Microbiology practicals

Question 1

Common symptoms in patients who present with skin and soft tissue infections and abscesses.

Answer 1

Local symptoms of inflammation - pain, swelling, redness, heat/temperature and loss of function.

(Sometimes systemic symptoms such as fever, sweats and rigors may be present if the infection results in release of toxins or bacteria into the circulation)

Question 2

What is a common cause of soft tissue infection?

Answer 2

Pathogens enter the soft tissue through breaches in the skin

(Breaches may be due to skin trauma, eczema, fungal nail infections or skin ulcers)

Question 3

Cellulitis

Answer 3

A spreading infection of the skin with visually indistinct borders that principally involves the dermis and subcutaneous tissue –> commonly in an extremity

Caused by: Streptococcus Pyogenes (sometimes S.aureus and lancefield B,C,G)

Symptoms of inflammation: redness (erythema), swelling (oedematous), heat, pain (tenderness)
Sometimes there is a golden yellow crust –> indicates s.aureus

Investigation -
Blood culture
Swab surface of wound and collect pus (if there is) and send for culture

Treatment - 1st line - Flucoxacillin,

clarithromycin, Co- amoxiclav

Question 4

Erysipelas

Answer 4

A distinct form of superficial cellulitis with lymphatic involvement. It is raised and sharply demarcated from uninvolved skin

Caused by: Streptococcus Pyogenes and S.aureus

Symptoms of inflammation: redness (erythema), swelling (oedematous), heat, pain (tenderness)

Investigation -
Blood culture
Swab surface of wound and collect pus (if there is) and send for culture

Treatment - 1st line - Flucoxacillin,

clarithromycin, Co- amoxiclav

Question 5

Impetigo

Answer 5

A superficial, contagious, blistering infection of the skin. (occurs when bacteria enters a break in the skin)

Mainly caused by S.aureus and S.pyogenes (less common).

Can be either bullous or non bullous. (more common in childhood)

More common - non bullous
- Occurs around mouth or nose with EXUDATE that dries to form a golden crust.

Less common - bullous impetigo (always caused by S.aureus)
Bacteria can produce toxins that break down proteins holding skin together which result in fluid filled vesicles to form on the skin –> which grow and burst to form a golden crust

Symptoms: Crusting (yellow/golden), itching, (possible vesicles - only in bullous impetigo)

Investigations - black charcoal swab and culture
Catalase test can differentiate Strep and staph.

Treatment
1st - Flucoxacillin

MRSA - Vancomycin (Teicoplanin)

Question 6

Bacterial causes of skin and soft tissue infection in an IVDU?

Answer 6

Can get wound infections caused by S.pyogenes, S.aureus, anaerobes, gram negative bacteria

Question 7

Common causes of soft tissue/skin infection/abscess (bacteria)

Answer 7

S.aureus + (s.pyogenes)

Question 8

Common causes of lung infection/abscess?

Answer 8

S.aureus, Klebsiella pneumoniae, anaerobic organisms, mycobacterium tuberculosis

Question 9

Common causes of liver infection/abscess?

Answer 9

Gram negatives like E.coli
Strep Milleri
Anaerobes like Bacteroides fragilis

(Entamoeba histolytica)

Question 10

Common causes of kidney infection/abscess?

Answer 10

E.coli
Klebsiella

Question 11

Common causes of bowel infection/abscess?

Answer 11

E.coli
Strep. milleri
Anaerobes - bacteroides fragilis