Staphylococci Flashcards
0
Q
What temperature is used for staph cultivation?
A
37C
1
Q
What type of air requirements are needed for staphylococci?
A
Facultative anaerobes
2
Q
What types of staph are spore forming?
A
Clostridium & bacillus
3
Q
What can subspecies be classified as?
A
Phage groups
Ribotypes
Strains
4
Q
How are staph encountered as?
A
Commensals
Pathogens
5
Q
How do staph gram stain as?
A
Gram positive cocci
6
Q
Staph are catalase positive or negative?
A
Positive
7
Q
What do staph ferment?
A
Sugars
8
Q
Are they motile or nonmotile?
A
Non motile
9
Q
Air requirements include what?
A
Aerobic
Facultative anaerobes
10
Q
What are they similar to?
A
Micrococcus
11
Q
Staph aureus (halo) produces what?
A
Boils Folliculitis Furuncles Carbuncles Purulent abcesses
12
Q
S. aureus can cause infections including what?
A
Skin, wound, blood, & toxin related diseases
13
Q
What are 3 types of cutaneous staph infections?
A
Folliculitis
Furuncle
Carbuncle
14
Q
What is folliculitis?
A
Infection of the hair follicles
15
Q
What are furuncles?
A
An acute, round, firm tender, circumscribed, perifollicular staph pyoderma that usually ends in central suppuration
16
Q
What are carbuncles?
A
Two or more confluent furuncles with separate heads
Infection is deeper
May cause fever/chills
17
Q
What is bullous impetigo?
A
Skin infection caused by staph that is highly infectious
By contact with patient, fomites, autoinnoculation
18
Q
What are some staph toxin related diseases?
A
Scalded skin syndrome
Toxic shock syndrome
Food poisoning
19
Q
Can staph cause food poisoning?
A
Yes
20
Q
Staph food poisoning is what?
A
An enterotoxin
21
Q
How is staph food poisoning gotten?
A
Contaminated food kept at a temp that allows bacterial growth & toxin release
Reheating food may kill bacteria but the toxin is heat stable
Symptoms occur 1-6 hours after ingestion
Self limit at 24 hours
22
Q
Toxic shock syndrome is caused by what toxin?
A
TSST-1 toxin 1
23
Q
What is toxic shock syndrome?
A
Rare potentially fatal multi-system disease with sudden fever, chills, vomiting, diarrhea, muscle aches, & desquamating rash
24
What is desquamating rash?
Rash that can lead to hypotension & shock
25
When was TSS originally described?
1978 - associated with highly absorbent tampon use
26
TSS is what kind of infection?
Localized infection
| Caused by systemic toxin
27
Scalded skin syndrome is more common in what?
Infants
28
What type of toxin is involved in scalded skin syndrome?
Epidermolytic toxin
29
What does epidermolytic toxin do?
Dissolves skin
30
What is scaled skin syndrome also known as?
Ritter disease
31
What are the characteristics of scalded skin syndrome?
Lesion has purulent material
Then cutaneous erythema followed by peeling of the epidermis
Lasts 2-4 days & spontaneously heals
32
What are gram positive bacteria treated with & why?
Treated with cell wall inhibitors
| Beta lactams & vancomycin
33
What are cell wall components for structural integrity?
b-lactams
Penicilins
Cephalosporins
Vancomycin
34
What are some 50S inhibitors?
Erythromycin
Clindamycin
Chloramphenicol
35
What are beta lactam antibiotics?
Naturally occurring
Synthetic
Semi-synthetic
36
What do cell walls do for organisms?
Helps organisms resist changes in osmotic conditions
37
How do b-lactams inhibit cell wall synthesis?
B-lactams are structural analogs to acyl D-alanyl-D-alanine
| Inhibit the transpeptidation reactions
38
What are types of b-lactams?
Penicillins
Cephalosporins
Monobactams
Cabapenems
39
What is vancomycin (glycopeptide)?
A narrow spectrum, limited to gram positive
Cannot penetrate outer cell membrane of gram negative
Links to peptide substrate to prevent transportation
40
Beta lactams interfere with cell wall synthesis - what are their characteristics?
Look like the next building block for cell wall synthesis
| If they are inserted by the penicillin binding proteins into the cell wall - cell wall synthesis will stop
41
What is MRSA?
A major nosocomial infection - HA-MRSA
| When acquired in the community - CA-MRSA
42
What is SCCmec cassette in MRSA?
MRSA strains with a large insertion into the chromosome that brings several genes
Usually antibiotic resistance & virulence genes
All have mecA gene
43
What gene do SCCmec cassette MRSA strains have?
mecA gene
44
What does mecA code for?
An alternate penicillin binding protein - PBP2a
45
Methicillin resistant staph are what?
Penicillin resistant strains can be treated with nfacillin or oxacillin - resistant to effects of penicillinase
46
What is MRSA resistant to?
Any penicillin drug
47
Why is MRSA resistant to penicillin drugs?
Due to the presence of the methicillin resistance gene (mecA) on the chromosome
mecA codes for PBP2a
PBP2a doesn't bind to penicillins
48
What is oxacillin used for?
To detect methicillin resistance
| A plate with high salt & polymixin make the media select for staph
49
What does CLSI recommend using for methicillin resistant staph?
Cefotoxin plates to induce the mecA gene because MR can show heteroresistance
50
How is staph resistant to vancomycin?
Vancomycin interferes with cell wall synthesis but is not a beta lactam
51
What are two vancomycin resistant staphs?
VISA
| VRSA
52
What is VISA?
Vancomycin intermediate S. aureus
| Can arise from vancomycin overuse
53
What is VRSA?
Resistant S. aureus
54
How can you find out if it is vancomycin resistant staph?
Screening by a vancomycin agar plate
55
How are staph resistant to macrolide?
Macrolide antibiotics that inhibit protein synthesis at the level of the ribosome - 50s
56
What are two examples of macrolide resistant staph?
Clindamycin & erythromycin
57
What do clindamycin & erythromycin do?
Usually don't have the same susceptibility pattern
When they don't, it could be because the organisms can be induced to be resistant once the patient starts to take the antibiotic
58
What is used to test inducible macrolide resistance?
D test
59
How does the D test work?
Places clindamycin & erythromycin in close proximity to each other on a Kinky Bauer plate
Erythromycin makes the bacteria around it express its erm gene
This demonstrates its resistance to the clindamycin
60
What does the D test do?
Determines in advance if the organism will respond to clindamycin
If the test is positive - report all macrolides as resistant
61
What color will MRSA turn a mannitol salt plate?
Pink
62
What happens when MRSA is on a chromagar plate?
Has color
63
What are rapid detection tests in positive blood cultures for MRSA?
PCR
| Fluoresenct in situ hybridization for mecA & staph aureus
64
What are virulence factors of staph aureus?
```
Enterotoxins
TSST-1
Exfoliative toxin
Cytolytic toxin
Enzymes
Protein A binds to Fc portion of antibody, blocks phagocytosis
```
65
What are types of cytolytic toxins?
```
alpha toxin
beta toxin
panton valentine - kills WBC
leucocidin
delta toxin
```
66
What does S. aureus gram stain as & what shape?
Gram positive cocci in clusters
67
What do S. aureus colonies look like on blood agar and what type of hemolysis do they have?
Smooth white creamy colonies with beta hemolysis
68
Are S. aureus catalase positive or negative?
Positive (virulence factor) that causes the release of oxygen (bubbles) from H2O2
69
Are S. aureus coagulase positive or negative?
Positive (virulence factor) that clumps plasma - clumping factor
May be on the bacterial surface & agglutinate immediately
May be secreted as extracellular staphylocoagulase which takes longer, & is demonstrated in a tube
70
What are characteristics of S. epidermidis?
Commensal
| Pathogen
71
What makes S. epidermidis a commensal?
Found on skin
| Common contaminant of wound, blood cultures
72
What makes S. epidermidis a pathogen?
Slime/biofilm
Endocarditis - in blood stream
Nosocomial UTI
73
What is the result of catalase test for S. epidermidis?
Positive
74
What is the result of coagulase test for S. epidermidis?
Negative
75
What is the bacitracin test result for S. epidermidis?
Resistant
| Negative
76
What is the novobiocin test result for S. epidermidis?
Positive
| Susceptible
77
What is S. saprophyticus?
A saprophyte
78
What is a saprophyte?
An organisms that grows on & derives its nourishment from dead or decaying organic matter
79
What is an example of S. saprophyticus?
Honeymoon cystitis - UTI from sex
80
Results of coagulase test for S. lugdunensis?
Negative with tube test
| Positive with agglutination test
81
What types of infections does S. lugdunensis cause?
CA - community acquired
| HA - hospital acquired
82
S. lugdunensis may contain what gene?
mecA gene
83
Why has S. lugdunensis been confused with S. aureus?
Can identified as PYR positive & ornithine decarboxylate positive
84
What is the microdase (oxidase) test result for micrococcus?
Positive
85
What type of fermenter is micrococcus?
Nonfermenter - staph ferment
86
What type of response to sugars does micrococcus give?
Asacchrolytic - no response
87
Is micrococcus susceptible to lysozyme?
Yes
88
Is micrococcus susceptible or resistant to lysostaphin?
Resistant
89
What is the bacitracin (A disk) test result of micrococcus?
Sensitive/Positive
90
Is micrococcus susceptible or resistant to Furazolidone?
Resistant
91
Stomatococcus mucilaginous is what?
Normal flora
92
What does is the colony morphology of Stomatococcus mucilaginous?
Medium white colony
93
What type of hemolysis is stomatococcus mucilaginous?
Nonhemolytic
94
What is the transmission of Stomatococcus mucilaginous?
Same as micrococcus
| Seen in bone marrow & malignancies
95
What is the result of A disk test for Stomatococcus mucilanginous?
Negative
| Micrococcus is positive
