Staphylococcus

Question 1

Morphological characteristics:
1) Gram Stain
2) Motility
3) Identifying tests
4) Unique behaviors/characteristics

Answer 1

1) Positive
2) Non-motile
3) Coagulase - coagulase positive (S. aureus) and everything else is negative
4) Form clusters when grown on media, form pairs or triads when grown in broth. Widely distributed in nature - growing on skin, skin glands, mucous membranes of mammals generally living symbiotically with their host. May develop a pathogenic lifestyle if they gain entry into host tissues through trauma

Question 2

What are the 3 medically important staphylococcus cultures we used in lab? How can we differentiate between them? What are their identifying traits (e.g., hemolytic pattern)? What are the main diseases they cause?

Answer 2

• Staphylococcus aureus: coagulase positive; nosocomial infections, food poisoning, toxic shock syndrome
• Staphylococcus epidermidis: alpha-hemolytic; coagulase negative; nosocomial infection caused by surgical implants, endocarditis, bacteremia, osteomyelitis, UTI, catheter related infections
• Staphylococcus saprophyticus: novobiocin resistant; gamma hemolytic; nongonococcal urethritis, wound infections, septicemia

Question 3

What is MRSA and VISA? What tests can we use to identify them? What characteristics differentiates them from regular S. aureus?

Answer 3

MRSA: Methicillin resistant s. aureus
VISA: Vancomycin-intermediate s. aureus
They can both be identified by using monoclonal antibody assay specific to PBP2a, agar screening plates, peptide nucleic fluorescent in situ hybridization (PNA FISH), and nucleic acid amplification protocols.

Question 4

Mannitol Salts Agar Plate:
1) What type of media is this?
2) Why was this media used?
3) What components of the media are important?
4) What does this media tell you about an organism grown on it?
5) How do we use it to differentiate?

Answer 4

1) Selective and differential
2) Used for isolation and identification of S. aureus
3) 7.5% NaCl inhibits most organisms except S. aureus, phenol red (pH indicator)
4) If it can ferment mannitol
5) There will be a color change around the colony from red yellow upon fermentation of mannitol - this identifies S. aureus and S. saprophyticus. Red colonies indicate negative identification for S. aureus. Any growth at all indicates staphylococcal species

Question 5

Coagulase Test:
1) What’s this media tell you?
2) What reagents are used?
3) Why did we use it in this lab?
4) How do we use it to differentiate?

Answer 5

1) Tests for the enzyme coagulase
2) Rabbit or human plasma
3) S. aureus is coagulase positive allowing us to identify it with this test
4) S. aureus can coat its surface with fibrin upon contact with blood which allows the bacteria to resist phagocytosis (it will not clump yielding a negative result)

Question 6

DNase Agar:
1) What type of media is this?
2) What does this test tell us about an organism?
3) What is the composition of this media and why is it important?
4) What reagents are used and what is a positive result?
5) How do we use it to differentiate?

Answer 6

1) Differential
2) Tests the ability of the organism to produce the enzyme DNase
3) Tryptic soy agar supplemented with DNA. Important because the DNA will tell us if DNase is present since it will be cleaved in this test if it is
4) Toluidine blue. Positive result if there is a red-purple color almost immediately after toluidine blue
5) DNase is produced by most coagulase-positive Staphylococcus (S. aureus)