Microbiology Flashcards
Microbiology of dermatological diseases
Are staphs generally coagulase negative or positive and which is the exception?
Generally coagulase negative however S. aureus is coagulase positive
Which bacteria may be commensals of the skin?
Staph. aureus
Staphylococcus epidermidis
Corynebacterium sp. (diphtheroids)
Propionibacterium
What is the antibiotic of choice for Staph aureus?
Flucloxacilin
What drugs ill work against MRSA strains?
Doxycycline Co-trimoxazole Clindamycin Vancomycin Linezolid (toxic reserve antibiotic)
Which kinds of toxins can different strains of S. aureus produce?
Enterotoxin = food poisoning
SSSST
PVL = panton valentine leukocidin
Describe Staphylococcus sp.
Gram positive cocci in clusters
Aerobic and facultatively anaerobic
2 imp. types are Staph aureus and coagulase negative Staph
Describe coagulase negative staphs
Skin commensals that are not usually pathogenic.
Example is Staph. epidermidis
When may coagulase negative staphs cause infectoin
In association with implanted artificial material
Describe Streptococcus sp.
Gram positive cocci in chains
Aerobic and facultatively anaerobic
Classified initially by haemolysis in blood
Which toxin is produced by beta haemolytic streptococci?
Haemolysin
Which serological group that beta haemolytic are further broken down into is important in skin?
Group A
Expample: Strep pyogenes
What are the 2 important categories of alpha haemolytic streptococci?
Strep. pneumoniae
Strep. viridans group
Non-haemolytic streptococci are commensals of where?
The bowel
What bacterial skin infections can strep pyogenes cause?
Infected eczema Impetigo Cellulitis Erysipelas Necrotising fasciitis
What will Strep. pyogenes be treated with?
Penicillin
Flucloxacillin will often be used as it also covers Staph. aureus
What is necrotising fasciitis?
A bacterial infection spreading long fascial planes below the skin causing rapid tissue destruction
What are the 2 types of necrotising fasciitis?
Type 1 - mixed anaerobes and coliforms
Type 2 - Group A Strep
When should swabs of leg ulcers be taken?
Only if sign of cellulitis or infection are present
Skin has many commensals so treat the ulcer not the lab result
What tissues do dermatophytes infect?
Keratinised tissues only
Skin, hair, nails
Describe Dermatophyte pathogenesis
Fungus enters abraded soggy skin
Increases epidermal turnover and provokes inflammatory response in the dermis
grows outward and heals in centre giving ring-like appearance
What are the sources of dermatophyte infection?
Other infected humans (most likely)
Animals
Soil (less common in UK)
What are the man dermatophyte causal organisms?
Trichophyton rubrum (~70%) Trichophyton mentagraphytes (~20%) Microsporum canis
How is diagnosis of dermatophyte infections made?
Clinical appearance
Woods light
Skin scraping for microscopy and culture
How is dermatophyte infection treated?
Topical cream such as clotrimazole
Nail paint like amorolfine
Terbinafine or itraconazole orally for more extensive cases
Where does candida cause infection?
In skin folds were it is warm and moist
How is candida diagosed?
Swab for culture
What is scabies caused by?
Sarcoptes scabiei
How does scabies present?
Intensely itch rash affecting finger webs, wrist and genital area
What is the incubation period of scabies?
Up to 6 weeks
How is scabies treated?
Malthion lotion applied over night to whole body, washed off next day Benzyl benzoate (avoid in children)
What causes chicken pox and shingles?
Varicella zoster virus
Explain the progression of chickenpox
Macules -> papules -> vesicles -> scabs -> recovery
What can cause chicken pox to be denser?
Already inflamed skin
What can pre-dispose to serious chickenpox?
Extremes of age
Immunosuppression
What causes neonatal VZV
Maternal chickenpox late in pregnancy
How does shingles present?
The reactivation of VZV in a dermatomal distribution
Stars with tingling pain
What is the nature of zoster related pain?
Neuralgic
Which dermatomes is shingles typical in in adults?
T or L dermatomes
Which dermatomes is shingles typical in in children?
Face of S dermatome
What is Ramsay Hunt syndrome?
Shingles infection affecting the facial nerve, can result in facial palsy
How can shingles be prevented?
Higher titre of chickenpox vaccine can reduce the impact
Routinely given to 70 year olds
What does HSV type 1 cause?
Recurrent cold sores typically at the vermilion border
What is herpetic whitlow?
Cold sore where nail meets finger
What is used as VZV and HSV therapy?
Aciclovir
Does aciclovir eliminate latent virus?
It does not eliminate latent virus
How does erythema multiforme present?
As target lesions with erythema shown
How does molluscum contagiosum present?
Fleshy, firm, umbilicated, pearlescent nodules
Erythema infectiosum is also known as what?
Slapped cheek disease
What causes Erythema infectiosum?
Parovirus B19
What are the complications of Erythema infectiosum?
Spontaneous abortion
Aplastic crisis
Chronic anaemia in immunosuppressed patients
How is erythema infectiosum confirmed?
Antibody testing
Parovirus B19 IgM
What is Orf?
Virus of sheep
Firm fleshy nodules in hands
Self-limiting
Is lab confimation necessary for Orf?
No, clinical diagnosis is made
How does primary infection of syphilis manifest?
Chancre
Painless ulcer at site of entry
How does secondary infection of syphilis manifest?
Red rash over body, prominent on soles of feet and palms
“Snail track” ulcers on mucous membranes
What is the vector for Lyme disease?
Ticks
What pathogen causes Lyme disease?
Borrellia burgdorfi
Bacterial
What is the early presentation of Lyme disease?
Erythema migrans
What is the late presentation of Lyme disease?
Heart block
Nerve palsies
Arthritis
What is the therapy for Lyme disease?
Doxycycline or Amoxicillin
How many people infected with Zika virus become ill
~ 1 in 5
What are the symptoms of Zika virus?
Fever Mild rash Headaches Arthralgia Conjunctivitis Presentation similar to dengue
What are complications of Zika virus?
Microcephaly
Guillain Barre Syndrome
What causes Toxic Shock Syndrome?
TSS toxin producing Staph aureus
How does toxic shock syndrome present?
Fever
Hypotension
Diffuse macular erythematous rash followed by desquamation of the skin
What is a super-antigen of S. aureus?
TSST-1
What are important virulence factors of group A streptococci?
M surface proteins
Why are M surface proteins important virulence factors in group A streptococci?
They inhibit opsonisation
What is a super antigen of Strep. pyogenes?
Pyrogenic exotoxins
Produced by lysogenic strains
