Microbial Diseases of the Skin and Wounds

Types of Symbiosis

• Symbiosis can be classified into several types based on the benefits or detriments to the involved organisms.

  • Mutualism:

  • Both partners benefit from the relationship.

  • Example: Pollinators and flowering plants.

  • Commensalism:

  • One organism benefits while the other is neither helped nor harmed.

  • Example:

    • Fungi secreting antibiotics inadvertently harming bacteria without direct competition.

    • This results in a microbial community where certain bacteria cannot proliferate due to the presence of antibiotics from fungi.

  • Parasitism:

  • One organism benefits at the direct expense of the other.

  • Typically associated with pathogens causing disease in their hosts.

  • Example: Pathogens exploiting host resources leading to health issues.

Microbiome Basics

• Microbiome:

  • The community of microorganisms living in and on the human body, primarily composed of bacteria.

  • Majority of these organisms are antagonistic, competing against harmful bacteria.

  • Antagonism:

    • The competitive behavior among microbes for resources and space.

  • Resident Microbiota:

  • Always present in the body, difficult to eradicate.

  • Example: Oral bacteria.

  • Transient Microbiota:

  • Temporary inhabitants that can change based on various factors like hormonal changes, lifestyle, and environmental conditions.

Establishment of Microbiome

• The microbiome is primarily established at birth, influenced by exposure to the mother's microbiome.

• Birth methods impact the microbiome:

  • Vaginal Birth: Exposes the infant to maternal vaginal and fecal flora.

  • Cesarean Birth: Establishes the microbiome through physical interaction rather than direct microbiota transfer.

• Factors leading to microbiome disruption:

  • Chemotherapy, antibiotics, and changes in pH or hormonal levels (e.g., douching).

Microbial Pathogenicity

• Microorganisms can behave as opportunistic pathogens:

  • These are usually harmless but can cause harm if they find themselves in a location they typically don't occupy or if conditions change.

• Pathology:

  • The study of disease, including etiology (cause of disease) and pathogenesis (development of disease).

• Infection:

  • The invasion or colonization of the body by pathogens that can lead to disease.

  • Some microbes can be asymptomatic and still present in the body.

• Factors triggering opportunistic pathogens include:

  • Hormonal changes, antibiotic treatments, or fluctuations in the immune system.

Disease Classification

• Disease: An abnormal state where the body does not perform optimally.

• Reservoirs of Disease: Three primary types include animal, human, and nonliving (e.g., soil, water).

  • Zoonotic Diseases:

  • Diseases transferred from animals to humans.

  • Typically one-way transmission to humans without reverse transmission back to animals.

  • Examples of zoonotic disease transmission incidents:

  • SARS: Demonstrated how diseases travel quickly via global travel.

  • Necropsy case: A park ranger contracting an infection due to improper handling of a dead animal.

Disease Terminology and Symptoms

• Definitions:

  • Morbidity: Rate of disease occurrence within a population.

  • Mortality: Rate of death caused by disease.

  • Symptoms: Changes felt by the patient (e.g., headache).

  • Signs: Observable indicators of disease (e.g., fever).

  • Syndrome: A collection of signs and symptoms characteristic of a particular disease.

  • Asymptomatic Infections: Presence of infection without noticeable symptoms.

Contamination vs Infection

• Contamination: When pathogens are present in the body but not yet causing disease.

• Infection: Occurs when pathogens overwhelm the immune system and lead to disease.

• Portals of Entry:

  • Three major pathways for pathogen entry into the body:

  • Skin.

  • Mucous membranes.

  • Placenta.

  • Parenteral Routes:

  • Introduced into the body via medical interventions (e.g., injections).

• Skin:

  • Acts as a barrier against pathogens, facilitated by the epidermis, which replenishes itself regularly.

• Mucous Membranes:

  • Designed to trap pathogens and prevent them from entering the bloodstream rather than acting as an armor.

Stages of Infectious Disease

• Stages:

  • Incubation: Time between infection and first symptoms.

  • Prodromal: Initial symptoms appear and the pathogen begins growing.

  • Period of Illness: Peak of disease with most severe symptoms.

  • Period of Decline: Symptoms begin to diminish as the immune system overcomes the pathogen.

  • Convalescence: Recovery phase with no symptoms.

Severity and Duration of Diseases

• Disease Types:

  • Acute: Quick onset, short duration.

  • Chronic: Slow onset, long-lasting.

  • Latent: Inactive phase followed by eventual activation.

• Herd Immunity:

  • Immunity in a majority of the population reducing the overall spread of disease.

Infection Categories

• Local Infection: Confined to a specific area.

• Systemic Infection: Spread throughout the whole body.

• Focal Infection: Originates at a specific site, spreads to other areas.

• Primary Infection: Initial infection that leads to illness.

• Secondary Infection: Follows a primary infection, often taking advantage of a weakened immune response.

• Subclinical Disease: No obvious symptoms or signs but may still be infectious.

Blood-Related Infections

• Terminology:

  • Bacteremia: Presence of bacteria in the blood.

  • Toxemia: Presence of toxins in the blood.

  • Septicemia: Blood poisoning and can lead to sepsis.

  • Sepsis: Overwhelming response to infection that can cause organ failure and death.

Pathogen Traits and Mechanisms

• Pathogenicity: Ability to cause disease.

• Virulence: Degree to which a pathogen causes disease.

• Factors affecting virulence include:

  • Adhesion factors, biofilms, extracellular enzymes, and toxins.

• Exotoxins: Secreted proteins that disrupt host cellular functions.

• Endotoxins: Released upon destruction of bacteria; can cause harmful immune responses.

• Antiphagocytic Factors: Prevent immune response from effectively clearing pathogens. For example, capsules that block phagocytosis.

• Antigenic Variation: Pathogens can alter surface proteins to evade immune detection.

Summary and Considerations

• Important to recognize the complexity in interactions between pathogens, hosts, and environmental factors.

• Understanding disease mechanisms aids in identifying potential treatment and prevention strategies.