Kozel: Skin and Soft Tissue Infections Flashcards
Any skin infection that is pyogenic
pyoderma
What is primary pyoderma?
primary pyoderma is called impetigo; it is a vesicular, later crusted, superficial infection of skin
What two bacteria can cause non-bullous impetigo? Which is the most common?
Streptococcus pyogenes
Staph aureus **most common
How does non-bullous impetigo typically present?
begins as erythematous papules that evolve into vesicles and pustules and rupture; they dry to form honey-colored crusts on an erythematous base
Does non-bullous impetigo typically scar?
no; non-bullous impetigo typically heals without scarring
What bacteria is responsible for bullous impetigo?
Staph aureus produces an exfoliating toxin that cleaves the dermal-epidermal junction
This is an ulcerative pyoderma of skin. It is a deeper form of impetigo that follows insect bites or trauma. Caused by Staph aureus or Strep pyogenes. It usually heals with scarring.
Ecthyma
So, what is the difference between impetigo and ecthyma?
ecthyma is a deeper form of impetigo
What are five purulent manifestations of primary pyoderma?
cutaneous abscess folliculitis carbuncles furuncles chancriform lesions
This is a collection of pus within the dermis and deeper tissue, usu caused by S. aureus
cutaneous abscess
This is pyoderma located within a hair follicle
folliculitis
This is an inflammatory nodule extending into subcutaneous tissue, follows folliculitis
Furuncle (boil)
This is a coalescent process involving multiple follicles
Carbuncle
One manifestation of purulent primary pyoderma is chancriform or ulcerative lesions; list three types of chancriform lesions
cutaneous anthrax (Bacillus anthracis; eschar) venereal infections (Treponema pallidum - syphilis) other infections (ex: franscisella tularensis)
These are diffuse, superficial, spreading skin infections
cellulitis and erysipelas
Infection involving upper dermis and subcutaneous fat
Follows previous trauma, often minor, or underlying skin lesion, e.g., furuncle or ecthyma
Pain, erythema, involved area very red, hot and swollen
Cellulitis
What causes cellulitis? What does cellulitis require?
Group A strep and others; less often S. aureus and other bacteria; requires antimicrobial therapy
Superficial cellulitis with prominent lymphatic involvement
Painful; sharp demarcation from adjacent normal skin
Erysipelas
What bug causes erysipelas? How does erysipelas differ from cellulitis?
almost entirely caused by S. pyogenes; more superficial than cellulitis, involves lymph nodes, and forms sharp demarcation from surrounding normal skin
Aggressive subcutaneous infection that tracks along the superficial fascia – all tissue between skin and underlying muscle
Most often an extension from a skin lesion
Systemic toxicity
Necrotizing fasciitis
What bugs can cause necrotizing fasciitis?
S. pyogenes
S. aureus
Vibrio vulnificus
Aeromonas
List three examples of systemic bacterial infections that produce rashes or skin lesions
Streptobacillus moniliformis: rat-bite fever with petechial/purpuric lesions
Borrelia burgdorfi: erythema migrans
Leptospirosis: macropapular rash
List three toxin-induces skin reactions
scarlet fever
scalded skin syndrome
toxic shock syndrome
Follows pharyngitis by group A streptococcus
Streptococcal pyogenic exotoxin A (SpeA)
Scarlet fever
Follows local infection by Staphylococcus aureus
Staphylococcal exfoliating toxin
Scalded skin syndrome
Follows infection by Staphylococcus aureus
Staphylococcal TSST-1 - superantigen
Toxic shock syndrome
List some examples of skin infections following animal contact
Cutaneous anthrax (seen in veterinarians)
Cat-scratch disease (Bartonella henselae)
Erysipeloid (contact w fish, marine animals, pigs, poultry)
Pasteurella multocida (dog and cat bites)
Bubonic plague (Yersinia pestis)
Tularemia (Francisella tularensis)
Presence of pus within individual muscle groups
Usually S. aureus (90%)
Most cases in tropics
pyomyositis
Necrotic damage to muscle tissue
Occurs after muscle injury and contamination with soil or other material containing spores
Extreme pain, crepitus due to gas formation, yellowish/bronze discoloration
Etiology: Clostridium perfringens (most common) and other clostridial species
gas gangrene
What is Group A strep (GAS) a synonym for?
Strep pyogenes
Are streptococci:
gram + or gram -
catalase + or catalase -
aerobic or anaerobic
gram +; catalase -; facultative anaerobes
**distinguish from staph, because staph is catalase +
What are 3 ways to classify streptococci?
hemolytic pattern on blood agar (alpha, beta, non-hemolytic)
antigenic (lancefield grouping)
biochemical properties
How can you tell alpha from beta from gamma or non-hemolytic on blood agar?
alpha - partial hemolysis and greening of agar
beta - complete hemolysis creating a clear zone
gamma - no hemolysis
Which hemolytic group- alpha, beta, or gamma- produces streptolysins O and S?
beta
Which bacterium has group A carbohydrate? Which bacteria has groups B, C, F, G, H, K, L carbohydrate? Which bacteria have groups E, M, N carbohydrate? What about group D?
S. pyogenes; normal flora of mucous membranes; bacteria found in lower animals; enterococcus
What is the serological classification for the following: S. pyogenes? S. agalactiae? S. pneumoniae? S. viridans?
S. pyogenes: A antigen, beta hemolytic
S. agalactiae: B antigen, beta hemolytic
S. pneumoniae: no antigen, alpha hemolytic
S. viridans: no antigen, alpha or beta hemolytic
What are two antigens that can be found on S. pyogenes? Which antigen induces type-specific protective immunity?
Lancefield carbohydrate and M protein
**M protein induces type-specific protective immunity
2 extracellular enzymes associated w S. pyogenes?
streptolysin O
DNAse
What can Group A strep (GAS or S. pyogenes) cause?
pharyngitis **most pharyngitis is viral, but this is the most common bacterial cause
skin infections: impetigo, erysipelas, cellulitis, myositis and necrotizing fasciitis
bacteremia
toxemia: scarlet fever and TSS
non-pus forming disease: glomerulonephritis and Rheumatic fever
What is unique about erysipelas?
it forms a fiery red or salmon colored cellulitis that has well demarcated edges
List four virulence factors that S. pyogenes presents with. What is the primary mechanism of virulence by each of these factors?
Lipoteichoic acid (in cell wall of gram + bacteria)
F protein
M protein
Hyaluronic acid capsule;
they all promote adherence of the bacteria to nasopharyngeal/epithelial cells
This antigen is ESSENTIAL for the virulence of S. pyogenes; it is anti-phagocytic, meaning it keeps the organism outside of phagocytic cells
M protein
What are two toxins associated with S. pyogenes, and what does each cause?
- streptococcal pyrogenic exotoxins (Spe): fever/rash of scarlet fever, TSS, due to superantigen release
- lipoteichoic acid: inflammation
Describe the rash seen in scarlet fever
red cheeks, but pale around the nose/mouth; fine, red rough-textured rash like sand-paper
This is the only antigen of S. pyogenes that confers long-term type-specific immunity to infection
M protein
What are two serological assays (antibody tests) that you might do to confirm infection by S. pyogenes?
Anti-streptolysin O *useful in diagnosing rheumatic fever
Anti-DNAse *useful if glomerulonephritis is suspected
One is one reservoir of S. pyogenes transmission?
asymptomatic carriers (carry S. pyogenes in nasopharynx)
What is the first choice for treatment of streptococcal infection?
penicillin
**prompt use reduces antibody response
What is the goal of treatment of streptococcal infections?
reduce the level of antigen in the body so that the patient does not have an immune response
What are some issues when administering penicillin for a streptococcal infection??
- possible mixed infection
- necrotizing fasciitis - need high dose penicillin + clindamycin + drainage
- allergy
What does Staph aureus usually look like on blood agar?
golden colored colonies
Is staph aureus:
gram + or gram -
catalase + or catalase -
alpha, beta, or non-hemolytic
gram +; catalase +; beta or non-hemolytic
What do Staph aureus bacteria carry?
plasmids and bacteriophages which confer antibiotic resistance and toxins
If 80% of the S. aureus genome is core genome, what is the remainder of the genome made up of?
mobine DNA with plasmids, bacteriophages, and transposons which may code for virulence factors and antibiotic resistance
What types of infections does Staph aureus cause?
impetigo: bullous and pustular
abscesses, folliculitis, furuncles and carbuncles
deep infections: bacteremia, osteomyelitis and septic arthritis, pneumonia
staph toxins: food poisoning, scalded skin syndrome, TSS
What are 3 diseases caused by staphylococcal toxins? Which is the most common?
- food poisoning **most common cause of food poisoning in the US
- scalded skin syndrome
- TSS
Is staph as virulent as strep?
no, it is only weakly virulent
Describe the lesions seen in staph infection
suppuration (pus)
irreversible tissue damage
scarring
What are some of the virulence factors for staphylococci?
antiphagocytic capsule lipoteichoic acids --> contribute to inflammation protein A coagulase catalase penicillinase
List some of the toxins produced by staph
cytotoxins: alpha, beta, delta, gamma, P-V leukocidin
exfoliating toxin: scalded skin syndrome
pyrogenic exotoxins: super-antigens like TSS or staph enterotoxins
Staph food poisoning is the number 1 cause of food poisoning in the US. It is due to the ingestion of (blank)
preformed staphylococcal enterotoxin
**in this form of poisoning, you ingest the toxin, not the organism that makes the toxin
What does staph food poisoning cause?
well, it targets the sensory smooth nerve endings in smooth muscle of the intestine causing nausea, cramps, vomiting, and diarrhea
Describe scalded skin syndrome caused by staph
It is an exfoliative skin disease; so, there is an infection w staph at a distant site, but the release of this exfoliating toxin (a serine protease) cleaves the dermal-epidermal junction and forms fragile thin-roofed vesicopustules
What is the local form of scalded skin syndrome called?
bullous impetigo
What are the symptoms of toxic shock syndrome caused by staph?
fever vomiting diarrhea rash shock
T/F: Superantigens can activate ~10% of your T cells all at once
True
These two bacterial exotoxins both cause fever and systemic effects and act as superantigens causing massive cytokine release and T cell activation
SpeA (strep pyrogenic exotoxin)
TSST-1
This test distinguishes Staph aureus from other staphylococci
coagulase test
Two ways to recognize MRSA?
chromogenic media with disks (like we did in lab)
PCR for mecA (which carries resistance to methicillin)
What is the primary reservoir for staph?
man
**staph makes up the normal flora of the large bowel, the skin, the anterior nares
How is staph infection acquired?
from air, direct contact, or endogenously
**high rate in hospitals which may require screening for nasal carriers and decontamination
Treatment of staph?
drain the lesion!!
control the underlying disease
antibiotics (like penicillinase-resistant penicillins, clindamycin, TMP-SMX)
What is the mechanism of resistance for VISA (vancomycin intermediate S. aureus)?
cell wall with free ala-ala groups; acts as a decoy for vancomycin
What is the mechanism of resitance for VRSA (vancomycin resistant S. aureus)?
ala-lactate production; acts as decoy for vancomycin
What does the mecA gene code for in MRSA?
an altered penicillin binding site with low affinity for beta-lactam antibiotics
This type of MRSA is associated with risk factors, i.e. surgery, indwelling catheter, etc
Health care-associated MRSA
This type of MRSA has no/limited risk factors. It is the most common cause of skin and soft tissue infections in community
Usually carries the PV leukocidin
Pauci-resistant
community-associated MRSA
