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Microbiology 2 > M9 Wound Infections > Flashcards

M9 Wound Infections Flashcards

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1
Q

What is normal flora for the skin?

A
  1. Diphtheroids (Corynebacterium & friends)
  2. Staphylococcus epidermidis
  3. Other coagulase-negative staphylococci
  4. Cutibacterium acnes

Note: Even S. aureus could be normal flora in small amounts.

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2
Q

What kind of organisms can infect wounds?

A

Bacteria, parasites, fungus & viruses. Toxins too!
Very diverse and complex, only main ones for us.
Can come from outside (invasion) or from blood

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3
Q

Do physicians often seek lab culture for wound infections? What do they rely on?

A

Physicians rely on appearance, and seek for culture when needed

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3
Q

What is the pathogenesis of superficial wound infections?

A
  1. Trauma or systemic spread.
  2. Local inflammation and immune response.
  3. Invasion of epithelium.
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4
Q

What epidermis infection is common in kids and what organisms typically cause it?

A

Impetigo, Erythematous lesion that may be bullous or nonbullous

Typically caused by S. aureus (bullous) or S. pyogenes (Gr. A - nonbullous).

Mostly a rash on the face (near mouth and nose).

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5
Q

What type of infections can be in the dermis (between the epidermis and the subcutaneous fatty region?

A

Dermis
“erysipelas”
“cellulitis

Note: Cellulitis - diffuse spreading infection involving deep layers of dermis

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6
Q

What region of the skin does cellulitis occur in?

A

Subcutaneous

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7
Q

What infections of the hair follicles can occur? Describe each of them.

A

Infection of Hair follicles
1. Folliculitis—(minor infection of hair follicles) Papules or pustules that are pierced by a hair and surrounded with redness
2. Furnuculosis (boil)
Abscess that begins as a red nodule in a hair follicle that ultimately becomes painful and full of pus
3. Carbunculosis - Furuncles that coalesce and spread more deeply to the dermis and subcutaneous tissues; they usually have multiple sites, which drain to the skin surface (sinuses)

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8
Q

What organisms can cause a papule skin infection?

A

Agents: Human papillomavirus (HPV), pox virus, scabies, Staphylococcus aureus, and Pseudomonas aeruginosa

Note: Papule is a elevated, solid lesions, smaller than nodule.

**Mariela highlighted as important for our lab.

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9
Q

What organisms can cause a nodule skin infection?

A

Agents: Corynebacterium diphtheriae**, Sporothrix schenckii, fungi,
Mycobacterium marinum, and Nocardia spp.

Note: Nodule is a raised, solid lesion, larger

**Mariela highlighted as important for our lab.

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10
Q

What kind of organisms can cause a pustule skin infection?

A

Agents: Candida spp., dermatophytes, herpes simplex virus (HSV), Neisseria gonorrhoeae, S. aureus, Group A streptococci, and varicella-zoster virus

Note: A pustule is a Raised, pus-filled lesion containing leukocytes and fluid

**Mariela highlighted as important for our lab.

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11
Q

What anaerobe is known to cause a ‘Bulla’? What other causative agents are there?

A

Clostridium spp.*,

Other causative agents:
HSV, gram-negative rods, S. aureus, and vibrios*

*Mariela highlighted as important for our lab.

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12
Q

What is the condition called that results in lesion with the loss of epidermis and dermis? Typical causative agents?

A

Ulcer

Agents: Bacillus anthracis, bowel flora, Haemophilus ducreyi, and Treponema pallidum

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13
Q

What two organisms typically cause cellulitis? What other organisms can also cause it (less commonly)?

A
  1. S.aureus
  2. S.pyogenes

Less common:
- Aeromonas spp.
- Vibrio spp.
- Haemophilus influenzae

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14
Q

What does Erysipelas infection look like on the skin? Symptoms?

A
  1. Painful, red, and swollen indurated lesions. (Induration is the thickening and hardening of soft tissue as a result of the inflammation process).
  2. Symptoms: Fever & regional lymphadenopathy
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15
Q

What organisms typically are involved in a erysipelas infection of the skin?

A

Etiologic factors
1. Group A streptococci
2. Sometimes group B, C, or G streptococci

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16
Q

What organisms often causes a chronic infection of the keratinized layer of the epidermis?

A

Infection is called Erythrasma

Agent: Corynebacterium minutissimum

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17
Q

What condition and its appearance is the organism Erysipelothrix rhusiopathiae
associated with?

A

Erysipeloid: Purplish, nonvesiculated skin lesion with an irregular, raised border.

Causes “erysipeloid” lesions in humans.

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18
Q

What is dermatophytosis?

A

Dermatophytosis—Fungal infection of the skin

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19
Q

What does Erysipelothrix rhusiopathiae look like (morphology) on a gram stain?

A

Erysipelothrix rhusiopathiae:
- small, slim rod or curved filamentous, Gram positive

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20
Q

What does Erysipelothrix rhusiopathiae produce and what damage to a person can it do?

A

Produce enzyme that may cause vascular damage/thrombosis
transmission: contaminated food, water, carrier pigs (occupational)
Erysipelothrix primarily swine associated

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21
Q

How is the organism that causes Erysipelothrix transmitted and what environment/animal is it associated with?

A

Transmission: contaminated food, water, carrier pigs (occupational)

Erysipelothrix primarily swine associated.

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22
Q

What is necrotizing fasciitis and what organisms typically cause it?

A

Muscle fascia and soft tissues become infected. Large areas of the body may become infected in a short amount of time.

Typically involves group A streptococci or Staphylococcus aureus.

23
Q

What is ‘Progressive bacterial synergistic gangrene’ typically a result of?

A

Chronic necrotic condition of the skin as a result of surgery

24
Q

What organism(s) are typically involved in ‘Progressive bacterial synergistic gangrene’?

A

Is usually polymicrobic with microaerophilic streptococci and S. aureus

25
Q

What is inflammation of the muscle called and its common cause?

A

Myositis - Is inflammation of the muscle. Most common cause of hematogenous spread is S. aureus

26
Q

What organisms are typically involved in an infection caused after an operation?

A

Postoperative infections: Typically include the patient’s normal microbiota or nosocomial organisms
Agents:
- Staphylococcus aureus (most common),
- gram-negative bacteria,
- anaerobes, and
- enterococci

27
Q

If a human bites another person, what organisms (i.e. their normal flora) can infect the other person?

A

Human bites or closed-fist injuries involve normal oral flora:
- viridans Strep,
- S. aureus,
- Eikenella corrodens,
- anaerobes

28
Q

What organisms from a cat or dog bite can cause an infection?

A

Animal bites are most often from domestic cats and dogs
Agents of animal bites include Pasteurella, Strep, Staph and Fusobacterium

29
Q

What are four type of skin infections related to burns the common infecting agents involved?

A

Four types are identified: impetigo, surgical, cellulitis, and invasive (systemic?)
Common agents:
- S. aureus,
- Pseudomonas aeruginosa,
- enterococci,
- Enterobacter spp., and
- Escherichia coli (Enterobact-erales)
Also some multidrug R including Acinetobacter or Stenotrophomonas (from hospital long-stays), also fungus and viruses

30
Q

What other condition is burn wound infections associated with?

A

Bacteremia

Infected burn wounds may be associated with bacteremia

31
Q

What is Pasteurella spp. morphology on a gram stain?

A

Gram negative coccobacilli (tiny!)

32
Q

What is the oxidase test result for Pasteurella spp. and does it grow on MAC?

A

Oxidase - Positive
Does not grow on MAC.

Note: Most common species is multocida but there are others…
Normal flora in animal’s mouth.

33
Q

Do you perform AST on Pasteurella?

A

No, AST is not done routinely: susceptible to Penicillin.

34
Q

What type of cellulitis/organisms is often associated with the extremities in Diabetes patients?

A

Anaerobic cellulitis is often identified in the extremities

35
Q

What infections can Diabetes patients have as a result of Diabetes related vascular or neurologic problems?

A

Foot infections ~ 25% of those with diabetes will develop a foot infeciton.

Excess glucose can result in impaired circulation and peripheral motor neuropathy

36
Q

What organisms are commonly associated with foot infections in Diabetes patients?

A

Common causes of diabetic foot infections:
1. Staphylococcus aureus
2. Group B streptococci
3. Enteric pathogens
4. Anaerobes

37
Q

What is the name and source of an organisms that can cause a wound infection and is GNB with one round end and one tapered?

A

Capnocytophaga spp: normal flora in dog’s mouth.

38
Q

What is suitable media and incubation temperature for Capnocytophaga spp.? What media does it not grow on?

A

Enriched media, incubated in CO2 (required).

No growth on MAC.

39
Q

What is the name and source of an organism that is known to pit the agar and smell like bleach?

A

Eikenella corrodens - Normal flora in mouth.

Infections in bites from humans, clenched-fist wounds, IV users that lick area or needle. It is the “E” in HACEK organisms

40
Q

What are the gram smear, culture and chemical test(s) that characterize Eikenella corrodens?

A

GNB, oxidase +,
No growth on MAC,
slow on BA-CA. Prefers CO2.

41
Q

What other typical culprits of wound infections is known to have toxigenic strains and needs to be sent to the reference for toxin testing?

A

Corynebacterium diphtheria, ulcerans and pseudotuberculosis (toxigenic strains).

if these species found, need to be sent to Reference Lab for Toxin test.

42
Q

What is the proper collection procedure for getting a micro lab sample from a surface wound infection?

A
  1. Collection surface decontaminate
  2. Sample from the active or growing edge of the wound
43
Q

If the wound infection is deep what other type of lab specimen is collected?

A

When lesions are deep, blood cultures done.

44
Q

What is the first step in analysis when a wound infection specimen is received in the micro lab?

A

Direct Gram Stain
1. Smear to be evaluated for polymorphonucleur cells.
2. Correlation with microorganism seen and primary plate growth
3. if direct smear does not correlate with growing culture, direct smear should be rechecked.

45
Q

What media are used for wound specimens for culturing?

A

BA and Mac. Add CA for bites & abscesses

Liquid broth such as thioglycolate or FAB (ONLY if aspirated and deep specimen was collected)

46
Q

What are the ingredients in thioglycolate or FAB broth and their purpose?

A
  1. Dextrose, peptones, yeast extract (energy sources)
  2. Sodium thioglycolate (reducing agent, consumes O2)
  3. Methylene blue/resazurin are atmospheric indicators
  4. Small amount of agar (O2 stops)
  5. Vitamin K (extra growth factor)
47
Q

How long are wound cultures kept before they are declared as ‘no growth’?

A

Routinely no growth cultures are re-incubated and kept for a period of 48-72hrs.

48
Q

What do you do if the broth shows organisms growing but there is no growth on the plates?

A

Broth growing but no growth on plates –> gram and subculture to plates (with media based on gram stain).

49
Q

When is the next step to work up the culture plates on wound infections for ID?

A

Plates and broth growing –> work up plates!

50
Q

What do you do if the direct smear shows pus 3+ but there is no growth on the plates?

A

if pus 3+ or greater and culture plates no growth re-incubate for longer (up to 5 days).

51
Q

What is the two main critical cases in wound infections to phone ASAP?

A

In general not critical UNLESS it is:
1. Necrotizing fasciitis diagnosis: in this case phone ASAP!
2. Or if the reported organism is listed as reportable or has an antimicrobial resistance that makes it critical: MRSA, VRE, carbapenemase, etc.

52
Q

What are the three basic criteria for determining how to report organisms cultured from wound specimens?

A
  1. Whether microorganism is a common wound pathogen
  2. Number of isolates and
  3. Amount of growth
53
Q

What organisms do you ID & do AST (if appropriate) if they are in any amount on a wound specimen culture?

A

S. aureus,
P. aeruginosa,
S. pyogenes or
Other beta-hem and
P. multocida (pure culture or not).

Also, less common:
- Aeromonas,
- Eikenella,
- Capnocytophaga,
- Vibrio.

54
Q

What are the common skin contaminants found in wound specimen collecitons?

A

Coagulase negative Staph, Viridans Strep, Cornyebacterium spp. and Micrococcus spp.

Note: This is a repeat question, but last time I did not see Micrococcus spp. mentioned.

55
Q

If an organisms is not a common wound pathogen what are the lab guidelines for determining what to do a full ID and AST on?

A
  • If PURE culture and growing 3+ or 4+ , ID and AST anything growing.
  • If PURE culture, and growing small amounts (1-2+) and the usual skin contaminants are presumptively ID (my words), you do not need full ID or AST
  • If not a pure culture and 2 isolates present–> ID and AST the common pathogens + Enterobacterales & Enterococcus IF predominant.
  • If 3 or more isolates present, ID and AST only the common pathogens. The rest are “listed” (minimal work to see if they are possible pathogens).

Note: Check wording on this to make sure point#2 is not taken the wrong way.

Microbiology 2 (22 decks)

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