microbiology

Question 1

what can defend the skin against infection

Answer 1

• 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

Question 2

what are features of staphylococcus species

Answer 2

• 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 )

Question 3

what are features of staphylococcus aureus

Answer 3

• 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)

Question 4

what can be seen when staphylococcus aureus is in the skin

Answer 4

• boils and carbuncles
• cellulitis
• infected eczema
• impetigo
• wound infection
• staphylococcal scaled skin syndrome

Question 5

what are MRSA treatment options

Answer 5

skin and soft tissue options

• doxycycline oral - bacteriostatic
• co-trimoxazole
• clindamycin
• NOT flucloxacillin

bactericidal options

• vancomycin
• daptomycin (can develop resistance when in use)

Question 6

what are streptococcus spectates classified by

Answer 6

classified initially by haemolytic on blood agar

• beta haemolytic (complete haemolytic)
• alpha haemolytic (partial haemolytic)
• gamma non haemolytic (no haemolytic)

Question 7

what are examples of streptococcus progenies (group A strep)

Answer 7

• infected eczema
• impetigo
• cellulitis
• erysipelas
• necrotising fasciitis

Question 8

what are 2 important categories of alpha haemolytic streotococci

Answer 8

• strep pneumonia - pathogen, commonest cause of pneumonia

- strep viridian’s group - commensals of mouth, throat, vagina- cause infection endocarditis

Question 9

what is necrotising fascitis

Answer 9

• 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

Question 10

in certain leg ulcers what are the organisms worth treating

Answer 10

• strep.pyogenes (groupA), staph.aureus

- other beta haemolytic streptococci (B,C,G)

Question 11

what is the dermatophyte pathogensis

Answer 11

• 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

Question 12

what are dermatophytes

Answer 12

Dermatophytes are fungi that require keratin for growth

Question 13

how do you diagnose dermatophytes infections

Answer 13

• 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

Question 14

what is a candida skin infection

Answer 14

• causes infection in skin finds where area is warm and moist “candida intertrigo”
• diagnoses - swab for culture
• treatment - clotrimazole cream, oral fluconazole

Question 15

what is scabies skin infection

Answer 15

• 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.