Podcast
Questions and Answers
Which of the following best describes the role of protein A in staphylococci?
What is the primary function of the enzyme coagulase in staphylococci?
Which staphylococcal enzyme promotes the spread of infection by hydrolyzing connective tissue components?
Which of the following conditions is NOT typically associated with staphylococcal infections?
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What is the significance of staphyloxanthin in staphylococci?
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Which class of skin appendages includes eccrine sweat glands?
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Which of the following tissues would most likely be directly affected by staphylococcal enzymes like proteases?
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Which characteristic differentiates facultative anaerobes from other bacterial types?
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What characterizes complete hemolysis as observed on blood agar?
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Which group of bacteria is usually non-hemolytic on blood agar?
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What is a characteristic feature of catalase-negative bacteria?
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What describes facultative anaerobes?
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Which factor contributes to the green pigment formation in blood agar?
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What is the main distinction between beta-hemolytic and non-hemolytic streptococci?
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Which characteristic is NOT typical of capnophilic bacteria?
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How are Streptococcus pneumoniae and viridans streptococci differentiated on blood agar?
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Which condition is characterized by inflammation or infection of the eyelids?
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What type of toxin is primarily responsible for tissue damage by disrupting cellular membranes?
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Which toxin is linked to the skin condition known as Staphylococcal Scalded Skin Syndrome (SSSS)?
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What are the most commonly contaminated foods associated with staphylococcal food poisoning?
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Which of the following conditions is characterized by rapid onset of severe vomiting, diarrhea, and abdominal cramping after eating contaminated food?
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What is the primary mechanism by which Toxic Shock Syndrome Toxin-1 (TSST-1) functions?
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Which of the following is NOT a systemic condition associated with blepharitis?
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Which of the following describes the effect of exfoliative toxins on the skin?
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What type of bacteria primarily produces enterotoxins resistant to heating at 100°C for 30 minutes?
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Study Notes
Gram-positive cocci
- Gram-positive cocci are a diverse collection of bacteria, spherical in shape, with cell walls containing peptidoglycan.
- Staphylococci and Micrococci are commonly found in various environments and are usually aerobic or anaerobic, can tolerate high salt concentrations.
- Catalase is an enzyme that converts hydrogen peroxide into water and oxygen gas (the presence of bubbles in a solution containing colonies and hydrogen peroxide indicates a positive result).
- Staphylococci are clustered while Micrococci may be clustered or in pairs.
- Streptococci are facultative anaerobes with diverse nutritional needs, often requiring blood or serum enriched media.
- Streptococci are frequently found in pairs or chains.
- Enterococci were previously classified as Lancefield group D streptococci, and are capable of growing in a wide range of pH (4.6 to 9.9) and high concentrations of sodium chloride and bile salts.
Catalase Test
- Catalase is an enzyme used to neutralize the bactericidal effects of hydrogen peroxide. It accelerates the decomposition of hydrogen peroxide (H₂O₂) into water (2H₂O) and oxygen (O₂).
- Catalase test helps differentiate catalase-positive bacteria (e.g., Staphylococcaceae and Micrococcaceae) from catalase-negative bacteria (e.g., Streptococcaceae and Enterococcaceae).
- The test also differentiates species within the same genera (e.g., Campylobacter species).
Staphylococcus - Genus Information
- The genus Staphylococcus contains 45 species and 24 subspecies.
- Staphylococcus aureus is the "golden" species and may exhibit a yellow color due to carotenoid pigments.
- Coagulase is a positive characteristic for Staphylococcus aureus; it catalyzes the conversion of fibrinogen to fibrin.
- Staphylococcus species are found as normal human flora on skin, large intestine, and vagina
- Virulent Staphylococcus aureus produces enterotoxins (food poisoning), cytotoxins (systemic toxins), and toxic shock superantigens.
Mannitol Salt Agar
- Mannitol salt agar (MSA) is both selective and differential. It is selective for organisms that tolerate high salt concentrations (7.5% to 10% NaCl), and is differential for those capable of fermenting mannitol.
- Staphylococcus aureus typically produces yellow colonies with a yellow zone.
- Other coagulase-negative staphylococci create small, pink, or red colonies without a color change to the medium.
Staphylococcus aureus Virulence Factors
- Capsule and slime layer protect the bacteria from phagocytosis and chemotaxis.
- Cell wall components like Teichoic acid give osmotic stability.
- Surface proteins allow adherence to host matrix proteins (fibronectin, fibrinogen, elastin, and collagen).
- Protein A binds to the Fc portion of IgG1-2 and IgG4, inhibiting phagocytosis.
Staphylococcus aureus Skin Diseases
- Boils (furuncles) are localized skin abscesses.
- Carbuncles are clusters of connected furuncles.
- Folliculitis is inflammation of hair follicles.
- Paronychia is an infection of the skin folds around the nails.
- Cellulitis is an infection of deeper skin layers with redness and swelling.
Staphylococcus aureus Hordeolum
- A hordeolum (stye) is an infection of the oil gland of the eyelid.
Staphylococcus aureus Toxins
- Cytotoxins (alpha, beta, delta, gamma): Lytic for erythrocytes, fibroblasts, leukocytes, macrophages.
- Exfoliative toxins (ETA, ETB): these toxins disrupt the intercellular bridges of the stratum granulosum.
- Enterotoxins (A-R): food poisoning, vomiting, diarrhea.
- Toxic shock syndrome toxin-1 (TSST-1): systemic effects including fever, hypotension, and diffuse rash.
Superantigens
- Stimulate proliferation of T cells and release cytokines.
- Not processed, but bind to MHC class II outside the peptide-binding groove.
- Cross-links MHC class II molecules.
- Systemic effects of these toxins can result in fever and cardiovascular shock in severe cases.
Clinical and Epidemiological Schema of Staphylococcus Species
- Categorization of coagulase is used to group coagulase-negative staphylococci (CONS) and coagulase-positive/variable staphylococci (CoPS)
- This categorization is based on the categorization of coagulase as a major virulence factor and its impact on human health.
Urinary Tract Infections (UTI)
- Staphylococcus saprophyticus is implicated in UTIs, especially in younger sexually active women.
Identification of S. saprophyticus
- S. saprophyticus produces a creamy white or bright white colonies on agar.
- Unable to reduce nitrate.
- It doesn't cause any hemolytic colonies on blood agar.
- Is catalase positive.
- Is novobiocin resistant.
Differentiation of Staphylococcus aureus from other Staphylococcus species
- Alpha toxin, acid produced from mannitol (Chapman agar).
- Coagulase reaction
- Clumping factor
- Pigment production
- DNase production
- Sensitivity to novobiocin
Streptococcus pneumoniae
- Pneumonia, meningitis, sepsis, sinusitis, and otitis media are potential diseases caused by S. pneumoniae.
- Characterized by growth characteristics such as a-hemolysis (incomplete or partial hemolysis), susceptibility to optochin, and solubility in bile.
Pneumococcal Vaccines
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PCV13 is recommended for children under 2 years of age and older adults with certain medical conditions.
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PPSV23 is recommended for adults 65 years or older, as well as other adults with certain medical conditions.
Intrinsic and Acquired Antimicrobial Drug Resistance in Enterococci
- Intrinsic resistance often associated with ẞ-Lactams (cephalosporins and penicillins) in E. faecalis compared to E. faecium.
- Low concentrations of aminoglycosides.
- High concentrations of aminoglycosides (HLAR).
- High concentrations of ẞ-lactams through alteration of PBPs or production of ẞ-lactamase.
Acquired Resistance Mechanisms
- Transfer of genetic information between bacteria (conjugation, transduction, transformation, transposition)
- Mutation in target proteins.
- Enzymatic modification of drugs (especially of aminoglycosides).
MRSA
- Methicillin resistance is often associated with the mecA or mecC gene, located on staphylococcal chromosomal cassettes.
- These genes encode enzymes that reduce the affinity of penicillin-binding proteins for β-lactam antibiotics.
- Alternatives for treating MRSA infections often include vancomycin, daptomycin, and other alternative second-line, or salvage therapy drugs such as telavancin, ceftaroline (V generations of cephalosporins), and linezolid
VRE
- Vancomycin resistance in enterococci often involves van genes.
- Different types of vancomycin-resistant enterococci include vanA, vanB, and vanC strains, each showing varying levels of resistance to vancomycin.
S. aureus Virulence Factors
- Cell wall proteins such as M protein, F protein, and lipoteichoic acid have key roles in virulence.
- Enzymes like streptolysin S and O, streptokinase A and B and DNases contribute to virulence through their actions on host tissues and immune systems.
- Streptococcal pyrogenic exotoxins (SPEs) or erythrogenic toxins are responsible for various effects in GAS infections.
S. pyogenes and Suppurative Diseases
- S. pyogenes is linked to various diseases, including pharyngitis, pyoderma (impetigo) and erysipelas, cellulitis and puerperal sepsis (childbirth related sepsis), and necrotizing fasciitis.
Laboratory Diagnosis of GAS
- Hemolytic patterns using blood agar plates (B-hemolysis).
- Catalase negative.
- Demonstration of the group-specific carbohydrate (Lancefield group A).
- Susceptibility testing (using bacitracin).
- Biochemical properties for species differentiation.
GAS - Nonsuppurative Infections
- Rheumatic fever is an inflammatory condition affecting the heart, joints, and blood vessels, leading to inflammation of heart valves, and damage to heart tissues.
- Acute glomerulonephritis is an inflammatory condition of the renal glomeruli characterized by edema, hypertension, hematuria, and proteinuria.
- Erythema nodosum is a type of panniculitis, marked by tender red nodules on the anterior shins, which are characteristic of a hypersensitivity reaction.
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Description
Test your knowledge on the role of enzymes and characteristics of staphylococci! This quiz covers the functions of key proteins, enzymes, and their impact on infection, as well as distinguishing features of bacterial types. Ideal for microbiology students or anyone interested in bacterial pathogenesis.
