Microbiology 2 Flashcards
What are three features of skin that prevent against infection?
- Dryness: dries out the organism
- Sebum: inhibits bacterial growth
- Competitive flora
What are some protective bacterial flora?
Staph. Epidermidis, Corynebacterium, Propionibacterium
How do you investigate a skin lesion where the surface is broken but is relatively superficial?
Swabs
How do you investigate a skin lesion where the surface is broken but is relatively deep?
Pus or tissue sample +/- blood cultures
How will staph aureus show on blood agar?
Golden
How will coagulase - staph show on blood agar?
White
Which variants of Staph are coagulase +?
Staph aureus only
Which variants of Staph are coagulase -?
All types except staph aureus, a good example is staph epidermidis
What will staph and strep be on a gram stain?
Positive
An organism is gram + cocci in clusters, what is this likely to be?
Staphylococcus
An organism is gram + cocci in chains, what is this most likely to be?
Streptococcus
Once you have decided an organism is staph, what test will decipher if it is staph aureus?
Coagulase test will be positive
Once you have decided an organism is strep, what test will decipher if it is Group A strep?
Haemolysis- will be B (complete) haemolysis
In what conditions will staph aureus grow?
Aerobic and facultatively anaerobic
Does staph aureus produce enzymes?
Yes (coagulase is an enzyme)
Where does staph aureus usually cause infections?
Bone, skin, joint and wounds
What is the antibiotic of choice for staph aureus?
Flucloxacillin
Can MRSA be treated with flucloxacillin?
No
What are some antibiotic options for MRSA?
Doxycycline, co-trimoxazole, clindamycin, vancomycin
What is the enterotoxin produced by staph aureus associated with?
Food poisoning
What are some skin infections which staph aureus can cause?
Minor skin sepsis Cellulitis Infected eczema Impetigo Wound infections
Where are most other staph organisms found?
As skin commensals, not usually pathogenic
When do coagulase - staph cause infections?
In association with foreign devices
What can staph saprophyticus cause?
UTIs in women of child bearing age
What conditions does strep grow in?
Aerobic and facultatively anaerobic
How is streptococci classified?
Haemolysis on blood agar
What does beta haemolytic strep mean?
Complete haemolysis- always pathogenic
What does alpha haemolytic strep mean? Give examples.
Partial haemolysis e.g. Strep pneumoniae, strep viridans
Where is strep viridans usually found? What can it cause?
Commensal of the mouth, throat, vagina
May cause infective endocarditis
In terms of skin infection, which type of strep is the most important?
Group A beta haemolytic strep
How is beta haemolytic strep further classified?
Based on antigenic surface structure
What can group A strep cause?
Throat and severe skin infections
What does group B strep cause?
Meningitis in neonates
What are some skin infections that group A beta haemolytic strep can cause?
Infected eczema
Impetigo
Cellulitis
Necrotising fasciitis
What is an example of a group A beta haemolytic strep which can cause impetigo, cellulitis and necrotising fasciitis?
Strep pyogenes
Group A strep are further divided into M protein groups. What are M1 and M3?
The major serotypes
Group A strep are further divided into M protein groups. What are M18 and M3?
Severe invasive disease
Describe impetigo?
This is a skin infection under the surface in the stratum corneum. It usually affects the face and may be linked with the lymphatic system.
Is impetigo infectious?
Highly contagious through contact with discharge from the face
Describe cellulitis?
A deeper skin infection in the dermis, but not associated with necrosis
Describe necrotising fasciitis?
Group A strep penetrates the mucus membranes and develops in lesions which rapidly destroys connective tissue
Do all skin infections require antibiotics?
Minor ones may not
What antibiotics target Group A strep?
Mainly penicillin, though flucloxacillin may also work
What is the treatment for necrotising fasciitis?
Immediate surgical debridement or amputation and antibiotics
How will necrotising fasciitis present?
Little to see on the skin but will cause severe pain
What are group 1 and 2 types of necrotising fasciitis?
1- mixed coliforms and anaerobes (usually post-abdominal surgery)
2- group A strep
When should you take swabs of leg ulcers?
If signs of infection/cellulitis are present
What antibiotic treats anaerobes?
Metronidazole
What is the main fungal infection of skin?
Tinea (ringworm)
What are TINEA:
a) capitus
b) barbae
c) corporis
d) manuum
e) unguium
f) cruris
g) pedis
a) head
b) beard
c) body
d) hand
e) nail
f) groin
g) foot
What is the common name for tine pedis?
Athlete’s foot
Where do fungi enter the skin?
Abraded or soggy skin
Where do fungi only infect?
Keratinised surfaces
Which sex is more likely to be affected by tinea infections? Which age group are they most common in?
- Males
- Children
Where do tinea infections come from?
Mainly from other humans, though can be from animals or soil
How do the lesions of tinea appear?
The lesions grow outwards and heal in the middle, giving a ring appearance
What are some diagnostic tests for tinea infection?
- Fluorescence (Wood’s lamp)
- Skin scrapings for microscopy and culture
How do you treat small tinea infected areas?
Clotrimazole cream or topical nail paint
What do you treat tinea corporis with?
Terbinafine
What is the most common organism causing tinea infections?
Trichophyton Rubrum
Where does microsporum canis come from?
Cats and dogs (cause of tinea infection)
Where do candida infections occur?
Skin folds where the area is warm and moist e.g. under breasts, groin areas, under abdominal skin folds
How do you treat candida infections?
Clometrizole cream or oral fluconazole
What is Norwegian scabies?
A chronic, crusted form of scabies which is highly infectious
What will scabies present with?
Intensely itchy rash affecting finger webs, wrists and genital areas
How do you treat scabies?
- Malathion lotion applied overnight and then washed off
- Benzyl benzoate
Who should benzyl benzoate not be used in?
Children
Who are some examples of infectious patients who would need in a separate room?
- MRSA
- Group A strep
- Scabies
