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Infectious Disease > Bacterial disease testing > Flashcards

Bacterial disease testing Flashcards

1
Q

Why are cultures performed?

A
  • confirm a dx
  • exclude a dx
  • screening
  • monitor the course of a disease
  • monitor response to therapy
  • stage the severity of the disease
  • provide a prognosis
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2
Q

How can results of a culture be altered?

A
  • Collection methods: swab, aspirate, expectorant
  • physiologic variables
    transient bacteremia
  • meds: especially abx
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3
Q

General culture interpretation guidelines

A
  • ## as a general rule: infection considered if >10^5 organisms found
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4
Q

How long does it take cultures to grow?

A

1 full day to grow the organism and then part or all of 1 day to ID it. It may take an add. day to isolate it b/f ID if there is a mix of organisms.
- a preliminary report for most cultures may be issued in 24 hours

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5
Q

What is important to ID from the infectious organisms?

A
  • normal flora from the infection

- normal flora and pathogens vary dependent on anatomic location

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6
Q

What is normal flora on the skin?

A

staph epiermidis, S. aureus, micrococcus, few gram - bacilli moist skin, corynebacterium, propionibacterium acnes

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7
Q

Pathogenic organisms on the skin?

A

strep. pyogenes
pseudomonas
proteus

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8
Q

Pathogens in the mouth?

A

strep pneumoniae, strep pyogenes, Neisseria meningitidis, H. influenza, N. gonorrheae

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9
Q

Potential pathogens and pathogens of oropharynx?

A

potentials: mycoplasma, bordatella pertussis, many others
pathogens: staph aureus, pseudomonas

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10
Q

normal flora in conjunctiva?

A

corynebacterium, Neisseria, moraxellae, staph, strep, occasional Haemophilus and parainfluenza

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11
Q

Pathogens of the conjunctiva?

A

pneumococcus, pseudomonas, strep

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12
Q

pathogens of the GI tract?

A

C. diff, salmonella, toxic strains of E. coli, Helicobactor pylori (in duodenum)

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13
Q

Pathogens of anterior urthera?

A

chlamydia, gonorrhea, syphilis

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14
Q

What does the normal flora of the vagina depend on?

A
  • varies with hormonal state
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15
Q

Pathogens of the vagina?

A

candida, trichomonas

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16
Q

What are important steps to collecting a specimen and achieving the highest diagnostic yield?

A
  • obtain specimen before abx
  • use strict aseptic technique
  • minimize contamination by skin and mucous membranes (be careful with swabbing)
  • collect an adequate volume and send tissue or fluid rather then a swab when possible (culture when possible)
  • label appropriately
  • fill out requisition slips completely and precisely
  • call microbio dept if you have any ???s
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17
Q

within how many hours of collection should samples arrive in the lab?

A

within 1-2 hours of collection, but if delay is unavoidable most specimens (except blood, CSF

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18
Q

Culture turnaround times?

A

blood cultures: 48-96 hours
most routine cultures (urine, throat, sputum): 24-48 hrs unless looking for unusual bacteria
- anaerobes: can take 48-72 hours

  • almost always get gram stain with culture in most settings
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19
Q

appropriate culture media?

A
  • routine: blood agar
  • chocolate agar -> gram negatives (GC & Haemophilus)
  • anaerobic blood agar: needs to be fresh
  • sabourad agar: fungi
  • GPS -> gram + selective media -> allows isolation of strep and staph and inhibits most gram - rods
  • MacConkey or eosin methylene blue agars: anaerobic gram - rods
  • Thioglycollate media: liquid media, enrichment broth used as supplement to plated media
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20
Q

Process of wound culture?

A
  • usually pus present
  • round up some pus on an applicator
  • culture of specimens from the skin edge is less accurate than culturing the suppurative material
  • if anaerobic organism suspected -> get anaerobic culturette from lab
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21
Q

Culture of abscess/boil/furuncle

A
  • incised and any fluid or material swabbed with culture swab and sent to lab
  • important to get pus/exudate from deep in the wound to avoid surface contamination
22
Q

Culture of the eye-> conjunctiva

A
  • gently swab to collect drainage

- place in approp. container and send to lab at 25 degrees C

23
Q

How to obtain throat cultures? when are these done?

A
  • done to rule out strep pharyngitis (GABS)
  • sore throat, inflamed tonsils
  • inform lab if trying to ID something else such as N. gonorrheae (this reqrs Thayer-Martin agar)
  • swab posterior pharynx and tonsils
  • avoid touching any other part of mouth
  • send to lab at 25 degrees C
  • often indicated if the in office rapid strep screen is negative
24
Q

Sputum culture indications

A
  • HAP
  • hosp patients with pneumonia (CAP) and any of the following criteria:
  • ICU admission
  • failure of output abx therapy
  • cavitary lesion
  • active alcohol use (aspiration pneumonia)
  • severe obstructive of structural lung disease
    • urine antigen test for pneumococcus
    • urine antigen test for Legionella
  • pleural effusion
25
Q

Sputum cultures are not indicated when:

A
  • for most outpatient CAPs
  • management of bronchitis
  • initial management of acute exacerbations of COPD
26
Q

How to obtain a sputum collection for optimal yield?

A
  • obtain prior to abx tx
  • have the pt rinse their mouth prior to expectoration
  • no food 1-2 hours prior to expectoration
  • inoculation of culture media immediately after specimen is obtained or immediately after prompt transport to microbio lab
  • bronchoscopy: sampling of lower airway is another potential dx method in patients w/ suspected pneumonia
27
Q

What may make a sputum culture inaccurate? When would you suspect a pathogen? When is the best time to get a sputum culture?

A
  • may be inaccurate due to mouth flora
  • suspect a pathogen if WBCs are present along with an overabundance pf 1 type of organism
  • first morning sputum will represent deeper pulmonary secretions
  • induce cough with nebs, pulmonary PT, aspiration, bronchoscopy
28
Q

What should you always get with a sputum sample?

A
  • always get a gram stain too!

- helpful for directing empiric therapy

29
Q

What will you see in a atypical pneumonia sputum culture (mycoplasma and legionella)?

A

The sputum will contain abundant PMNs and few or no organism will be seen on the gram stain

30
Q

What will you see on a sputum culture + with pneumococcal pneumonia?

A

abundant inflammatory cells and gram + diplococci

31
Q

What are the indications for ordering a blood culture?

A
  • bacteremia
  • septicemia
  • unexplained post operative shock
  • unexplained fever of several days duration
  • pneumonia
  • chills and fever in pts with:
    infected burns or UTIs
    rapidly progressing tissue infections
    post-op wound sepsis
    indwelling venous or arterial catheters
    -debilitated pts receiving:
    abx, corticosteroids, immunosuppressives, parenteral hyperalimentation (nutrition)
32
Q

When are blood cultures used to detect bacteremia (septicemia)

A
  • should mainly be considered in pts w/ temp >101 suspected of having endocarditis or other systemic pathogens
  • std of care for inpatients w/ pneumonia prior to starting abx
  • can repeat in 1 hour or if fever
    (transient bacteremia)
  • 2 specimens obtained from 2 separate sites 15 minutes apart (aerobic or anaerobic?)
  • # of organisms / site is low
  • helps id contaminants
  • total: 30-40 ml of blood
33
Q

Blood culture technique

A
  • clean site first with 70% alcohol
  • follow with butadiene x 2 minutes
  • wipe bottle tops with alcohol
  • go to lab immediately
  • don’t draw blood cultures through central lines or IV (contamination)
34
Q

How to collect a urine sample?

A
  • clean catch, mid void specimen
  • collect 5-50 ml of urine
  • cath
  • suprapubic tap
  • best culture is in the morning (most concentrated)
35
Q

Guideline of urine sample and transport

A
  • midstream clean catch urine by pt
  • need at least 1 ml
  • transport a 4 degrees centigrade
  • straight cath specimen: same parameters
  • indwelling cath: disinfect port with alcohol
    remove 5-10 ml of urine w/ needle and syringe -> transfer to sterile container, 4 C
  • suprapubic aspirate: at least 1 ml, at 4 C
  • always send as UA and urine C & S
36
Q

What does the urine dipstick test?

A
  • pH
  • specific gravity
  • bilirubin
  • protein (nephritis -> elderly)
  • glucose -> diabetics
  • ketones (diabetic ketoacidosis)
  • blood: can’t always rely on
  • nitrate: certain bacteria
  • leukocyte esterase (pyuria)
37
Q

indicators of possible pyuria

A

leukocyte esterase: if + on dipstick likely indicates pyuria

nitrite: indicates the presence of enterobacteriaceae that converts nitrate to nitrite

if neg but + symptoms of UTI still want urine culture

38
Q

Microscopic analysis of urine

A
  • eval of urine sediment from a spun sample
  • presence of squamous epithelial cells = contamination from genital region
  • normals:
    rbc: 0-5 HPF
    wbc: 0-5 HPF
    bacteria: absent
    casts: 0-4 hyaline LPF (kidney health)
    crystals
39
Q

Indications for a lumbar puncture

A
  • look for blood (possible subarachnoid hemorrhage)
  • find the organism causing the meningitis or brain abscess
  • can do gram stain early on while awaiting culture reports
  • cell and chemistry counts will aid in making the dx
40
Q

CSF Culture

A
  • suspected meningitis, high fever in infant
  • lumbar puncture collect 1-5 ml of CSF
  • transport at 25 degrees C
  • gram stain and bacterial culture
  • 4 tubes for: cell count, glucose and protein, gram stain and culture, and cell count to compare to tube 1
41
Q

Pleural fluid culture

A
  • thoracentesis
  • dx and/or therapeutic: therapeutic- relieves dyspnea (breathe easier)
    diagnostic: test the fluid for TB, CEA level (tumor marker), cytology, culture, gram stain, pH
42
Q

Go under or over rib while doing a thoracentesis?

A
  • over because nerves and vasculature along bottom of ribs
43
Q

Synovial fluid eval?

A
  • swollen joint
  • infection, inflammation or uric acid
  • meds shouldn’t be administered therapeutically at the same time because interfere with sample (corticosteroids, abx)
44
Q

Body fluids collection technique

A
  • peritoneal, pericardial, pleural, synovial
  • aspirate using sterile technique into sterile syringe (usually pt has fever or elevated WBCs)
  • remove needle and cap syringe to send to lab, sometimes put aspirate in a different container
  • min. of 1-10 cc, send as much fluid as possible
  • send at 4 degrees C
45
Q

Genital tract culture for women

A
  • swab cervix for gonorrhea, chlamydia as well as other organisms in suspected PID
  • swabs of urethra or urine testing for chlamydia
  • occasionally swabs of vagina are done
46
Q

guidelines for vaginal/cervical culture

A
  • no douching or tub bathing for 24 hours prior to collection
  • swab -> checking for gonorrhea, chlamydia
47
Q

When is a wet mount used?

A
  • helpful in evaluating vaginitis
  • saline wet mount of vaginal discharge can show epithelial cells covered with bacteria suggestive of bacterial vaginosis
  • trichomonads
  • can reveal multiple PMN’s
  • KOH (K+ hydroxide) wet mount can reveal candida organisms
48
Q

Swabbing male urethra indications

A
  • special smaller swabs for urethral sampling for gonorrhea and chlamydia and other less common infectious agents
  • urine samples for GC and chlamydia for nucleic acid amplification
  • nucleic acid amplification more sensitive than culture
49
Q

Urethral culture techniques

A
  • usually on men
  • culture for GC, chlamydia
  • rapid enzyme test available
  • Thayer martin/New York media
  • anaerobic transport
50
Q

Stool culture indications

A
  • routine culture (for those with prolonged diarrhea or haven’t been on abx or hospitalized)
  • > 2 grams, 4 degrees C
  • C. diff toxin: test of choice for those who develop diarrhea on abx or in hospital > 3 days
  • > 5 ml, 4 degrees C
51
Q

Stool culture guidelines

A
  • also check for ova & parasites
  • usually look for staph, salmonella, shigella
  • Don’t mix urine or TP with sample
  • rectal swabs: worms
  • ‘tape test’

Infectious Disease (27 decks)

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