Biology: Staphylococci Characteristics and Pathogenicity

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Questions and Answers

Where are Staphylococci mainly found?

In soil and water

On the skin, skin glands, and mucous membranes of mammals and birds (correct)

In the gastrointestinal tract of humans

In the respiratory tract of animals

Which of the following is more pathogenic than S.epidermidis and S.saprophyticus?

S.aureus (correct)

S.saprophyticus

S.epidermidis

All of the above are equally pathogenic

What is the main function of surface proteins in S.aureus?

To inhibit phagocytic engulfment

To produce toxins that lyse eukaryotic cell membranes

To enhance staphylococcal survival in phagocytes

To promote colonization of host tissues (correct)

What is the main cause of toxic shock syndrome caused by S.aureus?

Release of superantigens into the bloodstream Signup and view all the answers

What is S.epidermidis known to cause?

Prosthetic or indwelling device infections Signup and view all the answers

What is the main function of catalase in S.aureus?

To enhance staphylococcal survival in phagocytes Signup and view all the answers

What is S.saprophyticus mainly associated with?

Urinary tract infections in young females Signup and view all the answers

Which of the following is NOT a virulence factor of S.aureus?

Lipopolysaccharide Signup and view all the answers

Which Staphylococcus species is commonly associated with urinary tract infections, especially in girls?

S. saprophyticus Signup and view all the answers

What is the primary method of diagnosis for staphylococcal infections?

Culturing the bacteria from an infected site Signup and view all the answers

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

Round, convex, and 1-4 mm in diameter with a sharp border Signup and view all the answers

What is the primary function of Mannitol salt agar (MSA) in Staphylococcus identification?

To selectively isolate Staphylococcus from mixed cultures Signup and view all the answers

What is the purpose of phenol red in Mannitol salt agar (MSA)?

To act as a pH indicator Signup and view all the answers

Which Staphylococcus species is characterized by a bright yellow or white pigment on blood agar?

S. saprophyticus Signup and view all the answers

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

Beta-hemolytic activity Signup and view all the answers

What is the concentration of NaCl in Mannitol salt agar (MSA)?

7.5% NaCl Signup and view all the answers

Study Notes

Characteristics of Staphylococci

Staphylococci are typical Gram-positive bacteria that occur as irregular clusters of cocci.
They are widespread in nature, but mainly found on the skin, skin glands, and mucous membranes of mammals and birds.

Pathogenicity of Staphylococci

S. aureus is more pathogenic than S. epidermidis and S. saprophyticus.
S. epidermidis can cause hospital-acquired infections, such as prosthetic or indwelling devices.
S. saprophyticus is mainly associated with urinary tract infections in young, sexually active females.

Virulence Factors of S. aureus

Surface proteins that promote colonization of host tissues
Leukocidin, kinases, and hyaluronidase that promote bacterial spread in tissues
Capsule and Protein A that inhibit phagocytic engulfment
Carotenoids and catalase that enhance staphylococcal survival in phagocytes
Protein A and coagulase that act as immunological disguises
Hemolysins, leukotoxin, and leukocidin that are membrane-damaging toxins
TSST (toxic shock syndrome toxin) and ET (exfoliative toxin) that damage host tissues or provoke symptoms of disease
Inherent and acquired resistance to antimicrobial agents

Common Infections Caused by Staphylococci

S. aureus causes:
Superficial skin lesions (boils) and localized abscesses
Deep-seated infections, such as osteomyelitis and endocarditis
Hospital-acquired infections of surgical wounds
Food poisoning by releasing enterotoxins into food
Toxic shock syndrome by releasing superantigens into the bloodstream
S. saprophyticus causes urinary tract infections, especially in girls.

Diagnosis of Staphylococcal Infections

Diagnosis begins with attempting to culture the bacteria from an infected site.
Any area with pus, crusty drainage, or blisters should be cultured.
Blood from patients with sepsis, toxic shock syndrome, or pneumonia should be cultured.

Laboratory Identification of Staphylococci

S. aureus colonies on agar are round, convex, and 1-4 mm in diameter with a sharp border.
S. aureus usually displays a light to golden yellow pigment on blood agar.
S. aureus is usually beta-hemolytic on blood agar.
Mannitol salt agar (MSA) is a selective and differential media used for the isolation of Staphylococci.
MSA consists of 7.5% NaCl, which is selective for species of Staphylococcus.
Mannitol fermentation produces acid end products that turn the medium yellow.

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Description

Learn about the characteristics and pathogenicity of Staphylococci, a type of Gram-positive bacteria found on skin and mucous membranes. Understand the differences between S. aureus, S. epidermidis, and S. saprophyticus.