MICR 483 Module 1 Notes
Section 1
What is Normal Flora?
● Definition: Microorganisms (bacteria, fungi, viruses) that are normally found in or on the human
body.
● Found on:
○ Skin
○ Hair
○ Mouth
○ Ears
○ Nasal cavity
○ Gut
○ Vagina
○ Surfaces we touch (e.g., desks, food)
Understanding Normal Flora
● Mucous membranes are a key habitat for normal flora.
● Each body area has a unique ecological niche that certain microbes thrive in.
Body Area Common Flora Examples
Nasal cavity Streptococcus pneumoniae
Oral cavity Viridans streptococci
Gut Bacteroides fragilis, E. coli, Enterococci spp.
Vagina Lactobacillus spp.
Skin Staphylococcus epidermidis, S. aureus, Corynebacterium spp.
,Important Bacteria to Know
● Streptococcus pneumoniae: Gram-positive coccus; causes pneumonia.
● Escherichia coli: Gram-negative bacillus; some strains cause food poisoning.
● Enterococci spp.: Gram-positive cocci; can cause UTIs.
● Staphylococcus aureus: Gram-positive cocci; causes surgical site infections.
Points of Entry for Microorganisms
● Oral/Nasal cavities: Entry for bacteria like Streptococcus spp.
● Skin: Entry via cuts or insect vectors (e.g., Plasmodium falciparum via mosquito).
● Genital tracts: Normal flora exists, but also entry point for STIs like Neisseria gonorrhoeae.
Benefits of Normal Flora at Entry Points
● Ecological competition: Normal flora occupy niches, preventing pathogen colonization.
● Physiological support:
○ Lactobacillus spp. in vagina maintain acidic pH.
○ Gut flora aid in metabolism and protect against Clostridium difficile.
Components of Normal Flora
● Includes bacteria and fungi (viruses excluded in this course).
● Microbiome: Bacterial population of the body.
● Fungiome: Fungal population of the body.
Microbiome Facts
● Microbial cells outnumber human cells 10:1.
● Intestinal microbiome: ~10¹⁴ organisms, over 500 species.
, Types of Host-Flora Relationships
● Symbionts: Both host and microbe benefit.
● Pathobionts: Potentially harmful, but live as symbionts under normal conditions.
● Commensals: Microbe benefits; host is unaffected.
⚠️ Dysbiosis: Imbalance among these flora types → can lead to disease.
Skin Microbiome
● Mostly Gram-positive bacilli (rods) and cocci (spheres).
● Gram-positive bacteria: Thick peptidoglycan cell walls, retain violet stain.
Type Examples
Bacilli (rods) Coryneform bacteria, Propionibacterium spp.
Cocci (spheres) Staphylococcus spp., Streptococcus spp.
S. aureus (coagulase-positive) vs. CNS (Coagulase-Negative Staphylococci)
Respiratory Tract Microbiome
● Upper respiratory tract:
○ Very dense (≈10⁹ bacteria/mL)
○ Organisms: Staphylococcus spp., Streptococcus pneumoniae, Haemophilus spp., Anaerobes
● Lower respiratory tract:
○ Considered sterile
● Oral flora changes with age:
○ Teeth increase microbial diversity (anaerobes thrive in low-oxygen areas).
Section 1
What is Normal Flora?
● Definition: Microorganisms (bacteria, fungi, viruses) that are normally found in or on the human
body.
● Found on:
○ Skin
○ Hair
○ Mouth
○ Ears
○ Nasal cavity
○ Gut
○ Vagina
○ Surfaces we touch (e.g., desks, food)
Understanding Normal Flora
● Mucous membranes are a key habitat for normal flora.
● Each body area has a unique ecological niche that certain microbes thrive in.
Body Area Common Flora Examples
Nasal cavity Streptococcus pneumoniae
Oral cavity Viridans streptococci
Gut Bacteroides fragilis, E. coli, Enterococci spp.
Vagina Lactobacillus spp.
Skin Staphylococcus epidermidis, S. aureus, Corynebacterium spp.
,Important Bacteria to Know
● Streptococcus pneumoniae: Gram-positive coccus; causes pneumonia.
● Escherichia coli: Gram-negative bacillus; some strains cause food poisoning.
● Enterococci spp.: Gram-positive cocci; can cause UTIs.
● Staphylococcus aureus: Gram-positive cocci; causes surgical site infections.
Points of Entry for Microorganisms
● Oral/Nasal cavities: Entry for bacteria like Streptococcus spp.
● Skin: Entry via cuts or insect vectors (e.g., Plasmodium falciparum via mosquito).
● Genital tracts: Normal flora exists, but also entry point for STIs like Neisseria gonorrhoeae.
Benefits of Normal Flora at Entry Points
● Ecological competition: Normal flora occupy niches, preventing pathogen colonization.
● Physiological support:
○ Lactobacillus spp. in vagina maintain acidic pH.
○ Gut flora aid in metabolism and protect against Clostridium difficile.
Components of Normal Flora
● Includes bacteria and fungi (viruses excluded in this course).
● Microbiome: Bacterial population of the body.
● Fungiome: Fungal population of the body.
Microbiome Facts
● Microbial cells outnumber human cells 10:1.
● Intestinal microbiome: ~10¹⁴ organisms, over 500 species.
, Types of Host-Flora Relationships
● Symbionts: Both host and microbe benefit.
● Pathobionts: Potentially harmful, but live as symbionts under normal conditions.
● Commensals: Microbe benefits; host is unaffected.
⚠️ Dysbiosis: Imbalance among these flora types → can lead to disease.
Skin Microbiome
● Mostly Gram-positive bacilli (rods) and cocci (spheres).
● Gram-positive bacteria: Thick peptidoglycan cell walls, retain violet stain.
Type Examples
Bacilli (rods) Coryneform bacteria, Propionibacterium spp.
Cocci (spheres) Staphylococcus spp., Streptococcus spp.
S. aureus (coagulase-positive) vs. CNS (Coagulase-Negative Staphylococci)
Respiratory Tract Microbiome
● Upper respiratory tract:
○ Very dense (≈10⁹ bacteria/mL)
○ Organisms: Staphylococcus spp., Streptococcus pneumoniae, Haemophilus spp., Anaerobes
● Lower respiratory tract:
○ Considered sterile
● Oral flora changes with age:
○ Teeth increase microbial diversity (anaerobes thrive in low-oxygen areas).
