Microbiology Flashcards
How do staph and strep bacteria tend to enter the body?
Staph - through sebaceous glands
Strep - through damage in skin
What can toxins on staph aureus cause?
Toxic shock
Scalded skin syndrome
What skin infections can staph aureus cause?
Rash Folliculitis Abscess Carbuncle Impetigo Scalded skin syndrome
Which staphylococcus is coagulase positive?
Staph aureus
What are virulence factors?
The ways in which bacteria kill
What are examples of staph aureus virulence factors?
Coagulase Fibrinogen binding protein Superantigens Toxinoses (PVL (Panton-Valentine Leukotoxin), gamma and alpha toxin) Protease Capsule
What are examples of staph aureus virulence factors?
Coagulase Fibrinogen binding protein Toxinoses Adhesions PVL (Panton-Valentine Leukotoxin)
How does coagulase aid pathogenesis?
Physical protection that allows better adherence to a site
What is TSST-1?
A toxin released by staph aureus that causes toxic shock syndrome
Gets into blood and causes rapidly progressing, life-threatening illness
Overstimulates immune response
What are the clinical features of toxic shock syndrome?
Fever (39˚)
Diffuse malar rash and desquamation
Hypotension
>3 organ systems involved
Why is toxic shock syndrome associated with menstrual toxic shock?
If a tampon is contaminated with staph aureus, TSST-1 gets into the blood stream via the vagina
How do adhesions contribute to pathogenesis?
Increase ability to colonise a site
Bind to fibrinogen-binding, fibrontectin-binding and collagen-binding molecules
What does PVL positive staph aureus cause?
Sepsis
Necrotising fasciitis
- very severe, life-threatening
Who are at risk of staph epidermidis infection?
Immunocompromised
Does staph epidermidis coagulate plasma?
No - coagulase negative
What is MRSA?
Methylin resistant staph aureus associated with hospitals
Describe streptococcus pyogenes?
Group A strep Gram positive cocci in chains Catalase negative Beta haemolysis Lancefield classification A
What are examples of skin infections does strep pyogenes cause?
Impetigo
Cellulitis
Necrotising fasciitis
What are examples of non skin conditions that strep pyogenes causes?
Pharyngitis, tonsillitis (sore throat)
Rheumatic fever
Glomerulonephritis
What are the virulence factors of strep pyogenes?
Capsule M-protein (lets it bind to several proteins) Haemolysins Superantigenic toxins DNAases Fibronectin-binding proteins
What is impetigo?
Contagious infection of the superficial skin
What is cellulitis?
Deeper skin infection with invasion oft he dermis and subcutaneous fat
Patients have fever, rights, nausea
What is necrotising fasciitis?
Infection that penetrates deep, into muscles and other subcutaneous structures
Rapid destruction of connective tissue can lead to toxic shock, amputation
What are the causative organisms for type 1 and 2 necrotising fasciitis?
1 - clostridia
2 - strep pyogenes, staph aureus
What is streptomycin S (SLS)?
Pore-forming cytolysin - secretes substance that is toxic to cells
How does a capsule contribute to pathogenesis?
Anti-phagocytic
How does fibrinogen binding protein contribute to pathogenesis?
Adhesion
How do haemolysins alpha, beta, delta and gamma contribute to pathogenesis?
Cytolytic
How does coagulase contribute to pathogenesis?
Clots plasma
How does fibrinolysin contribute to pathogenesis?
Digests fibrin
How does leukocidin (PVL) contribute to pathogenesis?
Kills leukocytes
How does protein A contribute to pathogenesis?
Anti-phagocytic
What is the best antibiotic for staph aureus?
Flucloxacillin
What antibiotics are effective against MRSA?
Doxycycline
Co-trimoxazole
Clindamycin
Vancomycin (if more sick)
Which antibiotic that is effective against MRSA should be avoided, and why?
Clindamycin - one of the 4Cs, carries risk of C. diff
What is the key thing to know about staph epidermidis?
It is not as likely to be pathogenic as staph aureus - often just commensal
What skin conditions can be caused by strep pyogenes (group A strep)?
Infected eczema Impetigo Cellulitis Necrotising fasciitis Erysipelas
What is the treatment for strep pyogenes infection?
Penicillin
or flucloxacillin
What is suspected if there is a little bit of redness in skin which looks like cellulitis but patient in much more pain than you would expect?
Necrotising fasciitis
What is the treatment for necrotising fasciitis?
Immediate surgical debridement
What are the most important fungal diseases?
Candidisais
Tinea
What is the pathogenesis of fungal infections?
Fungus enters abraded or soggy skin
Hyphae spread in stratum corner
Infects keratinised tissues only
Increased epidermal turnover causes scaling
Inflammatory response provoked in the dermis
Hair follicles and shafts involved
Lesions grows outwards and heals in the centre, giving a ‘ring’ appearance
What is the most common organism to cause fungal infections?
Trichophyton rubrum
How are fungal infections diagnosed?
Clinical appearance
Woods light
Skin scrapings, nail clippings, hair
Which part of a lesion should a sample be taken from?
The edge - as it grows outwards and heals in the centre, the outside is where the organisms are
Why are fungal infections usually not cultured?
Can usually tell from appearance, takes ages and doesn’t change treatment
What is the treatment for a small fungal infection?
Clotrimazole cream
Topical amorolfine nail paint
What is the treatment for an extensive fungal infection?
Oral terbinafine or itraconazole
Which areas are candida infections common in?
Under breasts, groin, abdominal skin folds, nappy area in babies
How is diagnosis of candida infection done?
Swab for culture
What is the treatment for candida infection?
Clotrimazole cream
Oral fluconazole
What are the most common examples of parasitic infections?
Lice
Scabies
How does scabies present?
Intensely itchy rash affecting finger webs, wrists, genital area
What is the treatment for parasitic infections?
malathion lotion Benzyl benzoate (not in children)
What are examples of viral diseases that present in the skin?
HSV
HPV
Varicella-Zoster virus (chicken pox)
Viral exanthems
What are examples of viral exanthems?
Enterovirus Rubella EBV Adenovirus Dengue virus HIV
What are the erythematous exanthems that tend to start on the face?
Measles (with bit of conjunctivitis)
Rubella
What are the erythematous exanthems that tend to start on the trunk?
Scarlet fever
What are the paulo-vesicular exanthems (raised bumps with fluid)?
Chickenpox
What are exanthems of the extremities?
Hand foot and mouth disease
