Intro to Infectious DIsease and Bacterial Skin Infections

Question 1

What are the three lines of defense against bacterial infections?

Answer 1

innate intracellular defense

innate cellular defense

adaptive cellular defense

Question 2

What did Fredrick Griffith’s Experiment in 1928 tell us?

Answer 2

Two types of bacteria: S (smooth) and R (rough) - only the S are infectious to mice

Inject S = mice dies

Inject heat-killed S = mice lives

Inject R = mice lives

Inject R and heat-killed S = mide dies!!!!!!!!

Showed us that DNA was the mode of genetic info transfer and showed that virulence factors can be shared among bacteria

Question 3

what is a virulence factor?

Answer 3

any molecule of a microorganism that aides in its ability to establish and maintain a pathogenic infection

Question 4

What are the steps of the pathway to infection?

Answer 4

1. exposure to pathogens
2. adherence to skin or mucosa
3. invasion through epithelium
4. colonization and growth (production of virulence factors)
5. Toxicity (toxic effects are local or systemic) and invasiveness (further growth)
6. Tissue damage = disease

Question 5

What are the three general ways damage (leading to disease) comes from in bacterial infections?

Answer 5

1. the growht of the organism itself - leading to direct cell lysis, apoptosis, and autophagy
2. toxins produced by the microorganism
3. immune system collateral damage or malfunction

Question 6

WHat are some of the ways we can classify bacteria?

Answer 6

1. gram positive or negative
2. morphology: shape and organization
3. biochemical characteristics

Question 7

What makes skin such a good barrier against bacteria?

Answer 7

it’s dry

sweat has organic acids that block colonization

Question 8

What are some common types of skin bacterial infections?

Answer 8

folliculitis
- furuncles and carbuncles form after folliculitis

impetigo

erysipelas

cellulitis

abscess

gangrene

necrotizing fasciitis

arthropod borne infections

Question 9

what is folliculitis?

Answer 9

infection of the hair follicles = small, erythematous, often puritic lesions. Local therapy is typically sufficient treatment.

Question 10

What are furuncles and carbuncles?

Answer 10

Furuncles and carbuncles usually develop from folliculitis. Carbuncles involve deeper tissues and may have systemic symptoms but rarely involve bacteremia. Antibiotic therapy and sometimes surgery are needed.

Question 11

What is impetigo?

Answer 11

superficial infection involving the epidermis usually due to group A streptococcus infection. Presents as a purulent discharge with crusting and is highly contagious

Question 12

What is erysipelas?

Answer 12

cute inflammation of the dermis involving lymphatic vessels. Usually caused by group A strep. Fever and leukocytosis may occur. Butterfly wing rash on face.

Question 13

What is cellulitis?

Answer 13

involves all layers of skin to the subcutaneous tissue. Causes fever and leukocytosis and sometimes bacteremia. Group A strep and Staphylococcus aureus most common.

Question 14

What is an abscess?

Answer 14

localized collection of purulent material (pus), formation is caused by host defenses trying to wall off the infection.

Question 15

What is gangrene?

Answer 15

advanced stage of cellulitis that has lead to significant tissue necrosis and gas in the soft tissues. Typical organisms are streptococci, mixed infection with anaerobes, and clostridial infection (classic gas gangrene)

Question 16

What is necrotizing fasciitis?

Answer 16

rare but life-threatening infection of subcutaneous tissues. Commonly caused by group A strep.

Question 17

WHat is the most common infectious agent of the skin?

Answer 17

staphylococcus aureus

Question 18

What sorts of skin infections will staph aureus cause?

Answer 18

impetigo, cellulitis, folliculitis, furuncles and carbuncles

it’s a common infectious agent of surgical wounds

Question 19

what are the general characteristics of staph auerus?

gram?

shape?

biochemical characteristics? (2)

Answer 19

it’s a gram positive bacteria

cocci in clusters

catalase positive

coagulase positive

Question 20

What three virulence factors allow staph aureus to evade the host defenses?

Answer 20

protein A - it binds the Fc portion of IgG

coagulase - forms fibrin coat to protect the organism

hemolysins and leukocidins to destroy RBCs and WBCs

Question 21

What three virulence factors allow staph aureus to invade the deep tissue?

Answer 21

hyaluronidase - breaks down connective tissue

staphylokinase - lises formed clots

lipase - breaks down fat

Question 22

What two syndromes can staph aureus cause through toxin production?

Answer 22

toxic shock syndrome

scalded skin syndrome

Question 23

WHat happens in toxic shock syndrome?

Answer 23

the toxic shock syndrome toxin -1 (TSST-1) diffuses systematically.

it’s a superantigen, so it grabs onto the MHC class 2 and forces it to interact with a naive T cell even if that T cell isn’t specific for the antigen.

This activates the T cell inappropriatly and you get massive amounts of activated T cells and massive amounts of cytokines being released

This results in actue fever, rash, desquamation on palms and soles, hypotensive shock, organ dysfunction, and possible death

Question 24

Describe scalded skin syndrom

Answer 24

this is mostly in children

exfoliative toxins ET-A and ET-B diffuse systemically

the epidermis separates and the skin sloughs off

you get associated fluid loss, secondary infections, and possible death - 50% mortality rate in adults

RItter’s syndrome is severe in neonates - it’s an umbilical cord infection

Question 25

what types of skin infections are caused by strep pyogenes?

Answer 25

impetigo

erysipelas

cellulitis

Question 26

what are the two tosin mediated syndromes that can occur in streptococcus pyogenes infections?

Answer 26

toxic shock syndrome

necrotizing fasciitis

Question 27

What is the general pathology of strep pyogenes skin infections?

Answer 27

May be normal flora of the skin.

Can colonize in the skin (following trauma) leads to colonization  inflammation  pustular lesions and honeycomb-like crusts (impetigo) at the site of inoculation. Deeper infections lead to erysipelas and cellulitis.

Question 28

Will strep pyogenes skin infections lead to rheumatic fever of glomerulonephritis?

Answer 28

glomerulonephritis

Question 29

What are the general characteristics of strep pyogenes?

gram?

shape?

biochemical? (2)

sensitivities?

Answer 29

gram positive bacteria

cocci - in chains

catalase negative! but still an aerobe!

beta hymolysis

bacitracin sensitive

Question 30

What are 6 important virulence factors for the spread and inflammation of strep pyogenes infections?

Answer 30

1. streptokinase (converts plasminogen to plasmin)
2. M protein (resists phagocytosis)

hyaluronidase (breaks down connective tissue)

DNAse (digests DNA)

Streptolysin O (destroys RBCs)

Streptolysin S (destroys WBCs)

Question 31

Where are the streptokinase and hyaluronidase of strep pyogenes encoded?

Answer 31

a lysogenized prophage

Question 32

Describe the necrotizing fasciitis that occurs in streptodoccus pyogenes infections

Answer 32

trauma allows for deep seated infection  release of exotoxin B (protease)  rapid necrosis along fascial planes with no damage to muscles

Question 33

What is bullous impetigo? What is the normal pattern of an impetigo rash?

Answer 33

bullous impetigo involves pustules in the very superficial layers of the epidermis

the normal impetigo rash is a vasicular rash with a honeycomb pattern

Question 34

What are the two situations in which pseudomonas aeruginosa skin infections can occur?

Answer 34

burn wound infection (cellulitis)

and hot tub infections (folliculitis)

Question 35

What is the preferred environment of pseudomonas aeruginosa?

Answer 35

inhabits many environments such as the soil, water, and large intestine - typically warm areas

Question 36

What are the general characteristics of pseudomonas aeruginosa?

gram?

shape?

biochemical characteristics? (3)

Answer 36

gram negative bacteria

bacilli

lactose non-fermenter

oxidase positive

glucose non-fermenter

Question 37

What is hte most common vector-borne disease in the US?

Answer 37

Lyme disease

followed by rocky mountain spotted fever

Question 38

What are the 3 stages of lyme disease?

Answer 38

stage 1: 10 days after bite - erythema migrans

stage 2: weeks later - CNS involvement, CV involvement (carditis, AV nodal block), skin involvment (secondary annular lesions), joint involvement (migratory myalgias, transient arthritis)

stage 3: months to years later: chromic arthritis, encephalopathy, acrodermatitis chronicum atrophicans

Question 39

What is the causative microorganism of lyme disease?

what are its characteristics?

shape? staining?

Answer 39

Borelia Burgdorferi

it’s a spirochete bacteria

stain with giemsa and silver stains

microaerophilic

Question 40

What is the carrier for B. burgdorferi?

Answer 40

the Ixodes tick

it will transmit the bacteria from mice to humans

Question 41

What is the causative agent of rocky mountain spotted fever?

How does this microorganism get its energy?

Answer 41

rickettsia rickettsii

it’s an obligate intracellular bacteria because it can’t synthesize its own ATP

Question 42

What is the clinical presentation of RMSF?

Answer 42

you get fever, headache, maculopapular rash on palsm and soles that spreads to the trunk over time

the bacteria infects and proliferates in endothelial cells, so you get inflammation of the endothelial lining of small blood vessles (this causes the rash).

then you get widespread vasculitis, headache, CNS changes, and possibly renal damage

cam be fatal if untreated