Flashcards in Week 2 - Antifungal Case Studies Deck (26):
What are the three dermatophytes?
Microsporum, Tichophyton, Epidermophyton
What organism causes "cradle cap" or seborrheic dermatitis?
What organisms cause bacterial folliculitis?
Staphylococcus aureus or Pseudomonas
What are the limitations of a KOH test?
It is a fast result but it does't identify the species and has lower sensitivity.
What are the limitations of Wood's Lamp?
The fungi Trichophyton tonsurans does not fluoresce.
When would you take a bacterial culture if you think something is a fungal infection?
If you see inflammation, you want to take a bacterial culture just to rule out secondary infections.
What are the pros and cons of culturing fungi on Sabouraud's agar + antibiotics?
It takes longer (1-4 weeks) but its more sensitive and used for refractory cases. You can follow up with susceptibility tests ad strain identification through PCR.
What structures are seen in a KOH scraping of Microsporum?
Spindle shaped Macroconidia
What is the most common pediatric dermatophyte infection?
Tinea capitis (age 4-14)
What is unique about sebum?
What is the most common cause of tinea capitis?
Trichophyton tonsurans (90-95% of cases)
Second most common is Microsporum canis or audouinii which fluoresce blue-green under wood's lamp.
What are the three most common morphologies for dermatophytes?
Microsporum canis: spindle-shaped macroconidia and microconidia
Trichophyton tonsurans: Macroconidia are rare, Microconidia - looks like hairs with tiny little dots
Epidermophyton floccosum: Dumbbel-shaped macroconidia - No microconidia
What type of organism is Trichophyton tonsurans?
What type of transmission does Microsporum fulvum do?
It is geophilic (loving soil) and causes tinea corporis
How does Microsporum canis invade the hair follicle?
It is ectothrix so it penetrates AROUND the hair shaft. It tends to be chronic.
How does Trichophyton tonsurans invade the hair follicle?
It can penetrate within the hair shaft (endothrix).
What properties of dermatophytes promote cutaneous growth?
Dermatophytes adhere to keratinocytes and produce keritinase. They also have mannans in their cell wall that allows them to evade the host immune response.
What makes disseminated disease rare for dermatophytes?
The fungi are unable to grow at body temperature.
What treatment would you recommend for a patient with tinea capitis caused by Microsporum canis?
Systemic therapy - oral griseofulvin (microtubule inhibitor) for 8-10 weeks or until the layer of skin is sloughed off. - Griseofulvin needs to be taken with foods high in fat
(2nd choice: terbinafine - inhibits squalene epoxidase - but its not as effective for M. canis)
Onychomycoses is also referred to as:
Which fungi are most often associated with onychomycoses?
Subungal - Trichophyton rubrum, most common for tinea pedis, tinea corporis, and tinea cruris
White superficial - Trichophyton mentagrophytes - more common in children
Bacteria pseudomonas - blue-green nail infection
What does Candida albicans do as an onychomycosis?
It's more common on fingers and causes inflammation.
How do you diagnose a tinea pedis/onychomycosis infection?
1. Clean with alcohol to remove bacteria
2. Take a sample from nail bed for KOH test
3. False negative 5-15% of time - hyphae can be rare
4. Beware of Candida contamination
What is the pathogensis of Trichophyton rubrum that causes tinea pedis?
1. Conidia adhere to keratinocytes (sebum is inhibitory so they prefer soles of feet) and germinate
2. Chronic infection (slow growing) starts with big toe and spreads
3. Nail thickening may cause pain
4. Subungual hyperkeratosis can cause seperation of nail plate from nail bed
5. Can make individual more prone to secondary infections like gangrene
What treatment is used for Trichophyton rubrum?
-Discard exposed footwear and minimize moisture
-Regular trimming of nails
-Some doctors refuse to treat this because they believe its a cosmetic problem
-USE SYSTEMIC: Terbinafine or Itraconazole (for onchyomycoses)
-Need to monitor heptatoxicity - take baseline of liver enzymes
-Recurrance is common so need to treat for a week after symptoms stop - think of it as controllable, rather than curable