Normal Flora

OPTOMETRY · SEMESTER 2

Microbiology and Parasitology

NORMAL FLORA AND PATHOGENS

Learning Objectives

By the end of this session, students are expected to be able to:
Define normal flora, mycology, pathogen and vector
Identify normal flora found in different body parts

Explain the importance of normal flora Describe the classification and general characteristics of pathogens of medical importance

Definition of terms

Normal flora : Microorganisms (mostly bacteria, but also fungi and viruses) that naturally live on or inside the human body without causing disease.

They can be commensalisms or mutualists with regard to the hosts.

Basically, normal flora do not harm the host however can provide the benefits to the hosts NOTE:

Normal flora can cause disease when the defense mechanisms of the body is breached or when the micro-organism is placed in the abnormal body site or dislocated

Definition of terms cont..

Pathogen: Is an organism which is capable of causing pathological condition to another
organism.
Vector: Is an organism that conveys pathogens from one host to another.
Infection: refers to the invasion of the pathogen into the body .

Host : is an organism affected by the pathogen Note : for the disease to be caused by the pathogen the host body should be susceptible to infection

Definition of terms cont..

Mycology :Is the branch of microbiology which deals with the study of fungi
Virology: Is branch of microbiology which deals with the study of virus

Bacteriology : the branch of microbiology which deals with the study of bacteria

Types of normal flora

Normal flora, also known as microbiota, can be categorized based on their relationship with the host and their location in or on the body.

Normal flora can live permanently, temporary or just become infective when the immunity becomes compromised .

Based on Relationship with the Host

Type
Description

Resident Flora

Long-term, stable microbes that consistently inhabit specific body sites.

Transient Flora

Temporary microbes that may colonize for short periods but do not persist.

Opportunistic Flora

Normally harmless but can cause disease if the host's defenses are compromised.

Based on Location in the Body

Body Site

Common Microbes Found

Skin
Staphylococcus epidermidis, Corynebacterium, Propionibacterium

Nose/Nasopharynx

Staphylococcus aureus, Streptococcus pneumoniae

Mouth/Oral Cavity

Streptococcus mutans, Lactobacillus, Actinomyces

Gastrointestinal Tract

Escherichia coli, Bacteroides, Enterococcus, Clostridium
Vagina

Lactobacillus, Candida, Gardnerella

Urethra (distal)
Staphylococcus epidermidis, Enterococcus, Corynebacterium

External Ear

Staphylococcus, Corynebacterium, Propionibacterium

Normal flora found in different body parts

Normal flora tends to be commensal or mutual symbionts adapted to the special conditions found in various body locations.

Normal flora are found mostly in :
o skin
o Eyes
o Nose, pharynx and tonsils
o In mouth and oral cavity
o In urethra
o In lower GIT
o Urogenital tract

o External ear

Normal flora found in different body parts

Skin
Staphylococcus spp e.g. S.epidermidis, S.aureus
Corynebacteria spp
Propionibacterium spp
Fungi

Note the most common is s.epidermidis

Normal flora found in different body parts cont..

Eyes
Staphylococcus epidermidis and s.aureus
Neisseria species.
Haemophilus influenzae
Corynebacteria spp
Streptococcus species (viridans group)

Propionibacterium spp

Normal flora found in different body parts cont…

Nose
Staphylococcus epidermidis
Staphylococcus aureus
Streptococcus spp
Neisseria sp.
Haemophilus influenzae
Corynebacteria sp

Micrococcus spp

Normal flora found in different body parts cont…

Mouth and pharynx
Staphylococcus epidermidis
Staphylococcus aureus
Streptococcus spp
Neisseria sp.
Haemophilus influenza
Corynebacteria
Lactobacillus spp
Yeast e.g. candida albicans
Enterococcus faecalis
Actinomycetes
Spirochetes

Mycoplasmas

Normal flora found in different body parts cont…

Urethra
Staphylococcus epidermidis, S.aureus
Streptococcus mitis
Enterococcus faecalis
Neisseria sp
Corynebacteria

Mycoplasmas

Normal flora found in different body parts cont…

Lower GIT
Staphylococcus epidermidis, S.aures
Clostridium spp
Lactobacillus
Klebsiella spp
Streptococcus mitis
Enterococcus faecalis
Escherichia coli
Proteus sp
Bacteroides spp
Bifidobacterium bifidum
Spirochetes

Mycoplasmas

Normal flora found on body parts cont…

Vagina
Streptococcus spp
Staphylococcus spp
Enterococcus faecalis
Neisseria spp.
Lactobacillus spp
Corynebacterium
Mycoplasma

Candida albicans

Normal flora found on body parts cont.…

External ear

Bacterial Flora

Staphylococcus epidermidis – a dominant skin commensal
Staphylococcus aureus – may be present in small numbers
Corynebacterium species – part of the skin microbiota
Propionibacterium acnes (now Cutibacterium acnes) – associated with sebaceous glands
Alpha-hemolytic streptococci – including Streptococcus mitis and Streptococcus sanguinis
Candida species – occasionally present, especially in moist environments

Malassezia species – lipid-dependent yeasts found on skin

The body parts without normal flora

While many areas are colonized by these microbes, some body parts are typically sterile under normal conditions, meaning they do not harbor normal flora.

Here are the major body sites that are normally sterile:

Central Nervous System

Brain
Spinal cord

Cerebrospinal fluid (CSF)

The body parts without normal flora cont….

Cardiovascular System

Heart
Blood vessels
Blood

Lower Respiratory Tract

Trachea
Bronchi

Alveoli (lungs)

The body parts without normal flora cont…

Internal Organs and Tissues
Liver
Kidneys
Pancreas
Spleen
Muscles

Bones

The body parts without normal flora cont…

Body Fluids

Urine (from the kidneys and bladder — not the urethra)
Amniotic fluid
Synovial fluid (in joints)
Peritoneal fluid
Pleural fluid
Eyes

Internal structures like the aqueous humor and vitreous body

The body parts without normal flora cont…

Reproductive System

Uterus
Fallopian tubes
Ovaries

Testes

These areas are protected by physical barriers and immune defenses. If microbes are found in these locations, it often indicates infection or disease, such as meningitis (in the CSF), septicemia (in the blood), or pneumonia (in the lungs).

Advantages of normal flora

1. Protection Against Pathogens
Competes with harmful microbes for nutrients and space.
Produces substances like bacteriocins and acids that inhibit pathogen growth.

2. Aid in Digestion and Nutrient Absorption Helps break down complex carbohydrates and fibers. Enhances absorption of minerals such as calcium and magnesium.

Advantages of normal flora

3. Immune System Development and Regulation
Stimulates the development of immune tissues and cells.
Trains the immune system to distinguish between harmful and harmless agents.
4. Maintaining Homeostasis
Contributes to the stability of skin pH and normal conditions
5. Detoxification and Drug Metabolism
Some gut microbes can metabolize drugs and toxins (biotransformation)

May influence the effectiveness and breakdown of medications

Advantages of normal flora

6.Synthesizes essential vitamins like vitamin K, biotin, and B vitamins, the bacteria uses simple nutrients to make them (biosynthetic vitamins)

Disadvantages of normal flora

Opportunistic Infections When the immune system is weakened or the normal flora is displaced (e.g., due to injury or surgery), these microbes can cause infections. For example, E. coli from the gut can cause urinary tract infections if it enters the urinary trac Antibiotic Resistance Transfer Some normal flora harbor antibiotic resistance genes, which can be transferred to pathogenic bacteria, making infections harder to treat

Disadvantages of normal flora

Production of Harmful Metabolites Certain gut bacteria can produce toxic compounds like ammonia or hydrogen sulfide, which may contribute to diseases if not properly regulated

Disadvantages of normal flora cont..

Interference with Medical Treatments Normal flora can sometimes interfere with diagnostic tests or contaminate medical samples, leading to false results or complications.

Pathogen

A pathogen is any microorganism that can cause disease in its host.

These infectious agents invade the body, multiply, and disrupt normal bodily functions, often triggering an immune response. They're commonly referred to as germs.

Pathogens are divided into parasitological and microbiological pathogens

Classification of pathogens

Type
Description
Examples
Bacteria
Single-celled organisms that can reproduce quickly.
E. coli, Streptococcus
Viruses
Tiny infectious agents that require a host cell to replicate.
Influenza, HIV, COVID-19
Fungi
Includes yeasts and molds; can infect skin, nails, or lungs.

Candida, Aspergillus

Protozoa
Single-celled organisms often spread through contaminated water and other routes
Giardia, Plasmodium (malaria)
Helminths
Parasitic worms that live inside the host.

Tapeworms, roundworms

Characteristics of pathogens

Pathogens have the ability to infect the host, Ability to enter, survive, and multiply in the host, this includes finding a suitable portal of entry like the skin, respiratory tract, or digestive system Pathogenicity Capacity to cause disease. Not all microbes are pathogenic, those that have mechanisms to damage host tissues or disrupt normal functions Possess adherence Mechanisms They use structures like pili, fimbriae, or surface proteins to attach to host cells and tissues, which is crucial for colonization

Characteristics of pathogens cont..

They have the degree of virulence , Degree of damage a pathogen can cause. Highly virulent pathogens cause severe disease, while less virulent ones may lead to mild symptoms They possess several mode of transmissions Pathogens spread through various routes, direct contact, airborne particles, contaminated food/water, or vectors like mosquitoes

Characteristics of pathogens cont..

Evasion of Host Defenses Many pathogens have strategies to avoid detection or destruction by the immune system, such as hiding inside cells or producing immune-suppressing molecules Toxin Production Some pathogens release toxins that directly harm host cells or trigger damaging immune responses.

Examples include botulinum toxin and cholera toxin Survival Outside Host Some pathogens can survive in harsh environmental conditions, allowing them to persist until they find a new host

Characteristics of pathogens cont..

Adaptability and Mutation Pathogens can evolve rapidly, especially viruses, allowing them to resist treatments or vaccines and adapt to new host

Questions

What is a pathogen?
What is a normal flora?
What are the importance of normal flora?
List types of microbiological pathogens?