TBL 7: PROKARYOTIC STRUCTURE, GRAM STAIN, NORMAL FLORA, VIRULENCE & TOXINS

A comprehensive set of flashcards to help remember key concepts related to prokaryotic structure, gram staining, normal flora, virulence factors, and toxins for the upcoming exam.

What is a prokaryote?

A cell WITHOUT a nucleus and no membrane-bound organelles; includes bacteria and archaea.

What are key differences between prokaryotes and eukaryotes?

Prokaryotes lack a nucleus, have 70S ribosomes, circular DNA, and a cell wall made of peptidoglycan.

What is a capsule in bacteria?

A polysaccharide or protein coating outside the cell wall that protects bacteria from phagocytosis.

What is the function of the bacterial capsule?

Protects from phagocytosis, prevents desiccation, and helps adherence to surfaces.

Which bacteria are known to have a capsule?

Major encapsulated bacteria include Streptococcus pneumoniae, Klebsiella pneumoniae, and Haemophilus influenzae.

What is the Quellung test?

A test used to identify encapsulated bacteria by causing the capsule to swell when mixed with specific antibodies.

What is the main role of the cell wall in bacteria?

Maintains cell shape and protects from osmotic lysis.

What is peptidoglycan?

A unique polymer found in bacterial cell walls providing structural stability.

What are the two types of bacterial cell walls?

Gram-positive (thick peptidoglycan) and Gram-negative (thin peptidoglycan with an outer membrane).

What is the Gram stain used for?

A differential staining technique used to classify bacteria based on their cell wall structure.

Why do Gram-positive bacteria appear purple in a Gram stain?

They have a thick peptidoglycan layer that retains the crystal violet stain.

What do Gram-negative bacteria become after decolorization in Gram staining?

They lose the crystal violet stain and appear colorless until counterstained with safranin, turning pink.

What is the clinical significance of Gram staining?

Rapid identification of bacteria and guidance for empirical antibiotic therapy.

What are cocci?

Spherical-shaped bacteria.

What are bacilli?

Rod-shaped bacteria.

What are the arrangements of cocci?

Clusters (staphylococci), chains (streptococci), or pairs (diplococci).

What is an acid-fast stain used for?

To identify Mycobacteria, which have a waxy cell wall.

What is a major characteristic of Mycobacteria that necessitates special staining?

They have mycolic acids in their cell wall, making them resistant to Gram staining.

What is normal flora?

Microorganisms that normally live on or in the human body without causing disease.

Where does normal flora commonly reside?

Skin, mouth, nose, gastrointestinal tract, vagina, and distal urethra.

What are two major advantages of normal flora?

Colonization resistance and stimulation of the immune system.

What happens if normal flora translocates to a sterile site?

It can cause opportunistic infections.

What is C. difficile colitis?

A type of infection associated with symptoms of diarrhea after antibiotic use.

What role does the microbiota play in the GI tract?

Synthesize vitamins, metabolize bile acids, and ferment indigestible carbohydrates.

What is the most common cause of urinary tract infections (UTIs)?

E. coli is the most common causative organism.

What is the main virulence factor for E. coli that causes pyelonephritis?

P-pili, which allow adhesion to kidney cells.

What are virulence factors?

Microbial components that enhance the ability to cause disease.

Why might antibiotics disrupt normal flora?

Antibiotics can kill beneficial bacteria, leading to overgrowth of harmful organisms.

What type of infections can be caused by normal flora?

Opportunistic infections when the immune system is compromised or flora moves to the wrong location.

What is the most common healthcare-associated infection?

Catheter-associated urinary tract infections (CAUTIs).

What is the role of fimbriae in bacteria?

Fimbriae are surface projections that facilitate adhesion to host cells.

What is antibiotic resistance and how do bacteria develop it?

Bacteria can acquire resistance through genetic mutations, acquisition of plasmids, or expression of efflux pumps.

What is the main structure targeted by β-lactam antibiotics?

The bacterial cell wall, specifically the peptidoglycan layer.

What is the definition of endotoxin?

A component of the Gram-negative bacterial cell wall that triggers strong immune responses.

What is the primary toxic component of LPS in Gram-negative bacteria?

Lipid A.

How does the presence of endotoxin affect the body?

It causes fever, hypotension, and can lead to septic shock.

What is the difference between exotoxins and endotoxins?

Exotoxins are secreted proteins that are highly toxic; endotoxins are part of the bacterial cell wall and less toxic.

What type of bacteria are known to produce exotoxins?

Mostly Gram-positive bacteria and some Gram-negative bacteria.

What is the clinical significance of exotoxins?

They can cause severe disease and can be used to create toxoid vaccines.

Which toxin blocks neurotransmitter release at the neuromuscular junction?

Botulinum toxin blocks the release of acetylcholine.

What is the target of diphtheria toxin?

It inhibits the elongation factor 2 (EF-2), blocking protein synthesis.

What is the most important known function of teichoic acids?

They provide rigidity and also contribute to adherence of Gram-positive bacteria.

What are examples of spore-forming bacteria?

Bacillus (aerobic) and Clostridium (anaerobic) are the only genera that form spores.

What are the symptoms of tetanus?

Lockjaw, spastic paralysis, and muscle rigidity.

What is the distinguishing feature of viridans streptococci?

They are α-hemolytic and optochin-resistant.

What is the significance of the catalase test?

It differentiates Staphylococcus (catalase positive) from Streptococcus (catalase negative).

What is the function of coagulase in Staphylococcus aureus?

Coagulase converts fibrinogen to fibrin, causing clot formation around the bacteria.

What type of staining is best for identifying Mycobacterium species?

Acid-fast staining is used due to their waxy cell wall.

Which bacteria are typically treated with antibiotics that have high antibiotic resistance?

MRSA (methicillin-resistant Staphylococcus aureus) and other Gram-negative rods with ESBLs.

What is the role of plasmids in bacteria?

They are small, circular pieces of DNA that can carry antibiotic resistance genes.

What is the significance of the periplasmic space in Gram-negative bacteria?

It contains β-lactamases and other enzymes that provide antibiotic resistance.

Which bacteria are known to be encapsulated?

Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitidis.

What is an important characteristic of biofilms?

Biofilms are resistant to both antibiotics and the immune response.

What is the primary means of transmission for C. difficile?

It is commonly transmitted through spores found in the environment, particularly in healthcare settings.

What is the mechanism of cholera toxin?

It increases cAMP levels in intestinal cells, leading to excessive fluid secretion.

How is normal flora beneficial in the human body?

It aids in digestion, synthesizes vitamins, and provides colonization resistance against pathogens.

What clinical problems are associated with disruption of normal flora?

Opportunistic infections, such as C. difficile colitis and urinary tract infections.

How does antibiotic overuse contribute to bacterial resistance?

It selects for resistant strains, allowing them to proliferate while susceptible bacteria are eliminated.

What is the common treatment for C. difficile infection?

Oral vancomycin is the first-line treatment.

Why is hand washing with soap and water recommended for C. difficile prevention?

Alcohol-based sanitizers do not effectively kill C. difficile spores, so soap and water physically remove them.

What is a common property of biofilm-related infections?

They require the removal of the infected device (e.g., catheters) for resolution.