

• Definition: An illness caused by a pathogen (or its toxic product) transmitted from an infected source (person, animal, or contaminated object) to a susceptible host.
• Key Terms:
  • Pathogen/infectious agent: The causative microorganism.
  • Infection: The colonization and/or multiplication of a pathogen.
  • Host: A carrier for a pathogen, susceptible to infection.

Veterinary Infectious Diseases

• Causative Agents: Infectious diseases result from infectious agents:
  • Cellular: Bacteria, fungi, parasites
  • Acellular: Viruses, prions
• Pathogenesis: The outcome of host-pathogen interaction. Host damage from either the infectious agent itself or the host's immune response determines the disease outcome.
• Variable Factors: Host immune response, environment (immediate, local, regional, or global), and pathogen virulence all influence the outcome of infection.

Types of Infectious Agents

• Categorization:
  • Acellular: Prions, viruses
    • Prions: abnormal cellular proteins, become pathogenic through conformational change.
    • Viruses: nucleic acid in a protein coat and only multiply within living cells.
  • Cellular: Prokaryotes (bacteria, archaea); Eukaryotes (fungi, algae, parasites)

How do Infectious Agents Cause Disease?

• Pathogenesis: The process through which a disease develops, resulting from the interaction between host and pathogen.
• Host Damage: Either from the infectious agent itself or the host's immune response.

Infectious Disease Outcome

• Interaction: The pathogenic interaction is dynamic (affected by variable factors), creating a balance between host and pathogen. Outcomes differ based on virulence and environment.
• Outcome: May include host damage, pathogen survival, or a combination. Environment plays a large role in outcome.

Environmental Effects

• Infectious agent characteristics: microorganism category, genotype, environmental survivability, virulence, entry points, tissue tropism, dose, resistance to host defences, and vector need.
• Susceptible Animal Characteristics: Species, breed, age, sex, genotype, immune competence, and physiological status (skin, mucous membranes).
• Disease Outcomes (Clinical): Acute, subacute, chronic, subclinical, carrier state, and latent infections.
• Management and Environment factors: housing, space, ventilation, hygiene, nutrition, external climate, disease control programs.

Variable Outcomes

• Graphical Representation: Infectious diseases can be graphically represented, showing differing outcomes based on the variable interaction of factors including host response, environment, and pathogen virulence. This shows the range of outcomes, from no disease outcome to fatality.

Graphs 1 - 6 Explanation

• Pathogen examples and descriptions to various situations
• Descriptions of pathogen behavior based on weak and strong host responses.
• Descriptions of pathogens behaviors based on typical continuum of immune responses associated with the disease.

Outcome of Host-Pathogen Interaction

• Commensalism: Host-microorganism interaction causing no host damage.
• Colonization: Host-microorganism interaction with varying host damages (minimal to great) indicative of host and immune responses.
• Latency: Persistent microorganism with no obvious disease but possible host damage at the cellular or tissue level.
• Disease: Clinical outcome happening when the threshold level of host damage is surpassed.
• Other terms related to pathogenesis
  • Virulence: Pathogen's ability to cause damage.
  • Virulence factor: Pathogen component enabling damage.

Defining a Bacterial Species

• Phenotypic: similar characteristics (e.g., staining, shape, metabolic function).
• Genotypic:
  • DNA-DNA hybridization: measures DNA sequence similarity. >70% similarity usually indicates the same species.
  • Average Nucleotide Identity (ANI): measure of genomic similarity (greater than 95% suggesting the same bacterial species).

Characteristics of Bacterial Species

• Phenotypic, means of identifying bacterial species (e.g., gram stain, shape, motility, tests for enzymes).
• Genotypic, means of identifying bacterial species (e.g., DNA-DNA hybridization, ANI).

Categorization Below Species Level

• Type: Subgroup of species with specific characteristics.
• Strain: Pure culture from single cell.
• Isolate: Pure culture from a heterogeneous wild-type population.

Example

• Illustrated the progression of a particular type of bacteria, from non-pathogenic to pathogenic and the resulting types (e.g., E. coli) and strains.

General Veterinary Bacteriology

• Important information: General information about pathogens relevant to veterinary medicine, such as flagella,
• Information distinctions: Distinction of presence/absence of certain characteristics (e.g., flagella) among all bacterial pathogens.
• Gram stain classification: dividing all pathogens into gram negative versus gram positive, irrespective of other characteristics, such as the absence or presence of flagella.

Questions to ask When Dealing with Infectious Diseases

• Questions related to determining whether a disease is infectious or noninfectious
• Questions related to identifying the infectious agent.
• Questions related to relating clinical findings with the infectious agent.
• Questions related to identifying the source and how to treat the infection.
• Questions related to controlling the spread.
• Questions related to prevention of the infectious disease from occurring.

Bacterial Shapes (Microscopic)

• Describes different shapes of bacteria (e.g., coccus, bacillus, spirillum).

Staining Bacteria

• Reason for staining: Stain bacteria for easier identification and to reveal structural differences.
• Enhancing contrast: Contrast enhancement is needed for microscopy, and bacteria can be stained, or other methods can be used.
• High resolution microscopy: Higher resolution microscopy is needed to view smaller bacterial structures.

Typical Prokaryotic Cell

• Cellular structure within the bacteria, that contributes to its functionality.

Gram Positive vs Gram Negative Bacteria

• Distinguishes gram-positive and gram-negative bacteria based on cell wall structure.

Cytoplasmic Membrane

• Describes the cytoplasmic membrane of prokaryotic cells.

Cell Wall

• Describes different structural differences in cell walls of gram-positive and gram-negative bacterial cells.

Outer Membrane

• Describes the outer membrane of prokaryotic cells' structural differences, components, and function.

S-layer

• Describes the S-layer structure, function and presence.

Capsule

• Describes capsule function and structure.

Mycobacterial Cell Wall and Cell Membranes

• Describes cell wall and membrane structures, including mycolic acids, arabinogalactan, and peptidoglycan.

Bacterial Appendages

• Describes different structures on bacterial surfaces; fimbriae, pili, and flagella, and their functions.

Fimbriae

• Describing ultra microscopic protein structures.
• Interchangeable term with pili
• Function: attachment, movement and conjugation.

Types of Flagella

• Describes flagella structure and describes various ways flagella are present in bacterial cells.

Flagellum Structure

• Detailed description of flagellum structure's key components and their function.

Cytoplasm (Chromosome)

• Detailed description of the chromosomes that regulate bacterial function.

Ribosomes

• Detailed description of ribosomes structure, and how it contributes to cellular function.

Plasmids

• Description of Plasmids; how they replicate, number, advantage, virulence and antimicrobial resistance.

Cytoskeleton

• Description of bacterial cytoskeleton components, function and their relation to eukaryotic homologues.

Bacterial Inclusions

• Description of bacterial inclusion, nutrient storage components and their roles.

Endospore Formation

• Description of Endospore formation and its regulation process under unfavorable conditions.
• Presentation of potential bacterial spore positions.

Endospores in Stained Smear

• Staining and visualization of endospores.

Next Class

• Content related to bacterial DNA.