Normal Flora

Question 1

What are the two main categories of normal flora?

Answer 1

Resident flora and transient flora

Question 2

What enzyme in saliva cleaves peptidoglycan and kills bacteria?

Answer 2

Lysozyme

Question 3

What is the major organism responsible for dental plaque formation?

Answer 3

Streptococcus mutans

Question 4

Which bacteria are responsible for gingivitis?

Answer 4

Porphyromonas gingivalis

Question 5

What is the primary bacterial species colonizing the stomach?

Answer 5

Helicobacter pylori

Question 6

Which part of the small intestine contains the highest amount of normal flora?

Answer 6

The ileum

Question 7

Which vitamins are synthesized by intestinal microbes?

Answer 7

B12, pyridoxine, thiamin, and vitamin K

Question 8

What gases are commonly produced by intestinal microbes?

Answer 8

Hydrogen, carbon dioxide, and methane

Question 9

What are the three types of relationships between the host and normal flora?

Answer 9

Commensalism, mutualism, and opportunism

Question 10

What is commensalism in the context of normal flora?

Answer 10

A relationship where the microbe benefits, but the host is neither harmed nor benefited.

Question 11

What is mutualism in the context of normal flora?

Answer 11

A relationship where both the microbe and the host benefit.

Question 12

What is an example of a mutualistic relationship in the human body?

Answer 12

Gut bacteria synthesizing vitamins (e.g., Bacteroides producing vitamin K) while benefiting from the host environment.

Question 13

What is an opportunistic pathogen?

Answer 13

A microorganism that is usually harmless but can cause disease when the host’s defenses are compromised.

Question 14

How can normal flora become opportunistic pathogens?

Answer 14

When the immune system is weakened, or normal microbial balance is disturbed (e.g., antibiotic use leading to Clostridium difficile infection).

Question 15

What is an example of an opportunistic infection?

Answer 15

Clostridium difficile causing diarrhea after antibiotic treatment.

Question 16

Which type of relationship involves potential pathogens that produce infection when the host’s defenses are weakened?

Answer 16

Opportunism.

Question 17

What is a real-world example of a commensal relationship in the human body?

Answer 17

Staphylococcus epidermidis living on the skin without causing harm.

Question 18

How does the mutualistic relationship between normal flora and the host benefit the immune system?

Answer 18

Normal flora competes with harmful pathogens, preventing infections and helping to train the immune system.

Question 19

What type of relationship can be seen in a person who carries Staphylococcus aureus without showing symptoms?

Answer 19

Commensalism or asymptomatic carrier state.

Question 20

What happens when a commensal organism turns into an opportunistic pathogen?

Answer 20

It starts causing disease, usually when the immune system is suppressed or normal flora is disrupted.

Question 21

Why is Escherichia coli considered mutualistic in the gut but opportunistic in the urinary tract?

Answer 21

In the gut, it helps with digestion and vitamin production, but in the urinary tract, it can cause infections.

Question 22

What type of host-pathogen relationship occurs when the microbe benefits but harms the host?

Answer 22

Parasitism.

Question 23

What is an example of a disease caused by an asymptomatic carrier and example of bacterial parasite that benefits at the host’s expense?

Answer 23

Typhoid fever (Salmonella typhi - Typhoid Mary)
salmonella species

Question 24

What happens to sensitive bacteria when antibiotics are taken?

Answer 24

They die, leaving space in the gastrointestinal (GI) tract.

Question 25

Why does Clostridium difficile (C. diff) increase when antibiotics are taken?

Answer 25

Antibiotics kill competing bacteria, allowing C. diff to multiply and take up the free space.

Question 26

How does C. difficile cause diarrhea after antibiotic use?

Answer 26

It produces toxins, and when its population increases from 25 to 40, excess toxins cause diarrhea.

Question 27

Under normal conditions, how many toxins does C. difficile produce?

Answer 27

25 toxins, which the immune system can usually control.

Question 28

How does the immune system normally keep C. difficile in check?

Answer 28

By maintaining a balanced microbiome that prevents C. difficile overgrowth.

Question 29

What defines a parasitic pathogen?

Answer 29

A disease-causing organism that benefits at the expense of the host.

Question 30

What is a carrier in the context of infectious diseases?

Answer 30

A person who harbors a pathogen and can spread it, even if they show no symptoms.

Question 31

What are the two types of carrier status?

Answer 31

Symptomatic (showing symptoms) and asymptomatic (healthy but still infectious).

Question 32

What does chronic convalescent carrier status mean?

Answer 32

The bacteria remain in the body for a long time even after recovery.

Question 33

Which food is Salmonella often associated with?

Answer 33

Chicken

Question 34

What bacteria, besides Salmonella, can be carried asymptomatically?

Answer 34

Staphylococcus aureus.

Question 35

Is the system of a newborn free of flora at birth?

Answer 35

Yes, but colonization begins immediately after birth.

Question 36

How does an infant acquire normal flora?

Answer 36

Through exposure to the vagina, air, food, and other environmental factors.

Question 37

What factors influence the selective colonization of normal flora in a newborn?

Answer 37

pH, temperature, oxygen levels, and nutrients.

Question 38

How long does it take for a newborn to fully establish normal flora?

Answer 38

Approximately 1 year to 18 months.

Question 39

Does the microbiota remain constant throughout life?

Answer 39

No, microbiota changes with environmental changes.

Question 40

What are key factors that determine an infant’s gut microbiota?

Answer 40

Mode of delivery, feeding method, and environmental exposure.

Question 41

How does the mode of delivery affect gut microbiota?

Answer 41

Vaginally delivered infants acquire flora from the birth canal, while C-section infants acquire flora from the skin and hospital environment.

Question 42

What major factors influence gut microbiota in infancy?

Answer 42

Breastfeeding, formula feeding, introduction of solid foods, and overall diet.

Question 43

How does breastfeeding influence an infant’s microbiota?

Answer 43

It promotes beneficial bacteria like Bifidobacteria.

Question 44

Why does the introduction of solid food impact the microbiota?

Answer 44

It diversifies the gut microbiome by introducing new bacteria from food sources.

Question 45

What is the traditional belief about microbial colonization in neonates?

Answer 45

That the womb is sterile, and the neonate's microbiome is first seeded at birth.

Question 46

What recent studies suggest about microbial presence in the prenatal stage?

Answer 46

That microbial communities may exist in the placenta, amniotic fluid, and meconium.

Question 47

What is intrauterine seeding?

Answer 47

The hypothesis that microbes may colonize the fetus before birth.

Question 48

Where is it believed that many of the placenta’s microbes originate from?

Answer 48

The mouth.

Question 49

Which bacteria are commonly found in term neonates?

Answer 49

Lactobacillus and Bifidobacterium.

Question 50

What gut bacteria are prevalent in preterm neonates?

Answer 50

Enterobacteriaceae, Veillonella, Enterococcus, Staphylococcus.

Question 51

Which bacteria dominate the gut microbiota of breastfed infants?

Answer 51

Lactobacillus and Bifidobacterium.

Question 52

What gut bacteria are found in formula-fed infants?

Answer 52

Bacteroides, Staphylococcus, Clostridia, Enterococcus, Enterobacteria.

Question 53

How does the mode of delivery affect an infant's gut microbiota?

Answer 53

Vaginally delivered infants acquire Prevotella and Lactobacillus, while C-section infants acquire Corynebacterium, Staphylococcus, Propionibacterium.

Question 54

Why do vaginally delivered babies have more Lactobacillus?

Answer 54

Because they pass through the birth canal, where Lactobacillus is abundant.

Question 55

List the major location of normal flora

Answer 55

Skin Eyes Ears Respiratory Tract (upper RT and Lower RT) Digestive Tract Urinary Tract Reproductive Organ Circulatory system

Question 56

Which part of the respiratory tract is colonized by normal flora?

Answer 56

The upper respiratory tract (nose, throat).

Question 57

Which parts of the body are free of normal flora?

Answer 57

Blood, lymph, lower respiratory tract, middle and inner ear, bladder, kidneys, and the central nervous system.

Question 58

Which bacteria are commonly found in the upper respiratory tract?

Answer 58

Streptococcus pneumoniae, Staphylococcus aureus, Corynebacterium diphtheriae.

Question 59

Where is normal flora most concentrated in the body?

Answer 59

The colon (large intestine)

Question 60

What major bacterial species is present in the vagina after puberty?

Answer 60

Lactobacillus acidophilus

Question 61

What are two factors that prevent colonization of the skin?

Answer 61

Dryness and low pH

Question 62

What component of sweat acts as an antimicrobial agent?

Answer 62

Lysozyme

Question 63

How does the upper respiratory tract prevent colonization?

Answer 63

By continuous mucus flow, macrophage activity, and lysozyme production

Question 64

What pH-related factor prevents bacterial colonization in the stomach?

Answer 64

The highly acidic gastric environment.

Question 65

How does saliva help inhibit bacterial colonization in the mouth?

Answer 65

Through continuous flow and the presence of enzymes like lysozyme

Question 66

What change in the vaginal environment occurs after menopause that affects microbial colonization?

Answer 66

The vagina becomes glycogen-free and alkaline, reducing Lactobacillus acidophilus populations.