Faculty of Dental Medical: Gram Positive Cocci Lecture 9

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Questions and Answers

What is the number of medically important species of Staphylococcus?

3 (correct)

What is the arrangement of Staphylococcus in a microscope?

In chains

Randomly scattered

In a straight line

In pairs or clusters (correct)

What is the primary function of the catalase enzyme in Staphylococcus aureus?

To break down hydrogen peroxide into water and oxygen (correct)

To form biofilms on host tissues

To destroy white blood cells

To produce a protective fibrin clot

What is the main function of surface adhesions in Staphylococcus aureus?

To allow the bacteria to adhere to host tissues and form biofilm Signup and view all the answers

What is the characteristic of Staphylococcus aureus colonies on nutrient agar?

Large yellow-golden colonies Signup and view all the answers

What is the function of protein A in Staphylococcus aureus?

To allow the bacteria to evade the immune response Signup and view all the answers

What is the type of hemolysis caused by Staphylococcus aureus on blood agar?

β-hemolysis Signup and view all the answers

What percentage of people have Staphylococcus aureus in their nasal mucosa?

40%-50% Signup and view all the answers

What is a common feature of skin and soft tissue infections caused by S. aureus?

Pus, red, swollen, and painful areas on the skin Signup and view all the answers

What is the target of Toxic Shock Syndrome Toxin (TSST) in the body?

Gastrointestinal tract and blood vessels Signup and view all the answers

What is the characteristic of enterotoxin produced by S. aureus?

Heat stable and short incubation period Signup and view all the answers

What is the purpose of Catalase test in the identification of S. aureus?

To identify the bacterium as Gram positive or negative Signup and view all the answers

What is the characteristic of colonies of S. aureus on blood agar?

B hemolysin colonies Signup and view all the answers

What is the indicator used in Manitol salt agar?

Phenol red Signup and view all the answers

What is the purpose of Gram staining in the identification of S. aureus?

To identify the bacterium as Gram positive or negative Signup and view all the answers

What is the specimen used for the diagnosis of S. aureus?

Swap from lesions, pus, sputum, CSF, blood culture Signup and view all the answers

What is the selective media used for cultivating aureus colonies?

Manitol Salt Agar Signup and view all the answers

What is the purpose of cultivating the specimen from tampon or vaginal swab or serum on MSA for 24h at 37c?

Diagnosis of Toxic Shock Syndrome Signup and view all the answers

Why are semi-synthetic penicillins such as Methicillin, Oxacillin, and Nafcillin used to treat aureus infections?

Because aureus is resistant to natural penicillin Signup and view all the answers

What is the characteristic of S.epidermidis and S.saprophyticus on nutrient agar at 37c for 24h?

White colony Signup and view all the answers

What is the mechanism by which S.epidermidis acts as an opportunistic pathogen?

Both A and B Signup and view all the answers

What is the disease caused by S.saprophyticus?

Honeymoon cystitis Signup and view all the answers

What is the treatment for S.epidermidis?

Vancomycin, Gentamicin Signup and view all the answers

What is the active medicine for MRSA?

Linezolid, Daptomucin Signup and view all the answers

Study Notes

Gram-Positive Cocci: Staphylococcus

There are over 40 species of Staphylococcus, but only three are medically important: S. aureus, S. epidermidis, and S. saprophyticus.
Staphylococcus are Gram-positive cocci that arrange in pairs or clusters (grape-like).
They are facultative anaerobes and can grow on simple media.
They are catalase positive, which means they can break down hydrogen peroxide (H2O2) into water and oxygen.

Staphylococcus aureus

Morphology: Gram-positive cocci arranged in clusters, with some strains being capsulated.
Culture: Can grow in nutrient agar and blood agar at 37°C for 24 hours, forming large, yellow-golden colonies.
They are β-hemolytic on blood agar.
They can ferment mannitol sugar in mannitol salt agar, producing acid.

Virulence Factors of S. aureus

Surface adhesions: allow the bacteria to adhere to host tissues and form biofilms, providing protection from host defenses and antimicrobial agents.
Coagulase: an enzyme that converts fibrinogen into fibrin, creating a protective fibrin clot around the bacteria, shielding it from phagocytosis.
Leukocidin: destroys white blood cells.
Catalase enzyme: breaks down hydrogen peroxide (H2O2) produced by macrophages, allowing the bacteria to survive.
Nucleases: DNase and RNase.
Protein A: binds to antibodies, preventing the killing of bacteria and allowing S. aureus to evade the immune response.
β-lactamase: breaks down β-lactam antibiotics.
Exotoxins:
- Enterotoxin: causes food poisoning.
- Exfoliative toxin: causes scalded skin syndrome (SSSS).
- Toxic shock syndrome toxin (TSST): can cause toxic shock syndrome.

Diseases Caused by S. aureus

Skin and soft tissue infections, such as impetigo, pus, and red, swollen, and painful areas on the skin.
Staphylococcal scalded skin syndrome (SSSS): a severe skin infection caused by S. aureus that produces exfoliative toxins.
Toxic shock syndrome (TSS): caused by TSST, leading to fever, multi-organ dysfunction, and potentially life-threatening conditions.
Bacteremia and endocarditis: can cause bloodstream infections.
Pneumonia.
Food poisoning: characterized by nausea, vomiting, diarrhea, and a short incubation period of 1-6 hours.

Lab Diagnosis of S. aureus

Specimen: swap from lesions, pus, sputum, CSF, blood culture, or urine culture.
Direct smear: examination of the specimen under a microscope.
Cultivation: on nutrient agar or blood agar at 37°C for 24 hours.
Identification: on nutrient agar, the colonies are golden yellow or blood agar, with β-hemolysin colonies.
Identification is also done through Gram staining, catalase test, and mannitol salt agar.

Food Poisoning Diagnosis

Cultivation of the vomiting or diarrhea on mannitol salt agar.
ELISA test.

Toxic Shock Syndrome Diagnosis

Cultivation of the specimen from tampon or vaginal swab on MSA for 24 hours at 37°C.
ELISA test through serum.

Treatment of S. aureus Infections

Most S. aureus are resistant to penicillin, so semi-synthetic penicillin (methicillin, oxacillin, nafcillin) or other antibiotics like linezolide or daptomycin are used.
No vaccine available.
Prevention involves hand washing and avoiding sharing personal items.

S. epidermidis and S. saprophyticus

Both grow on nutrient agar at 37°C for 24 hours, forming white colonies.
Both grow on MSA, forming pink colonies.
Both are coagulase-negative and catalase-positive.
S. epidermidis:
- Commonly found on human skin as normal flora.
- Can act as an opportunistic pathogen, causing wound infections, UTI, and subacute endocarditis.
- Adheres to devices, such as teeth, by glycocalyx.
- Produces β-lactamase.
S. saprophyticus:
- Found in soil and water.
- Attaches to the genitourinary tract and causes honeymoon cystitis.
Treatment:
- S. epidermidis: vancomycin, gentamicin.
- S. saprophyticus: ciprofloxacin.

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Description

This quiz covers the general features of staphylococcus, including their morphology, characteristics, and medical importance. It is part of a lecture on gram positive cocci in a dental medical faculty.