Bacterial Virulence/Microbiology Flashcards by Niamh Berry

Virulence factor

Specific component of pathogen that causes disease

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Staphylococcus tends to cause infection through what?

Sebaceous glands and hair follicles

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Streptococcus tends to cause infection through what?

Damage in the skin

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Why is staph aureus an effective pathogen?

It has many different virulence factors

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Skin infections caused by staph aureus

Rash
Folliculitis
Abscess
Carbuncle
Impetigo
Scalded skin syndrome

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Toxinoses caused by staph aureus

Toxic shock

Scalded skin syndrome

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Where is staph epidermidis usually found in the human body?

Skin and mucous membranes, as well as intestinal tract

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When does staph epidermidis usually cause infection?

Tends not to cause infection unless person is immunocompromised, but can be associated with foreign devices associated with hospitals, e.g. catheters, cannula etc.

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2 common sites for staph aureus

Nasal passages and perineum

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Patients high risk for MRSA

Elderly and immunocompromised
Intensive care patients
Burns patients
Surgical patients

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Toxinoses

Discrete disease associated with a single protein component, a toxin or exotoxin

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Scalded skin syndrome:

Which age group is it normally found in?
Where does it usually occur on the body?
True or false - it is self-limiting

It is normally found in neonates
It usually occurs on the face, axilla and groin
True - it is self-limiting

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In scalded skin syndrome, which toxins target what?

ETA and ETB toxins target desmoglein-1

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Why is skin continuously shed from the body in scalded skin syndrome?

The toxin interferes with keratin cross-bridges

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True or false - TSST-1 which causes toxic shock syndrome has a slow progression

False - it has a rapid progression

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Symptoms of toxic shock syndrome

High fever
Vomiting
Diarrhoea
Sore throat
Muscle pain

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Superantigen

Type of antigen that results in excessive activation of the immune system - activate 1 in 5 T cells rather than 1 in 10,000

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Example of superantigen

TSST-1

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Diagnostic criteria for toxic shock syndrome

Fever 39˚
Diffuse macular rash and desquamation (“sunburn”)
Hypotension
≥3 organ systems involved

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How long can it take for toxic shock syndrome to cause death

Hours

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Adhesins

Extracellular matrix molecules that are present on epithelial, endothelial surfaces and as component of clots

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Types of adhesins

Fibrinogen binding
Fibronectin binding
Collagen binding

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Panton-Valentine Leukocidin has specific toxicity for which type of cell?

Leukocytes

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What is necrotising pneumonia?

Severe complication of quite mild infections due to destruction of immune cells

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What can necrotising pneumonia cause?

Respiratory distress and deterioration in pulmonary function Refractory hypoxaemia Multi-organ failure (all despite antibiotic therapy)

Which protein is key for evasion of host defences for staph aureus?

Protein A

How does protein A cause evasion of host defences?

Protein A binds antibodies the wrong way round and interferes with the marking of the cell for destruction

Which bacteria causes impetigo?

Group A streptococci

Entry point for impetigo

Small defect in skin

Which layer of the skin does impetigo tend to be limited to?

Stratum corneum

Treatment for impetigo

Improve hygiene and prescribe topical antimicrobials

Who tends to get impetigo?

Children and areas of poor hygiene

True or false: impetigo is not very contagious

False - it is highly contagious and can spread through contact with discharge on face, and scratching due to irritation

Which bacteria causes cellulitis?

Group A streptococci

Which layer of the skin does cellulitis affect?

Dermis and subcutaneous fat

Clinical features of cellulitis

Fever, rigors, nausea, redness, swelling

Which bacteria causes type 1 and type 2 necrotising fasciitis?

Type 1 = clostridia spp. | Type 2 = S pyogenes and S aureus

Diagnosis of skin infections

Often clinical Swab of surface if lesion is broken Pus or tissue if deeper lesion Blood cultures if systemically unwell

Colour of staph aureus and coagulase negative staph

Staph aureus = golden | Coagulase negative staph = white

Bacteria that may be commensals

Staph epidermidis Corynebacterium Propionibacterium

Antibiotic of choice for staph aureus

Flucloxacillin

Types of staph aureus toxins that can cause severe illness

Staphylococcus scalded skin syndrome (SSSST) Panton Valentine Leucocidin Food poisoning (enterotoxin)

Conditions that staph aureus causes

``` Boils and carbuncles Minor skin infections Cellulitis Infected eczema Impetigo ```

Skin and soft tissue options for MRSA treatment

Doxycycline oral Co-trimoxazole Clindamycin Linezolid

Side effects of clindamycin and linezolid

Clindamycin - can cause C.diff | Linezolid - associated with anaemia

Bactericidal options for MRSA treatment

Vancomycin | Daptomycin

Conditions caused by group A strep infection

``` Infected eczema Impetigo Cellulitis Erysipelas Necrotising fasciitis ```

Treatment for strep pyogenes

Penicillin

Treatment for necrotising fasciitis

Immediate surgical debridement and antibiotics

When are swabs taken for leg ulcers?

Only if cellulitis or infection are present

Fungal skin infections

Candidiasis Tinea - ringworm, athletes foot Pityriasis

Dermatophytes

Fungi that require keratin for growth

What type of skin do dermatophytes tend to enter?

Abraded/soggy skin

Which gender is most commonly affected by dermatophytes?

Males

Diagnosis of dermatophytes

Clinical appearance Woods light Skin scrapings (from scaly edge of lesion), nail clippings, hair

Treatment for small areas of infected skin, nails by dermatophytes

Clotrimazole (most common) | Topical nail paint

Where does candida cause infection?

In the skin folds where the area is warm and moist

Diagnosis of candida

Swab for culture

Treatment for candida

Clotrimazole cream, oral fluconazole

What causes scabies?

Sarcoptes scabiei

Crusted form of scabies

Norwegian scabies - highly infectious

Incubation period of scabies

Up to 6 weeks

Clinical features of scabies

Intense rash affecting finger webs, wrists and genital area

Treatment for scabies

Malathion lotion

Pediculis capitis

Head lice

Pedicuis corposus

Body lice

Patients with which infections require single room isolation?

Group A strep MRSA Scabies

Erythematous exanthems which tend to start on face

Measles Rubella Erythema infectiousum

Erythematous exanthems which tend to start on trunk

Roseola Scarlet fever Unilateral laterothoracic exanthem

Papulo-vesicular exanthems

Chicken pox | Gianotti-crosti syndrome

Exanthems of the extremities

Hand, foot and mouth disease

Direct methods of diagnosing viruses

``` Virus isolation (culture) Genome detection (PCR) Antigen detection ```

Indirect methods of diagnosing viruses

Serology IgM | Serology IgG