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421 - Micro Lab > Wound & Skin > Flashcards

Wound & Skin Flashcards

1
Q

Normal skin biota

A

Inhibit pathogens: compete nutrient, decrease pH
Mostly GP: Staph, diphtheroid, Propionibacteria/Cutibacterium, Candida
Significant/transient: Staph. aureus

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2
Q

Primary skin infection

A
  • Dermatitis
  • Pyoderma
  • Cellulitis/Abscess
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3
Q

Dermatitis

A
  • Intertrigo: Epidermis, rash - Candida, S. aureaus - Baby, obesity
  • Superficial candidiasis: Mucosa, mouth, genital - Candida - Antibiotic treatment, immunosuppressed
  • Tinea: Keratinized surface (skin, nail, hair) - Mold - Cooler temp is a reason
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4
Q

Pyoderma

A
  • Folliculitis: Hair follicle - S. aureus, P. aeruginosa - Adults - Shaving, hot tubs
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5
Q

Cellulitis & Erysipelas

A
  • One of the most common skin and soft tissue infection
  • Bac entry via breaches in the skin barriers
  • Skin erythema, edema, warmth
  • Cellulitis: deeper dermis & subcutaneous fat
  • Erysipelas: Upper dermis and superficial lymphatis
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6
Q

Skin abscess

A
  • Painful, fluctuant, erythematous nodule
  • Can develop via deep infection of a hair follicle: furuncle (boil) –> coalesce to form carbuncles
  • Back of neck, face, buttocks
  • Common in adults, body hair and obesity
  • S. aureus (MRSA)
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7
Q

Microbiology of primary skin infection

A
  1. Cellulitis:
    - Beta-hem strep (A, B, C, G, F) and group A is most common
    - Also S. aureus, GNR
  2. Erysipelas
    - Mostly beta-hemolytic strep
    - Erysipethrix rhusiopathiae: meat/fish handler
  3. Abscess
    - > 75% due to S. aureus
    - Can be caused by mixing culture
    - Oral bacteria can be found in injection site
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8
Q

Secondary

A

Bite, Burns, Diabetic Foot infection, Wound, Nodular lymphangitis, necrotizing fasciitis, gangrene

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9
Q

Human bites

A
  • Human oral bacteria: (aerobic, anaerobic) Stap. aureus, Streptococci
  • Primary pathogens: S. aureus, Strep. (A, S, agninosis) , Clostridium, Eikenellea, Prevotella, Peptostreptococccis, Fusobacterium,
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10
Q

Specimen processing

A
  1. Superficial Wound (non-sterile):
    - Swab, aspirate, biopsy
    - Gram stain & aerobic only
  2. Deep Wound (sterile):
    - Aspirate, biopsy, tissue
    - GS, aerobic, ana, broth. Isolation of fastidious/ana organism
  3. Tissue
    - Biopsy, tissue
    - GS, aero, ana, broth. Isolation fastidious/ana organism
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11
Q

Specimen collection

A

Transport: deliver aspirate and tissues to the lab within 30 min - RT

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12
Q

Primary agents of skin & soft tissue

A 
Staphylococcus aureus
Beta-hemolytic streptococci
Pseudomonas aeruginosa
Enterobacteriaceae
Anaerobes
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13
Q

Culture work up

A
  • Read plate daily
  • ID up to 3 organism if: PMN present, specimen from sterile site, no or low epi cells, organism seen on direct GS
  • Minimal testing to indicate the type of microbiota for noninvasively collected specimen if: numerous of epi cells, no evidence of infection, more than 3 organism in the culture
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14
Q

Skin flora

A 
Diphtheroids
Coagulase-negative staphylococcus
Yeast
Viridans groups strep
Enterococci
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15
Q

GI flora

A

GNR
Gram-positive aerobic organisms (including Yeast)
Anaerobes

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16
Q

Oral/mouth flora

A 
Diphtheroids
Coagulase-negative staphylococcus
Yeast
Viridans group strep
Enterococci
Rothia
Strep. anginosis (milleri) group
Haemophilus spp.
Lactobacillus
Eikenella
Capnocytophaga
17
Q

Potential Pathogens

A 
Beta-hem streptococci
S. aureus
Pseudomonas aeruginosa
Stenotrophomonas maltophilia
Clostridium perfringens
Actinomyces (hold plates 14 days)
Unusual: Vibrio, Listeria, N. gonorrhoeae, bioterroism 
NLF GNR
18
Q

CFS - Specimen handling

A
  • Micro. tube (tube 3) remain at RT prior to culture
  • Do not refrigerate CSF unless for viral study (Haemophilus, Neisseria, S. pneumoniae) are sensitive to cold temp.
  • Process CSF immediately (GS & culture = STAT test)
19
Q

CSF - Lab Routine test

A
  • Smear & culture on concentrated CSF (cytocentrifuge): sediment for culture, supernatant for other tests (chem, PCR)
  • Smear is used for: bacteria, fungi, WBC, RBC. Report of GS is positive
  • Culture always must be cultured: inoculate onto BA, CA, BHI. If from shunt/drain: add anaerobic plate with 14 days incubation
20
Q

CSF culture - analysis

A
  • If NG on media/BHI, continue reincubate for 3-7 days

- If Pos, proceed GS, spot test, MALD-TOF, do full ID and susceptibility

21
Q

Other Dx for CSF

A
  • Direct CSF latex agglutination for: C. neoformans, H. influenzae, N. meningitis, E. coli, S. pneumoniae, Group B Strep.
  • Direct: 16S rRNA for bacteria, 28S for fungal,
22
Q

Sterile eye fluid infection

A
  • Endophthalmitis: bacterial/fungal infection in vitreous and aqueous humors
  • Uveitis: infection caused by virus/parasite
23
Q

Endophthalmitis cause

A
  • Exogenous: trauma, eye surgery, extension of keratitis. Aqueous –> vitreous
  • Endogenous: bacteria, fungi seed the eye
24
Q

Endophthalmitis Dx

A
  • Positive aqueous, vitreous, biopsy

- Small volume

25
Q

Endophthalmitis pathogen

A 
Coagulase-neg Staph
S. aureus, Strep
Viridans Strep
Bacillus cereus
Haemophilus influenzae, Moraxella catarrhalis
26
Q

Peritonitis

A
  • Inflammation of the peritoneum caused by an infection
  • Dx: peritoneal fluid
  • Types: Spontaneous bacterial, Peritoneal dialysis, Secondary and Peritonitis
27
Q

Spontaneous bacterial peritonitis

A
  • Unknown source: monomicrobic, often caused by aerobic
  • GS; aerobic (anaerobic culture lower yield)
  • Inoculate to blood culture bottle
  • IDSA suggests: at least 10mL (not swabs of fluid)
  • Culture neg but evidence of infection –> suspect fastidious, slow growth, fungi, etc.
28
Q

Peritoneal dialysis associated peritonitis

A
  • Evaluation of dialysis fluid
  • Monomicrobic, aerobic
  • Agents:
    + GP: Staph, Strep, Coryn
    + GN: E. coli, Klebsiella, Enterobacter
    + Anaerobes, fungi (<10%)
  • Culture neg > 20% case
  • 10-15mL of dialysate
  • Additional test for fastidious & slow growth
29
Q

Secondary peritonitis

A
  • Caused by medical, accidental trauma
  • Polymicrobic, anaerobic
  • Agents:
    + GNR (ae/ana): Bacteroides, E. coli, Klebsiella
    + GP: Clostridium, Enterococcus, Bifidobacterium, Peptostreptococcus
    + GPC and yeast
  • Dx: GS, aerobic/anaerobic culture. Blood culture is not helpful
30
Q

Pleural space infection

A
  • Fluid collected by thoracentesis
  • GS, culture: Blood culture increase yield. Cell count, pH, protein, etc
  • Community-acquired: S. anginosus group, S. aureus, anaerobes, Strep, Enterobacteria, S. pneumoniae
  • HAI: Enterococcus, S. aureus, Strep (anginosus, pneumoniae), anaerobes.
31
Q

Joint infection

A
  • Common agent: S. aureus, Strep
  • GNR: neonates, elderly
  • Virus: parvovirus B19, rubella, Chikungunya
  • Subacute/chronic infection: M. tuberculosis, Borreia burgdorferi, fungi
  • Dx: collect synovial fluid –> GS, culture, cell count/diff
32
Q

Prosthetic joint infection

A
  • Knee, hip, shoulder, elbow
  • Common: S. aureus, Coag-neg staph, S. epidermidis
  • Others: Strep, enterococci, aerobic GNR, anaerobes
  • Cutibacterium acnes (shoulder arthroplasty infection)
  • Tissue culture: multiple specimens for aerobic, anaerobic culture
  • Intraoperative or a combination of preoperative and intraoperative: yield the same organism –> evidence.
33
Q

Intraamniotic infection

A
  • Infection of amniotic fluid, membranes, placenta, etc.
  • Migration of cervicovaginal flora thru cervix (polymicrobial: vaginal, enteric)
  • Hematogenous spread from maternal bacteremia (monomicrobial: Listeria, S. aureus)
  • Genital mycoplasms
  • Others: anaerobes (Gardnerella vaginalis, Bacteroides), enteric GNR, Group B Strep
  • Dx: clinical fever, elevated WBC, purulent fluid. Confirmed with positive GS, culture, low glucose
34
Q

Hugh-Leifson O/F medium

A
  • Fermenter: produce acid in both conditions (turn yellow)
  • Oxidative: acid only in aerobic (turn yellow only opened tube, the other is green)
  • Asaccharolytic: no media change (both green)

421 - Micro Lab (6 decks)

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