Micrococcaceae Flashcards
1
Q
Micrococcaceae
A
staphylococcus and micrococcus
2
Q
Staphylococcus species
A
S. aureus, S. epidermidis, S. hemolyticus, S. saprophyticus, S. intermedius
3
Q
Micrococcaceae general characteristics
A
- Gram-positive cocci, catalase positive, singly, pairs or in clusters
- Colony morphology: cream-colored, buttery on BA or CNA, some produce Beta hemolysis
- aerobic or falcultative anaerobes, non motile, non spore forming, non encapsulated
4
Q
exceptions to general characteristics
A
S. saprophyticus is an obligate anaerobe
5
Q
Micrococcus luteus
A
- Gram-positive, catalase positive, coagulase negative
- morphology: distinct yellow colony
- non-pathogen
6
Q
coagulase
A
staphylocoagulase enzyme clots plasma
7
Q
coagulase positive staphylococci
A
- S. aureus (human pathogen)
- S. delphini, S. intermedius, S. lutrae, S. hyicus (animal pathogens)
8
Q
coagulase negative staphylococci (CoNS)
A
- S. epidermidis (nosocomial infections)
- S. saprophyticus (UTI’s in young, sexually active females)
9
Q
Staphylococcus aureus
A
- exist in carrier state in 20-30% of population
- most virulent staph species
- superficial to systemic infections
10
Q
Virulence factors of S. aureus
A
- enzymes: coagulase, hyaluronidase, lipase
- enterotoxins, toxins A-E and G-I, exfoliative toxins, cytolytic toxin
- Protein A
11
Q
hyaluronidase
A
hydrolyzes the hyaluronic acid present in connective tissue and helps spread infection
12
Q
lipase
A
breaks down the fats and oil created by sebaceous glands on skin surfaces
13
Q
enterotoxins
A
heat-stable exotoxins that cause diarrhea and vomiting
14
Q
toxins A-E and G-I
A
- resistant to gastric acid and associated with food poisoning
- A, B, and D associated with staph food poisoning
- toxic shock syndrome toxin-1 (TSST-1)
- TSST-1, B, C, G, and I are superantigens
- causes toxic shock syndrome
15
Q
exfoliative toxin (epidermolytic toxin)
A
causes epidermal layer of skin to slough off; causes Scalded Skin Syndrome and bullous impetigo
16
Q
cytolytic toxins
A
alpha, beta, and gamma hemolysin
17
Q
alpha hemolysin
A
destroys platelets and tissues
18
Q
beta hemolysin
A
- acts on the sphingomyelin of RBC membranes, causing lysis
- hot-cold lysin because works at 37 and 4 degrees C
19
Q
gamma hemolysin
A
- also called Panton-Valentine leukocidin (PVL)
- exotoxin kills polymorphonuclear leukocytes to help prevent phagocytosis
- typically associated with community-acquired infections
20
Q
Protein A
A
- binds the fragment crystallizable (Fc) portion of an antibody to avoid phagocytosis by masking it immunogenic proteins with host proteins to look like “self”
- negates the protective effects of IgG
21
Q
Transmission of Staph. aureus
A
- colonizes nares (20-30% carriers)
- axillae, vagina, pharynx, other skin surfaces
- nosocomial
- fomites, poor hygiene
22
Q
Clinical cases of Staph. aureus include
A
localized (pyogenic) skin infections, impetigo
23
Q
Scalded Skin Syndrome
A
- extensive exfoliative dermatitis, most likely to occur in renal failure patients and ICP’s
- localized lesion to profuse peeling
- 2-4 days, can be fatal in adults, spontaneous recovery in children
24
Q
toxic shock syndrome
A
- associated with super-absorbent tampons
- high fever, rash of the trunk/extremeties, watery diarrhea, vomiting, dehydration, leads to hypotension
- Disseminated intravascular coagulation (DIC),
- increase in blood urea nitrogen (BUN) and creatinine
25
toxic epidermal necrolysis (TEN)
- causes: drug induced, infections, vaccines
- similar to Staph. Scaleded Skin Syndrome (SSSS), except steroids can be effective
- high mortality rate
26
- Gram-positive cocci, catalase positive, singly, pairs or in clusters
- Colony morphology: cream-colored, buttery on BA or CNA, some produce Beta hemolysis
- aerobic or falcultative anaerobes, non motile, non spore forming, non encapsulated
Micrococcaceae general characteristics
27
- Gram-positive, catalase positive, coagulase negative
- morphology: distinct yellow colony
- non-pathogen
Micrococcus luteus
28
- exist in carrier state in 20-30% of population
- most virulent staph species
- superficial to systemic infections
Staphylococcus aureus
29
hydrolyzes the hyaluronic acid present in connective tissue and helps spread infection
hyaluronidase
30
breaks down the fats and oil created by sebaceous glands on skin surfaces
lipase
31
heat-stable exotoxins that cause diarrhea and vomiting
enterotoxins
32
causes epidermal layer of skin to slough off; causes Scalded Skin Syndrome and bullous impetigo
exfoliative toxin (epidermolytic toxin)
33
destroys platelets and tissues
alpha hemolysin
34
- acts on the sphingomyelin of RBC membranes, causing lysis
| - hot-cold lysin because works at 37 and 4 degrees C
beta hemolysin
35
- also called Panton-Valentine leukocidin (PVL)
- exotoxin kills polymorphonuclear leukocytes to help prevent phagocytosis
- typically associated with community-acquired infections
gamma hemolysin
36
- binds the fragment crystallizable (Fc) portion of an antibody to avoid phagocytosis by masking it immunogenic proteins with host proteins to look like "self"
- negates the protective effects of IgG
Protein A
37
- extensive exfoliative dermatitis, most likely to occur in renal failure patients and ICP's
- localized lesion to profuse peeling
- 2-4 days, can be fatal in adults, spontaneous recovery in children
Scalded Skin Syndrome
38
- associated with super-absorbent tampons
- high fever, rash of the trunk/extremeties, watery diarrhea, vomiting, dehydration, leads to hypotension
- Disseminated intravascular coagulation (DIC),
- increase in blood urea nitrogen (BUN) and creatinine
toxic shock syndrome
39
- causes: drug induced, infections, vaccines
- similar to Staph. Scaleded Skin Syndrome (SSSS), except steroids can be effective
- high mortality rate
toxic epidermal necrolysis (TEN)
40
food poisoning
- enterotoxins A, B, and D, from enterotoxin-producing strains contaminating rich foods and inadequate refrigeration
- toxin causes the sickness, 2-8 hrs after ingestion, lasts 24-48 hrs, nausea, vomiting, abdominal pain, cramping
41
- enterotoxins A, B, and D, from enterotoxin-producing strains contaminating rich foods and inadequate refrigeration
- toxin causes the sickness, 2-8 hrs after ingestion, lasts 24-48 hrs, nausea, vomiting, abdominal pain, cramping
food poisoning
42
Other infections caused by staph species
secondary pneumonia, bacteremia and endocarditis, osteomyelitis, arthritis (if bacteria in joints)
43
- predominately nosocomial infections (skin flora introduced in catheters, CSF shunts and heart valves)
- produces a slime layer to adhere to prosthetics and avoid phagocytosis
- common cause of hospital-acquired UTI's
Staph. epidermidis
44
- causes UTI's in young, sexually active females
- increased adherence to epithelial cells of urogenital tract
- found in urine cultures
S. saprophyticus
45
- coagulase negative staph that mimics S. aureus infection
| - pathogen of infective endocarditis, septicemia, meningitis, skin and soft tissue infections, UTI's, and septic shock
Staph. lugdunensis
46
Opportunistic staphs
- S. warneri, S. capitis, S. simulans, S. hominis, S. schleiferi
- normal flora that can cause endocarditis and septicemia
- CoNS
47
- common CoNS found in wounds, bacteremia, endocarditis and UTI's
- may have resistance to vancomycin
S. haemolyticus
48
Isolation of Staphs
- grow well on blood agar and thioglycolate
- if contaminated specimen, can be selected for on mannitol salt agar, Columbia colistin-nalidixic acid agar (CNA), PEA, CHROMagar
49
Thioglycolate broth
- pancreatic digest of casein, soy broth and glucose
| - supports anaerobes, aerobes, microaerophilic and fastidious organisms
50
- colistin, nalidixic acid, and 5% sheep blood
| - selects for isolation of gram-positive cocci
Columbia colistin-nalidixic acid agar (CNA)
51
- peptone base, mannitol, 7.5% salt, phenol red indicator
- selective isolation for staph.
- turns yellow if mannitol is hydrolyzed (S. aureus)
Mannitol salt agar
52
CHROMagar
MRSA colonies show up magenta
53
Identification methods
oxidative-fermentative glucose medium, modified oxidase, catalase, coagulase, PYR, Bacitracin disk test, Novobiocin, antimicrobial susceptibility
54
Oxidative-fementative glucose medium
most Staph. ferment glucose, while Micrococci don't
55
modified oxidase
microdase disk will be positive for Micrococci and negative for most Staphylococci
56
Catalase test
- hydrogen peroxide becomes water and oxygen gas in the presence of enzyme catalase
- bubbling is positive, staph. are positive
57
coagulase
clumping factor that causes agglutination in plasma
58
coagulase test
- mix water or saline with organism and rabbit plasma
- if it clumps, it's positive
- if negative, tube test must be run
- hallmark test for S. aureus (other staph can be pos. too)
59
extracellular free coagulase
- extracellular enzyme that clots plasma
| - tube test: check for clotting 4 hrs and 24 hrs after inoculation
60
PYR
negative for S. aureus, but positive for other coagulase positive staph
61
Groups of Coagulase-positive staph
S. aureus group, S. hyicus group, S. intermedius group
62
PYR test
- detection of pyrrolidonyl arylamidase helps differentiate streptococci and enterococci
- color change to red if positive
63
Bacitracin disk test
- differentiates Micrococcus from CoNS
- Micrococcus luteus is susceptible
- CoNS are resistant (sapro, epidermidis)
64
Novobiocin test
- presumptive differentiation of CoNS
- if resistant, S. saprophyticus
- if susceptible, likely S. epidermidis
65
Rapid Identification
BBL staphloslide, Staphaurex, Bactistaph, Plasma-carrier coated particles detect clumping factor and protein A, PCR for MRSA and MSSA, qualitative nucleic acid hybridization assays, MALDI-TOF mass spectrometry
66
antimicrobial susceptibility
- most S. aureus are resistant, so you need to do Beta-lactamase test
67
MRSA
- community-acquired MRSA, health care-associated/community onset MRSA, hospital associated MRSA
- infection control by barrier protection, contact isolation and handwashing
- treat w/ vancomycin (susceptibility test with cefoxitin disk)
68
Borderline oxacillin-resistant S. aureus (BORSA)
can separate from MRSA on oxacillin salt agar plate
69
mecA gene
gene in MRSA that encodes penicillin-binding proteins (PBPs); very few express phenotype
70
Gold standard
mecA gene detected by PCR
71
VRSA
Vancomycin resistant staph. aureus
72
Macrolide resistance
- resistance to clindamycin may not be obvious
- if resistance to clindamycin and erythromycin are not the same, do a D test
- induced resistance if forms a D (on clindamycin side)
