Bacterial, fungal & parasitic Skin Infections Flashcards
What is the gram stain and shape of staphylococcus
Gram +ve (purple) cocci in clusters

Can staphylococcus grow in both aerobic and anaerobic conditions ?
Yes - grows best in aerobic conditions
So can streptococcus (grows in anaerobic conditions if it has too)
What are the 2 most important classifications of staphloccocus and how are the differentiated?
- Staph.arueus (coagulase positive)
- Coagulase negative Staph - (Staph. epidermidis, Staph. saprophyticus etc.)
What is the coagulase appearance of staph.aureus and coagulase negative staph (e.g. staph.epidermis)?
Staph.aurues is coagulase positive which shows up as golden
Coagulase negative shows up as white

Name and describe another test which can be down to distinguish staph.aureus from all the other strains of staph ?
Latex agglutination - Staph.aureus tests positive all other staph are negative
Note:
Latex agglutination test is a clinical method to detect certain antigens or antibodies in a variety of bodily fluids such as blood, saliva, urine or cerebrospinal fluid. The sample to be tested is sent to the lab and where it mixed with latex beads coated with a specific antigen or antibody.
What strain of staph is the only one which is Novobiocin resistant ?
Staph. saprophyticus
Describe some of the main features of staph.aureus including - some of the common infections it causes and some of the toxins/enzymes it produces
Causes wound, skin, bone & joint infections
Some strains produce toxins:
- Enterotoxin – food poisoning
- SSSST – staph. scalded skin syndrome toxin
- PVL – Panton Valentine Leukocidin
Produces enzymes, including coagulase, an enzyme that clots plasma hence coagulase positive
What is the first line antibiotic used to treat Staph.aureus?
If penicillin allergic then what would you give ?
Flucloxacillin
If penicillin allergic then give doxycycline
Are coagulase negative staph usually pathogenic ?
No usually just skin commensals but can cause infections
Note (staph.aureus is a common human pathogen)
What are the sort of infections that staph.epidermis is associated with ?
May cause infection in association with implanted artificial material, such as artificial joints, artificial heart valves, IV catheters
What infection is staph. saprophyticus associated with ?
Causes UTI in women of child bearing age
Describe the gram stain appearance of Streptococci
Gram +ve cocci in chains

How are the different types of streptoccoci classified ?
By haemolysis:
- β(beta)-haemolytic (complete haemolysis)
- α(alpha)-haemolytic (partial haemolyis)
- γ(gamma) or non-haemolytic (no haemolysis)

Describe some of the features of beta-haemolytic strep - including
They are pathogenic organisms
Produce enzymes (toxins) - e.g. haemolysin (hence complete haemolysis) that damage tissues
How are beta-haemolytic strep further classified and what type of infections are the 2 main classifications associated with ?
Further classified by antigenic structure on surface (serological grouping)
- Group A (throat, severe skin infections)
- Group B (meningitis in neonates)
What are the two most important types of alpha-haemolytic strep ?
Strep. pneumoniae and Strep.viridans
What infections are strep.pneumoniae and strep.viridans associated with ?
Strep.penuomiae - commonest cause of pneumonia
Strep.viridans - commensals of mouth, throat, vagina - rarely cause infection
Give some examples of non-haemolytic strep (gamma) and the type of infection they are mainly associated with
Enterococcus species (E. faecalis, E. faecium)
- Commensals of bowel
- Common cause of UTI
What are some of the defence features of the skin against infection ?
- Barrier
- Sebum - fatty acids - inhibit bacterial growth
- Competitive bacterial flora
Give a couple examples of the micro-organisms involved in the competitive bacterial flora of the skin
- Staphylococcus epidermidis
- Corynebacterium sp. (“diphtheroids”)
- Proprionobacterium sp.
List some of the skin infections which staph.aureus can cause
- Boils and Carbuncles
- Other minor skin sepsis (infected cuts etc.)
- Cellulitis
- Infected eczema
- Impetigo
- Wound infection
- Staphylococcal scalded skin syndrome
What bacterial complications can develop as a result of atopic dermatitis ?
- People with atopic dermatitis also seem to have a reduced ability to fight against these common bacteria on the skin.
- As a result, they frequently suffer from bacterial skin infections such as boils, folliculitis and impetigo.
What is impetigo?
- A common acute superficial bacterial skin infection. Characterised by pustules and honey-coloured crusted erosions (‘school sores’).
- It can be a primary infection or a complication of an existing skin condition such as eczema (in this case), scabies or insect bites
What is the main causative organisms of impetigo?
- Staph. Aureus
- Or sometimes Streptococcus pyogenes







