Skin and soft tissue infections

Question 1

What is an uncomplicated ssti? List a few uncomplicated SSTIs and the type of bacteria that usually cause them

Answer 1

More superficial, not deeper than epidermis or dermis. Cellulitis, impetigo, boils, simple abscess
Gram positive

Question 2

What is a complicate ssti? List a few complicated SSTIs and the type of bacteria that cause them

Answer 2

Deeper than dermis. Decubitus ulcers, necrotizing fasciitis, gangrene
Gram negative

Question 3

Describe cellulitis and the organisms usually responsible for causing the infection and what antibiotics to use

Answer 3

It is an acute, spreading infectious process affecting the epidermis and dermis. There is inflammation but little to no necrosis. Lymphatic involvement, fever, chills, leukocytosis. Potential for bacteremia
Usually caused by staphylococcus aureus or streptococcus pyogenes. Treat with a 1st generation cephalosporin.

Question 4

What 2 organisms are most commonly responsible for wound and soft tissue infections?

Answer 4

S. aureus (20%) and enterobacteriaceae.

Question 5

A patient presents with an infected foot that is red, swollen and covered in fluid-filled blisters. They complain of intense pain. They tell you they got the injury from stepping on glass in the ocean. What causal organism would be your first guess? What is the prognosis?

Answer 5

Vibrio vulnificus. 50% of patients require surgical debridement or amputation. Bacteremia has a high mortality.

Question 6

Name 3 bacteria or groups of bacteria most commonly associated with burn infections

Answer 6

S. aureus, enterobacter cloacae, coagulase negative staph

Question 7

Name 2 bacteria commonly involved with animal bite infections

Answer 7

Pasteurella maltocida, Capnocytophaga canimorsus

Question 8

Name and describe 4 staphylococcal enzymes/toxins involved in staphylococcal infections

Answer 8

1) Coagulase: helps to establish a localized infection and protect the pathogen from phagocytosis.
2) Hyaluronidase: hydrolyzes hyaluronic acids in host connective tissue, facilitating spread of the infection
3) Exfoliative toxin (SSSS): carried on plasmis, unknown mechanism that disturbs cells ability to adhere in the stratum granulosum layer of the epidermis
4) Toxic shock toxin: superantigen responsible for toxic shock syndrome

Question 9

A baby presents with blisters and red peeling skin covering the entire body. The parents say the erythema began a day prior and started around the baby’s mouth. What is the disease, causal organism and prognosis?

Answer 9

Staphylococcal scalded skin syndrome. Caused by exfoliative toxin produced by staphylococci. Common in babies but not older people because they produce neutralizing antibodies. Scarring is not seen because the exfoliation is on a very superficial layer (stratum granulosum of the epidermis).

Question 10

Describe toxic shock syndrome

Answer 10

Usually a result of localized staphylococcal infections leading to systemic absorption of TSST-1. TSST-1 is a superantigen that directly binds with T cell receptor leading to massive polyclonal T cell activation. This may cause excessive cytokine release leading to fever, sunburn-like rash, hypotension and multi-organ failure.

Question 11

What are 4 different infections Streptococcus pyogenes can cause?

Answer 11

Phayngitis, necrotizing fasciitis, cellulitis, toxic shock

Question 12

How would you treat someone with group A streptococcal necrotizing fasciitis? Justify your choice of antibiotics

Answer 12

Give penicillin, clindamycin and IV immunoglobulin. Penicillin is used because beta hemoloytic strep are never resistant to it. Clindamycin to inhibit protein synthesis and stop toxin production. IV Ig has been found to be very effective in stopping the disease

Question 13

Describe the organism most commonly associated with dog bites.

Answer 13

Pasteurella maltocida is a small, fastidious gram negative rod. It is catalase and oxidase positive. Will grow on SBA/Choco but not MacConkey. It is intrinsically resistant to oral cephalosporins.

Question 14

Describe the organism Capnocytophaga spp.

Answer 14

Long fusoform, capnophilic, gram negative rods commonly associated with cat and dog bites. Canimorsus and cytodegmi are the most common pathogens. Can be a serious disease in asplenic and immunocompromised patients.

Question 15

What are 3 bacteria associated with cat bites?

Answer 15

Pasteurella, capnocytophaga and bartonella

Question 16

Describe Bartonella henselae. How is an infection with it diagnosed?

Answer 16

Aerobic, fastidious gram negative hemin-dependent cocco-bacilli associated with cat scratch fever and endocarditis. It is rarely cultured, diagnosed by serology.

Question 17

What antibiotics would treat an cat or dog bite with?

Answer 17

Amoxicillin and clavunlinic acid: lots of oral anaerobes, resistant to beta lactams

Question 18

Name and describe the bacteria most often associated with human bites and clenched fist injuries

Answer 18

Eikenella corrodens. Small, facultative gram negative rods. Catalase negative, oxidase positive. Requires hemin unless grown in 5-10% CO2. Doesn’t grow on MacConkey and no acid produced on TSI slants. Produces a bleachy odour on agar and pitts into the agar.

Question 19

A patient enters the ER after she was bitten by her pet rat. Name and describe the most commonly associated pathogen

Answer 19

Streptobacillus monoliformis, pleomorphic gram negative rod requiring 15% sheep or rabbit blood. Catalase and oxidase negative.

Question 20

Describe the 3 ways osteomyelitis can occur:

Answer 20

1) Directly through a skin wound communicating with bone, usually as a complication of an open fracture
2) Direct spread from a neighbouring soft tissue
3) Indirectly through the blood stream: hematogenous spread is the most common cause of osteomyelitis

Question 21

What is the difference between aseptic arthritis and osteomyelitis?

Answer 21

Aseptic arthritis is infection of the joint spaces, caused by S aureus, streptococcus spp., or gram negative bacilli.
Osteomyelitis is infection of bone caused by S aureus or S pyogenes, H influenzae or gram negative bacilli