Week 2 - E(1) - Microbiology - Staph / Strep (species, treatment), tinea, canidida, scabies/lice/lyme's disease Flashcards
What is a gram positive cocci in clusters? What is a gram positive cocci in chains?
Gram positive cocci in clusters - staphylococcus
Gram positive cocci in chains - streptococcus
How do you differentiate between different species of staph? What is the only positive staphylococcus species?
Coagulase tests allows differentiation between species of staph- blood will clot at bottom of test tube
Staph aureus is the only staph species to produce the coagulase enzyme causing blood to clot
Staph aureus- coag pos
All other staph species - coag neg
What is the difference in the colour of staph grown on an agar plate?
Staph aureus (coag pos) - golden
Coagulase negative staph - white
What is a method of differentiating between coagulase nagtive staph? Give two examples Which is a skin commensal? Which is found to sometimes cause a UTI in women of child-bearing age?
Differentiation between coagulase negative staph -
Staph saprophyticus is novobiocin resistant (resistant to this antibiotic) - basically all other staph are nobobiocin resistant
Coag neg staph epidermis - skin commensal
Coag neg staph saprophyticus - UTI cause in women of child-bearing age
What is used to treat staph aureus infections? What are the resistant strains of staph known as? - what is usually substituted to treat these?
Flucloxacillin is the oral antibiotic of choice to treat staphylococcus aureus infection
Resistant strains are known as methicillin resistant staph aureus (MRSA) - treatment here usually involves giving vancomycin (ie for staph skin infection give flucloxacillin, if allergic or resitant give vancomycin)
Give 4 example toxins that are strains of staph auerus can produce and what they can cause?
* Enterotoxins - causes food poisoning
* Staphylococcal scalded skin syndrome toxin (SSST) - causes staphylococcal scalded skin syndrome
* Panton Valentine Leucocidin (PVL) - directly attacks leucocytes eg in necrotising fasciitis and necrotising pneumonia
* Toxic shock syndrome toxin (TSST) - causes toxic shock syndrome
Give some examples of bacterial skin infections that can be caused by staph aureus?
Cellulitis Infected eczema
Impetigo - bullous and non bullous
Osteomyelitis
Necrotising fasciiitis/pneumonia
TSST
Staph scolded skin syndrome
Which organisms are the most common causes of prosthetic valve endocarditis? What is the empirical treatment of this condition?
Prosthetic valve endocarditis - staph epidermis and staph aureus
Empirical antibiotic treatment (to cover main organisms) - IV vancomycin, gentamicin and rifampicin PO
What are the gram positive organisms in chains? How can you differentiate within the genus? State the different classifications
Gram positive cocci in chains is stretpococci
Different classifications within the genus is initially classified by the haemolysis on blood agar
- alpha-haemolytic - partial haemolysis
- beta-haemolytic - complete haemolysis gamma
- non-haemolytic - no haemlysis
What are the two different alpha haemolytic strep? What can they cause?
Streptococcus pneumonia - pathogen - most common cause of pneumonia, also causes eg meningitis, otitis media
Strep viridans - commensal of mouth, throat - causes endocarditis
What are the main beta-hempolytic strep? What can they cause?
Group A beta haemolytic strep aka strep pyogenes - strep sore throat, severe skin infections
Group B beta haemolytic strep aka strep agalactiae - neonatal meningitis (colonises vaginal flora)
What are the types of non-haemolytic strep? What are they a commensal of? What are they a common cause of?
Non-haemolytic strep aka gamma haemolytic strep - enterococcus species
Commensals of bowel
Common cause of UTI
What are the different bacterial skin infections caused by strep? Which species of strep causes them also?
it is group A strep (strep pyogenes) that causes severe skin infections
Skin infections similar to staph aureus
- * Infected eczema
- * Impetigo
- * Cellulitis
- * Erysipelas
- * Necrotising fasciitis
What is the antibiotic of choice for strep pyogenes (Group A beta haemolytic strep) treatment?
Penicllin- can also use flucloxacillin
How does necrotising fasciitis present? What is the mechanism of the spread?
Necrotising fasciitis presents normally with little to see on the skin surface but severe pain - there may be blistering and necrosis of the skin if advanced
Bacterial infection spreads along fascial planes below skin surface causing rapid tissue destruction
What is the common causative organism of necrotising fascititis? How is necrotising fasciitis diagnosed? How is treated?
Usually caused by Group A strep infection
Diagnosed via tissue swabs rather than wound swabs
Urgent surgical opinion and debridement required - antibitoic depends on organsms isolated from tissue taken at operation
Dermatophytes are fungi that require keratin for growth. These fungi can cause superficial infections of the skin, hair, and nails. There are three different genus of fungi that are grouped together to be called dermatophyte infections What are the three genera? What are the dermatophyte infections known as due to their appearance?
Dermatophyte infections are fungi that require keratin for growth
- * Microsporum
- * Epidermophyton
- * Tricophyton
Due to their appearance they are known as ringworm infections aka tinea
What is the typical presentation of a tinea infection?
Tinea infections typically result in a red, itchy, scaly, circular rash
Tinea infections have different names based on where they affect State the different names for infections affecting the
- * Scalp
- * Hand
- * Beard
- * Body
- * Groin
- * Nails
- * Foot - what is this better known as?
Scalp - tinea capitis
Hand - tinea manuum
Beard - tinea barbae
Body - tinea corporis
Groin - tinea cruis
Nails - tinea unguium
Foot - tinea pedis - better known as athlete’s foot
What is the pathogenesis of a dermatophyte infection?
Fungus enters abraded or soggy skin
Hyphae spread in stratum cornneum infecting keratinised tissues only (skin, hair, nails)
Increased epidermal turnover causes scaling and inflammatory response provokes
Hair follicles and shafts become invaded
How do the lesions grow in ringworm? Which sex is most commonly affected? What is the most likely source of infection?
The lesions grow outward and heal in the centre- giving a ring appearance
Males are most commonly affected
Spread from other humans is the most likely source of infection (anthropophilic fungi)
Other sources are animals (zoophilic fungi) and soil (geophilic fungia)
Which of the three fungi causing dermatophyte infections is the most common?
Trichophyton infections account for majority of dermatophyte infections
How is tinea diagnosed? (how is sample obtained and the investigation)
Diagnosed usually based on clinical appearance If investigations- take skin scrapings from the edge of the lesion because lesions grow outwards and heal in the middle and send for Woods light (fluorescence)
What is the treatment for tinea infections?
1st line Can use topical clotrimaole cream or terbinafene cream
For scalp infections - give oral terbinafene or oral intraconazole
