Micro: bacterial Infection

Question 1

Major virulence factor of Staph epidermidis

Answer 1

Biofilm formation

Question 2

Most common microbe in skin infections

Answer 2

S. aureus

Question 3

Honey crusted lesions

Answer 3

Impetigo

-caused by S aureus and S. pyogenes

Question 4

Cause of Scalded Skin Syndrome.

Answer 4

Exfoliative toxins produced by S. aureus

• usually infants and IC elderly patients
• mortality of the disease is due to dehydration and secondary infection

Question 5

Cause of bullous Impedigo

Answer 5

Exfoliative toxins produced by S. aureus

-localized form of Scalded Skin Syndrome

Question 6

Cause of Toxic Shock Syndrome and its general pathogenesis.

Answer 6

TSST-1 superantigen toxin released by S. aureus

• toxin induces massive immune response leading to fever, hypotension and shock, macular erythematous rash
• eventual multiple system organ failure from the shock

Question 7

Major cause of cellulitis

Answer 7

S. pyogenes infection of subcutaneous tissue

-following some type of skin trauma

Question 8

Describe the 3 types of Necrotizing Fasciitis

Answer 8

Type 1: polymicrobial, at least 1 anaerobe along with more than 1 facultative bacteria
Type 2: S. pyogenes w/ or w/o S. aureus
Type 3: Gas gangrene caused by Clostridium perfringens

Question 9

Diagnostic feature of Necrotizing Fasciitis noted on physical exam.

Answer 9

Pain that is disproportionate to the appearance of the infected area.

Question 10

Cause of Scarlet Fever

Answer 10

Complication of pharyngitis caused by S. pyogenes

-result of damage caused by pyrogenic exotoxins

Question 11

Which S. pyogenes exotoxins can cause a Toxic Shock-like Syndrome?

Answer 11

Spe A and Spe C

-both are considered superantigens that can induce a massive immune response

Question 12

Cause of Erysipelas

Answer 12

Butterfly pattern bright red rash appears on the face with raised borders due to a superficial skin reaction to the S. pyogenes exotoxin.
-there is notable lymphadenopathy

Question 13

Major causative agent of acne and the pathogenesis of the lesions.

Answer 13

Propionibacterium acnes
-excessive sebum production by hormones causes increased bacterial growth and recruitment of WBCs resulting in inflammation and pimples

Question 14

Causative agent of Hansen Disease and the two types.

Answer 14

Mycobacterium leprae

1. With good cell mediated immunity (CMI): tuberculoid leprosy
2. With poor CMI: lepromatous leprosy

Question 15

Describe the presentation of Tuberculoid leprosy.

Answer 15

Dry, blotchy, red patch lesion with associated nerve damage leading to sensation loss

Question 16

Describe the presentation Lepromatous leprosy.

Answer 16

Skin thickens and nodules form. Thickening of nostrils, ears, and cheeks with possible destruction of the nasal septum.

Question 17

Fish tank granuloma.

Answer 17

Small papule caused by infection of Mycobacterium marinum. Microbe enters thru a break in the skin.

Question 18

Folliculitis after spending time in a hot tub.

Answer 18

Pseudomonas a.

Question 19

Characteristic ulcerated skin lesion when a Pseudomonas a. infection enters the bloodstream.

Answer 19

Ecthyma Gangrenosum

Question 20

Painless black eschar

Answer 20

Cutaneous Anthrax

-caused by B. anthracis

Question 21

Describe the anthrax toxin.

Answer 21

PA is present with either EF or LF (not both)
1. Protective Antigen (PA): binds cell membrane and mediates endocytosis of EF or LF

2. Edema Factor (EF): activates adenylate cyclase increasing cAMP and disrupting water homeostasis
3. Lethal Factor (LF): induces cellular apoptosis

Question 22

Unique structural feature of B. anthracis

Answer 22

Glutamic acid capsule

Question 23

Virulence factors of N. meningitidis

Answer 23

Capsule
LOS
Pili

Question 24

Lab test to differentiate the two major Neisseria species.

Answer 24

meningitidis metabolizes maltose and glucose

gonorrhoaea metabolisms only glucose

Question 25

Complication of Meningococcemia caused by N. meningitidis.

Answer 25

Waterhouse-Friderichsen syndrome

-bilateral hemorrhage of the adrenal glands causing coma and death

Question 26

Copper colored rash over entire body.

Answer 26

Sequelae of secondary Syphilis (Treponema pallidum)

Question 27

Describe the progression of Lyme Disease

Answer 27

Infection by Borrelia burgdorferi

1. Stage 1: erythema migrans (bullseye rash at tick bite site)
2. Stage 2: arthritis, fatigue, Bell Palsy, meningitis, peripheral neuropathy, AV node block
3. Stage 3: chronic arthritis, encephalopathy

Question 28

Pathogenesis of Rocky Mountain Spotted Fever.

Answer 28

Rickesttsia rickettsii infects phagocytes

• spreads to vascular endothelium where it infects the endothelial cells
• causes a rash that begins on the hands and feet and spreads inward toward the trunk (cenTRIPETAL spread)
• vector is a tick

Question 29

Pathogenesis of Scrub Typhus.

Answer 29

Orientia tsutsugamushi infects endothelial cells causing an itchy rash that starts on the trunk and spreads to the extremities (cenTRIFUGAL spread)

Question 30

Pathogenesis of Gas Gangrene

Answer 30

Clostridium perfringens infects a deep cut

• bacteria use alpha toxin (lecithinase) which breaks down lipid cell membranes primarily in muscle cells
• also produces gas bubbles leading to a crepitus sound noted on physical exam
• considered a form of necrotizing fasciitis so the presentation will be pain out of proportion to the appearance of the lesions

Question 31

Infectious agent causing a lesion, by gram positive rod, after coming into contact with contaminated meat or animals.

Answer 31

Erysipelothrix rhusiopathiae

Question 32

Wound exposed to salt water.

Answer 32

Vibrio vulnificus

-can cause systemic disease with a 50% mortality rate if untreated

Question 33

Describe the pathogenesis of Cat Scratch Fever.

Answer 33

Infection by Bartonella henselae

• bacteria grow intracellular causing inflammatory reaction
• in IC patients can progress to Bacillary Angiomatosis with cutaneous papules resembling Kaposi sarcoma

Question 34

Bi-polar staining and bone pain.

Answer 34

Infection with Pasteurella multocida

• usually from dog or cat bite
• infection causes osteomyelitis