Pathogen-Host Interactions & Normal Flora

Question 1

What is a pathogen?

Answer 1

A biological agent capable of causing disease.

Example: Bacteria, viruses, fungi

Question 2

Define pathogenicity.

Answer 2

The ability of a pathogen to produce an infectious disease in an organism.

Example: Salmonella causing food poisoning

Question 3

What is pathogenesis?

Answer 3

The process by which disease or disorder develops, including factors contributing to onset, progression, and maintenance of disease.

Example: Cancer pathogenesis involves genetic mutations

Question 4

What is virulence?

Answer 4

The degree of damage done by a pathogen or its ability to cause disease.

Example: Highly virulent strains of E. coli

Question 5

Differentiate between a true pathogen and an opportunistic pathogen.

Answer 5

True pathogens cause disease in healthy individuals, while opportunistic pathogens cause disease only in compromised individuals or in the wrong location.

Example: Candida albicans as an opportunistic pathogen

Question 6

What are virulence factors?

Answer 6

Properties that enable a bacterium to establish itself within a host and cause disease.

Example: Toxins, adhesins

Question 7

Give an example of a virulence factor.

Answer 7

Siderophores, which are molecules that bind and transport iron in microbial environments.

Example: Siderophores help bacteria acquire iron for growth

Question 8

What are exotoxins?

Answer 8

Secreted toxins by pathogenic bacteria that damage host cells and tissues.

Example: Botulinum toxin

Question 9

What are haemolysins?

Answer 9

Pore-forming proteins secreted by bacteria that lyse red blood cells.

Example: Streptolysin O

Question 10

What role do adhesins play in bacterial pathogenicity?

Answer 10

Adhesins allow bacteria to adhere to host cells, facilitating infection.

Example: Adhesins help bacteria stick to the gut lining

Question 11

What is the significance of pili/fimbriae in bacterial adherence?

Answer 11

These hair-like structures enable bacteria to attach to host cells, aiding colonization and infection.

Example: Pili in Neisseria gonorrhoeae

Question 12

What is a biofilm?

Answer 12

A community of microbes embedded in an extracellular matrix, providing protection to the bacteria.

Example: Dental plaque biofilm

Question 13

What are pathogenicity islands?

Answer 13

Gene clusters on bacterial chromosomes that encode virulence factors.

Example: E. coli pathogenicity islands

Question 14

How do flagella contribute to bacterial pathogenicity?

Answer 14

They provide motility, allowing bacteria to move towards favorable environments (chemotaxis).

Example: Salmonella flagella for movement

Question 15

What is the normal microbiota?

Answer 15

The collection of bacteria, fungi, and protozoa that live on or in healthy individuals without causing disease.

Example: Lactobacillus in the gut

Question 16

What is the role of the normal gut microbiota?

Answer 16

It helps ferment unused energy substrates, produce vitamins, and prevent colonization by pathogens.

Example: Bacteroides aiding in digestion

Question 17

How do gut bacteria benefit the host?

Answer 17

They produce vitamins like Vitamin K and B vitamins and help train the immune system.

Example: E. coli synthesizing Vitamin K

Question 18

What is the hygiene hypothesis?

Answer 18

It suggests that reduced microbial exposure in early life may lead to increased autoimmune diseases due to altered immune system development.

Example: Asthma prevalence in developed countries

Question 19

What is the primary cause of pneumonia?

Answer 19

Often, Streptococcus pneumoniae, a common upper respiratory tract colonizer, leads to infection.

Example: Pneumococcal pneumonia

Question 20

What are probiotics?

Answer 20

Formulations containing live microbes that help restore a healthy gut microbiota.

Example: Lactobacillus probiotic supplements

Question 21

What is the purpose of prebiotics?

Answer 21

Nutrient formulations designed to support the growth of healthy gut microbiota.

Example: Inulin as a prebiotic

Question 22

What causes Clostridium difficile infections?

Answer 22

Overgrowth of C. difficile after antibiotic use, leading to severe diarrhea and intestinal damage.

Example: C. difficile spore formation

Question 23

What is a fecal microbiota transplant (FMT)?

Answer 23

A procedure that transfers stool from a healthy donor to a patient to restore healthy gut microbiota.

Example: FMT for recurrent C. difficile infection

Question 24

What is the significance of sterile body sites in diagnostics?

Answer 24

The presence of bacteria in sterile sites like the blood or cerebrospinal fluid indicates infection.

Example: Blood culture for sepsis diagnosis

Question 25

What are the implications of normal flora for respiratory infections?

Answer 25

Normal flora from the upper respiratory tract can cause infections if introduced into the lower respiratory tract.

Example: Nasopharyngeal flora causing pneumonia

Question 26

What is bacterial swarming motility?

Answer 26

Coordinated movement of bacterial populations across surfaces, often associated with virulence.

Example: Proteus mirabilis swarming on agar plates

Question 27

What is the function of the bacterial flagellar hook?

Answer 27

It connects the flagellar filament to the motor and transmits rotational torque, allowing movement.

Example: Hook protein in flagellar structure

Question 28

What is chemotaxis in bacteria?

Answer 28

The movement of bacteria in response to chemical stimuli, towards or away from a chemical source.

Example: E. coli moving towards nutrients

Question 29

What are non-fimbrial adhesins?

Answer 29

Cell surface proteins that allow bacteria to adhere to host cells without fimbriae.

Example: Fibronectin-binding proteins

Question 30

What role do exopolysaccharides play in biofilms?

Answer 30

They form the extracellular matrix that protects the biofilm and allows bacterial adhesion.

Example: Alginate in Pseudomonas aeruginosa biofilms

Question 31

What is commensalism?

Answer 31

A type of symbiosis where one organism benefits while the other is neither harmed nor helped.

Question 32

What is mutualism?

Answer 32

A symbiotic relationship where both organisms benefit.

Question 33

What is parasitism?

Answer 33

A relationship where one organism benefits at the expense of the other, often causing harm.

Question 34

How does bacterial motility contribute to pathogenicity?

Answer 34

Motility enables bacteria to move towards favorable environments, avoid immune defenses, and colonize hosts.

Question 35

What are siderophores?

Answer 35

Molecules produced by bacteria to scavenge iron from the host, essential for bacterial growth and virulence.

Question 36

What is the significance of pili in bacterial infections?

Answer 36

Pili allow bacteria to attach to host cells, preventing clearance by bodily fluids like urine or mucus.

Question 37

How do bacteria use flagella to avoid host defenses?

Answer 37

Flagella enable bacteria to swim through viscous environments like mucus, avoiding host immune defenses

Question 38

What is a pathogenicity island (PAI)?

Answer 38

A section of the genome containing genes responsible for a pathogen’s ability to cause disease

Question 39

How do toxins contribute to bacterial virulence?

Answer 39

Toxins disrupt host cell functions, damage tissues, and evade immune responses, enhancing bacterial survival.

Question 40

What is chemotaxis?

Answer 40

The ability of bacteria to move in response to chemical gradients, either towards attractants or away from repellents.

Question 41

What are afimbrial adhesins?

Answer 41

Non-fimbrial proteins on the bacterial surface that mediate adherence to host cells

Question 42

Why is adherence important for bacterial pathogens?

Answer 42

it is the first step in colonization, helping bacteria attach to host cells and resist mechanical removal, like urination or peristalsis.

Question 43

What are pore-forming toxins (PFTs)?

Answer 43

Toxins that create pores in host cell membranes, leading to cell lysis and death.

Question 44

What is swarming motility?

Answer 44

The coordinated movement of bacterial populations across surfaces, often associated with virulence in pathogens like Proteus mirabilis.

Question 45

What is biofilm, and why is it important in bacterial infections?

Answer 45

A biofilm is a community of microbes embedded in a protective extracellular matrix, providing resistance to immune attacks and antibiotics.

Question 46

How do bacteria invade host cells

Answer 46

They either induce host cell endocytosis or survive phagocytosis to gain entry and establish infections.

Question 47

How do normal flora prevent pathogen colonization?

Answer 47

by occupying receptor sites on host cells, producing antimicrobial substances, and outcompeting potential pathogens.

Question 48

What is the role of gut microbiota in vitamin production?

Answer 48

Gut bacteria like E. coli synthesize vitamins such as Vitamin K and B group vitamins for the host.

Question 49

What are transient flora?

Answer 49

microorganisms that are temporarily present in or on the body and may be removed after a short time due to washing, immune defenses, or other factors.

Question 50

What are nosocomial infections?

Answer 50

Infections acquired in a hospital setting, often involving antibiotic-resistant bacteria.

Question 51

How does Streptococcus pneumoniae cause pneumonia

Answer 51

As a common colonizer of the upper respiratory tract, it can invade the lower respiratory tract, causing inflammation and fluid buildup in the alveoli.

Question 52

How does a fecal microbiota transplant (FMT) help treat Clostridium difficile infections?

Answer 52

FMT restores a healthy gut microbiome, which outcompetes C. difficile and helps resolve infection.

Question 53

What is the proton motive force (PMF), and how does it drive flagellar movement?

Answer 53

PMF is an electrochemical potential difference across a membrane, used to power flagellar rotation and other cellular processes.

Question 54

What is magnetotaxis in bacteria?

Answer 54

The movement of bacteria in response to magnetic fields, often used by aquatic bacteria to orient themselves in relation to the Earth’s magnetic field.

Question 55

How does the microbiota influence the immune system?

Answer 55

It helps “train” the immune system by exposing it to microbial antigens, potentially reducing the risk of autoimmune diseases.

Question 56

Why is the distinction between sterile and non-sterile body sites important in diagnostic microbiology?

Answer 56

The presence of bacteria in sterile sites like blood or cerebrospinal fluid indicates infection, while bacteria in non-sterile sites may be normal flora.

Question 57

How does antibiotic use disrupt normal flora?

Answer 57

Antibiotics can kill beneficial microbes, allowing opportunistic pathogens like Clostridium difficile to overgrow and cause infections.

Question 58

What is the significance of fimbriae in urinary tract infections?

Answer 58

Fimbriae on uropathogenic E. coli allow them to attach to urinary tract cells, leading to infection and resistance to being flushed out by urine

Question 59

What is the chaperone-usher pathway?

Answer 59

A mechanism used by Gram-negative bacteria to assemble pili on their surface, crucial for attachment to host cells.

Question 60

What are flagellar filaments made of?

Answer 60

Flagellar filaments are made of polymerized flagellin protein subunits, forming a spiral structure used for bacterial movement.