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Questions and Answers
Staphylococcus is a genus of Gram-negative bacteria.
Staphylococcus is a genus of Gram-negative bacteria.
False
Staphylococci appear spherical and form in clusters.
Staphylococci appear spherical and form in clusters.
True
Coagulase-positive staphylococci can colonize dry skin areas.
Coagulase-positive staphylococci can colonize dry skin areas.
False
Staphylococci are obligate aerobes.
Staphylococci are obligate aerobes.
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The coagulase test is used to differentiate types of staphylococci.
The coagulase test is used to differentiate types of staphylococci.
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Staphylococcus aureus is a coagulase-negative staphylococcus.
Staphylococcus aureus is a coagulase-negative staphylococcus.
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Clinically important staphylococci can cause infections.
Clinically important staphylococci can cause infections.
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There are no prevention measures for infections caused by staphylococci.
There are no prevention measures for infections caused by staphylococci.
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The coagulase test differentiates Staphylococcus aureus from coagulase-negative staphylococci.
The coagulase test differentiates Staphylococcus aureus from coagulase-negative staphylococci.
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Staphylococcus epidermidis is more likely to cause infections in healthy individuals than Staphylococcus aureus.
Staphylococcus epidermidis is more likely to cause infections in healthy individuals than Staphylococcus aureus.
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The catalase test is used to distinguish staphylococci from bacilli.
The catalase test is used to distinguish staphylococci from bacilli.
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Staphylococcus aureus can be methicillin-sensitive or methicillin-resistant.
Staphylococcus aureus can be methicillin-sensitive or methicillin-resistant.
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A furuncle is a painful lump caused by an infection of a hair follicle.
A furuncle is a painful lump caused by an infection of a hair follicle.
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Catalase is an enzyme that converts fibrinogen to fibrin.
Catalase is an enzyme that converts fibrinogen to fibrin.
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The presence of bubbles indicates a positive catalase test.
The presence of bubbles indicates a positive catalase test.
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Coagulase-negative staphylococci are not common skin commensals in humans.
Coagulase-negative staphylococci are not common skin commensals in humans.
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Fibrin/fibrinogen binding proteins are involved in attaching to blood clots and traumatised tissue.
Fibrin/fibrinogen binding proteins are involved in attaching to blood clots and traumatised tissue.
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S.aureus can evade the immune system by enhancing phagocytosis.
S.aureus can evade the immune system by enhancing phagocytosis.
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EXOtoxins from S.aureus are responsible for causing toxic shock syndrome.
EXOtoxins from S.aureus are responsible for causing toxic shock syndrome.
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Scalded skin syndrome is caused by specific types of EXOtoxins produced by S.aureus.
Scalded skin syndrome is caused by specific types of EXOtoxins produced by S.aureus.
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Food poisoning caused by S.aureus has a long incubation period and is often severe.
Food poisoning caused by S.aureus has a long incubation period and is often severe.
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Bone and joint infections, such as osteomyelitis, can be caused by S.aureus.
Bone and joint infections, such as osteomyelitis, can be caused by S.aureus.
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Person-to-person transmission of S.aureus can occur through direct contact via skin.
Person-to-person transmission of S.aureus can occur through direct contact via skin.
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Cytotoxins such as alpha and beta are produced by S.aureus.
Cytotoxins such as alpha and beta are produced by S.aureus.
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Staphylococcus is a genus of Gram-positive bacteria that typically appears rod-shaped.
Staphylococcus is a genus of Gram-positive bacteria that typically appears rod-shaped.
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Coagulase-positive staphylococci, such as Staphylococcus aureus, can colonize the nasal passages.
Coagulase-positive staphylococci, such as Staphylococcus aureus, can colonize the nasal passages.
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Staphylococci are obligate anaerobes that cannot survive in the presence of oxygen.
Staphylococci are obligate anaerobes that cannot survive in the presence of oxygen.
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The coagulase test is used to differentiate between coagulase-positive and coagulase-negative staphylococci.
The coagulase test is used to differentiate between coagulase-positive and coagulase-negative staphylococci.
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All staphylococci have no clinical significance and cannot cause infections.
All staphylococci have no clinical significance and cannot cause infections.
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Staphylococcus epidermidis is the most common cause of infections in healthy individuals compared to Staphylococcus aureus.
Staphylococcus epidermidis is the most common cause of infections in healthy individuals compared to Staphylococcus aureus.
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Scalded skin syndrome is related to specific types of EXOtoxins produced by Staphylococcus aureus.
Scalded skin syndrome is related to specific types of EXOtoxins produced by Staphylococcus aureus.
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Food poisoning caused by S.aureus is characterized by a short incubation period and is often severe.
Food poisoning caused by S.aureus is characterized by a short incubation period and is often severe.
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The catalase test is used to differentiate staphylococci from streptococci.
The catalase test is used to differentiate staphylococci from streptococci.
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Coagulase-negative staphylococci are typically responsible for healthcare-associated infections.
Coagulase-negative staphylococci are typically responsible for healthcare-associated infections.
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Presence of coagulase indicates a bacterium's ability to form blood clots.
Presence of coagulase indicates a bacterium's ability to form blood clots.
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Staphylococcus saprophyticus is the most common pathogen causing skin infections.
Staphylococcus saprophyticus is the most common pathogen causing skin infections.
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Fibrin/fibrinogen binding proteins do not contribute to the attachment of S.aureus to trauma sites.
Fibrin/fibrinogen binding proteins do not contribute to the attachment of S.aureus to trauma sites.
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A furuncle and carbuncle are types of abscesses formed in the skin.
A furuncle and carbuncle are types of abscesses formed in the skin.
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The production of invasins by S.aureus helps in promoting tissue invasion.
The production of invasins by S.aureus helps in promoting tissue invasion.
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Toxic shock syndrome is caused by enterotoxins produced by S.aureus.
Toxic shock syndrome is caused by enterotoxins produced by S.aureus.
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S.aureus can be found in the nasopharynx of healthy humans.
S.aureus can be found in the nasopharynx of healthy humans.
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All strains of Staphylococcus aureus are resistant to methicillin.
All strains of Staphylococcus aureus are resistant to methicillin.
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Scalded skin syndrome is associated with exfoliative toxins produced by S.aureus.
Scalded skin syndrome is associated with exfoliative toxins produced by S.aureus.
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S.aureus infections can be classified solely as systemic and invasive.
S.aureus infections can be classified solely as systemic and invasive.
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The infection described in the clinical case is likely endogenously sourced due to skin flora.
The infection described in the clinical case is likely endogenously sourced due to skin flora.
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Endocarditis is typically a primary infection caused by S.aureus.
Endocarditis is typically a primary infection caused by S.aureus.
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Cytotoxins produced by S.aureus include leukocidin and alpha toxins.
Cytotoxins produced by S.aureus include leukocidin and alpha toxins.
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Food poisoning from S.aureus results in a long incubation period and severe symptoms.
Food poisoning from S.aureus results in a long incubation period and severe symptoms.
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Study Notes
RCSI Staphylococci Lecture Notes
- RCSI is the Royal College of Surgeons in Ireland.
- The lecture is on staphylococci, a genus of Gram-positive bacteria.
- Staphylococci are spherical (cocci) and form in clumps or clusters.
- They are facultative anaerobes.
- Staphylococci are traditionally divided into two groups based on their ability to clot blood plasma (coagulase reaction/test).
- Coagulase-positive staphylococci, like S. aureus, colonize nasal passages and moist skin areas (axilla, groin).
- Coagulase-negative staphylococci (over 30 species), like S. epidermidis, are common human skin commensals.
Coagulase Test
- A laboratory test to differentiate S. aureus (coagulase-positive) from other staphylococci (coagulase-negative).
- Coagulase is an enzyme that causes blood clot formation (converting fibrinogen to fibrin).
- This process allows bacteria to coat themselves with fibrin, possibly resisting phagocytosis.
Catalase Test
- Used to differentiate staphylococci from streptococci.
- The presence of catalase (an enzyme) is determined by the bacteria's ability to reduce hydrogen peroxide into water and oxygen, resulting in bubble production.
- Staphylococci are catalase-positive.
Clinical Case 1
- A 19-year-old male presents with a painful, red lump on his neck.
- The most likely diagnosis is a furuncle.
- The most likely causative pathogen is S. aureus.
Staphylococcus aureus
- Found in moist skin folds, mucosal surfaces, and the nasopharynx.
- 20-40% of healthy humans are colonized.
- Colonization risk increases with conditions like diabetes mellitus, injecting drug use, or a foreign body/implant.
- Distinguished as methicillin-sensitive (MSSA) or -resistant (MRSA).
S. aureus Pathogenesis
- Portal of entry: Ingestion, penetration (break in skin, mucous membranes).
- Attachment to cells: Surface proteins, capsule, fibrin/fibrinogen binding proteins (clumping factor), matrix-binding proteins.
- Immune evasion: Inhibition of phagocytosis, production of extracellular substances (invasins, enzymes).
- Damage to host cells: Direct damage to peptidoglycan wall, enzymes, toxins.
- Spread: Person-to-person contact, environment (surfaces).
S. aureus Toxins
- List of toxins is in Table on Page 50.
- Toxins are involved in infections.
S. aureus: Pathogenesis/Classifications of Infections
- Skin and soft tissue infections. Include discussed skin infections (styes, boils, furuncles), systemic infections and toxin mediated infections. Examples include food poisoning and gastroenteritis, which is covered in a separate module. Other infections include scalded skin syndrome and toxic shock syndrome. This is covered in a separate module.
- Systemic infections: Bloodstream infection (BSI), endocarditis, bone and joint infections (e.g., septic arthritis, osteomyelitis), deep abscesses (e.g., brain, spine, psoas muscle), pneumonia. These types of infections are usually secondary to another infection and often need longer treatment than other soft-tissue infections.
- Toxin-mediated: Food poisoning and gastrointestinal issues, scalded skin syndrome, toxic shock syndrome. These cases often have short incubation periods.
Laboratory Diagnosis of S. aureus Infections
- Day 0: Patient specimen (e.g., blood culture).
- Day 1+: Gram stain, culture setup, team reviews patient.
- 24 hours later: Read agar culture plates, coagulase test, team/patient communication. Further antibiotics will need to change as needed from empirical to targeted therapy.
- 24 hours later: Alter empiric antibiotic therapy as needed. If MRSA, infection control precautions.
Management of S. aureus Infections
- History, especially timing and symptoms.
- Clinical examination
- Examine potential sources and spread of infection.
- Inspect skin IV/ indwelling device sites, surgical wounds, soft tissue. Examine potentially problematic cardiovascular (CVS) organs. Examine musculoskeletal system for issues like bone or joint pain.
- Investigations
- General blood tests (FBC, U&E, CRP, lactate).
- Microbiology tests (specimen depends on site- pus or tissue better than a skin swab; sputum/broncho-alveolar lavage for pneumonia; joint fluid for septic arthritis; etc).
- Other investigations like imaging could be needed depending on the individual case.
- TSS management: Treat quickly with resuscitation and critical care including rapid IV antimicrobials. Source control (debride, drain).
Prevention of Staphylococcal Infections
- Prevent transmission from patient to patient: Hand hygiene, equipment/environmental hygiene.
- Implement precautions based on MRSA: Isolate/cohort, contact precautions (gloves, gown).
- Protect the skin.
- Control wounds effectively; especially concerning IV/medical device sites.
- Remove infectious medical devices promptly.
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Description
This quiz focuses on staphylococci, a genus of Gram-positive bacteria, emphasizing their classification, coagulase, and catalase tests. Participants will learn about the differences between coagulase-positive and coagulase-negative staphylococci and the clinical significance of these bacteria. Test your knowledge and understanding of essential microbiological concepts related to staphylococci.
