skin and soft tissue infections I - Kozel Flashcards
1
Q
How are infections of the skin classified?
A
- Pyoderma
- Subcutaneous tissue infection
- Secondary infections complicating pre-existing skin lesions
- Cutaneous involvement in systemic infection
- Scarlet fever syndromes
- Wound infections
2
Q
What is pyoderma?
A
Any skin infection that is pyogenic or pus-forming. Primary pyodermas can be purulent or non-purulent.
3
Q
What is the definition of pyogenic?
A
Pus forming or pus producing.
4
Q
What is the definition of purulent?
A
Consisting of, containing or discharging pus.
5
Q
Name some primary pyodermas.
A
- Impetigo - bullous and non-bullous
- Ecthyma
- Cutaneous abcess
- Folliculitis, carbuncles and furuncles
- Chancriform lesions
6
Q
What is impetigo?
A
It is a pyoderma that causes a superficial infection of the skin which presents with vesicles and later forms a honey-colored crust.
7
Q
Describe non-bullous impetigo.
A
- begins as erythematous papules that evolve into vesicles and pustules that later rupture
- the ruptured vesicles form a honey-colored crust on an erythematous base
- infection is superficial so it typically heals without scarring
8
Q
What bacteria are responsible for impetigo?
A
- Staph aureus is the most common cause
- Strep pyogenes causes about 20-30% of cases
- mixed infections are possible
9
Q
How is bullous impetigo different from non- bullous?
A
Bullous impetigo is caused by a strain of S. aureus that produces an exfoliating toxin. This toxin cleaves the dermal-epidermal junction and causes a blister.
10
Q
What is Ecthyma?
A
This infection is an ulcerative pyoderma of the skin.
11
Q
Describe some characteristics of Ecthyma.
A
- a deeper form of impetigo
- follows insect bites or minor trauma
- heals with scarring since it affects deeper tissues
- caused by S. aureus and/or S. pyogenes
12
Q
What is a cutaneous abscess?
A
A primary pyoderma that is purulent. It is characterized by collections o cpus within the dermis and deeper tissues. Typically caused by S. aureus but can be polymicrobial.
13
Q
What is folliculitis?
A
A pyodermic infection within a hair follicle.
14
Q
What is a Furuncle or boil?
A
A pyodermic infection that is characterized by an inflammatory nodule extending into subcutaneous tissue. It follows folliculitis.
15
Q
What is a carbuncle?
A
A pyodermic infection that is characterized by a coalescing involving multiple follicles or furuncles.
16
Q
What microbe causes folliculitis, carbuncles and furuncles?
A
S. aureus.
17
Q
What is a chancriform lesion? Give examples.
A
A chancriform lesion is an ulcerative, pyodermic, purulent lesion. Examples are cutaneous anthrax, some venereal infections and some other infections also, such as those caused by Francisella tularensis, Mycobacterium ulcerans, and Mycobacterium marinum.
18
Q
Describe cutaneous anthrax.
A
- caused by direct inoculation with Bacillus anthracis
- begins as a painless pruritic papule that enlarges and vesiculates
- the malignant pustule becomes necrotic and is covered by an eschar
- can cause periorbital edema if on the face and local edema at site of inoculation - due to edema factor
19
Q
What are some microbes that cause chancriform lesions in venereal infections?
A
- Treponema pallidum
2. Haemophilus ducreyi - not really found in US, mainly in Africa where it was associated with HIV infection
20
Q
What are Erysipelas and cellulitis?
A
These are diffuse, superficial spreading skin infections. These types of infections are not associated with pus.
21
Q
Would you drain a lesion caused by Erysipelas or cellulitis?
A
No. These infections are not associated with pus. They require antimicrobial therapy to heal whereas a purulent lesion often heals after draining.
22
Q
Describe some characteristics of Cellulitis.
A
- infection involving upper dermis and subcutaneous fat
- follows previous trauma, often minor or underlying skin lesion such as a furuncle or ecthyma
- lesions are painful, erythematous and often present as very red, hot and swollen
- Caused mainly by Group A strep but sometimes S. aureus
- very rarely can involve other bacteria - especially if history includes trauma, water contact or animal insect or human bites
23
Q
Describe Erysipelas.
A
- superficial cellulitis with prominent lymphatic involvement
- painful, sharp demarcation from adjacent normal skin
- almost entirely caused by S. pyogenes
24
Q
Name some different types of subcutaneous tissue infections.
A
- necrotizing fasciitis
- synergistic necrotizing cellulitis
- clostridial anaerobic cellulitis
- misc. infections secondary to trauma
25
Describe necrotizing fasciitis.
1. aggressive subcutaneous infection that tracks along the superficial fascia - all tissues between skin and underlying muscle
2. most often an extension from a skin lesion
3. causes systemic toxicity
4. can involve S. pyogenes, S. aureus, Vibrio vulnificus, Aeromonas hydrophila and can be polymicrobial
26
Name some infections that are examples of systemic bacterial infections that produce rashes or skin lesions.
1. bacteremia - caused by S. aureus, group A strep, N. meningitidis
2. Leptospirosis or Weil's disease - caused by Leptospira interrogans
3. Rat-bite fever - caused by Streptobacillus monofiliformis
4. Annular erythema seen in Lyme's disease - caused by Borrelia burgdorferi
5. Rocky mountain spotted fever - caused by Rickettsia rickettsii
27
What are some toxin-induced skin reactions?
1. Scarlett fever - follows pharyngitis by Group A strep, caused by streptococcal pyogenic exotoxin or SpeA
2. Scalded skin syndrome - follows local infection by S. aureus, caused by Staphylococcal exfoliating toxin
3. Toxic shock syndrome - follows infection by S. aureus, caused by Staphylococcal TSST-1 super- antigen
28
Name some infections that can follow animal contact.
1. cutaneous anthrax - vetrinarians at risk, caused by Bacillus anthraces
2. Cat-scratch fever - caused by Bartonella henselae, follows cat scratch or bite
3. Pasteurella multicoda causes infection after dog or cat bites
4. Bubonic plague - caused by Yersinia pests
5. Tularemia - caused by Francisella tularensis
6. Erysipeloid - caused by Erysipelothrix rhusiopathiae, follows exposure to infected fish, marine animals, swine or poultry
29
Name some microbes that cause wound infections.
1. Serratia marcesens - infects surgical wounds, found in hospitals and moist environments
2. Aeromonas spp.- infects cuts and abrasions, found in fresh water
3. Pseudomonas aeruginosa - infects burn wounds and is found in the environment
4. Vibrio parahemolyticus - infects cuts and abrasions, found in salt water and brackish water
5. Vibrio vulnificus - infects cuts and abrasions, found in salt water
6. Acinetobacter baumanii - infects battlefield injuries, found in hospitals
7. Eikenella corrodens - infects human bite wounds and fistfight wounds, found in the human mouth
30
What is Pyomyositis?
An infection characterized by presence o cpus within individual muscle groups. 90% of cases caused by S. aureus and most cases are in the tropics.
31
What is Myonecrosis/gas gangrene?
1. an infection characterized by necrotic damage to muscle tissue
2. occurs after muscle injury and contamination with soil or other material containing spores
3. involves extreme pain, crepitus and yellowish-bronze discoloration
4. most commonly caused by Clostridium perfringens and other Clostridial species
32
Name some general features of streptococci.
1. gram-positive cocci that form chains or pairs
2. most are facultative anaerobes
3. typically require complex media
4. are catalase-negative
33
How are streptococci classified?
1. hemolytic patterns on blood agar
2. antigens - Lancefield grouping
3. biochemical/physiological properties
34
What are the two general groups of streptococci?
1. B-hemolytic - classified by Lancefield grouping
| 2. a-hemolytic and y-hemolytic streptococci - classified by biochemical testing
35
Antigens of Streptococci are usually what kinds of structures?
Polysaccarhides.
36
What is one test that can differentiate between Staph and Strep?
The catalase test. Staph are catalase positive and Strep are catalase negative.
37
What is alpha hemolysis?
When some bacteria are put on a blood agar, they cause reduction of hemoglobin of the RBC's. This will show up in the growing colony as a greening of the surrounding agar.
38
Which Strep species are alpha hemolytic?
1. S. salivaris
2. S. mitis
3. both of these are normal flora of mucous membranes
39
What is Beta hemolysis?
When some bacteria are grown on blood agar they cause a complete hemolysis of the RBC's under and around them. This will look like a lightening or clearing on the agar.
40
What toxins are associated by Beta hemolysis?
1. Streptolysin O
| 2. Streptolysin S
41
What is gamma hemolysis?
This is the absence of hemolysis when some bacteria are grown on blood agar. Some miscellaneous normal flora, opportunistic bacteria and anaerobic bacteria are classified as gamma hemolytic.
42
What is Lancefield grouping?
A classification system based on type of carbohydrate antigen present in the cell walls of primarily Beta hemolytic streptococci (some are alpha or gamma hemolytic).
43
What are the Lancefield groups?
1. Group A - S. pyogenes (most are human pathogens)
2. Groups B,C,F,G,H,L and L - normal mucosal flora that are occasional pathogens
3. Groups E, M and N - found in lower animals
4. Group D - Enterococcus faecalis
44
How are streptococci in the same Lancefield group differentiated?
Via their biochemical properties.
45
What Lancefield group are strep pyogenes in?
Group A. Group A strep is another name for S. pyogenes. The carbohydrate antigen on it's surface is called the C carbohydrate.
46
Describe the C carbohydrate.
This is the name for the carbohydrate antigen found in the matrix of the cell wall of S. pyogenes. It is a polymer of rhamnose and N-acetyl glucosamine.
47
What is M protein?
M protein is another cell wall antigen of group A streptococci. It is used to classify the Group A streps into more than 10 different types. It is called a protective antigen because it induces type specific protective immunity.
48
What extracellular enzymes do group A streps release?
Streptolysin O, DNAase and hyaluronidase. All but hyaluronidase are antigenic so if a patient has been infected but the bacteria are cleared you can test them for antibodies to these and retroactively give a diagnosis.
49
Name some infections caused by Group A strep.
1. pharyngitis - if bacterial then group A strep is most common cause
2. skin and wound infections such as impetigo, erysipelas, cellulitis, myositis and necrotizing fasciitis
3. bacteremia
4. toxemia
5. non-suppurative disease-post streptococcal sequelae such as rheumatic fever and glomerularnephritis
50
What is the most common cause overall of pharyngitis in kids?
Viruses.
51
What virulence factors of S. pyogenes are involved in adherence?
1. Lipoteichoic acid - in cell wall of gram positives, mediates adhesion to epithelial cells.
2. F protein or Sfbl (streptococcal fibronectin binding protein I) - binds fibronectin and mediates adhesion to nasopharyngeal epithelial cells.
3. M protein - mediates binding to epithelial cells.
4. Hyaluronic acid capsule - facilitates adhesion to nasal mucosa, essential for early colonization
52
What virulence factors of S. pyogenes are associated with avoiding phagocytosis?
1. hyaluronic acid capsule
2. M protein - is antiphagocytic, essential to virulence, induces solid type specific immunity and is a candidate for vaccine development
53
What virulence factor of S. pyogenes are associated with or are toxins?
1. Streptococcal pyrogenic exotoxins or Spe - erythrogenic toxin and scarlet fever toxin
2. Lipoteichoic acid
54
What are the functions of the strep exotoxins?
1. cause rash in scarlet fever
2. have a role in toxic shock-like syndrome
3. are super antigens that stimulate release of ILL-1. IL-2, IL-6, TNF-a, IFN-y
4. these exotoxins are coded by lysogenic bacteriophages.
55
What is the function of Lipoteichoic acid
Activates steps in inflammation and septic shock such as complement cascade, cytokine secretion and the coagulation cascade.
56
What virulence factors of S. pyogenes are associated with tissue damage and spread of infection?
Hemolysins and enzymes.
1. Streptolysin O - a porin that is oxygen labile and antigenic
2. Streptolysin S - oxygen stable and non-antigenic
3. Streptokinase - converts plasminogen to plasmin and lyses blood clots
4. Streptodornase - a DNAase that reduces viscosity of abscess material
5. Hyaluronidase
57
Describe the rash associated with Scarlet fever.
1. fine, red and rough textured
2. blanches upon pressure
3. characteristic red cheeks and pale area around the mouth
4. strawberry tongue appearance - enlarged fungiform papillae
58
Describe Botulism toxin.
1. neurotoxin
2. causes flaccid paralysis
3. blocks neurotransmission by inhibiting release of Ach
59
Describe cholera toxin.
1. causes leakage of cells in intestinal lumen
2. causes diarrhea
3. mechanism- ADP-ribosylates protein regulating adenylate cyclase
60
Describe Diptheria toxin.
1. causes inhibition of protein synthesis and cell death
| 2. mechanism includes ADP-ribosylation of EF
61
Describe E. coli toxin.
1. causes leakage of cells in intestinal lumen
2. causes diarrhea
3. mechanism - ADP-ribosylates EF-2
62
Describe pertussis toxin.
1. causes dysregulation in cell
| 2. mechanism - ADP ribosylates G proteins, blocking signal transduction
63
Describe Pseudoman exotoxin A.
1. inhibition of protein synthesis leading to cell death
| 2. mechansim - ADP-ribosylated EF-2
64
Describe SpeA.
1. causes fever, rash and systemic effects
2. these toxins are super antigens
3. they cause cytokine release - IL-1, IL-2, IL-6, TNF-a and INF-y
65
Describe tetanus toxin.
1. causes spastic paralysis
| 2. mechansim - inhibits GAB and glycine release from nerve terminals
66
Describe TSST-1.
1. causes fever and systemic effects
2. is a superantigen
3. causes cytokine release - IL-1, IL-2, IL-6, TNF-a and INF-y
67
Describe some characteristics of the two post-streptococcal sequelae.
Infection by S. pyogenes can sometimes lead to either acute glomerulonephritis or Rheumatic fever.
1. both have latent period of 7-21 days
2. there will be no live streptococci in the lesions
68
How is acute glomerulonephritis (AGN) different from Rheumatic fever?
AGN:
1. site of infection is skin
2. one exposure to S. pyogenes enough
3. somewhat common occurrence
4. rare to have repeated attacks
5. M protein involved are nephritogenic strains
6. complement levels will be decreased
7. immune complex mediated
69
How is Rheumatic fever different from AGN?
1. site of infection is the pharynx
2. more than one exposure to S. pyogenes needed
3. rare occurrence
4. repeated attacks in those who have had an episode are common
5. prophylaxis is necessary if acquire S. pyogenes infection
6. M protein involved are rheumatogenic strains
7. complement levels will be normal
8. possibly mediated by cytotoxic antibodies
70
What types of specimens are taken for S. pyogenes infections?
1. throat swabs
2. pus sample
3. blood sample
MUST take samples before antibiotics are started or identification can't be made
71
How is laboratory identification made for S. pyogenes infections?
If infection by S. pyogenes is suspected it can be cultured and isolated on blood agar or samples can be directly examined. A gram stain can be done or a quick strep test can be performed. The quick strep test uses lateral flow technology an d detects Lancefiled carbohydrate antigens.
72
What are some characteristics of S. pyogenes that are used to differentiate it from other microbes?
1. gram-pos coccus
2. beta-hemolytic
3. catalase negative
4. Bacitracin sensitive
5. Lancefield specific antigen
73
What two virulence factors are involved with testing an S. pyogenes sample to see if it is B-hemolytic?
1. Streptolysin O- oxygen labile so must 'stab' the sample into agar to get below surface where exposed to oxygen.
2. Streptolysin S - oxygen stable so can put sample on surface of agar
3. Not all strains of S. pyogenes has both of these lysins
74
How can Streptolysin O and DNAase be involved with retrospective diagnosis of S. pyogenes infection?
Streptolysin O is antigenic so infection leads to production of anti-streptolysin O antibodies which can be detected even when infection cleared (usually in strains that can cause rheumatic fever). DNAase enzyme is also antigenic so antibodies can be detected after a skin infection.
75
What type of antibodies can you test for if you suspect a patient has had pharyngitis caused by S. pyogenes?
You can test for anti-streptolysin O antibodies if a patient has had pharyngitis of unknown origin and you want to give prophylaxis to prevent rheumatic fever. the test is typically negative in patients who have had a skin infection.
76
What type of antibodies can you test for if you suspect a patent has had a skin infection caused by S. pyogenes?
You can test for Anti-DNAase antibodies. You can do this test if acute glomerulonephritis is suspected.
77
How are S. pyogenes infections transmitted?
1. pharyngitis - via airborne droplets
2. skin infection - via direct contact - hygiene is a major factor
3. asymptomatic carriers are a reservoir for transmission - can have up to 5-20% depending on the season
4. control - prompt and complete treatment, eliminate carriers
78
If you get an infection with one strain of S. pyogenes are you immune from another infection?
There is long term immunity to S. pyogenes infections - if you are infected by strain with one specific M type you can have immunity to only that type specific strain - not the others.
79
Describe the treatment of S. pyogenes infections.
1. Penicillin - if not allergic
2. all strains are sensitive to penicillin and want to treat promptly before antibody response to reduce risk of rheumatic fever and AGN
3. if the infection is mixed with S. aureus then can treat with oxacillin or vancomycin (clindamycin if allergies)
4. want to give antibiotic prophylaxis for patients at risk for rheumatic fever
5. if skin infection is necrotizing fasciitis then treat with high dose penicillin and clindamycin and do drainage and debridement
80
What are some characteristics of community acquired MRSA?
1. caused by locally circulating strains in a community
2. can cause necrotizing fasciitis but is unusual as a mono microbial cause
3. can carry genes for methicillin resistance- mec gene and panton-valentine leukocidin or pvf gene
4. its genome is distinct from noscomial MRSA clones
81
What some species of importance in the staphylococcus genus?
1. S. aureus
2. S. epidermis (coagulase neg)
3. other coagulase neg. Staphylococci
82
Describe some characteristics of Staphylococcus bacteria.
1. gram pos. cocci in grape like clusters
2. aerobic
3. catalase pos
4. may have golden pigment
5. beta or non-hemolytic depending on hemolysins the strain produces
6. carry multiple plasmids and bacteriophages
7. 80% of genome is core genome and conserved among species and strains
83
What are some virulence factors that are carried on plasmids and bacteriophages?
1. penicillinase or beta lactamase
2. genes responsible for toxin production
3. 20% of genome is mobile
84
Twenty percent of the genome of Staphylococcus is mobile. What types of elements are involved?
1. bacteriophages
2. plasmids
3. transposons
4. staphylococcal chromosomal cassette - is like a transposon
85
The mobile genome of Staphylococcus carries what type of genes?
1. virulence factor genes
2. antibiotic resistance genes
3. regulation is usually operon-like
86
What types of infections are caused by Staph aureus (and other staph)?
1. infections of the skin
| 2. infections of the sub Q tissues
87
Name some infections involving skin and sub Q tissues.
1. impetigo - bulbous and pustular
2. abcesses
3. foliculitis
4. furuncles
5. carbuncles
88
Name some deeper infections caused by Staph.
1. bacteremia
2. osteomyelitis
3. septic arthritis
4. pneumonia
5. staph enterocolitis - follow upset of normal flora by use of broad spectrum antiobiotics
89
Name some diseases caused by Staph toxins.
1. food poisoning
2. scalded skin syndrome
3. bullous impetigo
4. toxic shock syndrome
90
Describe some characteristics of Staph aureus.
1. weakly virulent - minimal infecting dose large and needs predisposing conditions
2. causes supperation, irreversible tissue damage and scarring
3. catalase and coagulase positive
91
What is coagulase?
An enzyme that converts fibrinogen to fibrin. It is a marker for species of staph.
92
What is catalase?
An enzyme that facilitates intracellular survival.
93
What are some virulence factors of S. aureus that are structural?
1. capsule - 75% of clinical isolates are type 5 or 8, confers antiphagocytic properties
2. peptidoglycan and lipoteichoic acid - contribute to inflammation
3. protein A - on surface of staph aureus, binds to Fc fragment of antibody
94
What are some virulence factors of S. aureus that are enzymes?
1. coagualse
2. catalase
3. penicillinase
95
What are some virulence factors of S. aureus that are cytotoxins?
1. alpha, beta, delta and gamma toxins
2. PV leukocidin
3. these are toxic to erythrocytes, leukocytes and platelets through various mechanisms
96
What two toxins made by S. aureus are involved in scalded skin syndrome?
Exfoliating toxins:
1. ETA
2. ETB
97
Describe S. aureus' pyrogenic exotoxins.
1. many different toxins, encoded by plasmids
2. are super antigens that cause release of IL-1, TNF-a and others
3. have other toxic activities distinct from super antigen effects
98
What are some examples of pyrogenic exotoxins produced by S. aureus?
1. enterotoxins - SEA, SEB, SEC,SED,SEE
| 2. toxic shock syndrome toxin - TSST-1
99
Describe staphylococcal food poisoning.
1. caused by ingestion of preformed staph enterotoxin
2. resistan to heat and gastric acid
3. 1-6 hour incubation
4. targets sensory nerve endings in smooth muscle of intestines
5. causes nausea, cramps, vomiting and diarrhea
6. usually recover in 24 hours
100
Describe Staphylococcal scalded skin syndrome.
1. is an exfoliative skin disease
2. caused by toxemia - infection at distant site with release of exfoliating toxin
3. bullous impetigo is a local form
4. the toxin is a serene protease
5. cleaves dermal-epidermal junction to form fragile, thin-roofed vesicopustules
6. seen primarily in children
101
Describe staphylococcal toxic shock syndrome.
1. toxemia producing fever, vomiting, diarrhea, rash and shock
2. possible mechanisms are induction of cytokine release, increased susceptibility of endogenous endotoxin, direct effects on vascular endothelial cells
3. TSSST-1 toxin production stimulated by poor growth conditions
4. blood cultures are usually negative
102
What type of specimens are usually taken in S. aureus infections?
1. pus
2. purulent fluids
3. throat swab
4. nasal and nasopharyngeal swabs
5. urine
103
How can lab identification be made?
1. direct examination of pus and CSF
| 2. isolate on blood agar or selective media
104
What type of selective media can be used to grow S. aureus?
1. mannitol salt agar
| 2. MRSA - chromogenic media with disks of oxacillin or cefoxitin
105
What are some characteristics of S. aureus that help in its differentiation?
1. gram pos coccus
2. coagulase pos - distinguishes S. aureus from of staph
3. catalase pos - distingushes staph from strep
4. ferments mannitol
5. MRSA - chromogenic media or PCR for mecA gene
6. antibiotic sensitivity testing is essential
106
When is subspecies typing done for S. aureus infections?
1. done to identify epidemic strains
| 2. to identify strains when situation is critical - i.e.. outbreak in neonatal ICU
107
What types of things are looked at to determine subspecies?
1. antibiotic sensitivity patterns
2. biochemical profiles
3. susceptibillity to bacteriophage infection
4. nucleic acid analysis
108
Describe the epidemiology and control of S. aureus infections.
1. man is primary reservoir - part of normal flora of lower colon, skin and anterior nares
2. infections acquired from air, direct contact or can be from endogenous source
3. carrier rate may be 30% in normal population and much higher in hospital population
4. no immunity - reinfection is common and no vaccine is available
5. screening for nasal carriers and decontamination via mupirocin is important
109
What types of treatment are used in S. aureus infections?
1. drain lesion
2. control underlying diseases
3. antibiotics - MRSA a factor
110
What are some antibiotics that are used to treat S. aureus infection?
1. penicillinase resistant penicillins like oxacillin
2. clindamycin
3. TMP-SMX
4. doxycycline
5. linezolid
6. vancomycin
7. daptomycin
111
Describe some ways that S. aureus has become resistant to antibiotics.
1. penicillinase production
2. VISA - resistance to intermediate levels of vancomycin - thicker more disorganized cell wall with free terminal alanine groups to act as decoy for vancomycin
3. VRSA - vancomycin resistant due to vanA gene operon encoding alanine-lactate production - still rare
4. MRSA
112
Describe MRSA.
1. some S. aureus are resistant to penicillins
2. resistance is via the gene staph chromosome cassette or SCCmec carried on a mobile genetic element
3. control of MRSA associated wit decolonization of colonized patients or carries via 1 week of body washing with clorhexidine and nasal mupirocin
113
What genes are carried on SCCmec cassette?
1. regulator genes such as the negative repressor operon
| 2. mecA - encodes PBP 2a wit low affinity for beta lactam antibiotics
114
What factors are important in nosocomial MRSA infection?
1. risk factors such as surgery, indwelling catheters, etc.
| 2. multi-resistance of strain
115
What factors are important in community associated MRSA infection?
1. no/limited risk factors
2. most common cause of skin and soft tissue infections in community
3. usually carries the PV leukocidin
4. Pauci- resistant
