L11- Skin bacteria

Question 1

What bacteria are part of the skin flora?

Answer 1

• Coagulase negative staphylococci +
• Coryne forms- corynebacteria, brevibacteria, cutbacteria +
• Acinetobacter -

Question 2

What are the + staphylococci?

Answer 2

• S. aureus- yellow/white/cream colony colour, coagulase positive, protein A positive
• S. epidermis- white colony colour, coagulase negative, protein A positive

Question 3

What do coagulase negative Staph. do?

Answer 3

They can cause infections in certain conditions such as when there is indwelling prosthesis (catheter, valve)
• Breaches of skin barrier and insertion of medical devices give CNS access to host tissues to form biofilms

Question 4

What do biofilms do?

Answer 4

They protect the CNS bacteria from the host immune response and the actions of antibiotics

Question 5

What is the distribution of S. aureus on human skin surfaces?

Answer 5

• Nose has the greatest
• Perineum second greates
• Axilla, toewebs
Carriage increases in eczema

Question 6

What are the diseases caused by staphylococci?

Answer 6

• Coag neg staph- peritonitis, endocarditis, septiscaemia (diseases associated with prostheses and implants)
• S. lugdunensis- coag neg but causes endocarditis, UTI, endopthalmitis
• S. aureus- pyogenic

Question 7

What does pyogenic mean?

Answer 7

• Produce pus
• Boils and furuncles
• S. aureus can cause superficial or secondary infection

Question 8

What is impetigo?

Answer 8

• Large vesicle bursts and discharge forms thin honey coloured stuck on crusts which are self healing
• Bullous impetigo is when a blister forms, small amounts of toxins responsible

Question 9

What are toxin-mediated diseases?

Answer 9

• Staphylococcal scalded skin- S. aureus produces epidermolytic toxin (protease that splits skin at stratum granulosum)
• Food poisoning- enterotoxin producing S. aureus strains
• Toxic shock syndrome- infection with S. aureus strain producing TSST-1

Question 10

What are superantigens?

Answer 10

• Act by binding outside the antigen presenting groove making stimulation non-specific
• Results in excitation of up to 20% of T cells leading to immense cytokine and inflammatory mediator release

Question 11

What is PVL?

Answer 11

• Panton Valentine Leucocidin
• Some S.aureus strains produce this and are linked to furuncles, abscesses
• PVL produces pores in pmn which trigger cytokine release and cell death

Question 12

What are the S.aureus pathogenicity factors?

Answer 12

• Protein A- reacts with Fc of Ig
• Coagulase- converts fibrinogen to fibrin
• Phospholipase- degrades phospholipid
• Enterotoxins- induces D+V, superantigen
• Epidermolytic toxin- causes blistering skin
• TSST-1- superantigen, multisystem effects

Question 13

What are streptococci?

Answer 13

• Gram +ve cocci
• May be in chains
• Identified by haemolysis and lancefield group

Question 14

What are the normal streptococcal flora and sites of carriage?

Answer 14

• Oral- Str. salivarius, Str. sanguis, Str. oralis
• Respiratory tract- Str. sanguis, Str, oralis
• Intestinal tract- Str. agalactiae

Question 15

What diseases do streptococci cause?

Answer 15

• Pyogenes causes sore throat, impetigo, erysipelas, scarlet fever
• Agalactiae causes neonatal infection, abortion, meningitis, pneumonia

Question 16

What are the streptococcal superantigens?

Answer 16

• Streptococcal pyrogenic exotoxins ( erythrotoxins) or SPE
• SPE B- present in many strains, cysteine protease
• SPE A/C- reported from strains causing scarlet fever

Question 17

What is the M protein?

Answer 17

• Strep. pathogenicity factor
• In cell membrane and wall
• Associated with sequelae to Strep. infections

Question 18

What are the diseases caused by corynebacteria?

Answer 18

• Erythrasma (rash)

* Trichomycosis axillaris (bacteria on hair)

Question 19

What is brevibacterium?

Answer 19

• Cause of toeweb infection

* From milk and cheese and also found on human skin