MED MICRO
• Skin infections and Staph. Aureus infections
•
MRSA and Soft Tissue Infections
• Common cause of skin lesions in nonhospitalized people
• Resistant to multiple antibiotics
• Infections tend to be raised, red, tender, localized lesions
• Often feature pus and feel hot to the touch
• Occur in breaks in the skin from injury, shaving, or abrading
Staphylococcus aureus:
Gram-positive coccus that forms grape-like clusters
Nonmotile
Sturdiest of all nonendospore-forming pathogens
Withstand high salt, extremes in pH, and high temperatures
Causative Methicillin-resistant
Organism Staphylococcus aureus
Common Modes Direct contact, indirect contact
of Transmission
Virulence Factors Coagulase, other enzymes, superantigens
Culture/Diagnosis PCR, culture and Gram stain, coagulase and catalase
tests, multitest systems
Prevention Hygiene practices
Treatment Clindamycin + TMP/SMZ; in Serious Threat category in
CDC Antibiotic Resistance Report
Epidemiology Community-associated MRSA infections most common in
children and young to middle-aged adults; Incidence
increasing in communities (decreasing in hospitals)
Impetigo
A superficial bacterial infection that causes the skin to flake or peel off
• Caused by either S. aureus or S. pyogenes, or a mixture of the two
• Children are the primary victims
• Symptoms are the same regardless of the organism causing the infection
Staphylococcus aureus Virulence Factors
Exotoxins called exfoliative toxins A and B
• Attack a protein that is important for epithelial cell-to-cell binding; breaking
this protein leads to the characteristics blistering
Coagulase
• Coagulates plasma and blood
• Causes fibrin to be deposited around the bacteria, concentrating exotoxin in
an area of local damage
,Streptococcus pyogenes
• Also causes strep throat, scarlet fever, pneumonia, puerperal fever,
necrotizing fasciitis, bloodstream infections, and rheumatic fever
• Gram-positive coccus, beta-hemolytic
• Adhesive elements: LTA, M protein, hyaluronic acid capsule
• Produces hyaluronidase
Impetigo Disease Table
Causative Staphylococcus Streptococcus pyogenes
Organism(s) aureus
Common Direct contact, Direct contact, indirect
Modes indirect contact contact
of Transmission
Virulence Exfoliative toxin A, Streptokinase, plasminogen-
Factors coagulase, other binding ability, hyaluronidase,
enzymes M protein
Culture/ Routinely based on Routinely based on clinical
Diagnosis clinical signs; when signs; when necessary,
necessary, culture and culture and Gram stain,
Gram stain, coagulase coagulase and catalase
and catalase tests, tests, multitest systems, PCR
multitest systems,
PCR
Prevention Hygiene practices Hygiene practices
Treatment Topical mupirocin or Topical mupirocin or
retapamulin, oral retapamulin
dicloxacillin,
cephalexin, or TMP-
SMZ; MRSA is in the
CDC Serious Threat
category
Distinguishing Seen more often in Seen more often in newborns
Features older children, adults
Staphylococcal Scalded Skin Syndrome (SSSS) (1)
Dermolytic condition caused by S. aureus
• Develops predominantly in newborns and babies
• A systemic form of impetigo
• Phage-encoded exfoliative toxins A and B are responsible for symptoms
Bullous lesions:
• Caused by exfoliative toxins A and B
• Have the appearance of wrinkled tissue paper
• Lead to widespread desquamation of the skin
• Patients are left vulnerable to secondary bacterial infections
Causative Staphylococcus aureus
, Organism
Common Modes Direct contact, droplet contact
of Transmission
Virulence Factors Exfoliative toxins A and B
Culture/Diagnosis Histological sections; culture performed but false
negatives common because toxins alone are
sufficient for disease
Prevention Eliminate carriers in contact with neonates
Treatment Immediate systemic antibiotics (current
recommendation is cloxacillin)
Distinguishing Split in skin occurs within epidermis
Features
Epidemiological Mortality 1 to 5% in children, 50 to 60% in adults
Features
Gas Gangrene
Also known as clostridial myonecrosis
• Endospores found in the soil, human skin, human intestine, and vagina
• Requires anaerobic conditions to manufacture and release endotoxins
Two forms:
• Anaerobic cellulitis: remains localized
• True myonecrosis: spreads to healthy tissue
Clostridium perfringens
Produces several active exotoxins:
• Alpha toxin: causes red blood cell rupture, edema, tissue damage
• Collagenase
• Hyaluronidase
• DNase
Causative Organism Clostridium perfringens, other bacteria
Common Modes Vehicle (soil), endogenous transfer
of Transmission from skin, GI tract, and so on
Virulence Factors Alpha toxin, other exotoxins, enzymes,
gas formation
Culture/Diagnosis Gram stain, CT, scans X-ray, clinical
picture
Prevention Clean wounds, debride dead tissue
Treatment Surgical removal, clindamycin +
penicillin, oxygen therapy
• Skin infections and Staph. Aureus infections
•
MRSA and Soft Tissue Infections
• Common cause of skin lesions in nonhospitalized people
• Resistant to multiple antibiotics
• Infections tend to be raised, red, tender, localized lesions
• Often feature pus and feel hot to the touch
• Occur in breaks in the skin from injury, shaving, or abrading
Staphylococcus aureus:
Gram-positive coccus that forms grape-like clusters
Nonmotile
Sturdiest of all nonendospore-forming pathogens
Withstand high salt, extremes in pH, and high temperatures
Causative Methicillin-resistant
Organism Staphylococcus aureus
Common Modes Direct contact, indirect contact
of Transmission
Virulence Factors Coagulase, other enzymes, superantigens
Culture/Diagnosis PCR, culture and Gram stain, coagulase and catalase
tests, multitest systems
Prevention Hygiene practices
Treatment Clindamycin + TMP/SMZ; in Serious Threat category in
CDC Antibiotic Resistance Report
Epidemiology Community-associated MRSA infections most common in
children and young to middle-aged adults; Incidence
increasing in communities (decreasing in hospitals)
Impetigo
A superficial bacterial infection that causes the skin to flake or peel off
• Caused by either S. aureus or S. pyogenes, or a mixture of the two
• Children are the primary victims
• Symptoms are the same regardless of the organism causing the infection
Staphylococcus aureus Virulence Factors
Exotoxins called exfoliative toxins A and B
• Attack a protein that is important for epithelial cell-to-cell binding; breaking
this protein leads to the characteristics blistering
Coagulase
• Coagulates plasma and blood
• Causes fibrin to be deposited around the bacteria, concentrating exotoxin in
an area of local damage
,Streptococcus pyogenes
• Also causes strep throat, scarlet fever, pneumonia, puerperal fever,
necrotizing fasciitis, bloodstream infections, and rheumatic fever
• Gram-positive coccus, beta-hemolytic
• Adhesive elements: LTA, M protein, hyaluronic acid capsule
• Produces hyaluronidase
Impetigo Disease Table
Causative Staphylococcus Streptococcus pyogenes
Organism(s) aureus
Common Direct contact, Direct contact, indirect
Modes indirect contact contact
of Transmission
Virulence Exfoliative toxin A, Streptokinase, plasminogen-
Factors coagulase, other binding ability, hyaluronidase,
enzymes M protein
Culture/ Routinely based on Routinely based on clinical
Diagnosis clinical signs; when signs; when necessary,
necessary, culture and culture and Gram stain,
Gram stain, coagulase coagulase and catalase
and catalase tests, tests, multitest systems, PCR
multitest systems,
PCR
Prevention Hygiene practices Hygiene practices
Treatment Topical mupirocin or Topical mupirocin or
retapamulin, oral retapamulin
dicloxacillin,
cephalexin, or TMP-
SMZ; MRSA is in the
CDC Serious Threat
category
Distinguishing Seen more often in Seen more often in newborns
Features older children, adults
Staphylococcal Scalded Skin Syndrome (SSSS) (1)
Dermolytic condition caused by S. aureus
• Develops predominantly in newborns and babies
• A systemic form of impetigo
• Phage-encoded exfoliative toxins A and B are responsible for symptoms
Bullous lesions:
• Caused by exfoliative toxins A and B
• Have the appearance of wrinkled tissue paper
• Lead to widespread desquamation of the skin
• Patients are left vulnerable to secondary bacterial infections
Causative Staphylococcus aureus
, Organism
Common Modes Direct contact, droplet contact
of Transmission
Virulence Factors Exfoliative toxins A and B
Culture/Diagnosis Histological sections; culture performed but false
negatives common because toxins alone are
sufficient for disease
Prevention Eliminate carriers in contact with neonates
Treatment Immediate systemic antibiotics (current
recommendation is cloxacillin)
Distinguishing Split in skin occurs within epidermis
Features
Epidemiological Mortality 1 to 5% in children, 50 to 60% in adults
Features
Gas Gangrene
Also known as clostridial myonecrosis
• Endospores found in the soil, human skin, human intestine, and vagina
• Requires anaerobic conditions to manufacture and release endotoxins
Two forms:
• Anaerobic cellulitis: remains localized
• True myonecrosis: spreads to healthy tissue
Clostridium perfringens
Produces several active exotoxins:
• Alpha toxin: causes red blood cell rupture, edema, tissue damage
• Collagenase
• Hyaluronidase
• DNase
Causative Organism Clostridium perfringens, other bacteria
Common Modes Vehicle (soil), endogenous transfer
of Transmission from skin, GI tract, and so on
Virulence Factors Alpha toxin, other exotoxins, enzymes,
gas formation
Culture/Diagnosis Gram stain, CT, scans X-ray, clinical
picture
Prevention Clean wounds, debride dead tissue
Treatment Surgical removal, clindamycin +
penicillin, oxygen therapy
