Microbial Interactions with Humans

Microbial Interactions with Humans

Types of Interactions: Symbiosis
* Symbiotic Relationships

Overview of Human-Microbial Interactions
* Pathogens
* Pathogenicity
* Virulence
* Opportunistic Pathogen

Infection Versus Disease
* Infection
* Disease

Opportunistic Pathogens
* Don’t normally cause disease, but may under some circumstances
* 3 circumstances for gaining control/disease

Types of Interactions:
Normal Flora
* Normal Flora
* Factors that influence normal flora

Normal Flora
* Hundreds of different niches associated with human
* Some normal flora are pathogenic
* Resident versus transient flora
* Considered part of the first line of defense!
* Microbial antagonism
* Competitive exclusion

Portals of Entry
* Skin
* Mucous membranes

Preferred Portal
* Many microorganisms have to enter in a specific way and in a certain place to cause disease.
* Skin Portal

Skin
* Epidermis and Keratin
* Hair often deters microbial contact with skin
* Dermis and subcutaneous tissue
* Apocrine and sebaceous glands
* Eccrine glands (sweat)

Skin as a Barrier
Mucous Membranes
* Found in mouth, pharynx, esophagus, GI, respiratory, and urinary tracts
* Epithelial cells coated with protective glycoprotein layer (mucous)
* Less protection than skin
* Cilia and mucous produced by goblet cells

Mucous Membranes
* Respiratory tract Portal
* Respiratory Normal Flora
* Respiratory Barrier Mechanisms
* Gastrointestinal tract portal
* GI Normal Flora

Gastrointestinal Tract
* Large intestine
* GI Barrier
* Genitourinary tract Portal
* Genitourinary Tract Normal Flora
* Genitourinary Tract Barrier

LD50 and ID50
* LD50: Number of microbes in a dose that kill 50% of the organisms infected in a sample
* ID50: Number of microbes in a dose that causes disease in 50% of the organisms infected
* The higher the virulence the lower the ID50 or LD50

Microbial Virulence
Microbe Versus Host
* To cause disease a microbe must…
* Why it is difficult for microbes…
o Skin, antimicrobial sweat
Microorganisms and Mechanisms of Pathogenesis

Line of Defense
* First line: Skin and mucous membranes, normal flora
* Second line: phagocytes, inflammation, fever and antimicrobial substances
* Third line: (specific response) special lymphocytes (B and T cells) and antibodies

Step One: Adherence
* Specific adherence
* Pathogens have attachment structures
* Pathogens have attachment structures

Step 2: Invasion/Colonization
* Increase in numbers beyond the point of attachment.
* Three goals

Step 2: Invasion/Colonization
* Localized versus Systematic infections
* Bacteremia, viremia, toxemia
* Septicemia

Step 3: Cause Damage
* Virulence
* Three Ways to cause damage

Virulence Factors
* Usually help organism colonize and grow
* Coagulase
* Siderophores
* Collagenase
* Protease

Another Way to Classify Exotoxins
* Descriptive classifications
A-B toxin
* Cholera toxin (Vibrio cholera)—cholera

The Action of Chlorea Enterotoxin
More A-B toxin examples
Botulinum Toxin
Tetanus Toxin
Membrane Disrupting Toxins
Superantigens
Endotoxins
* Gram type negatives
* Part of outer portion of cell wall (outer membrane)
* Lipid A portion
* Exert effects when G- microbe lyses
* Same symptoms for different species of microbe
* No antitoxins produced by host
* Very stable—can’t destroy easily
* Rarely fatal
* Disseminated intravascular clotting
* General symptoms

Pyrogenic Response
* Macrophage ingestion
* Release of interleukin-1 in bloodstream
* Interleukin-1 to hypothalamus and production of prostaglandins
* Resetting of bodies thermostat

Susceptibility/Resistance of Host
* Species specificity
* Tissue specificity
* Age
* Stress
* Diet
* Pre-existing disease (Genetic and Infectious)
* Gender
* Behavior
* Weather?
* Your first line of defense—Review this

Microbial Interactions with Humans.ppt