L30 - High yield

Q: Are Staphylococci Gram-positive or Gram-negative?

A: Gram-positive.

Q: What is the morphology and arrangement of Staphylococci?

A: Spherical (cocci), arranged in grape-like clusters.

Q: Are Staphylococci catalase-positive or catalase-negative?

A: Catalase-positive.

Q: How can S. aureus be distinguished by its appearance on sheep blood agar?

A: Produces golden pigment.

Q: Is S. aureus coagulase-positive or coagulase-negative?

A: Coagulase-positive (associated with prothrombin).

What are the major pathogenic species of staphylococcus?

• Staphylococcus aureus

• Staphylococcus epidermidis

• Staphylococcus saprophyticus

Q: What is the structural organization of S. aureus from outermost to innermost?

A: Microcapsule (outermost protective layer)→ Thick peptidoglycan cell wall → Cell membrane containing penicillin-binding proteins (transpeptidases).

Q: What are the penicillin-binding proteins (PBPs) found in the cell membrane of S. aureus?

Transpeptidases

Q: What defensive and offensive weapons does S. aureus possess?

A: Numerous proteins that protrude from the microcapsule or are secreted from the cytoplasm.

Q: What three components are highlighted in the S. aureus cell wall diagram?

A: Protein A, lipoteichoic acid, and β-lactamase.

Q: What is the function of Protein A in S. aureus?

A: Binds the Fc portion of IgG, protecting bacteria from opsonization and phagocytosis.

Q: What is the function of Coagulase in S. aureus?

A: Forms fibrin around bacteria, protecting them from phagocytosis.

Q: What is the function of Hemolysins (α, β, γ, δ) in S. aureus?

A: Destroy RBCs, neutrophils, macrophages, and platelets.

Q: What is the function of Leukocidins in S. aureus?

A: Destroy leukocytes (WBCs).

Q: What is the function of Penicillinase in S. aureus?

A: Secreted β-lactamase that disrupts the β-lactam ring of penicillin.

Q: What is the function of Penicillin-Binding Proteins (PBPs), and how can they contribute to antibiotic resistance?

A: Transpeptidases necessary for peptidoglycan formation; some bacterial strains possess resistant novel PBPs.

Q: What is the function of Novel Penicillin-Binding Proteins (PBPs/Transpeptidases) in S. aureus?

A: Necessary for peptidoglycan formation; some bacterial strains possess resistant novel PBPs that contribute to antibiotic resistance.

Q: What is the function of Hyaluronidase in S. aureus?

A: Breaks down proteoglycans in connective tissue.

Q: What is the function of Staphylokinase in S. aureus?

A: Lyses formed fibrin clots (similar to streptokinase).

Q: What is the function of Lipase in S. aureus?

A: Degrades fats and oils on the body's surface, facilitating colonization of sebaceous glands.

Q: What is the function of Protease in S. aureus?

A: Destroys tissue proteins.

Q: What is the function of Exfoliatin in S. aureus?

A: Diffusible exotoxin that causes skin to slough off (scalded skin syndrome).

Q: What is the function of Enterotoxins in S. aureus?

A: Cause food poisoning, resulting in vomiting and diarrhea.

Q: What is the function of Toxic Shock Syndrome Toxin (TSST-1) in S. aureus?

A: Analogous to the pyrogenic toxin of Streptococci, but described as far more deadly.

Q: What causes Gastroenteritis associated with S. aureus?

A: S. aureus grows in food and produces exotoxin; illness results from ingestion of contaminated food.

Q: What are the characteristic symptoms of S. aureus Gastroenteritis?

A: Increased intestinal peristalsis, nausea, vomiting, diarrhea, and abdominal pain.

Q: What are the characteristic symptoms of Toxic Shock Syndrome (TSS) caused by S. aureus?

A: Multisystem organ dysfunction, erythematous rash, and desquamation of palms.

Q: What are the associated causes of Toxic Shock Syndrome (TSS)?

A: Tampons, infected sutures, cutaneous/subcutaneous infections, and infections following childbirth or abortion.

Q: What causes Scalded Skin Syndrome (SSS) in S. aureus?

A: Exfoliative toxins A and B, which can diffuse from a localized infection and cause distant effects.

Q: What are the characteristic symptoms of Scalded Skin Syndrome (SSS)?

A: Skin sloughing/peeling; described on the slide as having symptoms similar to TSS.

Q: What diseases can S. aureus cause through direct organ invasion?

A: Pneumonia, meningitis, osteomyelitis, acute bacterial endocarditis, septic arthritis, skin infections, bacteremia/sepsis, and urinary tract infections.

Q: Which bacterium is associated with acute bacterial endocarditis?

A: Staphylococcus aureus.

Q: What are the characteristics of Pneumonia caused by S. aureus?

A: Rare but severe cause of community-acquired pneumonia that usually follows a viral influenza upper respiratory illness.

Q: What are the characteristic symptoms of Meningitis, Cerebritis, and Brain Abscess caused by S. aureus?

A: High fever, stiff neck, headache, coma, and focal neurological signs.

Q: What is Osteomyelitis, and which population is emphasized for S. aureus infection?

A: Bone infection occurring in boys younger than 12 years of age.

Q: What are the characteristic symptoms of Acute Endocarditis caused by S. aureus?

A: Violent, destructive infection of heart valves with sudden onset of high fever, chills, and myalgias.

Q: How does Acute Endocarditis differ from Subacute Bacterial Endocarditis (SBE)?

A: Acute Endocarditis (S. aureus) has a sudden onset, whereas SBE (Viridans and Group D Streptococci) has a more gradual onset.

Q: What causes Septic Arthritis in S. aureus infections?

A: S. aureus invades the synovial membrane, resulting in a closed infection of the joint cavity.

Q: What are the characteristic symptoms of Septic Arthritis?

A: Acute painful, red, swollen joints with decreased range of motion.

Q: What is the treatment for Septic Arthritis?

A: Joint drainage and antimicrobial therapy.

Q: What are the characteristic symptoms of Impetigo caused by S. aureus?

A: Usually occurs on the face, causing small vesicles that develop into pustules and crust over to become honey-colored, wet, and flaky.

Q: What are the characteristic symptoms of Cellulitis caused by S. aureus?

A: Deeper infection causing tissue to become hot, red, shiny, and swollen.

Q: What are Local Abscesses (Folliculitis) caused by S. aureus?

A: Infection of a hair follicle that produces an abscess.

Q: What are Furuncles caused by S. aureus?

A: Abscesses that penetrate deep into subcutaneous tissue.

Q: What are Carbuncles caused by S. aureus?

A: Furuncles that bore through to produce painful lesions communicating under the skin.

Q: What can result from wound infections caused by S. aureus?

A: Any skin wound can become infected, resulting in an abscess, cellulitis, or both.

Q: How does S. aureus cause blood and catheter infections?

A: S. aureus migrates from the skin and colonizes central venous catheters.

Q: What complications can result from S. aureus blood and catheter infections?

A: Bacteremia, sepsis, septic shock, and acute endocarditis.

Q: Why are most Staphylococci resistant to penicillin?

A: They secrete penicillinase, which disrupts the β-lactam ring of penicillin.

Q: Which penicillinase-resistant antibiotics kill most susceptible strains of S. aureus?

A: Methicillin, nafcillin, and other penicillinase-resistant penicillins.

Q: What is MRSA?

A: Methicillin-resistant Staphylococcus aureus; a strain resistant to methicillin and nafcillin.

Q: What gene is responsible for methicillin resistance in MRSA?

A: mecA, an acquired gene encoding a new penicillin-binding protein (PBP2a).

Q: How does PBP2a contribute to antibiotic resistance in MRSA?

A: PBP2a has reduced affinity for β-lactam antibiotics, allowing peptidoglycan synthesis to continue.

Q: What is a common route of MRSA spread?

A: Nasal carriage.

Q: What are the two categories of MRSA based on where they are acquired?

A: Community-acquired MRSA (CA-MRSA) and Hospital-acquired MRSA (HA-MRSA).

Q: What toxin is associated with CA-MRSA, and what does it cause?

A: Panton-Valentine Leukocidin (PVL), which causes skin abscesses.

Q: How do CA-MRSA and HA-MRSA transfer their resistance genes according to the slide?

A: Through transposons.

Q: What antibiotic is listed for the treatment of MRSA?

Vancomycin

Q: What is VISA, and what is its vancomycin MIC according to the slide?

A: Vancomycin Intermediate S. aureus; MIC of 8–16 µg/mL.

Q: What antibiotic resistance is associated with VISA?

A: Reduced susceptibility to glycopeptide antibiotics, including vancomycin.

Q: What is VRSA, and what is its vancomycin MIC according to the slide?

A: Vancomycin Resistant S. aureus; MIC >32 µg/mL.

Q: What gene is responsible for vancomycin resistance in VRSA?

A: vanA, acquired through a chromosomal transposon DNA element.

Q: How does vanA cause vancomycin resistance in VRSA?

A: Modifies the peptidoglycan terminus from D-alanine–D-alanine to D-alanine–D-lactate, resulting in low affinity for vancomycin.

Q: Is S. epidermidis coagulase-positive or coagulase-negative, and where is it normally found?

A: Coagulase-negative; part of the normal bacterial flora widely found on the body.

Q: What is the major mechanism by which S. epidermidis causes infections on medical devices?

A: Forms biofilms on IV catheters, pacemakers, and prosthetic devices.

Q: What infections can S. epidermidis cause through biofilm formation on IV catheters and pacemakers?

A: Bacteremia and catheter-related sepsis.

Q: What prosthetic devices can become infected by S. epidermidis?

A: Prosthetic joints, heart valves (subacute bacterial endocarditis), and peritoneal dialysis catheters.

Q: Which hospitalized patients are particularly susceptible to S. epidermidis infections?

A: Compromised hospital patients with urinary catheters and intravenous lines.

Q: Why is S. epidermidis frequently found in blood cultures?

A: It is a common skin contaminant of blood cultures.

What are the strains of staph - gram pos

Staph. aureus, Methicillin-Resistant S. aureus (MRSA), Vancomycin Intermediate/Resistant S. Aureus (VISA & VRSA), Staph. epidermidis, Staph. saprophyticus

What are the virulence factors of Staph. aureus?

Microcapsule and proteins

What does the microcapsule in staph aureus do?

• surrounds a huge peptidoglycan cell wall, which in turn surrounds a cell membrane containing penicillin binding proteins (PBPs) called Transpeptidase 

What types of proteins are assiciated with staph aureus

Proteins that disable immune defenses, tunnel through tissues, and serve as a, exotosin assault weapin

What proteins are associated with disabled immune defenses?

Protein A, coagulase, hemolysins, leukocidins, penicillinase, and novel penicillin binding protein

(proteins that disable immune defenses) What does protein A do?

sites bind Fc portion of IgG; protects the bacteria from opsonization & phagocytosis

(proteins that disable immune defenses) what does Coagulase do?

fibrin formation around bacteria, protecting from phagocytosis

(proteins that disable immune defenses) what does Hemolysins do?

alpha, beta, gamma, delta destroy RBCs, neutrophils, macrophages, platelets

(proteins that disable immune defenses) What does lekocidins do?

Destroy leukocytes (WBCs)

(proteins that disable immune defenses) what does penicillinase do?

secreted form of Beta-lactamase that disrupts the Beta-lactam ring of penicillin

(proteins that disable immune defenses) what does novel penicillin binding protein (transpeptidase)?

necessary for peptidoglycan formation; some strains have resistant novel PBP

What diseases are associated with exotoxin release of Staph. aureus?

• Gastroenteritis - food poisoning 

• Toxic Shock Syndrome

• Scalded Skin Syndrome

What diseases are associated with direct organ invasion seen in of Staph. aureus?

• Pneumonia 

• Meningitis

• Osteomyelitis

• Acute Bacterial Endocarditis 

• Septic Arthritis

• Skin Infections

• Bacteremia/Sepsis 

• Urinary Tract Infection

Most staphylococci secrete ______ & are resistant to _____. 

penicillinase; penicillin

treatment of Staph. aureus?

Methicillin, Nafcillin, & other penicillinase resistant penicillins kill most strains of S. aureus.

What proteins are associated with tunneling through tissue seen in staph aureus?

Hyaluronidase, staphlykinase, lipase, and protease

(proteins associated with tunnelling through tissue) what does hyaluronidase do in staph aureus?

breaks down proteoglycans in connective tissue

(proteins associated with tunnelling through tissue) what does Staphylokinase do in staph aureus?

• lyses formed fibrin clots (similar to streptokinase) 

(proteins associated with tunnelling through tissue) what does Lipase do in staph aureus?

degrades fats & oils that accumulate on surface of our body; facilitates S. aureus colonization of sebaceous glands

(proteins associated with tunnelling through tissue) what does Protease do in staph aureus?

• destroys tissue proteins 

What are the 3 exotoxin assault weoponry options of staph, aureus and what do othey do?

• Exofoliatin - diffusible exotoxin that causes skin to slough off (Scalded Skin Syndrome) 

• Enterotoxins - cause food poisoning, vomiting, diarrhea 

• Toxic Shock Syndrome Toxin (TSST-1) - analogous to pyrogenic toxin by streptococci but far more deadly

what is MRSA?

Strain of S. aureus that has acquired multidrug resistance against methicillin & nafcillin. 

what is the reistance of methicillin in MRSA mediated by?

• mecA - acquired chromosomal DNA segment that encodes a new penicillin binding protein 2A.

• Transposons - pass resistance genes

______ carriage is most common route of spread of MRSA. 

Nasal

What types of MRSA diseases are there?

• Community acquired MRSA (CA-MRSA)

• Hospital acquired MRSA (HA-MRSA)

in MRSA, __________ (PVL) toxin is encoded by CA-MRSA that causes skin abscesses 

Panton-Valentine Leukocidin

how to treat MRSA?

Vancomycin

ancomycin Intermediate/Resistant S. Aureus (VISA & VRSA)

____ - resistance to all glycopeptide antibiotics (Vancoymycin, Bleomycin) 

_____ - acquired a chromosomal transposon DNA element called vanA

VISA

VRSA

What does VanA (substrain of VRSA) do?

encodes proteins that modify D-alanine to confer low affinity to vancomycin

virulence factor of staph epidermis?

coagulase negative

Staph epidermis - Coagulase ______ (unlike S. aureus); part of the normal ______ widely found on the body. 

negative; bacterial flora