Pathogen-Host Interactions & Normal Flora Flashcards
What is a pathogen?
A biological agent capable of causing disease.
Example: Bacteria, viruses, fungi
Define pathogenicity.
The ability of a pathogen to produce an infectious disease in an organism.
Example: Salmonella causing food poisoning
What is pathogenesis?
The process by which disease or disorder develops, including factors contributing to onset, progression, and maintenance of disease.
Example: Cancer pathogenesis involves genetic mutations
What is virulence?
The degree of damage done by a pathogen or its ability to cause disease.
Example: Highly virulent strains of E. coli
Differentiate between a true pathogen and an opportunistic pathogen.
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
What are virulence factors?
Properties that enable a bacterium to establish itself within a host and cause disease.
Example: Toxins, adhesins
Give an example of a virulence factor.
Siderophores, which are molecules that bind and transport iron in microbial environments.
Example: Siderophores help bacteria acquire iron for growth
What are exotoxins?
Secreted toxins by pathogenic bacteria that damage host cells and tissues.
Example: Botulinum toxin
What are haemolysins?
Pore-forming proteins secreted by bacteria that lyse red blood cells.
Example: Streptolysin O
What role do adhesins play in bacterial pathogenicity?
Adhesins allow bacteria to adhere to host cells, facilitating infection.
Example: Adhesins help bacteria stick to the gut lining
What is the significance of pili/fimbriae in bacterial adherence?
These hair-like structures enable bacteria to attach to host cells, aiding colonization and infection.
Example: Pili in Neisseria gonorrhoeae
What is a biofilm?
A community of microbes embedded in an extracellular matrix, providing protection to the bacteria.
Example: Dental plaque biofilm
What are pathogenicity islands?
Gene clusters on bacterial chromosomes that encode virulence factors.
Example: E. coli pathogenicity islands
How do flagella contribute to bacterial pathogenicity?
They provide motility, allowing bacteria to move towards favorable environments (chemotaxis).
Example: Salmonella flagella for movement
What is the normal microbiota?
The collection of bacteria, fungi, and protozoa that live on or in healthy individuals without causing disease.
Example: Lactobacillus in the gut
What is the role of the normal gut microbiota?
It helps ferment unused energy substrates, produce vitamins, and prevent colonization by pathogens.
Example: Bacteroides aiding in digestion
How do gut bacteria benefit the host?
They produce vitamins like Vitamin K and B vitamins and help train the immune system.
Example: E. coli synthesizing Vitamin K
What is the hygiene hypothesis?
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
What is the primary cause of pneumonia?
Often, Streptococcus pneumoniae, a common upper respiratory tract colonizer, leads to infection.
Example: Pneumococcal pneumonia
What are probiotics?
Formulations containing live microbes that help restore a healthy gut microbiota.
Example: Lactobacillus probiotic supplements
What is the purpose of prebiotics?
Nutrient formulations designed to support the growth of healthy gut microbiota.
Example: Inulin as a prebiotic
What causes Clostridium difficile infections?
Overgrowth of C. difficile after antibiotic use, leading to severe diarrhea and intestinal damage.
Example: C. difficile spore formation
What is a fecal microbiota transplant (FMT)?
A procedure that transfers stool from a healthy donor to a patient to restore healthy gut microbiota.
Example: FMT for recurrent C. difficile infection
What is the significance of sterile body sites in diagnostics?
The presence of bacteria in sterile sites like the blood or cerebrospinal fluid indicates infection.
Example: Blood culture for sepsis diagnosis
What are the implications of normal flora for respiratory infections?
Normal flora from the upper respiratory tract can cause infections if introduced into the lower respiratory tract.
Example: Nasopharyngeal flora causing pneumonia
What is bacterial swarming motility?
Coordinated movement of bacterial populations across surfaces, often associated with virulence.
Example: Proteus mirabilis swarming on agar plates
What is the function of the bacterial flagellar hook?
It connects the flagellar filament to the motor and transmits rotational torque, allowing movement.
Example: Hook protein in flagellar structure
What is chemotaxis in bacteria?
The movement of bacteria in response to chemical stimuli, towards or away from a chemical source.
Example: E. coli moving towards nutrients
What are non-fimbrial adhesins?
Cell surface proteins that allow bacteria to adhere to host cells without fimbriae.
Example: Fibronectin-binding proteins
What role do exopolysaccharides play in biofilms?
They form the extracellular matrix that protects the biofilm and allows bacterial adhesion.
Example: Alginate in Pseudomonas aeruginosa biofilms
What is commensalism?
A type of symbiosis where one organism benefits while the other is neither harmed nor helped.
What is mutualism?
A symbiotic relationship where both organisms benefit.
What is parasitism?
A relationship where one organism benefits at the expense of the other, often causing harm.
How does bacterial motility contribute to pathogenicity?
Motility enables bacteria to move towards favorable environments, avoid immune defenses, and colonize hosts.
What are siderophores?
Molecules produced by bacteria to scavenge iron from the host, essential for bacterial growth and virulence.
What is the significance of pili in bacterial infections?
Pili allow bacteria to attach to host cells, preventing clearance by bodily fluids like urine or mucus.
How do bacteria use flagella to avoid host defenses?
Flagella enable bacteria to swim through viscous environments like mucus, avoiding host immune defenses
What is a pathogenicity island (PAI)?
A section of the genome containing genes responsible for a pathogen’s ability to cause disease
How do toxins contribute to bacterial virulence?
Toxins disrupt host cell functions, damage tissues, and evade immune responses, enhancing bacterial survival.
What is chemotaxis?
The ability of bacteria to move in response to chemical gradients, either towards attractants or away from repellents.
What are afimbrial adhesins?
Non-fimbrial proteins on the bacterial surface that mediate adherence to host cells
Why is adherence important for bacterial pathogens?
it is the first step in colonization, helping bacteria attach to host cells and resist mechanical removal, like urination or peristalsis.
What are pore-forming toxins (PFTs)?
Toxins that create pores in host cell membranes, leading to cell lysis and death.
What is swarming motility?
The coordinated movement of bacterial populations across surfaces, often associated with virulence in pathogens like Proteus mirabilis.
What is biofilm, and why is it important in bacterial infections?
A biofilm is a community of microbes embedded in a protective extracellular matrix, providing resistance to immune attacks and antibiotics.
How do bacteria invade host cells
They either induce host cell endocytosis or survive phagocytosis to gain entry and establish infections.
How do normal flora prevent pathogen colonization?
by occupying receptor sites on host cells, producing antimicrobial substances, and outcompeting potential pathogens.
What is the role of gut microbiota in vitamin production?
Gut bacteria like E. coli synthesize vitamins such as Vitamin K and B group vitamins for the host.
What are transient flora?
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.
What are nosocomial infections?
Infections acquired in a hospital setting, often involving antibiotic-resistant bacteria.
How does Streptococcus pneumoniae cause pneumonia
As a common colonizer of the upper respiratory tract, it can invade the lower respiratory tract, causing inflammation and fluid buildup in the alveoli.
How does a fecal microbiota transplant (FMT) help treat Clostridium difficile infections?
FMT restores a healthy gut microbiome, which outcompetes C. difficile and helps resolve infection.
What is the proton motive force (PMF), and how does it drive flagellar movement?
PMF is an electrochemical potential difference across a membrane, used to power flagellar rotation and other cellular processes.
What is magnetotaxis in bacteria?
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.
How does the microbiota influence the immune system?
It helps “train” the immune system by exposing it to microbial antigens, potentially reducing the risk of autoimmune diseases.
Why is the distinction between sterile and non-sterile body sites important in diagnostic microbiology?
The presence of bacteria in sterile sites like blood or cerebrospinal fluid indicates infection, while bacteria in non-sterile sites may be normal flora.
How does antibiotic use disrupt normal flora?
Antibiotics can kill beneficial microbes, allowing opportunistic pathogens like Clostridium difficile to overgrow and cause infections.
What is the significance of fimbriae in urinary tract infections?
Fimbriae on uropathogenic E. coli allow them to attach to urinary tract cells, leading to infection and resistance to being flushed out by urine
What is the chaperone-usher pathway?
A mechanism used by Gram-negative bacteria to assemble pili on their surface, crucial for attachment to host cells.
What are flagellar filaments made of?
Flagellar filaments are made of polymerized flagellin protein subunits, forming a spiral structure used for bacterial movement.
