Bacterial Infections of the Skin and Joints

Question 1

what are the two factors that influence the microbiota in different locations of the body?

Answer 1

moisture content and sebaceous glands

Question 2

why do pathogens prefer more alkaline moist conditions?

Answer 2

normal dry skin decreases bacterial colonization but in moist environments like sebaceous glands, pathogens can metabolize sebum and encourage the growth of pathogens

Question 3

what areas do Propionibacterium acnes, S. aureus and S. pyogenes prefer?

Answer 3

• sebaceous glands
• moist skin in the armpits, inguinal areas and interdigital areas or under medical dressings

Question 4

what are the distinguishing features of S. pyogenes?

Answer 4

• gram + cocci in chains, seen from systemic blood samples
• usually beta-hemolytic
• does not contain catalase (main distinguisher from staph)
• Bacitracin sensitive

Question 5

what are the distinguishing features of Staphylococcus aureus?

Answer 5

• gram + cocci in clusters, seen from systemic blood samples
• beta-hemolytic
• catalase positive
• coagulase positive (only S. aureus)

Question 6

what is MRSA and what are the two types?

Answer 6

Methicillin Resistant Staphylococcus aureus contains a mecA gene that encodes an alternative penicillin binding protein (PBP2a) resistant to all beta-lactam antibiotics
- HA-MRSA
- CA-MRSA

Question 7

what is the difference between community acquired MRSA and hospital acquired MRSA?

Answer 7

• HA: often resistant to other antibiotics, containg the mobile genetic element SCCmecII encoding more genes for resistants
• CA: contains the mobile genetic element SCCmecIV that is smaller but contains ACME for better skin survival

Question 8

what are the 3 ways ACME in CA-MRSA aid in better colonization of the skin?

Answer 8

1. NH₄- produced by arcABCD neutralizes acidic sweat pH
2. S. aureus uses ldh1 to resist NO, while arcABCD depletes L-arginine to limit NO production by host immune cells
3. L-ornithine is converted into polyamines, S. aureus expresses speG to neutralize toxic polyamines

Question 9

What is Impetigo?

Answer 9

highly contagious bacterial disease of the skin caused by S. aureus and S. pyogens

Question 10

Who does Impetigo mainly infect and what are the symptoms?

Answer 10

most common in children
- starts with one or more itchy sores, that quickly burst and become red or raw and crust over
- glands near sores may be swollen
- no scaring unless scratching cuts deep into the skin

Question 11

what is the treatment for Impetigo?

Answer 11

topical antibiotics
- mupirocin
- retapaulin

Question 12

what is Erysipelas?

Answer 12

rapid and sudden inflammatory infection of the epidermis and upper layers of the dermis caused by S. pyogenes

Question 13

who does Erysipelas infect and what are the symptoms?

Answer 13

both adults and children
- presents as redness and warmth of the skin with a defined edge and fever and malaise common
- children mainly are infected in the face
- adults mainly are infected in the legs

Question 14

what are Boils/Abcesses?

Answer 14

skin infection caused by S. aureus

Question 15

Which virulence factors allow S. aureus to survive and cause boils/abscesses?

Answer 15

• Fibronectin-binding proteins: Help bacteria adhere to skin and tissues
• Protein A: Binds Fc region of IgG to block opsonization and phagocytosis
• Coagulase: Triggers fibrin clot formation around the bacteria, shielding it from immune cells (major distinguishing factor of S. aureus)

Question 16

What are the five key steps in boil/abscess formation caused by Staphylococcus aureus?

Answer 16

• Colonization – usually in the nose
• Dissemination to skin – by sneezing or touch
• Minor trauma – like scratching or friction opens the skin
• Subcutaneous invasion – rapid spread into deeper tissue
• Boil/abscess formation – often with high pus production, but can be pus-free

Question 17

what is Cellulitis and what are the two types?

Answer 17

acute inflammation arising from infection leading to redness warmth and tenderness
- superficial involvement or deeper involvement

Question 18

what is the difference between superficial and deep Cellulitis?

Answer 18

• Superficial: involves the epidermis and upper dermis, more rapid onset with a raised edge, involving beta-hemolytic S. pyogenes
• Deep: involves the entire dermis, slower onset with subtler edge involving Streptococcus species and S. aureus

Question 19

what is Fasciitis?

Answer 19

a deep infection that spreads in a plane parallel to the skin, spares the underlying muscles and limited redness

Question 20

what is Necrotizing Fasciitis?

Answer 20

life threatening deep infection that degrades muscle producing pain, redness, fever and toxic appearance most commonly caused by S. pyogenes “flesh eating bacteria”

Question 21

what are the clinical signs of Necrotizing Fasciitis and what is the treatment?

Answer 21

• formation of gas bubbles that are palpable
• antibiotics and surgical debridement required
• clindamycin is used to disrupt production of toxins

Question 22

what are deep tissue infections common in diabetic patients?

Answer 22

• Polymicrobial infections and Gas Gangrene

Question 23

what are examples of polymicrobial infections that occur in diabetic patients?

Answer 23

• Bacteroides (Gram negative rod)
• Fusobacterium (Gram negative rod)
• Peptostreptococcus (Gram positive cocci)
• Clostridium
• facultative organisms such as Escherichia
  coli and Enterococcus faecalis

Question 24

what is Gas Gangrene?

Answer 24

Infection with gas production, tissue necrosis with gangrene – black necrotic tissue – following anaerobic conditions mainly caused by Clostridium perfringens
- crepitation on palpation and gas from fermentation of carbs

Question 25

what is Staphylococcal Scalded Skin Syndrome?

Answer 25

disease of neonates and children by S. aureus producing exfoliative toxins - usually following upper respiratory infection, inner ear infection or conjunctivitis in children - passed via umbilical in neonates

Question 26

what are the symptoms of Staphylococcal Scalded Skin Syndrome?

Answer 26

-localized blisters on over 90% of body - fever, malaise, lethargy, rash which spreads

Question 27

what is myositis and pyomyositis?

Answer 27

Purulent (pus filled) infection of muscle usually arising from systemic sepsis most commonly caused by S. aureus or beta-hemolytic streptococci (S. pyogenes) - If the bacterium is a toxin-producer there can be features such as fever, low blood pressure and organ malfunction (toxic shock)

Question 28

what are the treatments for skin infections?

Answer 28

1. Drainage: - infections with pus: * This can be accomplished surgically * For some patients, drainage will occur spontaneously - infections in deep tissues (fasciitis and myositis): * surgical drainage can be life-saving 2. Antibiotics - When streptococcus is most likely, a penicillin or cephalosporin is best - If S. aureus is likely, MRSA coverage is now essential: - Oral: Trimethoprim - sulfonamides, linezolid, doxycycline, clindamycin - IV: Vancomycin, daptomycin, linezolid, clindamycin, ceftaroline

Question 29

what are the skin infections that can arise from systemic disease?

Answer 29

- Neisseria gonorrhoeae: In disseminated disease, a small number of papular or pustular lesions may be seen (Gram stain can be useful) - Neisseria meningitidis: Dissemination to skin can occur during bacteremia - Endocarditis: Can produce metastatic lesions in skin as well as many other body sites

Question 30

What is Pasteurellosis and what causes it?

Answer 30

Infection of the soft tissues, bones or joints caused by pasteurella multocida a gram negative coccobacilli transferred to humans after an animal bite

Question 31

What are the soft tissue infections, bones and joint infections caused by Pasteurellosis?

Answer 31

Cellulitis Possible necrotizing fasciitis Osteomyelitis Septic arthritis if previous damage to joint to implants

Question 32

What is Borrelia burgdorferi and what diseases does it cause?

Answer 32

- pathogenic spirochete transferred to humans via ticks lymph’s or nymphs to cause Lyme Disease and arthritis

Question 33

What are the early symptoms of Lyme Disease and arthritis?

Answer 33

- papule appears within a month - becomes lesion with raised boarder with a bulls eye “erythema migrants” - fever, fatigue, headache, arthralgia, joint pain and neck stiffness common

Question 34

What occurs during the second stage of Lyme disease?

Answer 34

Only occurs if erythema migrants does not appear and can cause cardiac and neurological abnormalities

Question 35

What is the late stage of Lyme Disease?

Answer 35

Most common manifestation is arthritis that occurs in 2/3 of untreated patients appearing months to years later due to missed diagnosis from no typical erythema migrants rash

Question 36

What is the diagnosis strategy for Lyme Disease?

Answer 36

- history abs clinical observation - antibody titers to B. burgdorferi using immunoflorescence or RLISA - positive results can be confirmed by western blot

Question 37

What is the treatment and prevention strategy for Lyme Disease?

Answer 37

- Antibiotic treatment should be initiated as soon as possible - Doxycycline and amoxicillin are drugs of choice – also works for treating arthritis - Prevention is focused on preventing tick bites (clothing, insect repellents) - Check for ticks and remove immediately – it takes 24 hrs for Borrelli burgdorferii to transfer

Question 38

What is Septic Arthritis and what are the most common causes in children and adults?

Answer 38

* infection of a joint during sepsis or following surgery * usually affects knee or hip * most common causes in adults o Staphylococcus o Streptococcus * most common causes in children o Haemophilus influenzae – Gram-negative coccobacilli – causes pneumonia and meningitis in children especially serotype B (Hib) o Group B streptococci (Streptococcus agalactiae) – meningitis and pneumoniae in newborns