30 Questions
What color do inflammatory cells, background tissue debris, and proteinaceous material generally stain in properly gram stained specimens?
Pink to red
What type of medium is Blood agar medium (BAM)?
Enriched medium
What does Mannitol salt agar (MSA) select for?
Staphylococci
What inhibits the growth of other organisms in Mannitol salt agar (MSA)?
High salt concentration (7.5% NaCl)
What color does Mannitol fermentation result in on Mannitol salt agar (MSA)?
Yellow
What does the high salt concentration in Mannitol salt agar (MSA) selectively allow the growth of?
Halotolerant staphylococci
How are Staphylococcal colonies described in terms of size and color?
Medium to large (1-2 mm in diameter), off-white or gray
What distinguishes some S.aureus colonies?
They produce golden yellow pigments 'lipochrome'
What is the significance of the name 'aureus'?
It means 'golden'
Describe the colonies produced by S.epidermidis.
Small to medium, opaque, gray-white
What distinguishes colonies of S.saprophyticus?
They are large, very glossy, smooth, opaque, butyrous, convex
What do Mannitol-fermenting staphylococci produce on MSA?
Yellow colonies with yellow discoloration of the medium
What is the purpose of colistin and nalidixic acid in Columbia CNA Agar?
To render the medium selective for G+ bacteria by inhibiting G- bacteria.
Why should PEA Agar not be used for determination of hemolytic reactions?
Atypical reactions may be observed.
How is the selectivity of Vogel-Johnson (VJ) Agar achieved?
Through potassium tellurite, lithium chloride, and glycine which inhibit nonstaphylococcal organisms, both G+ and G- bacteria.
What is the indicator of acid production in Vogel-Johnson (VJ) Agar?
Phenol red
How does S.aureus produce distinctive colonies on Vogel-Johnson (VJ) Agar?
By reducing tellurite to metallic tellurium, resulting in black or gray-black colonies.
Why is it important to have the prior written permission of SLU before reproducing or distributing the document?
Because the document is the property of SLU and is for their exclusive use.
What role does δ-Hemolysin play in S.aureus infections?
Acts primarily as a surfactant or a detergent-like molecule that interacts with cell membranes and forms channels resulting in slow leakage of cellular contents.
What is the composition of γ-Hemolysin and how does it affect white blood cells?
Composed of two proteins designated S and F. It lyses white blood cells by causing pore formation in the cellular membranes, increasing cation permeability, leading to degranulation, cell swelling, and lysis.
What is the function of Panton-Valentine Leukocidin (PVL) and how does it affect neutrophils?
PVL is produced by lysogenized strains of S.aureus and is active against neutrophils, causing tissue necrosis. It consists of two components, S and F, that act synergistically on the white blood cell membrane.
What is Toxic Shock Syndrome Toxin (TSST-1) and how does it contribute to toxic shock syndrome?
TSST-1 is a superantigen that promotes the manifestations of toxic shock syndrome. It stimulates T cells non-specifically, resulting in polyclonal T-cell activation.
What is the mechanism of action of superantigens like TSST-1 on T cells?
Superantigens stimulate T cells non-specifically by directly cross-linking T-cell receptor (TCR) to MHC class II molecules on APCs outside of the antigen-binding site.
What cellular effects are observed when γ-Hemolysin affects white blood cells?
Affected cells undergo degranulation of the cytoplasm, cell swelling, and lysis.
What is the purpose of the Oxidation-Fermentation (O-F) test?
To determine whether bacteria can utilize glucose in the presence or absence of oxygen.
How is the O-F test set up?
Two tubes are inoculated by stabbing; one tube is overlaid with sterile mineral oil (closed tube) and the other tube is exposed to oxygen (open tube).
Why does the medium in the open tube turn yellow for Micrococci?
Because Micrococci are oxidative, producing acids from glucose only in the presence of oxygen.
What type of bacteria are Staphylococci in terms of utilizing glucose?
Staphylococci are fermentative, utilizing glucose and producing acids in both presence and absence of oxygen.
How can you differentiate Staphylococci using the O-F test?
Staphylococci can be differentiated by the yellow color change of the medium in both open and closed tubes due to bound coagulase production.
What role does the pH indicator bromthymol blue play in the O-F test?
Bromthymol blue is used as a pH indicator in the O-F test.
Learn about δ (delta)-Hemolysin and γ (gamma)-Hemolysin in Staphylococcus aureus, their mechanisms of action on cell membranes, and their roles in diseases. Understand how these peptides interact with cell membranes to cause cell lysis or leakage of cellular contents.
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