BACT211: Clinical Bacteriology Week 5

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Questions and Answers

What is the principle of the Bacitracin Test?

determine the effect of a small amount of bacitracin (0.04U) on an organism

What is the result of the Bacitracin Test when there is a presence of a zone of inhibition around the disk?

(b) No change in color; no acid production

(d) No acid production (correct)

(a) Yellow medium; acid production

What is the function of Staphylocoagulase?

Responsible for a positive tube coagulase test result. Also present in various Staphylococcus species.

In the Oxidation-Fermentation (O/F) Reactions, glucose is converted to Pyruvic Acid and then to $CO2$ through ________.

glycolysis Signup and view all the answers

Staphylococci produce mixed acids such as lactic acid, propionic acid, and succinic acid.

True Signup and view all the answers

Which toxin acts on sphingomyelin in the plasma membrane of erythrocytes?

Hemolysin β Signup and view all the answers

Enterotoxins A, B, and D are heat-stable causes of staphylococcal food poisoning. (True/False)

True Signup and view all the answers

Match the enzyme types with their specific tests:

Bound coagulase/clumping factor = Slide Coagulase Test Free coagulase/Staphylocoagulase = Tube Coagulate Test L-pyrroglutamylaminopeptidase = PYR Test Signup and view all the answers

__________ permits bacteria to spread through connective tissues.

Hyaluronidase Signup and view all the answers

What is the Voges-Proskauer (VP) Test used to determine?

determine the ability of some organisms to produce neutral end products from glucose fermentation Signup and view all the answers

Match the enzyme with its function:

Staphylocoagulase = Responsible for positive coagulase test results β-Lactamase = Enzyme that cleaves the ring structure of certain antibiotics Catalase = Mediates the breakdown of hydrogen peroxide into oxygen and water Signup and view all the answers

What is the color of colonies associated with Staphylococci?

Cream-colored Signup and view all the answers

What does the term 'Staphle' mean in the context of Staphylococci?

Bunches of grapes Signup and view all the answers

Staphylococci are obligate anaerobes.

False Signup and view all the answers

Fastidious strains of Staphylococci have requirements for CO2 hemin or menadione with at least 48 hrs of incubation. Hemin is also known as Factor ________.

X Signup and view all the answers

Which pathogen causes Mild inflammation of a hair follicle or oil gland?

Staphylococcus aureus Signup and view all the answers

Match the following Staphylococcus infections with their associated diseases:

S.aureus = Toxic shock syndrome (TSS) S.epidermidis = Nosocomial infections S.saprophyticus = Urinary Tract Infections (UTI) S.haemolyticus = Wound Septicemia S.lugdunensis = Catheter-related bacteremia and endocarditis Signup and view all the answers

Study Notes

Characteristics of Staphylococci

Staphylococci belong to the family Staphylococcaceae
They are catalase positive (+) and coagulase positive (+) or negative (-)
They are gram positive (+) cocci that exist singly, in pairs, and in clusters
They resemble the family Micrococcaceae and genus Micrococcus
Micrococci are catalase positive (+), coagulase negative (-), and exist in pairs, tetrads, and irregular clusters

Differentiation between Staphylococci and Micrococci

Modified oxidase (Microdase) test: Staphylococci are negative (-), Micrococci are positive (+)
Anaerobic acid production from glucose: Staphylococci are positive (+), Micrococci are negative (-) except for M. kristinae and M. varians
Anaerobic acid production from glycerol in the presence of erythromycin: Staphylococci are positive (+), Micrococci are negative (-)
Growth on Furoxone-Tween 80-oil red agar: Staphylococci are negative (-), Micrococci are positive (+)
Resistance to bacitracin (0.04 U): Staphylococci are resistant (R), Micrococci are sensitive (S)
Resistance to lysostaphin (200 ug/mL): Staphylococci are sensitive (S), Micrococci are resistant (R)

Staphylococci Pathology

Staphylococci can cause cutaneous infections such as folliculitis, furuncles, and carbuncles
They can also cause food poisoning, scalded skin syndrome, toxic shock syndrome, and toxic epidermal necrolysis
S. aureus can cause bullous impetigo, which differs from streptococcal nonbullous impetigo in that staphylococcal pustules are large and surrounded by a small zone of erythema
Other staphylococcal species can cause nosocomial infections, wound infections, septicemia, UTIs, and native valve infections

Virulence Factors of Staphylococcus aureus

Enterotoxins (Groups A-E and G-J) cause staphylococcal food poisoning
Toxic shock syndrome toxin-1 (TSST-1) causes toxic shock syndrome
Exfoliative toxins (A and B) cause scalded skin syndrome and bullous impetigo
Cytolytic toxins (α, β, γ, and δ hemolysins) affect red blood cells and leukocytes
Protein A binds to the Fc portion of immunoglobulin G (IgG) and blocks phagocytosis
Enzymes such as coagulase, protease, hyaluronidase, and lipase aid in bacterial spread and infection

Laboratory Diagnosis of Staphylococci

Culture media used include SBA, MSA, CAN, PEA, and CHROMagar Staph aureus
Incubation at 35-37°C for 18-24 hours
Macroscopic examination reveals colonies that are round, smooth, white, and creamy for S. aureus, and small-to-medium-sized, nonhemolytic, gray-to-white colonies for S. epidermidis
Microscopic examination reveals gram-positive (+) cocci in singly, in pairs, and in clusters
Mannitol salt agar (MSA) is selective for S. aureus, which ferments mannitol and forms colonies surrounded by a yellow halo### Staphylococci Characteristics
Produce hemolytic zones around colonies on Sheep's Blood Agar (SBA)
Gram-positive cocci, often in clusters, with polymorphonuclear cells
Catalase test: positive, with bubble formation, indicating breakdown of hydrogen peroxide into oxygen and water

Microdase Test (Modified Oxidase Test)

Principle: oxidase enzyme reacts with oxidase reagent and cytochrome C to form indophenol, a colored compound
Result: positive, with blue to purple-blue color, indicating micrococci and staphylococci

Biochemical Tests

Bacitracin Test: determines effect of bacitracin on an organism, with positive result indicating presence of zone of inhibition around the disk
Oxidation-Fermentation (O/F) Reactions: determines whether an organism uses carbohydrate substrates to produce acid byproducts, with positive result indicating acid production
Coagulase Test: differentiates Staphylococcus aureus from CoNS by detecting enzyme coagulase, with positive result indicating fibrin clot formation

Coagulase Enzyme

2 forms: bound coagulase (clumping factor) and free coagulase (staphylocoagulase)
Bound coagulase: reacts directly with fibrinogen in plasma, resulting in fibrin clot formation
Free coagulase: extracellular protein enzyme, reacts with coagulase-reacting factor (CRF) to form coagulase-CRF complex, resulting in fibrin clot formation

Pyrrolidonyl Arylamidase (PYR) Test

Principle: differentiates S.aureus from other CoNS by presence of enzyme L-pyrroglutamylaminopeptidase
Result: positive, with bright red color, indicating S.lugdunensis, S.intermedius, and S.schleiferi

Methicillin-Resistant Staphylococcus aureus (MRSA)

Penicillin-resistant (β-lactam) strains of S.aureus due to presence of mecA gene
Requires penicillinase-resistant penicillins, such as nafcillin, oxacillin, or cefoxitin
Types: CA-MRSA, HA-MRSA, MRSA, MRSE

Vancomycin-Resistant Staphylococcus aureus (VRSA)

VRSA: vancomycin-resistant S.aureus
VISA: vancomycin-intermediate S.aureus
TOC: Vancomycin

Macrolide Resistance

Resistance to clindamycin
Modified double disk diffusion test (D-zone test)

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Description

This quiz covers the characteristics of Staphylococci in Clinical Bacteriology, including colonies, family, and catalase properties. It is part of the 2nd semester course for S.Y. 2021-2022.

BACT211: Clinical Bacteriology Week 5 - Staphylococci

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