Bacterial skin infection Flashcards
What are some skin infections that require patients to isolate?
GAS
MRSA
Scabies
How can skin infections be spread?
Patients with exfoliative skin conditions shed huge numbers of skin scales and associated bacteria into the environment
Gram +ve bacteria can survive in the environment because of their cell wall structure
These may then become a source of infection for other patients
What diagnostic test can be performed on infection of broken skin?
Swabbing and culturing of the lesion
What diagnostic test can be performed on deep infective lesions?
Pus or tissue samples
What are some examples of bacterial skin infective agents?
- Staphylococcus aureus
- Streptococcus pyogenes (GAS)
- Polymicrobial infection
Describe the features of staphylococcus?
Staphylococcus are gram positive cocci that form clusters
They are aerobic and facultatively anaerobic, meaning they grow best in air, but can grow anaerobically
What are some toxins produced by staphylococcus aureus?
- Staphylococcal scalded skin syndrome toxin
- Panton Valentine Leukocidin
- Enterotoxin (Food poisoning)
- Toxic Shock Syndrome Toxin (TSST-1)
What is the antibiotic of choice in methicillin sensitive S.aureus?
Flucloxacillin
What are some antibiotics used in MRSA?
doxycycline PO, co-trimoxazole PO, clindamycin and linezolid
What are some skin infections associated with staphylococcus aureus?
- Boils
- Carbuncles
- Cellulitis
- Infected eczema
- Wound infection
- Staphylococcal scalded skin syndrome
- Impetigo
- Infected hair follicles
What are some virulence factors associated with S.aureus?
- Capsule
- Fibrinogen binding protein
- Haemolysins
- Coagulase
- Hyaluronidase
- Protein A
- Epidermolytic toxins A/B
Is S.aureus coagulase negative or positive?
Positive
What are some examples of coagulase negative staphylococci?
Staphylococcus epidermidis
Staphylococcus saprophyticus
What are some infections caused by coagulase negative staphylococci?
They are usually skin commensals
UTIs
Artificial material infection
Name the infection
Infected eczema
Name the infection
Impetigo - Infection in the stratum corneum
What causes toxic shock syndrome?
S.aureus producing TSST-1 toxins
How does toxic shock syndrome occur?
TSST1 acts as a super-antigen, activating MHCII complexes and resulting in the massive release of cytokines and activating an immune response
What are the diagnostic criteria for toxic shock syndrome?
- Fever (>39ºC)
- Diffuse macular rash and desquamation (Diffuse macular erythroderma = Sunburn)
- Hypotension (≤90mmHg)
- ≥3 organ systems involves
What are some symptoms of toxic shock syndrome?
High fever, vomiting, diarrhoea, sore throat and muscle pain
How does menstrual toxic shock syndrome occur?
Menstrual toxic shock syndrome is a common cause of TSS in which TSST-1 toxins, from S.aureus in a tampon, pass through the perineum and into the blood stream
What causes staphylococcal scalded skin syndrome?
Release of SSSST toxin from S.aureus
What is the main symptom of staphylococcal scalded skin syndrome?
Separation and lifting of the skin
Name the condition
Staphylococcus scalded skin syndrome
What is necrotising fasciitis?
This is a bacterial infection spreading alon the fascial planes below the skin surface
What occurs as a result of necrotising fasciitis?
This results in rapid tissue destruction beneath the skin, while the surface may not look too abnormal, meaning there will be disproprotionate pain to the skin presentation
What are the 2 main types of necrotising fasciitis?
- Type I - Mixed anaerobes and coliforms (Usually post abdominal surgery
- Type II - Group A strep infection
How can necrotising fasciitis be diagnosed?
Crepitus beneath the skin surface and space on x-ray or CT will show necrotising fasciitis
What are some organisms worth treating in leg ulcers?
- Streptococcus pyogenes
- Staphylococcus aureus
- Other ß-haemolytic streptococci
- Anaerobes in diabetic patients
- Gram-negatives
What is necrotising pneumonia?
This is a preceding influenza-like syndrome with a rapid progression
This results in acute respiratory distress, deterioration of pulmonary function, refractory hypoxaemia and multi-organ failure (Despite antibiotic therapy)
What are virulence factors?
Virulence factors are factors responsible for pathology and variation in virulence within and between groups of pathogens
What are some types of virulence factors?
- Adhesin
- Invasin
- Impedin
- Aggressin
- Modulin
What is the function of adhesins?
Enables binding of the organism to the host
What is the function of invasins
Enables the organism to invade the host cell
What is the function of impedins?
Enables the organism to avoid defence mechanisms
What is the function of aggressins?
Causes damage to the host directly
What is the function of modulins?
Induces damage to the host indirectly
Describe the features of streptococci?
Streptococci are gram positive cocci in chains
They are aerobic and facultatively anaerobic
How are streptococci classified?
Based on haemolysis on blood agar
What are the 3 classes of streptococcus?
Alpha haemolytic
Beta haemolytic
Gamma haemolytic
What is meant by alpha haemolysis?
Partial haemolysis of blood agar
What is meant by beta haemolysis?
Complete haemolysis of blood agar
What is meant by gamma haemolysis?
No haemolysis
What colour will alpha haemolysis show on blood agar?
Green tinge
What colour will beta haemolysis show on blood agar?
Yellow/Clear
What colour will gamma haemolysis show on blood agar?
Red
How are the groups of streptococcus classified?
By antigenic surface structures
What are some examples of infections caused by group A streptococcus (S.pyogenes)?
- Infected eczema
- Impetigo
- Cellulitis
- Erysipelas
- Necrotising fasciitis
What skin infection is shown?
Erysipelas
What is a toxin produced by GAS?
Streptococcus pyogenes can produce SPE toxins, which act as super antigens and which damage blood vessels
This results in Scarlet fever
What are the 20 major serotypes of streptococcus?
A-H and K-V
How can streptococci be minority classified?
By M-protein antigens
What M-protein antigen subtypes are major sub-types?
M1 and M3
What M-protein antigen subtypes are serve invasive diseases
M3 and M18
What are some common commensal bacteria?
- Staphylococcus epidermidis
- Corynebacterium sp.
- Proprionibacterium sp.
How is necrotising fasciitis usually managed?
Surgical debridement
How will Lyme’s disease present on the skin?
Target rash
What causes Lyme’s disease?
Infected tick bite with borellia burgdorferi
