Microbe-Human Interactions: Health and Disease
Definitions
- Infection: Condition where a pathogenic microorganism enters host defenses, tissues, and multiplies.
- Disease: Pathologic state occurring upon infection; not all infections lead to overt disease.
Factors Leading to Disease
- Infections: Pathogenic organisms causing disease.
- Other Factors: Aging, malfunctioning organs.
Types of Germs
- Bacteria, Fungi, Protozoa, Viruses, Prions: Considered germs, can cause infectious diseases.
Normal Biota
- Normal Microbiota: Microbes residing on body surfaces that don't cause harm; include bacteria, fungi, protozoa, viruses.
- Location: Found on skin, mucous membranes, upper respiratory tract, GI tract, external genitalia, etc.
- Inside Tissues: Should not have microbes; presence indicates infection.
Microbiota and Health
- Benefits: Compete with harmful microbes, aid in digestion, vitamin production.
Susceptibility to Infection
- Factors: Age, genetic defects, pregnancy, surgery, underlying diseases, stress, fatigue.
Endogenous Infections
- Definition: Disease caused by normal microbiota entering sterile parts of the body.
- Examples: Cut-induced infections, urinary tract infections.
Acquisition of Normal Biota
- Birth: Initial colonization from maternal vaginal biota and breast milk.
Pathogens
- Definition: Microbe with a parasitic relationship with host.
- True Pathogen: Causes disease in healthy individuals.
- Opportunistic Pathogen: Causes disease when host defenses are compromised.
Virulence and Virulence Factors
- Virulence: Degree of pathogenicity of a microbe.
- Virulence Factors: Traits aiding in causing disease.
Infectious Dose (ID)
- Definition: Minimum number of microbes required for infection.
- ID50: Amount needed for 50% of a population to become infected.
Microbial Pathogenesis
- Portal of Entry: Skin breaks, mucosal surfaces.
- Attachment: Via fimbriae, capsules, spike proteins.
- Surviving Host Defenses: Avoidance of immune response.
- Damaging the Host: Enzymes, toxins causing tissue damage.
- Exiting the Host: Via respiratory, fecal, urinary tracts, skin.
Infections in Special Sites
- Placenta: Generally a barrier, but some microbes can cross.
Types of Toxins
- Exotoxins: Proteins, heat liable, provoke immune response.
- Endotoxins: Lipid A, found in gram-negative bacteria, heat stable.
Patterns of Infection
- Localized vs. Systemic: Localized in one spot vs. widely spread.
- Primary and Secondary Infections: Initial vs. subsequent infections.
Signs vs. Symptoms
- Signs: Measurable, e.g., fever.
- Symptoms: Experienced by patient, e.g., headache.
Disease Stages
- Incubation: Pathogen growing, no symptoms.
- Prodromal: Early symptoms appear.
- Acute Phase: Full-blown symptoms.
- Convalescence: Recovery phase.
Transmission and Vectors
- Reservoir vs. Source: Natural habitat vs. site of acquisition.
- Carriers: Individuals harboring pathogens.
- Vectors: Living organisms transmitting disease.
Koch’s Postulates
- Steps to link a pathogen to a disease using isolation and infection of other hosts.
This lecture covers essential concepts of pathogenic microorganisms, their interaction with human hosts, and the fundamentals of infectious diseases, including transmission, virulence, and immune evasion.