MICROBIOLOGY-CATALASE POSITIVE, GRAM-POSITIVE COCCI (STAPHYLOCOCCUS, MICROCOCCUS, AND SIMILAR ORGANISMS) Flashcards
1
Q
- Gram positive cocci
- Catalase positive
- Aerobic or facultative anaerobic
- Most are members of the indigenous flora and commonly isolated from a wide variety of diseases
A
Micrococcaceae
2
Q
Name two species of the Micrococcaceae family that are obligate anaerobes.
A
Staphylococcus aureus subsp. anaerobius and Staphylococcus saccharolyticus
3
Q
Are Staphylococcus aureus subsp. anaerobius and Staphylococcus saccharolyticus catalase positive or negative?
A
catalase negative
4
Q
- Gram-positive
- Catalase-positive
- Nonmotile
- Facultative anaerobes
- Species are initially differentiated by the coagulase test
A
Staphylococcus
5
Q
What are the characteristics of Staphylococcus aureus
A
- Gram-positive cocci in
grape-like clusters - Catalase positive
- Coagulase positive
- β-hemolytic
- Yellow or golden colonies on
blood agar (staphyloxanthin) - Ferments mannitol
6
Q
Where are common habitats of Staphylococcus aureus in the human body?
A
- Anterior nares
- Nasopharynx
- Perineal area
- Skin
- Colonizer of
mucosa
7
Q
What are the modes of transmission for Staphylococcus aureus?
A
- Endogenous strain: sterile site
by traumatic introduction - Direct contact: person to
person, fomites - Indirect contact: aerosolized
8
Q
Identify
Inhibits phagocytosis
A
Polysaccharide capsule
9
Q
Identify
Allows organism to adhere to inorganic surfaces or inhibits the penetration
of antibiotics
A
Slime layer or biofilm
10
Q
Identify
Activates complement, interleukin 1 (IL-1), and acts as chemotactic factor for the recruitment of PMNs
A
Peptidoglycan
11
Q
Identify
- Surface protein
- Bound to the cytoplasmic membrane of the organism
- Decreases the immune-mediated clearance of organisms from the site of
infection
A
Protein A
12
Q
Identify
- Major virulence factor of the specie
- Builds and insoluble fibrin capsule
A
Coagulase
13
Q
Identify
- Prevents the spread of infection
- Hydrolyzes hyaluronic acid
A
Hyaluronidase
14
Q
Identify
- Facilitates colonization on the skin surface
- Spread in fat-containing areas of the body
A
Lipase
15
Q
Identify
Hemolysis of RBCs
A
Alpha and beta hemolysis
16
Q
Identify
Toxic to WBC
A
Panton-Valentine leucocidin (PVL)
17
Q
IDENTIFY
- Works in conjunction with alpha toxin
- Catalyzes the hydrolysis of membrane phospholipids: cell lysis
A
Beta toxin
18
Q
IDENTIFY
- Cytolytic to erythrocytes
- Nonspecific membrane toxicity to other mammalian cells
A
Delta toxin
19
Q
IDENTIFY
- Produced by all strains of S. aureus
- Functions in association with Panton-Valentine leucocidin (PVL)
A
Gamma toxin
20
Q
IDENTIFY
- Resistant to hydrolysis by GI enzymes
- Found in milk products
- Associated with enterocolitis and toxic shock syndrome
A
Heat stable enterotoxin
21
Q
IDENTIFY
- Enterotoxin F
- Superantigen leading to toxic shock syndrome
A
Toxic shock syndrome toxin (TSST-1)
22
Q
IDENTIFY
- Serine protease that splits the intracellular bridges of the epidermis
A
Exfoliative toxin or epidermolytic
toxin
23
Q
IDENTIFY
- Disrupts smooth muscles in blood vessels
- Toxic to erythrocytes, leukocytes, hepatocytes, and platelets
A
Alpha toxin
24
Q
Common SSTIs include?
A
folliculitis, furuncles, carbuncles, impetigo, mastitis, and surgical site infections.
25
is a toxin-mediated skin condition, usually affects neonates but can also occur in adults with chronic renal failure or those who are immunocompromised.
Scalded skin syndrome (Ritter's disease)
26
A multisystem disease, characterized by high fever, rash, shock, hypotension, desquamation of the hands and feet, and potentially death.
Toxic shock syndrome (TSS)
27
What toxin is responsible for scalded skin syndrome?
exfoliative toxin
28
Which toxin is associated with toxic shock syndrome (TSS)
Enterotoxin F, also known as toxic shock syndrome toxin-1 (TSST-1).
29
TSS has been associated with tampon use in women
T or F
T
30
Can toxic shock syndrome (TSS) affect both sexes?
Yes, TSS can occur in both sexes
31
What are the primary toxins involved in Staphylococcus aureus food poisoning?
staphylococcal enterotoxins A and D heat-stable toxins
32
How soon do symptoms of Staphylococcus aureus food poisoning appear after ingestion? Symptoms usually resolve within?
-symptoms appear rapidly, typically 2-6 hours
-8-10 hours after onset.
33
occur through hematogenous spread or local introduction at a wound site and most common cause of septic arthritis in prepubertal children.
osteomyelitis and septic arthritis
34
Can Staphylococcus aureus be responsible for septic arthritis in adults?
T or F
T
35
sequestered focus of osteomyelitis arising in the metaphyseal area of the long bone
Brodie abscess
36
o Common cause of nosocomial pneumonia
o Usually followed by aspiration of endogenous nasopharyngeal organisms
Pneumonia
37
What are some predisposing factors for Staphylococcus aureus pneumonia?
include measles, influenza A virus, cystic fibrosis, and immune deficiency.
38
Left-sided valvular heart disease and IV drug users (tricuspid valve)
Acute endocarditis
39
what are the Community-associated infections
o Serious soft tissue infections
o Frequently mediated by methicillin resistant S. aureus (community-acquired
MRSA or CA-MRSA)
o Associated with PVL
40
What is typically observed in microscopy for Staphylococcus aureus infections?
Numerous gram-positive cocci in clusters with polymorphonuclear cells are usually seen.
41
What type of colonies does Staphylococcus aureus form on sheep blood agar?
Round, smooth, white or pigmented (yellow-orange) colonies that are β-hemolytic.
42
Which selective media can be used for the isolation of Staphylococcus aureus?
Phenylethyl alcohol (PEA) agar and Columbia colistin-nalidixic acid (CAN) agar.
43
a selective and differential medium used for the identification of methicillin-resistant Staphylococcus aureus (MRSA) and contains cefoxitin, to which MRSA is resistant
CHROMagar
44
What color of colonies does Staphylococcus aureus form on CHROMagar?
mauve-colored
45
what is the concentration, carbohydrate present and pH indicator of mannitol salt agar?
High concentration of salt (10%)
Carbohydrate: mannitol
pH indicator: phenol red
46
primary purpose of the Coagulase Test?
To separate Staphylococcus aureus from other species collectively referred to as coagulase-negative staphylococci.
47
What are the two types of coagulase produced by Staphylococcus aureus?
Bound coagulase (clumping factor) and extracellular coagulase (free coagulase).
48
How does the coagulase enzyme function in the Coagulase Test?
It binds to plasma fibrinogen, causing the plasma to clot.
49
Which test is used to detect bound coagulase?
The rapid slide test.
50
Which test is used to detect extracellular coagulase (free coagulase)?
The tube coagulase test.
51
How long does it typically take for a positive result to appear in the tube coagulase test?
1-4 hours after inoculation.
52
Differentiates catalase-positive micrococcal and staphylococcal species form
catalase-negative streptococcal species
Catalase test
53
What is the function of the catalase enzyme in bacteria?
It converts hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen (O₂).
54
positive result for the Catalase Test?
copious bubbles
55
negative result for the Catalase Test?
No or few bubbles are produced
56
Which two species are the most common Coagulase-negative Staphylococci isolated in infections?
Staphylococcus epidermidis and Staphylococcus saprophyticus.
57
What type of infections are Coagulase-negative Staphylococci often associated with?
associated with hospital-acquired infections.
58
In which conditions are antibodies to teichoic acid commonly found?
In long-standing or deep-seated staphylococcal infections, such as osteomyelitis.
59
What are some predisposing factors for CoNS infections?
Predisposing factors include catheterization, prosthetic device implants, and immunosuppressive therapy.
60
How do CoNS compare in virulence to Staphylococcus aureus?
CoNS are less virulent than Staphylococcus aureus.
61
VIRULENCE FACTORS OF STAPHYLOCOCCUS AUREUS
Polysaccharide capsule
Slime layer or biofilm
Peptidoglycan
Protein A
Coagulase
Hyaluronidase
Lipase
Alpha and beta hemolysis
Panton-Valentine leucocidin (PVL)
62
CHARACTERISTICs of Staphylococcus
epidermidis
* Gram-positive cocci in
clusters
* Catalase–positive
* Coagulase-negative
* Novobiocin sensitive
* Whitish, non-hemolytic
colonies on blood agar
63
Where are common habitats of Staphylococcus epidermidis in the human body?
* Skin
* Mucous
membranes
64
What are the modes of transmission for Staphylococcus epidermidis
* Endogenous strains:
implantation of medical devices
(shunts, prosthetic devices)
* Direct contact: person-to person
65
VIRULENCE FACTORS of Staphylococcus
epidermidis
-Polysaccharide capsule
-Slime layer or biofilm
-Peptidoglycan
-Delta toxin
66
What is typically observed in microscopy for Staphylococcus epidermidis?
Numerous gram-positive cocci in clusters
67
What type of colonies does Staphylococcus epidermidis form on sheep blood agar?
small to medium; opaque, gray-white colonies; most colonies are nonhemolytic; slime-producing strains are extremely sticky and adhere to agar surfaces
68
Characteristics of Staphylococcus
saprophyticus
* Gram-positive cocci in
clusters
* Catalase-positive
* Coagulase-negative
* Novobiocin resistant
* Whitish, non-hemolytic
colonies on blood agar
69
Where are common habitats of Staphylococcus saprophyticus in the human body?
* Skin
* Genitourinary
tract
* Mucosa
70
* Community-acquired urinary tract infections in young, sexually active females
* Not associated with health care-associated infections
* Second most common cause of UTI (after E.coli) in young females
Staphylococcus saprophyticus
71
What are the modes of transmission for Staphylococcus saprophyticus
* Endogenous strain: sterile
urinary tract (young sexually active females)
72
VIRULENCE FACTOR NI Staphylococcus
saprophyticus
Peptidoglycan
73
What type of colonies does Staphylococcus saprophyticus form on sheep blood agar?
large; entire very glossy, smooth, opaque butyrous, convex; usually white but colonies can be yellow to orange
74
How many milligrams are used in a Novobiocin disk?
A 5mg Novobiocin disk is used.
74
How does Staphylococcus saprophyticus differ from Staphylococcus epidermidis in Novobiocin susceptibility?
Staphylococcus saprophyticus is resistant, while Staphylococcus epidermidis is susceptible to Novobiocin.
75
What are some coagulase-positive or variable staphylococci that are part of the normal microbiota of various animal species?
Staphylococcus intermedius, Staphylococcus pseudintermedius, and Staphylococcus delphini
75
What reagent is used in the modified oxidase test?
6% tetramethyl phenylenediamine hydrochloride in dimethylsulfoxide + growth on filter paper
76
Which staphylococcal species is an important agent in dog bite wound infections and may be misidentified as Staphylococcus aureus?
Staphylococcus intermedius.
77
Identify
* Environmental organisms
* Gram-positive
* Coagulase-negative
* Low pathogenic significance
* Normal flora in the respiratory tract or other sites in the body
Micrococcus
78
What is the result of a positive modified oxidase test for Micrococci?
Dark blue color within 2 minutes.
79
On what medium is the bacitracin susceptibility test performed?
Sheep blood Mueller-Hinton medium.
80
How many unit of the bacitracin disk used in the susceptibility test?
0.04 U
81
Micrococcus are resistant to bacitracin
T or F
F; Susceptible to bacitracin.
82
How many micrograms of furazolidone used in the susceptibility test?
100 mcg
83
What is the expected result for Micrococcus in the furazolidone susceptibility test?
Resistant to furazolidone.
84
Identify
* Normal oral flora
* Rarely isolated from infection
* Colonies adhere strongly to the agar surface
Stomatococcus
85
What is the percentage of penicillin resistance in S. aureus isolates?
85-90%
86
is an enzyme produced by Staphylococci that inactivates β-lactam antibiotics. It’s a common resistance mechanism.
β-lactamase
87
-MRSA stands for?
-MRSE stands for?
-Methicillin-resistant S. aureus
-Methicillin-resistant S. epidermidis.
88
-ORSA stands for?
-ORSE stands for
-Oxacillin-resistant S. aureus, which is another name for MRSA.
-Oxacillin-resistant S. epidermidis, another name for MRSE.
89
What is the alternative treatment for MRSA and how effective is it?
Vancomycin is an alternative treatment for MRSA. However, vancomycin resistance has also been increasing.
90
What kind of infections are MRSA known to cause?
MRSA are etiologic agents of serious nosocomial (hospital-acquired) and community-acquired infections.
