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Lab Medicine > Micro > Flashcards

Micro Flashcards

1
Q

Gram Stain

A

Useful initial test to determine presence of Gram positive or Gram negative bacteria

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2
Q

Peptidoglycan thickness

A

Gram positive - thick
Gram negative - thin

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3
Q

Gram indeterminate bacteria

A

Mycobacterium

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4
Q

Gram stain sample collection

A

sputum, blood, urine or any other specimen- in a sterile container sent to the lab

If collecting sample with a swab, separate swabs to avoid contamination

1 swab for gram stain
1 swab for culture and sensitivity

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5
Q

Acid Fast Staining

A

Mycobacteria are resistant to acid decolorizing, so can’t identify with Gram staining

Used for quick identification when TB organism suspected

Generally need 3 consecutive days worth of samples. First morning sputum is the best.

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6
Q

AFB Cultures

A

Mycobacteria is a slow growing organism requiring up to 6-8 weeks to confirm no growth

2 common organisms
Mycobacterium tuberculosis
Mycobacterium avium-intracellulare (MAC)

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7
Q

QuantiFERON-TB Gold In-Tube (QFT-GIT)

A

measures the interferon gamma released by T cells in response to the presence of mycobacteria TB presence

does not differentiate between latent or active TB

does not react to a patient that received Bacille

Calmette-Guérin (BCG) vaccination
Mycobacterium bovis

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8
Q

Sputum Sampling

A

Key is to get a deep sample with minimal contaminate

Good sample: high WBC, low epithelial cells

Normal flora: alpha-hemolytic strep, Neisseria species, diphtheroids, some Haemophilus species, pneumococcus

Pathogenic species: Strepococcus pneumonia, Mycobacterum tuberulosis, Klebsiella pneumoniae, H. influenzae, and many more

No spit!!!

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9
Q

Culture and Sensitivity

A

routine cultures – C&S culture and sensitivity report

does not include acid-fast bacilli (mycobacterium)
does not include fungal (unless routine such as Candida species)

usually not include anaerobes (exception deep wound culture)

does not include less common pathogens requiring special media

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10
Q

Antibiotic Sensitivity Results

A

Broken down into 3 types:

Sensitive
Intermediate
Resistant

Minimal Inhibitory Concentration (MIC)
Indicates the minimal amount of antibiotic needed to prevent growth

Rarely changes the dosage regimen, or choice of antibiotic

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11
Q

Blood Cultures

A

Inoculating culture media with blood sample

Can identify 67% of pathogens within 24hrs; 90% within 72hrs

Pathogens generally enter blood via lymphatic system
Need to know which antibiotics have already been given!

Strange results often mean drawing another set to confirm
Staph epidermidis

Surveillance cultures are drawn to confirm clearing on infection

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12
Q

Blood Culture Collection

A

Prep collection site with povidone-iodine wiping clockwise outward motion

Need to collect adequate amount, refer to culture vial
Two vials: 1 aerobic, 1 anaerobic

Need to collect from 2 sites when possible

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13
Q

Urinalysis

A

Also known as “urine dipstick”

Can be done in the lab or in the office/hospital setting
Urine sample is collected from the patient

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14
Q

Clean Catch

A

Clean-Catch=urethral area is cleaned with antiseptic wipe before urine is obtained in a sterile container

Inspect urine for color-yellow/straw colored=normal; dark yellow=dehydration; red=blood; brown=excess bilirubin or blood

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15
Q

Urinalysis Inspection

A

Inspect for clarity- Clear=normal, Cloudy with
sediment= infection,

high protein content; Frothy= significant proteinuria

Odor-sweet=glucose in urine

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16
Q

Urine Cluture

A

The external genitalia must be cleaned with an antiseptic wipe

Sample should be midstream
Best samples are first morning void

Catheterization can also be used for aseptic collection
Sometimes an initial dipstick is done first

17
Q

Urine Culture Results

A

Final results are given after 48hrs

More than 2 species normally indicates contamination. Get repeat sample.

Results also include the quantity of bacteria
<100,000 colonies/mL sometimes considered negative depending on clinical scenario

Medical diuresis can also effect results

18
Q

Throat Culture

A

Generally used to identify group A beta-hemolytic streptococci, also less often…

Neisseria meningitidis, C. diphtheria, B. pertussis, Staph aureus, H. influenzae, Candida species

19
Q

Gonorrhea and Chlamydial Testing

A

Standard for urogenital infections in men and women is a nucleic acid amplification (NAAT) urine testing

Oral and rectal testing needs to be performed with a swab culture

Cultures are still normally taken in cases of rape kits

20
Q

Wound Culture

A

Used to identify the pathogenic organism
Swab (more contaminates)

Curettage
Needle aspiration
Need separate samples for aerobic and anaerobic

21
Q

Suitable Anaerobic samples

A

blood
bile
bone marrow
cerebrospinal fluid

direct lung aspirate
tissue biopsy from a normally sterile site
fluid from a normally sterile site (like a joint)

dental abscess
abdominal or pelvic abscess
knife, gunshot, or surgical wound
severe burn

22
Q

Not suitable Anaerobic samples

A

coughed throat discharge (sputum)
rectal swab
nasal or throat swab

urethral swab
voided urine

23
Q

Types of Anaerobes

A

Obligate: harmed by the presence of oxygen

Aerotolerant: cannot use oxygen for growth, but tolerate its presence

Facultative: which can grow without oxygen but use oxygen if it is present

24
Q

Fungal Culture

A

Not routinely done

Fungemia generally only found in
immunocompromised

long term intravenous access
broad spectrum abx use
Topical fungal infection generally doesn’t require culture for treatment

25
Q

KOH Prep

A

Used for skin/nail scraping and vaginal swab for presence of fungus (dermatophytes or yeast)
Tinea, Candida species

Prep with potassium hydroxide (KOH)

26
Q

Vaginal Wet Mount (KOH)

A

Also used to diagnose bacterial vaginosis and trichomoniasis

Same procedure as KOH prep, different finding

Not done during menstruation, or within 24 hours of sex or vaginal irrigation

27
Q

Vaginal Wet mount Interpretation

A

Vaginal candidiasis: hyphae and buds

BV: >20% are clue cells
Thin, milky, fishy odor discharge
pH >4.5

Trichomoniasis: yellow-green, foamy, foul smelling
Mobile trichomonads visible

28
Q

Tzanck Smear

A

Used to find multinucleated giants cells
Herpes simplex
Herpes zoster/Varicella
Pemphigus
Cytomegalovirus

Similar to KOH but fixated with methanol and stained with Giemsa, methylene blue or Wright’s stain

29
Q

Viral Culture

A

A swab of the infected area is placed with a culture of a cell type that the virus can infect

Detection of antigens produced by infected cells indicates a positive test

Viruses that can be identified:

adenovirus, cytomegalovirus, enteroviruses, herpes simplex virus, influenza virus, parainfluenza virus,

rhinovirus, respiratory syncytial virus, varicella zoster virus, measles and mumps

30
Q

Viral Detection by Polymerase Chain Reaction (PCR)

A

Faster method of viral detection by rapid replication of viral genome

31
Q

Stool Culture

A

The GI tract is filled with organisms that are considered normal flora. Only looking for specific organisms

Shigella, Salmonella, Campylobacter jejuni

Make note of recent antibiotic therapy

32
Q

Clostridium Difficile Detection

A

Routine stool cultures are not used for detection of C.Diff

C.Diff specific cultures can be used but are slow to produce results

Toxin A and B ELISA

True negative require 3 samples from separate days

33
Q

C-Diff via PCR

A

Probably the most common
More sensitive than ELISA testing
Specific for Toxin B gene

Cannot distinguish between active and inactive disease

Sample MUST be liquid
No need to repeat testing

34
Q

Stool Ova and Parasite

A

Round worms, hook worms, tape worms, amoebas, giardia

Need to avoid mineral oil (enemas), bismuth (pepto), antidiarrheals, barium, antibiotics for 7 – 10 days prior to samples

3 samples from 3 consecutive days

35
Q

CSF Analaysis

A

Measure CSF pressure

Aid diagnosis of bacterial or viral meningitis, subarachnoid hemorrhage, tumors, and brain abscess

Aid diagnosis of neurosyphilis
Prepare patient that it takes at least 15 minutes

Sometimes followed by headache from LP. Lay flat 6 hours Get consent.

36
Q

Lumbar puncture adjoining test

A

Always obtain a head CT prior to an LP to rule out a mass occupying lesion

concern for brain herniation when removing fluid below the brain

37
Q

CSF Findings

A

Lab Medicine (6 decks)

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