microbiology Flashcards
what can defend the skin against infection
- intact skin is less likely to be infected
- dry - desiccates microorganisms
- sebum - fatty adits - inhibit bacterial growth
- competitive bacterial flora
- concept of resident and transient flora
what are features of staphylococcus species
- most common
- gram positive clusters
- aerobic and facultatively anaerobic ( grows best aerobically but also grows anaerobically)
- 2 important types = staph.aureus and coagulase negative staph (staph epidermis )
what are features of staphylococcus aureus
- common
- causes wound, skin, bone and joint infections
- produces enzymes including coagulase, an enzyme that clots plasma. That distinguishes itself from other staph.species
- antibiotic of choice = flucloxacillin
- some stains produce toxins - SSSST (staphylococcal scaled skin syndrome toxin), PVL(Panton valentine Leucocidin) and enterotoxin (food poisoning)
what can be seen when staphylococcus aureus is in the skin
- boils and carbuncles
- cellulitis
- infected eczema
- impetigo
- wound infection
- staphylococcal scaled skin syndrome
what are MRSA treatment options
skin and soft tissue options
- doxycycline oral - bacteriostatic
- co-trimoxazole
- clindamycin
- NOT flucloxacillin
bactericidal options
- vancomycin
- daptomycin (can develop resistance when in use)
what are streptococcus spectates classified by
classified initially by haemolytic on blood agar
- beta haemolytic (complete haemolytic)
- alpha haemolytic (partial haemolytic)
- gamma non haemolytic (no haemolytic)
what are examples of streptococcus progenies (group A strep)
- infected eczema
- impetigo
- cellulitis
- erysipelas
- necrotising fasciitis
what are 2 important categories of alpha haemolytic streotococci
- strep pneumonia - pathogen, commonest cause of pneumonia
- strep viridian’s group - commensals of mouth, throat, vagina- cause infection endocarditis
what is necrotising fascitis
- bacterial infection spreading along fascial planes below skin surface
- little to see on skin surface but severe pain
- antibiotic treatment depends on organisms isolated from tissue taken at operation
- rapid tissue destruction
- urgent surgical opinion and debridement required
- 2 types = type 1 - mixed anaerobes and coliform, usually post abdominal surgery. type 2 - group A strep infection
in certain leg ulcers what are the organisms worth treating
- strep.pyogenes (groupA), staph.aureus
- other beta haemolytic streptococci (B,C,G)
what is the dermatophyte pathogensis
- fungus enters abraded or soggy skin
- hyphae spread in stratum corneum
- infects keratinised tissue only
- increased epidermal turnover causes scaling
- inflammatory response provoked (dermis)
- hair follicles and shafts invaded
- lesions grows outward and heals in centre, giving a ‘ring’ appearance
what are dermatophytes
Dermatophytes are fungi that require keratin for growth
how do you diagnose dermatophytes infections
- clinical appearance
- woods light (fluorescence)
- skin scrapings, nail clippings, hair - send to laboratory “dermapak” for microscopy and culture. N.B. culture takes 2 week
skin scrapings should be taken from the scaly edge of the lesion
what is a candida skin infection
- causes infection in skin finds where area is warm and moist “candida intertrigo”
- diagnoses - swab for culture
- treatment - clotrimazole cream, oral fluconazole
what is scabies skin infection
- caused by sarcoptes scabiei
- chronic crusted form is termed “Norwegian scabies” (highly infectious)
- incubation period up 6 weeks
- intensely itchy rash affecting finger webs, wrists, genital area
- treatment = malathion lotion, applied overnight to whole body and washed off next day.
