ch 17-18
No description yet. This curated deck is ready for daily study.
Card preview (24)
The catalase test: In general, which bacteria are catalase negative?
Streptococcus and Enterococcus
The catalase test: How is it used to distinguish streptococci and staphylococci, the two clinically important gram-positive cocci?
The catalase test checks whether bacteria produce the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen (bubbles). Bubbles = Staphylococcus No bubbles = Streptococcus
Oxidase test diagnosis as a part of the organism’s oxygen requirement - which organism is positive for the oxidase test?
-Pseudomonas -aeruginosa -neisseria -micrococcus (most aerobes)
Examples of serological testing and serotyping in medical diagnosis
Serological tests rely on antigen–antibody binding and include: Agglutination tests Complement fixation ELISA Fluorescent antibody tests Serotyping for bacterial antigens
What is the basis for mannitol salt agar (MSA) as a selective and differential medium?
MSA selects for staph because of high salt, and it differentiates them by whether they can ferment mannitol (yellow = S. aureus).
Where should you swab if you want to determine the S. aureus carriage status of a patient or health care worker?
anterior nares (nostrils)
What diseases can be caused by S. aureus?
Skin infections (boils, abscesses, impetigo) Food poisoning Scalded skin syndrome Toxic shock syndrome Systemic infections (pneumonia, septicemia, endocarditis)
What is a coagulase?
enzyme that clots plasma
What is coagulase’s role in S. aureus pathogenesis?
Helps S. aureus hide from immune cells by forming a protective clot around the bacterium
How is coagulase used in S. aureus diagnosis?
S. aureus = coagulase-positive while it is rarely seen in other staphylococci
What is the role of hyaluronidase in S. aureus pathogenesis?
Breaks down intercellular “glue” and allows bacteria to spread through tissues (“spreading factor”).
Which staphylococcal toxin is frequently associated with the menstrual toxic shock syndrome in women?
TSST — Toxic Shock Syndrome Toxin (superantigen).
Which S. aureus toxin is a hemolysin? What’s the difference between a, b and y -hemolysis?
Alpha toxin = main hemolysin Alpha → partial, green Beta → complete, clear Gamma → none
Is S. aureus a or b hemolytic?
B hemolytic
What is an enterotoxin? What disease is associated with staphylococcal enterotoxins?
Enterotoxin targets intestinal lining. Causes staphylococcal food poisoning
S. aureus is an opportunistic pathogen. During its commensal phase, is the golden pigment required, according to researchers?
No — the golden pigment (staphyloxanthin) is important for surviving respiratory burst in infection, but not needed when living harmlessly on the skin
The anntiphagocytic factors of S. aureus and how they help S. aureus evade destruction by phagocytes
Capsule Leukocidin (kills neutrophils) Coagulase (hides bacteria in clots) Staphyloxanthin pigment (antioxidant) Protein A (binds Fc of IgG → prevents phagocytosis)
What is MRSA? Why are they bad?
MRSA = Methicillin-Resistant Staphylococcus aureus A type of S. aureus bacteria that cannot be killed by many common antibiotics, especially β-lactams (like methicillin, penicillin, oxacillin).
Cellular molecule used to classify streptococci in the Lancefield classification system; Can all streptococci be classified this way?
Based on cell wall carbohydrate antigen (A, B, C…) Not all Streptococci can be classified this way
Which species is called the group A strep (GAS)? Is it a or b-hemolytic?
S. pyogenes = Group A Strep (GAS) β-hemolytic
What diseases does Streptococcus pyogenes cause?
Pharyngitis (strep throat) Skin infections Scarlet fever Rheumatic fever Glomerulonephritis
What is the cause of rheumatic fever and glomerulonephritis (involvement of molecular mimicry)?
S. pyogenes has M protein that looks similar to human tissues. The immune system makes antibodies against the bacteria. Bc of molecular mimicry, those antibodies also attack the body’s own tissues Results: Molecular mimicry after Group A strep infection causes the immune system to attack the heart (rheumatic fever) and kidneys (glomerulonephritis).
Why is a rapid strep test needed for patients suspected of bacterial pharyngitis?
To quickly detect Group A antigen and prevent complications.
Which species is called the group B Strep (GBS) and what disease does it cause in humans? Which populations are the most susceptible? Who should be screened for it?
S. agalactiae = Group B Strep Causes neonatal infections (sepsis, meningitis), and adult wound/urinary infections. Highest risk: newborns, pregnant women → pregnant women screened.