Week 2 - E(1) - Microbiology - Staph / Strep (species, treatment), tinea, canidida, scabies/lice/lyme's disease

Question 1

What is a gram positive cocci in clusters? What is a gram positive cocci in chains?

Answer 1

Gram positive cocci in clusters - staphylococcus

Gram positive cocci in chains - streptococcus

Question 2

How do you differentiate between different species of staph? What is the only positive staphylococcus species?

Answer 2

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

Question 3

What is the difference in the colour of staph grown on an agar plate?

Answer 3

Staph aureus (coag pos) - golden

Coagulase negative staph - white

Question 4

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?

Answer 4

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

Question 5

What is used to treat staph aureus infections? What are the resistant strains of staph known as? - what is usually substituted to treat these?

Answer 5

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)

Question 6

Give 4 example toxins that are strains of staph auerus can produce and what they can cause?

Answer 6

* 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

Question 7

Give some examples of bacterial skin infections that can be caused by staph aureus?

Answer 7

Cellulitis Infected eczema

Impetigo - bullous and non bullous

Osteomyelitis

Necrotising fasciiitis/pneumonia

TSST

Staph scolded skin syndrome

Question 8

Which organisms are the most common causes of prosthetic valve endocarditis? What is the empirical treatment of this condition?

Answer 8

Prosthetic valve endocarditis - staph epidermis and staph aureus

Empirical antibiotic treatment (to cover main organisms) - IV vancomycin, gentamicin and rifampicin PO

Question 9

What are the gram positive organisms in chains? How can you differentiate within the genus? State the different classifications

Answer 9

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

Question 10

What are the two different alpha haemolytic strep? What can they cause?

Answer 10

Streptococcus pneumonia - pathogen - most common cause of pneumonia, also causes eg meningitis, otitis media

Strep viridans - commensal of mouth, throat - causes endocarditis

Question 11

What are the main beta-hempolytic strep? What can they cause?

Answer 11

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)

Question 12

What are the types of non-haemolytic strep? What are they a commensal of? What are they a common cause of?

Answer 12

Non-haemolytic strep aka gamma haemolytic strep - enterococcus species

Commensals of bowel

Common cause of UTI

Question 13

What are the different bacterial skin infections caused by strep? Which species of strep causes them also?

Answer 13

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

Question 14

What is the antibiotic of choice for strep pyogenes (Group A beta haemolytic strep) treatment?

Answer 14

Penicllin- can also use flucloxacillin

Question 15

How does necrotising fasciitis present? What is the mechanism of the spread?

Answer 15

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

Question 16

What is the common causative organism of necrotising fascititis? How is necrotising fasciitis diagnosed? How is treated?

Answer 16

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

Question 17

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?

Answer 17

Dermatophyte infections are fungi that require keratin for growth

• * Microsporum
• * Epidermophyton
• * Tricophyton

Due to their appearance they are known as ringworm infections aka tinea

Question 18

What is the typical presentation of a tinea infection?

Answer 18

Tinea infections typically result in a red, itchy, scaly, circular rash

Question 19

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?

Answer 19

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

Question 20

What is the pathogenesis of a dermatophyte infection?

Answer 20

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

Question 21

How do the lesions grow in ringworm? Which sex is most commonly affected? What is the most likely source of infection?

Answer 21

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)

Question 22

Which of the three fungi causing dermatophyte infections is the most common?

Answer 22

Trichophyton infections account for majority of dermatophyte infections

Question 23

How is tinea diagnosed? (how is sample obtained and the investigation)

Answer 23

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)

Question 24

What is the treatment for tinea infections?

Answer 24

1st line Can use topical clotrimaole cream or terbinafene cream

For scalp infections - give oral terbinafene or oral intraconazole

Question 25

What fungus causes a candida infection? Where are candida skin infections seen? What does it look like?

Answer 25

Candida infections are caused by candidia albicans

Causes infections in skin folds where area is warm and moist eg under breasts in females, abdominal skin folds, groin areas (also mouth and vagina)

Candidiasis of the skin often causes a red, itchy rash to form,

Question 26

How is candida skin infection treated?

Answer 26

Treatment involves topical clotrimaole usually - can give oral fluconazole

Question 27

SKIN INFESTATIONS What parasite causes scabies? What is the incubation period?

Answer 27

Scabies is caused by sarcoptes scabie The incubation period lasts for up to 6 weeks

Question 28

Once the infected by the sacropties scabie mite, where do the parasites burrow into?

Answer 28

Sacroptes scabie burrows through the keratin layer of the skin

Presentation of a patient with scabies may be the presence of burrows + an intense itch affecting finger webs, wrists and genital area

Question 29

What is the treatment of scabies?

Answer 29

Permethrin cream or Malathion cream

Both applied to whole body before bed and washed off the next day

Question 30

What is the highly infectious chronic crusted form of rabies known as and who is it usually seen in?

Answer 30

Hoghly infectious chronic crusted form known as Norwegian Scabies - seen in elderly or immunocompromised

Question 31

What is lice also known as? What is it called when it affects the head, body and pubic area?

Answer 31

Lice is also known as pediculosis

Pediculosis capitis - head louse infection

Pediculosis corporis - body louse aka Vagabond’s disease

Pediculosis pubia aka phthirus pubis - pubic louse aka crabs

Question 32

What is the presentation of lice? What is the treatment?

Answer 32

Lice presents as an intense itch - can closely examine the head or pubic area and will often see small lice

Lice are wingless parasites with legs to climb hair shafts

Treatment is with malathion lotion or meticulous combing

Question 33

What is the serious infection that can be caused by tick bites and due to what organism?

Answer 33

Tick bites can cause serious health problems as they can transmit the spirochaete bacteria - Borrelia Burgdorferi - the organsims responsible for Lyme disease

Question 34

How long does the tick need to be attached to the patient for usually to cause Lyme disease?

Answer 34

Transmission is very rare in the 1st 24 hours and peak infection rises dramatically after 48 hours

Question 35

There are three stages of Lyme disease What are they?

Answer 35

Early localised stage - where there is the appearance of erythema migrans (erythema chronicum migrans)

Early disseminated stage aka borrelia lymphocytoma

Late disseminated stage - acrodermatitis chronic atrophicans

Question 36

What is erythema migrans also known as due to its appearance? How soon after the tick bite is this seen?

Answer 36

It is also known as a bullseye- lesion due to its apperance

Seen on average 2 weeks after the bite

Question 37

What else is seen in the early localised stage of lyme’s disease? (1/3rd of patients do not see a rash)

Answer 37

Non sepecific syptoms - pain/pruritus, lymphadenopathy, arthralgia, fever, malaise, headache

Question 38

The second stage is early disseminated spread What is it also known as? What happens in this stage? How long after the initial bite usually?

Answer 38

aka borrelia lymphocytoma

There is bluish-red swelling of earlobes /nipples as well as tender local lymphadenopathy

Can cause a lymphocytic meningitis picture

Also can cause neurological features and carditis

Happens wks to months after initial bite (avg 6 mths)

Question 39

What is the third and final stage of lyme disease known as? What is seen here and how long after intitial infection?

Answer 39

Acrodermatitis chronica atrophicans - characteristic blue/red discoloration of skin progressing to skin atrophy - focal inflammation then atrophic skin

Lyme arthritis occurs here as well

Question 40

What is the treatment for lyme disease?

Answer 40

Doxycycline (amoxicillin is an alternative)

More severe cases usually require IV penicillin or ceftriaxone

Question 41

WHat is the reaction which may occur in a small percentage of patients usually within the 1st 24 hours of antibiotic treatment? - there is the release of endotoxin due to large numbers of organisms being killed which can lead to sepsis

Answer 41

This is known as Jarisch Herzheimer reaction - traditionally associated with antibiotic treatment of syphilis but also seen in other diseases caused by spirochaetes such as lymes disease