Skin microbiology Flashcards
How can staph. aureus be distinguished from other staphylococcal types and why?
Staph. aureus is coagulase positive - will coagulate at the bottom of a test tube
Also shows up golden on an agar plate
What property is unique to staph. aureus (compared to other staphylococcus)?
Produces enzymes including coagulase, an enzyme that causes clots to form
What are examples of toxins produced by staph. aureus?
Enterotoxin (food poisoning)
Staph. scalded skin syndrome toxin
Panton Valentine Leukocidin (MRSA)
Which bacteria is likely to stick to prosthetic materials in the body and why?
Staph. epidermidis
Produces a ‘slime’ that allows it to stick to these materials
Which species of staphylococcus causes UTIs in women of child-bearing age?
Staph. saprophyticus
What are the characteristics of beta-haemolytic streptococci?
Pathogenic
Produce toxins including haemolysin
What kind of infections are caused by group A beta-haemolytic bateria?
Throat infections
Severe skin infections
What kind of infections are caused by group B beta-haemolytic streptococci?
Meningitis in neonates
What are the characteristics of non-haemolytic streptococci?
Enterococcus species (E. faecalis, E. faecium)
Commensals of bowel
Common cause of urinary tract infection
What skin infections does staph. aureus cause?
Boils and Carbuncles
Other minor skin sepsis (infected cuts etc.)
Cellulitis
Infected eczema
Impetigo
Wound infection
Staphylococcal scalded skin syndrome
What skin infections does strep. pyogenes cause?
Infected eczema
Impetigo
Cellulitis
Erysipelas
Necrotising fasciitis – (N.B. may also be caused by mixed bacterial infection)
What does tinea mean?
Ringworm
How does tinea infection occur?
Fungus infection enters soggy/abraded skin
Hyphae spread in stratum corneum
Increased epidermal turnover causes scaling
Inflammatory response provoked (dermis)
Hair follicles and shafts invaded
Lesion grows outward and heals in centre, giving a “ring” appearance
Where does tinea infection occur?
Only occurs on keratinised surfaces e.g. nails, hair, body
Are males or females more commonly affected by ringworm?
Males
Which patients does scalp ringworm mainly affect?
Children
Which patients does foot and groin ringworm tend to affect?
Male patients
Which is the most common causal organism of dermatophytes?
Trichophyton rubrum
How is fungal infection of the skin diagnosed?
Clinical appearance
Woods light (fluorescence)
Skin scrapings, nail clippings, hair
Send to laboratory in a “Dermapak” for microscopy and culture (N.B. culture takes 2 weeks)
How should small areas of fungally infected skin/nails be treated?
Clotrimazole (Canestan) cream or similar
Topical nail paint (amorolfine)
How should extensive fungal skin nfection or scalp infection be treated?
Terbinafine orally
Itraconazole orally
Which areas of the body are usually affected by scabies?
Finger webs
Wrists
Groin
What is the treatment for scabies?
Malathion lotion, applied overnight to whole body and washed off next day
Benzyl benzoate (avoid in children)
What is the treatment for lice?
Malathion
What are some of the complications of chickenpox?
Secondary bacterial
Pneumonitis
Haemorrhagic
Scarring
Encephalitis
Which skin diseases are due to varicella zoster virus?
Chickenpox
Shingles
A 26-year-old man presented with a 5-day history of cough, fever, and mild dyspnea
He had an exanthematous vesicular rash that had started 3 days before the respiratory symptoms began
He smoked cigarettes (30 per day for the previous 14 years)
His daughter had recently had chickenpox; he had not been vaccinated against the disease nor did he have a history of it
A skin examination revealed a polymorphic rash with vesicles, pustules, and crusty lesions
On Xray: multiple small nodules in both lungs
On CT: no liver or CNS involvement
What is the diagnosis?
Varicella pneumonia/chickenpox
This diagnosis was made on the basis of the rash, pulmonary symptoms, and contact with a child with chickenpox
How is development of chickenpox in the neonate prevented?
Prevention with Varicella Zoster Immune Globulin in susceptible women in contact
How does shingles present?
Dermatomal distribution
Tingling pain
Erythema
Vesicles
Crust
In which patients is the incidence of shingles highest?
Elderly
Immunocompromised
What is the diagnosis here and the management?
Opthalmic shingles/zoster (see involvement of tip of nose)
Requires urgent referral to opthalmology
Which nerve is involved in opthalmic zoster?
Opthalmic division of trigeminal nerve
What are the features of Ramsay-Hunt syndrome?
Facial nerve palsy
Vestibulocochlear nerve irritation - deafness, vertigo, tinnitus
Vesicles and pain in auditory canal and throat
What is Ramsay-Hunt syndrome?
Geniculate or otic herpes zoster
What is the diagnosis here?
Primary gingivostomatisis - herpes simplex infection
Which patients are affected by primary gingivostomatitis and how long does it last?
Pre-school children
Ulceration lasts around a week
What are the characteristics of type 1 herpes simplex virus?
Main cause of oral lesions
Causes half of genital herpes
Causes encephalitis
What are the characteristics of type 2 herpes simplex virus?
Rare cause of oral lesions
Causes half of genital lesions
Encephalitis / disseminated infection (particularly in neonates)
What is the treatment for herpes simplex virus and varicella zoster virus?
Aciclovir
Does aciclovir affect latent viruses?
No
How does aciclovir work?
It is selectively incorporated into viral DNA, inhibiting replication
What are the nodules in molluscum contagiosum like?
Fleshy, firm, umbilicated, pearlescent nodules
1 to 2 mm diameter
How can molluscum contagiosum be treated?
Usually self-limiting but can take months to disappear
Local application of liquid nitrogen
What is herpangina?
A blistering rash of the back of the mouth
What organism causes herpangina?
Enterovirus:
Coxsackie virus
Echovirus
What is slapped cheek disease and what causes it?
Erythema infectiosum
Caused by parovirus B19
What does slapped cheek disease look like?
Erythematous rash on the cheeks
As the rash on the face fades a lacy macular rash on the body appears
In adults rash may be absent and an acute polyarthritis of the small joints eg of the hands may be more prominent
How is parovirus confirmed in the lab?
Parvovirus B19 IgM test
. A 23-year-old woman presented to the emergency department after 1 day of fever, sore throat, arthralgia, and rash
Diffuse erythema (Panel A) that blanched on pressure was noted over the face, neck, trunk, and arms, along with posterior cervical lymphadenopathy
The next day, the fever and rash subsided, but she reported pain in the oral cavity
Examination revealed petechial hemorrhages on the soft palate (Panel B) that disappeared spontaneously in 2 days
She had no history of rubella vaccination
What is the diagnosis and what would show up on lab tests?
Testing for rubella IgG antibody was negative, and testing for rubella IgM antibody was positive, which confirmed the clinical diagnosis of rubella
What is the causal organism in syphilis?
Treponema pallidum
