31 Questions
Which of the following is a basic laboratory feature of staphylococci?
They appear spherical and form in clumps/clusters
Which of the following is a feature of coagulase-positive staphylococci?
They can colonise nasal passages and other moist skin areas
What is the traditional division of staphylococci based on?
Their ability to clot blood plasma
Which of the following is a characteristic of coagulase-negative staphylococci?
They are common human skin commensals
Which test is used to differentiate S. aureus from other staphylococci based on the presence of an enzyme that causes blood clot formation?
Coagulase test
Which enzyme is determined by the ability of bacteria to reduce hydrogen peroxide into water and oxygen, resulting in the production of bubbles?
Catalase
What is the most likely causative pathogen for the painful, red lump on the neck of the 19-year-old male?
Staphylococcus aureus
Is the infection exogenous or endogenous?
Exogenous
Does this infection require any further management?
Yes
What percentage of healthy humans are colonized by Staphylococcus aureus?
20-40%
What is the main factor contributing to increased colonization of Staphylococcus aureus in humans?
Diabetes mellitus
What is the distinguishing factor between methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) Staphylococcus aureus?
Resistance to usual treatment
What is the portal of entry for S. aureus infections?
Penetration through a break in the skin or mucous membranes
Which factor facilitates the attachment of S. aureus to blood clots and traumatised tissue?
Fibrin/fibrinogen binding protein (clumping factor)
What is the main factor contributing to the spread of S. aureus infections person-to-person?
Direct contact via skin carriage
In which category of S. aureus infections does endocarditis usually occur?
Bloodstream infection (BSI)
Which of the following is a characteristic of infections caused by clinically important streptococci?
They are commonly treated with penicillin
What is the main factor contributing to the pathogenesis of infections caused by clinically important streptococci?
Production of exotoxins that damage host tissues
What is the recommended approach for diagnosing infections caused by clinically important streptococci?
Culture and sensitivity testing of clinical specimens
What is the portal of entry for pneumococcal infections?
Respiratory droplets
Which infection can result from turbulent flow through the heart, leading to bacterial attachment and vegetation formation?
Enterococcal endocarditis
Which bacterium is typically found in the bowel flora and is associated with common vancomycin resistance?
Enterococcus faecium
Which bacterium accounts for over 25% of clinical anaerobes and can cause aspiration pneumonia, sinusitis, brain abscess, and intra-abdominal abscesses?
Peptostreptococcus
What laboratory test is used to differentiate Streptococcus pyogenes from other staphylococci based on the presence of an enzyme that causes blood clot formation?
Coagulase test
What is a distinguishing feature of Streptococcus pneumoniae when observed under a microscope?
Beta-hemolytic cocci in chains
What is the main factor contributing to increased colonization of Staphylococcus aureus in humans?
Recent antibiotic use
What type of resistance can pneumococci develop by altering penicillin-binding proteins?
Low-level, intermediate, or high-level resistance
Which infections can be caused by Enterococci in at-risk patients, especially in hospital settings?
Urinary tract infections
What is the diagnosis of streptococcal infections reliant on, in addition to clinical suspicion?
Laboratory tests like gram stain and culture
Which country ranks 8/29 in the EU/EEA for resistance rates of S. pneumoniae, highlighting the importance of knowing local resistance patterns when treating infections?
Ireland
What is the main mode of spread for S. aureus infections person-to-person?
Direct contact
Study Notes
Bacterial Infections: Pneumococcal Disease, Enterococci, and Streptococci
- Pneumococcus is a Gram-positive bacterium carried in the nasopharynx by 5-10% of healthy adults and 20-40% of healthy children, with over 90 serotypes and vaccines available against some.
- Pneumococcus causes invasive diseases like pneumonia, sinusitis, otitis media, and meningitis, spreading via respiratory droplets and invading the oropharynx.
- Pneumococcal pneumonia presents symptoms such as pleuritic chest pain, shortness of breath, and may lead to complications like parapneumonic effusion and bacteraemia.
- Enterococci, including E. faecium and E. faecalis, are typically found in the bowel flora, with common vancomycin resistance and causing infections in at-risk patients, especially in hospital settings.
- Enterococcal infections include urinary tract infections, endocarditis, bloodstream infections, wound infections, and intra-abdominal infections, particularly in patients with recent surgery, underlying diseases, or prolonged hospitalization.
- Infective endocarditis can occur due to turbulent flow through the heart, leading to bacterial attachment and vegetation formation, often following procedures that damage epithelial barriers.
- Anaerobic streptococcus Peptostreptococcus, which accounts for over 25% of clinical anaerobes, can cause a range of infections, such as aspiration pneumonia, sinusitis, brain abscess, and intra-abdominal abscesses.
- The diagnosis of streptococcal infections relies on clinical suspicion, appropriate sample collection, and laboratory tests like gram stain, culture, and identification techniques such as Lancefield grouping and antibiotic susceptibility testing.
- Laboratory diagnosis of Streptococcus pyogenes involves bacitracin disk testing, gram stain showing beta-hemolytic cocci in chains, and other specific identification methods.
- Laboratory diagnosis of Streptococcus pneumoniae involves identifying Gram-positive cocci in chains or diplococci, being alpha-hemolytic, and showing susceptibility to optochin.
- Pneumococci can develop antimicrobial resistance, altering penicillin-binding proteins and leading to low-level, intermediate, or high-level resistance, which is important to consider when treating patients.
- Antimicrobial resistance in S. pneumoniae varies geographically, with Ireland ranking 8/29 in the EU/EEA for resistance rates, highlighting the importance of knowing the local resistance patterns when treating infections.
Test your knowledge on the laboratory features and pathogenesis of staphylococci with this quiz from RCSI Royal College of Surgeons in Ireland. This quiz is designed for Year 1 undergraduate medicine students and covers essential learning outcomes from the lecture by Prof. Manaf Al-Qahtani.
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