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Questions and Answers
Which Staphylococcus species is considered the most clinically relevant?
Which Staphylococcus species is considered the most clinically relevant?
Staphylococcus species are exclusively harmful pathogens.
Staphylococcus species are exclusively harmful pathogens.
False
What is the role of the coagulase enzyme produced by Staphylococcus aureus?
What is the role of the coagulase enzyme produced by Staphylococcus aureus?
It clots citrated plasma.
Many Staphylococcus strains have developed resistance to common __________.
Many Staphylococcus strains have developed resistance to common __________.
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Match the following Staphylococcus characteristics with their descriptions:
Match the following Staphylococcus characteristics with their descriptions:
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What pigment is typically produced by Staphylococcus aureus?
What pigment is typically produced by Staphylococcus aureus?
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Staphylococci are Gram-negative bacteria that appear as clusters resembling grapes.
Staphylococci are Gram-negative bacteria that appear as clusters resembling grapes.
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What type of culture media is typically used for isolating Staphylococci?
What type of culture media is typically used for isolating Staphylococci?
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Staphylococci exhibit _____ hemolysis on blood agar.
Staphylococci exhibit _____ hemolysis on blood agar.
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Match the Staphylococcus species with their respective pigment production:
Match the Staphylococcus species with their respective pigment production:
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Which of the following tests is used to differentiate between staphylococci and streptococci?
Which of the following tests is used to differentiate between staphylococci and streptococci?
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A positive coagulase test indicates the presence of Staphylococcus epidermidis.
A positive coagulase test indicates the presence of Staphylococcus epidermidis.
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What is the temperature range preferred for the growth of the bacteria identified as Staphylococcus aureus?
What is the temperature range preferred for the growth of the bacteria identified as Staphylococcus aureus?
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The enzyme _______ in Staphylococcus aureus causes blood plasma to clot.
The enzyme _______ in Staphylococcus aureus causes blood plasma to clot.
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What does a positive slide coagulase test indicate?
What does a positive slide coagulase test indicate?
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Coagulase positive staphylococci cannot ferment mannitol.
Coagulase positive staphylococci cannot ferment mannitol.
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Match the following tests with their functions:
Match the following tests with their functions:
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What is the enzyme detected in the DNase test?
What is the enzyme detected in the DNase test?
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What indicates a positive catalase test?
What indicates a positive catalase test?
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Coagulase-positive staphylococci can cause blood clotting.
Coagulase-positive staphylococci can cause blood clotting.
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The presence of a clear zone around a bacterium in a DNase test indicates a __________ result.
The presence of a clear zone around a bacterium in a DNase test indicates a __________ result.
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Match the test with its purpose:
Match the test with its purpose:
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Name the reagent used in the coagulase test.
Name the reagent used in the coagulase test.
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What is the primary characteristic that differentiates pathogenic Staphylococcus aureus?
What is the primary characteristic that differentiates pathogenic Staphylococcus aureus?
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Mannitol salt agar contains a concentration of 5% sodium chloride.
Mannitol salt agar contains a concentration of 5% sodium chloride.
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Which pigment is produced by Staphylococcus saprophyticus?
Which pigment is produced by Staphylococcus saprophyticus?
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Staphylococci are Gram-positive cocci that appear in clusters resembling grapes.
Staphylococci are Gram-positive cocci that appear in clusters resembling grapes.
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What type of agar is commonly used to test hemolytic reactions in Staphylococcus species?
What type of agar is commonly used to test hemolytic reactions in Staphylococcus species?
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Staphylococci are typically cultured on nutrient-rich media like __________ or mannitol salt agar.
Staphylococci are typically cultured on nutrient-rich media like __________ or mannitol salt agar.
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Match the following Staphylococcus species with their pigment production:
Match the following Staphylococcus species with their pigment production:
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What percentage of the population are nasal carriers of Staphylococcus aureus?
What percentage of the population are nasal carriers of Staphylococcus aureus?
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Staphylococcus aureus is primarily found in the environment rather than on human skin.
Staphylococcus aureus is primarily found in the environment rather than on human skin.
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Name one virulence factor produced by Staphylococcus aureus.
Name one virulence factor produced by Staphylococcus aureus.
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Staphylococcus aureus typically forms clusters of _______ cells.
Staphylococcus aureus typically forms clusters of _______ cells.
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Match the following Staphylococcus strains with their characteristics:
Match the following Staphylococcus strains with their characteristics:
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What type of hemolysis is produced by Staphylococcus aureus on blood agar?
What type of hemolysis is produced by Staphylococcus aureus on blood agar?
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Catalase testing is used to differentiate between staphylococci, which are catalase positive, and streptococci, which are catalase negative.
Catalase testing is used to differentiate between staphylococci, which are catalase positive, and streptococci, which are catalase negative.
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What is the main enzyme that Staphylococcus aureus produces that contributes to blood clotting?
What is the main enzyme that Staphylococcus aureus produces that contributes to blood clotting?
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Staphylococcus aureus prefers a temperature of _____°C for optimal growth.
Staphylococcus aureus prefers a temperature of _____°C for optimal growth.
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Match the following Staphylococcus tests with their functions:
Match the following Staphylococcus tests with their functions:
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Study Notes
Microbiological Identification of Medically Important Staphylococci
- Staphylococci are Gram-positive bacteria commonly found on human and animal skin and mucous membranes.
- Some species are harmless commensals, while others can cause serious infections in immunocompromised individuals.
- Staphylococcus aureus is a medically significant species known for its virulence factors and ability to cause various diseases.
- Staphylococcus epidermidis and Staphylococcus saprophyticus are coagulase negative species often found as part of the normal flora.
Introduction to Staphylococci
- Staphylococci are ubiquitous, meaning they are present in many environments frequented by humans.
- Clinically relevant species include Staphylococcus aureus and coagulase-negative staphylococci (CoNS). These species can cause serious infections, and some have developed resistance to antibiotics, making treatment challenging.
Staphylococcus aureus
- Morphology: Gram-positive cocci arranged in clusters.
- Cultural characteristics: Facultative anaerobes that grow by aerobic or microaerophilic respiration at 37°C. Colonies are round, smooth, raised, and range in color from grey to golden yellow.
Medically Important Staphylococci
- Staphylococcus aureus: coagulase positive, beta-hemolytic on blood agar; associated with diseases like endocarditis, food poisoning, toxic shock syndrome, and osteomyelitis.
- Staphylococcus epidermidis: coagulase negative, no hemolysis, part of normal flora often associated with infections in medical devices, and related to nosocomial infections.
- Staphylococcus saprophyticus: coagulase negative, no hemolysis, part of normal flora often associated with urinary tract infections in young women.
Asymptomatic Colonization of S. aureus
- A significant percentage of the human population carries S. aureus asymptomatically, often in the nasal passages.
- S. aureus can colonize various moist areas like skin folds, oropharynx, GI tract, and urogenital tract.
- A higher proportion of carriers exists within hospital staff.
Virulence Factors
- Coagulase enzyme: An enzyme-like protein that clots citrated plasma.
- Exfoliative toxin
- Enterotoxins: Cause food poisoning.
- DNase
- Haemolysins The presence of these factors can distinguish medically important strains.
S. aureus Reservoir
- Frequently found in environments frequented by humans.
- Easily isolated from fomites (inanimate objects).
- Healthy adults have a carrier rate of 20-60%, primarily in anterior nares, skin, nasopharynx, and intestine.
Sample Collection and Processing
- The process involves collecting samples from the affected site, such as nasal swabs, skin lesions, or blood.
- Samples are promptly transported to the lab, inoculated onto appropriate culture media, and incubated at 35-37°C for 18-24 hours.
- The presence of distinct colonies characteristic of staphylococci is then observed.
Laboratory Identification of Staphylococcus aureus
- Direct smear with Gram stain showing Gram-positive cocci in clusters within pus cells.
- Culture on blood agar (for hemolytic reactions) and nutrient agar (for pigment production).
- Golden yellow pigment indicates S. aureus.
The Gram Stain
- A critical initial step in identifying staphylococci.
- Staphylococci stain as Gram-positive cocci in clusters.
- Observing the gram-positive and the arrangemnt helps distinguish between staphylococci and other bacteria.
Culture Media and Growth Characteristics
- Staphylococci are typically cultured on nutrient-rich media like blood agar or mannitol salt agar.
- Colonies form with characteristic features such as shape, size and color.
- Many Staphylococcus species produce a golden-yellow carotenoid pigment which aids differentiating them.
- Staphylococci demonstrate various hemolytic reactions, such as alpha or beta hemolysis, on blood agar; this is helpful for identifying them.
Biochemical Tests
- Complete hemolysis on blood agar
- Catalase positive
- Coagulase positive
- Ferments mannitol on mannitol salt agar.
Catalase Test
- A microscopic examination helps confirm the morphology of bacterial cells, specifically confirming the presence of Gram-positive cocci arranged in clusters.
- Obtaining a fresh bacterial colony and mixing it with hydrogen peroxide will demonstrate the presence of bubbles, indicating a positive catalase test for staphylococci.
Coagulase Test
- The coagulase test detects the presence of coagulase enzyme in pathogenic staphylococci.
- A positive result, where plasma clots, indicates the presence of S. aureus.
- A negative result, no clotting of plasma, indicates the presence of less virulent species.
Tube Coagulase Test
- Diluting the plasma and adding the species into tubes.
- Incubating the tubes at 35-37°C
- Observing for clotting at intervals.
- Positive results produce a clot.
- Negative results don't clot (plasma remains liquid.)
Slide Coagulase Test
- A drop of saline is placed on a slide.
- The bacterial colony is emulsified into two thick suspensions.
- A drop of undiluted plasma is added to one suspension and mixed gently.
- Clumping of organisms within 10 seconds indicates a positive result.
DNase Test
- The procedure involves inoculating a bacterial colony onto a DNase test agar plate and incubating it.
- Presence of a clear zone around the colony indicates a positive result, characteristic of Staphylococcus species.
Mannitol Fermentation
- This test differentiates staphylococci based on their ability to ferment mannitol.
- Pathogenic S. aureus ferment mannitol, turning the media yellow while coagulase-negative staphylococci do not.
Mannitol Salt Agar
- Selective for staphylococci due to high sodium chloride concentration.
- Differential due to pH indicator (phenol red) which changes color depending on the fermentation of mannitol.
- A yellow color indicates mannitol was fermented causing an acidic pH.
Antibiotic Susceptibility Testing
- Disk diffusion: A method that determines the susceptibility of a bacterium to an antibiotic by measuring the zones of inhibition around antibiotic disks.
- Automated systems: Rapidly identify bacteria and test their susceptibility to a panel of antibiotics.
- Molecular techniques: Detect antibiotic resistance genes to guide treatment.
S. aureus Diseases
- Infections range from localized (e.g., abscesses, folliculitis) to systemic (e.g., bacteremia, osteomyelitis).
- Toxigenic diseases, such as food poisoning, toxic shock syndrome, and scalded skin syndrome, are also caused by specific types of S. aureus.
Case Studies and Clinical Relevance
- Case studies highlight the clinical manifestations and relevance of Staphylococcus species.
- Examples include osteomyelitis, surgical site infections, and MRSA bacteremia.
Coagulase-Negative Staphylococci
- Staphylococci that test negative for coagulase.
- Staph epidermidis: White pigment on nutrient agar, frequently found in medical devices.
- Staph saprophyticus: Lemon yellow pigment on nutrient agar, associated with urinary tract infections.
Novobiocin Test
-Differentiates between Staph epidermidis and Staph saprophyticus.
- Staph epidermidis is sensitive and Staph saprophyticus is resistant
Micrococcus
- Gram-positive cocci found in tetrads (clusters of four).
- Usually non-pathogenic.
- Distinguishing factor: Catalase-positive.
Methicillin-resistant Staphylococcus aureus (MRSA)
- A variant of Staphylococcus aureus resistant to methicillin and other beta-lactam antibiotics.
- Hospital-associated (HA-MRSA) and community-associated (CA-MRSA) are the two types.
- Vancomycin is often the drug of choice for treating MRSA.
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Test your knowledge about Staphylococcus species, their characteristics, and clinical significance. This quiz covers topics such as coagulase production, resistance to antibiotics, and isolation techniques. Ideal for microbiology students and health professionals.
